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New build for the 6.5 Grendel Wildcat fans... 6mm Fat Rat

Fried Chicken Blowout

Fried Chicken Blowout

Sergeant
Full Member
Minuteman
May 15, 2011
379
0
Meeker, Colorado
Due to the utter lack of information I was able to find on some of these wildcat AR15 calibers, I'm gonna do up an information post on this build. I'm not really looking for suggestions of what I should have done or so please keep your suggestions of how I should have built an AR10 to yourself :rolleyes:... I've always had an interest in the Grendel spin-offs as well as the Grendel in order to keep with the AR15 parts I already have and stretch out the usable distance and improve wind performance. So I finally ordered an upper.

Initially I was interested in the 6mm Turbo 40 Improved but could not get a response via email or voice mail from the smith that makes them. Inadvertently I stumbled across Lee Wells and his company Accurate & Reliable Rifles offering the 6mm Fat Rat which is pretty close of the 6mm Turbo 40 Improved. I'm not sure the difference and won't get into that. Lee answered the phone on my first call and was willing to work with some ideas I had with the build to meet my desires.

Initially I had asked for the build to be a 22" barrel as that's the max length allowed for the "Carbine" shooter at the Wyoming Tactical Rifle Championships. But after thinking about it, I didn't want to handicap the build in any way and end up abandoning the cartridge based on a decision I made so I went with Lee's suggestion on the 26" barrel and extended gas system. Here's the build parts list...

Items supplied by Lee Wells:
- MilSpec upper (Unknown Brand) - Appears to be of good quality with an excellent finish. I would have preferred a VLTOR upper, but didn't have one on hand to provide at the time. Lee's opinion is that heavy wall uppers are not needed and I'm undecided on the real difference they make.
- MilSpec Full Auto Bolt Carrier with an Alexander Arms 6.5 Grendel Bolt Head.
- Krieger Stainless 1-8" 6mm barrel blank finished by Lee to 26" with an extended gas system. It looks to be a raw blank that has not been finished under the hand guard so I assume its 1.25". The gas block is 0.936 and 0.8" in front of the gas block, finished with a 5/8" thread.
- Hornady 2-Die Set with Micrometer Seating Adjustment
- Bore Guide
- Modified 6mm Fat Rat modified case for use with Hornady OAL Guage

Items supplied by me to Lee to finish the upper:
- Carbon Arms 15" Free Float Hand Guard
- JP Adjustable Gas Block
- Suppressor Armament Systems 5/8" TOMB Brake. Still waiting on the Form 4 for the SAS Reaper.

Items I added after receiving the upper yesterday to get it ready for business:
- 2" Rail segment intended for the JP hand guards to mount the Atlas
- Impact Weapon Components sling mounts intended for the JP hand guards
- Lapua sticker for an extra 50 FPS at the muzzle


For now I'll be using the lower from my .223 long range build. I have a Seekins lower on order that I'll build for this upper. At this point it's ready to shoot if I had ammo. Won't be till next week until I can get the time to size and load my fire forming loads. The cases need to be necked down to 6mm of course, no turning is said to be needed. The fire forming blows out the shoulder to 40 degrees and increases the case capacity to 36.7 - 37 vs 35 grains of water for the 6.5 Grendel.

Looks like I'll be using 28-29gr of Reloader 15 and some cheap Nosler 108gr bullets for fire forming the Lapua brass. Lee's claim is that I'll shoot pretty good with the fire forming loads and will shoot 1/2 MOA with my finish loads. After that I have an assortment of Berger HPBT and Hybrid bullets as well as Sierra HPBT bullets to work up loads with. All loads will be to mag length so I'm assuming the Hybrids will make the jump the best. I'm not sure how far the jump is at this point. Mags will be the ASC 6.5 Grendel mags.

I've got a bunch of work ahead of me and I'll be adding to this post as I fire form, work up loads and get the rig fielded. Check back for more and I'll leave you with some photos for now.




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Here's the weight as pictured above...


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I have a 26" barrel on order from Accurate and Reliable rifles so I'll be interested in your findings.
 
Hummerdawg said:
I have a 26" barrel on order from Accurate and Reliable rifles so I'll be interested in your findings.
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What's your lead time so far with the barrel order? Lee's delay right now is the AA Bolt Heads, I assume he's sitting on a large stock of barrel blanks. He actually gave me his bolt head out of his personal rifle with a couple hundred rounds on it to get my order done. Seems like a great guy and was willing to work with all my requests. If this works out well, I'm sure I'll end up with a shorter version at some point and I'll order it as a barrel only to build myself.


1slow01z71 said:
Im interested in seeing the process of making the brass.
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I'm thinking next tuesday I'll get my first batch of fire forming loads done. I'll shoot a bunch of photos and cover the process in detail. This will be my first time fire forming any loads and my initial lack of knowledge is what has kept me from getting into this sooner. Hopefully I can make this a decent resource for others on the fence.
 
I placed my order first part of March. Last email I got he was waiting on bolts. I have been busy building a couple limited and open 2011 pistols so I haven't really been going to crazy with the anticipation :) Hopefully you will have all the load kinks worked out by the time mine gets here
 
making brass is prety easy, run 6.5 grendel brass in the 6MM fat rat sizer die, load it, shoot it, pick it up and it is done, ready for round two.
 
To: FriedChickenBlowout (I think this name is great), I've seen 1000's of AR's, they're all pretty much the same, or so over-done they look stupid, your rifle on the other hand is clean-and look really good-please post some follow-up load data and your work-ups(load wise), this 6mm thing might just be catching on (an attempt at humor)! All jokes aside, I'm very interested in your load data-good luck - if it shoots a good as it looks a lot of guys are going to want to know more. thanks for the great post-and the scale photo(that "kinda removes all doubt).
 
Update #1 - Sizing

Okay boys and girls, we have our first update ready from today. I didn't get much done, but I fit in what I could today. I'll get some fire forming rounds loaded on Sunday and fired next week at some point.

First off, Hornady makes the dies for the 6mm Rat for Lee Wells. What I actually have and all that is being produced at this point is 6mm Fat Rat chambers. These chambers differ from the initial 6mm Rat in that the neck diameter of the Fat Rat is wider to allow the chamber to handle higher pressures then the initial Rat with the larger bullets. The dies just show 6mm Rat but that's fine, since the difference is in the chamber's neck. If anyone can elaborate on what this is technically referred to that would be great. The dies include the Hornady micro-meter stem which is not installed correctly in the photo and I've correctly it.



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In the next photo you can just see that the edge of the inside of the sizing die is highly polished. This is new to me, the other Hornady dies I've used were not polished on the inside. Not sure if these are a different quality tier than the standard dies but the polished interior is nice to see.



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In this next shot you see the shim that is included with the dies from Lee. The sits on top of the shell holder when adjusting the die for the initial fire forming loads. This adds an extra shoulder to the case. I think there would still be a shoulder in the neck without this, but this increases the size of the shoulder. This shoulder is actually what head spaces the case when fire forming and keeps the case head pushed back against the bolt face.



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The shell holder I'm using is the Redding #12. This was purchased on it being for the 6mm PPC if I remember correctly, as Redding didn't have one listed for the Grendel.



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Installed in the press with the shim on top. The ram is raised and the dies screwed down lightly and secured touching the shim.



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Game on with my first 100 cases. I have 700 of them on hand but I'll use 100 of them to make sure all is well with the setup before I start forming more. At $90 for a box of cases this isn't cheap.



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My new Redding Big Boss II seems a little big for this tiny case, but overkill is never enough.



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Here's a 6.5 Grendel case next to a newly sized fire forming case for the 6mm Fat Rat. You can see the shoulder that will head space the case.



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I knocked out all the 100 cases in short order and dropped them in the tumbler to get cleaned up for loading.
 
Upate #2 - OAL Measurements

I've seen several warnings about these custom type guns needing to be checked for OAL depth so I'm not gonna ignore that. There are so many different bullet ogives lengths that you can end up loading up at mag length for one 105gr bullet and have a good jump, while another 105gr bullet may end up with bullet set back due to ramming the lands upon chambering at mag length. This was shown to be the case with the Berger vs Nosler bullets I'll be using.



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Before I could get to measuring the OAL, I needed to modify the Hornady tool. It's designed for longer cases and I needed to remove 0.150 from the length of the stem inside the case to make sure I had enough room to seat the bullets into the case once the modified case was installed on the tool. This modified case was supplied from Lee Wells at an extra cost, but as it turns out it's worth the money.



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The Nosler bullets are super cheap and will be used for the fire forming loads. The 105gr Berger Hybrids are the best BC I can find in the 6mm 105gr - 107gr bullets. They are also specifically designed to be flexible with the amount of jump they are required to do. If anyone knows of a 6mm 105-107gr bullet with a G1 BC better than 0.547 please let me know so I can check them out. If the Berger Hybrids fail to get the accuracy results I'm after, I also have Sierra 107gr as well as several other Berger bullets on hand to try. I was also specifically cautioned about not using VDL bullets at mag length due to the amount of jump they would be required to do. I don't have any to measure to see what the differences would be. As you can see here, the Berger Hybrids are going to hit the lands before I even load to mag length. It's a good thing I checked before just loading out to mag length with them and calling it good.

The OAL measurement for the Berger bullets to the lands ended up being 2.260 on the nose. Almost like they were designed for this gun.



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As you can see here, the mags will allow loading longer than most AR mags that I've dealt with. With the ASC mags measuring 2.314 for the inside length, I have some flexibility.



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But you can see the Nosler ogive is much farther back. But with the mag length it should not be too bad. Won't matter much any ways with the fire forming loads. 2.365 is about what I figured it would be to the lands for most BTHP bullets.



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So anyone with experience with the Berger Hybrids have any suggestions on how far off the lands to load them?
 
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wow, impressive write up... very interesting rifle and cartridge... ill need to keep an eye on this thread to see where it goes being that i'm mostly a .223 / .308 AR boy.... very cool looking stick BTW!
 
Fried Chicken Blowout said:
So anyone with experience with the Berger Hybrids have any suggestions on how far off the lands to load them?
Click to expand...

I got some of the first 6.5 140 Hybrids. According to Eric Stecker and Bryan Litz, they were designed to give the high BC of a secant ogive with the loading depth forgiveness of a tangent ogive. I found this to be true.... sort of. They weren't nearly as picky for me as the VLD's (secant) but not NEARLY as forgiving as the Lapua 139's or Hornady 140 BTHP's (tangent). I would run them as close as possible and watch carefully for accuracy issues as the lands wear. YMMV.

John
 
Update #3 - Brass Inspection

After getting my first set of brass sized and cleaning the lube off, I gave it a once over for any issues. The primer pockets appear to be the correct depth since my uniforming cutter didn't remove any material and there appears to be really no flash hole burr at all so I didn't deal with that. A measurement of the neck ID show it to be 0.2365 after sizing.


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Measurements of the bullets I'll be using found the Berger Hybrids to be the largest OD at 0.244 giving me a total difference of 0.0075 for neck tension which I believe is pretty tight but should avoid any setback when feeding. If anyone has any clean knowledge that this is too tight on the bullet please let me know.


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The 6mm Fat Rat calls for a brass trim length of 1.520 and a MAX case length of 1.525 and these new sized cases are coming it all within 0.0005 of each other at 1.5215 so on the money and won't need to trim anything. Plus due to the 40* shoulder they should have very little flow with firing.


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That's all for now. I'll get to loading tomorrow or Monday.
 
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I built my own 6mmAR last year and can't get over why this caliber is not popular. The 6.5 Grendel should have been a 6mm to begin with IMHO.
 
This is really getting my attention.

Im thinking a fast, flat shooting 6mm based on a light weight AR-15 package might make the ultimate semi auto tactical match rifle.

The size and weight savings gives it an edge over the AR-10 sized platforms in a run and gun style match and build components are cheaper.

Most of the matches over here on the east coast give away the majority of their points inside 700 yards so I dont think a caliber like this would suffer much in that regard.



Thats an awesome looking rifle sir.
 
Update #4 - Loading

Lee Wells stated that I could jump right to 30gr of Reloader 15 for 105gr bullets as a fire forming load, but being a little cautious I decided I would basically do a ladder of 0.1gr jumps from 29.0 to 29.9 of only one round each just to see what the cases looked like upon firing. These will be my first rounds fired through to the gun for barrel break-in. Making the assumption that 29.0 and 29.5 will work within reasonable pressure ranges I went ahead and loaded 20 round of each of those so I can complete my break-in process and fire form a total of 50 cases on the first trip to the range. But if anything looks shady in the first 10 test rounds at any load I'll know if I can fire the other 40 rounds safely.

Lee requested that I shoot 1 and clean for 5, then shoot 5 and clean for 5 rounds and then call it good, which is what I will do.


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For this loading I'll be using Reloader 15, CCI 41 primers and Nosler 105gr BTHP bullets. The these bullets will have a huge jump as they touch the lands at 2.365" and I'll be loading right around mag length at 2.300"


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As you can see in this photo, in the unfire formed cases, 29.0gr of Reloader 15 is a full load right up to the base of the neck of the case.


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Then at 29.5gr we creeped up into the neck.


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In short order I've got my first set of rounds loaded and I'll be headed to the range on Wednesday. I'll update you'll about the results.


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I hope all goes well for you. Finally found my load for my 6mmAR and live the thing to. The fat rat should get better velocities then the 6mmAR
 
btw, .065" jump is HUGE! totally interested on how this works on the range... please keep us all updated.

nice info, very nice! nice pics also!
 
I've fired around 8,000 rounds of 6mm Turbo 40 in NRA Highpower competition since 2011 and I think it's a great cartridge. For 600 yards and in, I don't think it gives up anything to ANY cartridge for my type of shooting. I have also shot it in a few 1000 yard prone matches, and if the wind is not blowing too bad, it can do ok. It is definitely not the best choice at this range and will get beat handily by rounds with more horsepower. If you are not shooting for score, or only shoot long range occasionally, you may be perfectly happy with it's performance. A few of my observations on loading, etc:

1. Don't automatically relegate your Fire forming load to just blasting, as it may be just as accurate as your formed load. I initially just used the FF rounds for practice, but they shoot so well that I have no hesitation using them at 200 and 300 yard stages of matches. Lots of clean 200's at those distances with FF loads. I am sure they would be just fine at the 600 yard line also, but I have not tried. 28.5 grains of Reloader 15 or Varget shoots great with any bullet in my experience. Personally, I use 95 gr SMK's for fire forming and for all 200 and 300 yard match stages - great bullet.

2. You CAN use too much powder. When I first started with this round, I was loading at about the max with 30.0 gr of Re-15 and while it shot great, it ruined brass quickly. With that much powder, some case would not make it to 3 firings without the primer pockets being trashed. I backed down to 28.5 for the 95's and 29.0 for the 105's and it shoots just as well. A bit slower, obviously, but no accuracy loss and brass lasts longer.

3. The 105 Hybrid is the best bullet in it's class for this round and is worth the extra money. I have shot quite a few clean 600 yard targets using both the 105 Hybrid and the 105 A-max, but the Hybrid will consistently shoot more X's than the A-Max or the 107 SMK. I jump them .015" and this has consistently produced good results.

4. Barrel life is good, not great. I am on my 3rd barrel(1 PacNor and 2 Bartleins), and have gotten almost exactly 3000 rounds on the first 2 before noticing an accuracy loss at 600 yards. I shot both for another 500 rounds or so, but was seeing too many surprises at that point and changed them out. Both still hammered at 300, and depending on the intended use, you could go a good ways beyond that. I have 2 identical uppers, so the first Bartlein is actually still on my 2nd upper and I intend to continue using it for practice and short-course matches. Loads have been the same with all 3 barrels, I did not have to change anything when switching to a new barrel, aside from adjusting sizing die.

5. Reloader-15 and Varget are basically interchangeable in this caliber. I started out shooting Re-15, but switched to Varget this year because it works better with my powder measure system. Charges of the same weight of either powder basically produce the same accuracy results and very close velocity when I've bothered to chrono them.

6. I've seen a lot of complaints about them, but personally, I've had great luck with C-Products mags. I bought all of mine with my first upper in 2011, so I don't know if they are the same as the mags they sell now. They have blue 6.5 Grendel followers. I have 8 10-rounders and I use all 8 of them at every match. I have never had a mag-related malfunction.

Anyways, I don't really post much here, but I figured it's something I have some experience with, so maybe it'll be helpful. I think you will really like the cartridge and hopefully yours will shoot as good as it looks.

Good luck,
Erik
 
Erik,

Thank you very much for this post. I think it's the single best post I've seen on this subject while researching this type setup and it answers a bunch of my questions... Mainly how good is R15 going to do for me? Are the Hybrids the right choice for what I'm trying to do? How much should I jump them? How long will the brass last? Will it be picky and hard to develop a good load? All these questions and more were answered above. Looks like I'm headed in the right directions. I do have a couple question...

1. Based on the fact that I'm using this for steel matches (one shot per target - no sighters allowed) and not NRA style shooting do you have any specific suggestions for loads? Meaning, is it worth the loss of brass life to get the extra wind resistance from the speed by loading them hot or not? Most rounds will be shot at less than 550 yards as long as I'm shooting the Carbine position. If I decided to take an underdog chance and shoot the "Rifle" position with this setup then we're looking at 1000 yards max, most shots at 800 yards or less.

2. For extreme temperatures swings here in Colorado at 4500 - 5500 ft from 0 degrees to 110 degrees would you suggest one powder over another? I've been looking for H4895 as suggested by Lee Wells, but I can't find ANY! My understanding is the IMR 4895 is not the same powder. Reloader 15 actually works great in my Hornady Auto Charge so that's not a concern for me but if it's crazy temp sensitive, that is an issue.

Thank you for taking the time to post your comments above!

Jason
 
No problem Jason, glad you found it useful. As far as your questions go:

1. Personally, I don't think the marginal increase in wind bucking would be worth the shortening of brass life. At first I kind of leaned the other way on this issue, but after backing the load down and shooting just as good of scores with the reduced load I don't think it's worth it. The 10-ring on the 600 yard NRA target is 12" and the X-ring is 6" and either load is capable of holding the 10-ring with over 50% X-count shooting with a sling and sights. This is over the course of a 20-shot string. As expensive as Grendel brass has gotten(never see it under $70/100 anymore and rarely in stock) I try to get as much as I can out of it. At 550 yards this round is as good as anything and better than most. Still good at 800, and getting iffy but still capable at 1k.

2. I have found Varget to be more temperature-stable, but Re-15 worked just fine and the temp sensitivity was totally predictable. I live and shoot in MN, so we have similar temp swings from winter to summer. My 30° zero with Re-15 was 1.5 MOA lower than 85° zero. Pretty easy to keep track of though, and never had any surprises. The Varget so far has proved to be about dead stable from February to July so I'm pretty pleased. I wouldn't run out to buy Varget if you have lots of Re15 on hand, it will work just fine. I've heard good things about H4895 in this cartridge, but have never tried it. I had tons of R15 on hand for other calibers when I first got the Turbo so I tried to use it and it worked.

Regards,
Erik

Here's a pic of mine:
ImageUploadedByTapatalk1373932764.783570.jpg
 
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Jon A said:
Erik,

What velocities do you end up at with the 105's? I assume that's a 28" barrel?
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Jon,
29.0 Varget put the 105 Hybrids right at 2780 last time I chrono'd them. Barrel is 26".

Erik
 
Thanks, I'm still getting the feel for this round. My current FF load with the 105 Hybrid is 31 grains of CFE223 which is giving around 2815 in warm weather from my 28". I didn't really intend to have a FF load that "full power" but it shot so well I didn't feel like changing it. CFE223 is compact and fits in the case well. I had tried 32 grains in cooler weather for a full power load (with fireformed cases) and they shot well, but now I'm thinking they'd probably be well over 2900 in August temps which is probably too hot.
 
Update #5 - Initial Firing

Got out to the range yesterday to get the first 50 rounds fired. First up was a ladder of single rounds loaded with CCI #41, Nosler 105gr BTHP and Reloader 15. The first round was 29gr and each one stepped up 0.1gr to a max of 29.9gr for a total of 10 rounds. I wanted to see how the load effected the forming of the brass and make sure I was within a safe range to load anywhere in that zone for loading. I went ahead and closed the gas adjust screw all the way on the JP Gas Block to start adjusting it from a closed position.

With the gas adjust screw closed, the first round fired with 29gr of Reloader 15, cycled and locked the bolt to the rear. Done deal, the gas system was adjusted. Even with 2" extended gas system and the adjustment closed as tight as it will go, the gun has enough gas to cycle without any issues. The ejection pattern is exactly the way I like it, 45 degrees to the rear with little to no contact with the brass deflector.

As I worked up the ladder of loads, there was no change in appearance of the primer and no significant signs of pressure until I got to the last 3 cases where ejector marks appeared and then deepened, but there was no change in the primer. There was also some burrs that appeared in the case head and rim at the higher pressures. I'll be taking a look at my bolt face to see if there is anything that needs to be smoothed out or if there's some debris that are stuck in the bolt head. All cases were formed the exact same and I was amazed at how much they changed from the Grendel cases. The Grendel has a significant taper to the case and that is gone with the firing as well as the shoulder being blown out a good degree. The necks of the cases appear significantly shorter because of the shoulder growth upward.



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There was some lesson to be learned about the mags as well. The stated "17-Round" magazine that is the same form factor as the 20 round .223/5.56 mags will really only hold 13 rounds. I'm not sure why they insist on calling them 17 round mags as this would keep me from being able to purchase any additional mags due to our new 15-Roun mag limit in Colorado. But I have 10 of these on hand and I'm not too worried about it at this point. But the 17-Round mags really only hold 13-Rounds and better yet, they don't work with any more than 11-Rounds. If loaded with 12 or 13 rounds the pressure on the feed lips is SO TIGHT the round it captured in the mag and is forced to nose dive into the front of the mag damaging the tip of the bullet. This may change with the fire formed cases not being tapered but we'll see.

If any one has any links to a "how-to" improve these mags I would appreciate that. I'm assuming I can either cut the spring or trim the follower to starting fixing the capacity issues. But I don't want to make them unreliable at the lower round count so I'm a little hesitant in messing with them.

All my mags are ASC, new production mags direct from them. I did however install USGI Mag-Pul Ranger Plates on them all. This in itself may increase spring pressure a tad and reduce the capacity by 1 round which is what I found with the .223/5.56 mags.



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Besides the whoops with the mags, the complete system ran flawless. My .223 long range gun with an adjustable gas block feels sluggish the way I have it adjusted, but this does not have the same feel. The recoil was solid but not significant. The barrel was very quick to clean when cleaning between rounds and required a 1.5" patch on my normal .223 Dewey jag so I don't have to switch jags when switching between guns. The bore guide was a great fit and cut shorter than most of the .223 bore guides which helped as I could use my existing .223 rod. If the bore guide was any longer, my longest .223 rod would not have worked.

I ended up making a mess of the target and didn't take any photos to post. I had issues dealing with the Zero Stop on the Bushnell XRS scope and ended up having to zero the gun from the mechanical bottom of it's adjustment and I didn't switch targets. What I ended up with at the end of the 50 rounds (well actually 48 rounds since I f'ed up two bullets) was a significant difference between the 29gr groups and 29.5gr groups. I made 20 rounds of 29gr and 20 rounds of 29.5gr. Remember this is what a bullet that is making a significant jump to the lands as posted above. The 29gr loads would hold right at 1 MOA for as many rounds as I wanted to fire. The 29.5gr loads had one 5 shot group with the first two rounds out to 0.8" and the last 3 going though the same hole below the flyers. My last group of the day with the barrel getting a little fouled ended up with all 5 rounds touching at just under 1/2 MOA. I'm assuming the change in accuracy is solely related to me cleaning the barrel closely before the 29gr load groups. I'll make more up at 29gr since I know it fire forms perfect and see if the groups tighten up as I get more rounds through the barrel.

I'll update more when I get a chance to shoot more. My plan at this point is to go ahead and make sure I'm happy with the 29gr load and load up all the 200 remaining Nosler bullets for some groups and get a little dope. After that I have 200 Hornady BTHP that I'll load with the same load and continue fire forming brass. I will likely end up shooting my first match with the fire forming loads and just see how it goes. After that I'll begin working up a load for the Berger Hybrids on the formed brass.
 
Erud said:
1. Don't automatically relegate your Fire forming load to just blasting, as it may be just as accurate as your formed load.
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I'll say. I just shot a 7.5" group at 1000 yds with fireforming rounds in less than ideal conditions. This round rocks.
 
I'm having Lee contour and chamber a 6mmAr barrel for me when he get's back from Perry. I'm going with a similar setup that are in the pics. I may regret not going with the Rat or the Turbo though. But I do enjoy hearing about the final results of Lee's craftsmanship.
 
scout_79 said:
I'm having Lee contour and chamber a 6mmAr barrel for me when he get's back from Perry. I'm going with a similar setup that are in the pics. I may regret not going with the Rat or the Turbo though. But I do enjoy hearing about the final results of Lee's craftsmanship.
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Is there an advantage to using the 6mmAR? I assume its just a necked down Grendel?
 
No advantage really, it's just a straight neck down to 6mm for the 6.5 grendel brass. I had the reamer, dies, and gages for a CZ527 build but decided it would get more use in an Ar platform. My barrel blank (which I bought from another forum member) could go to 28" but I think I'm gonna stick with the 26".
 
It would be nice to have your own reamer so you can have multiple rifles come out exactly the same. After I test this out for a while ill likely have another upper made in a slightly lighter 22" barrel to meet the rules of more competitions.
 
What supplies do you use for your cleaning of the barrel? After the first 30 rounds what cleaning regimen are you going to follow?
 
1slow01z71 said:
What supplies do you use for your cleaning of the barrel? After the first 30 rounds what cleaning regimen are you going to follow?
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Bore guide, Dewey Rod, Pro Shot Patches, Pro Shot Copper Solvent for break-in and copper removal if needed afterwards, M-Pro 7 for carbon removal after break in. The bore cleaned super easy during break in so I only used patches, no brush. I normally just remove carbon every 200-300 rounds from my rifles and don't really worry about copper unless theres an issue. And I'm really only cleaning the bore every 200-300 because I feel compelled to clean the chamber and I do a full cleaning then. I'm normally shooting suppressed so there's a good amount of carbon build up on everything.
 
I had a 6mmAR Turbo 40 for about 3 years.

It worked well at first but after 500 rounds the barrel "started" coming loose from the extension, this happened gradually. It took me 4-5 months, new rings, a new scope and another 500 rounds figure out what the problem was. The interesting thing was that it would shoot tight groups but next outing I'd have to sight it in again because the group would move slightly .1-.2 mil in any direction. Of course as time went by and the barrel got looser the shifts became worse.

The cartridge did well at long range. Once I lent it to a guy interested in trying long range with us at our club. There were 3-4 guys shooting 243's, 260's, etc, at 10" plate at 800Y and getting occasional hits. Christopher's turn came up and he proceeded to hit the plate 5 times in a row. Everybody was kind of humbled by the tiny cartridge that day. I won a few long range matches with it as well.

My most used load was 30.2 grains of H4895, cci450 primers and 105amax at 2.265" at 2885 fps. The load was a hot load but I never found a load that would shoot as good as it did. Turns out that load was the cause of a malfunction that happened occasionally. I think the brass was grabbing the chamber walls from the extra pressure. That brass lasted 5-6 firings. Later on after fireforming a new batch of brass and getting a new 8lb keg of powder the 30.2 grains of H-4895 was way too hot so I had to work up a new load. The barrel had almost 2000 rounds through it by then so I decided to pick the lowest node to save barrel life which was 28.4 grains of H-4895/2740 fps. It was accurate but the new load blew too much in the wind compared to the old one. It never malfunctioned again was the nice thing. When I sold it it was still capable of sub MOA groups but not nearly as accurate as when new.

I think the .547 BC of the new Berger 105's would really make this cartridge sing! I wish I had explored the Berger 95 grain VLD more. Probably could have got 2900+ fps with .480 BC.

If I ever do a Grendel based AR again I'd try the 22AR and shoot the 90 grain bullets just to save some recoil and powder.

Enjoy your new 6mm FAT RAT. Great thread!
 
Steve,

I think I saw another post about the barrel extension coming loose when I was doing my initial research. I would assume it was a freak occurrence unless it was related to the super hot loads. Those loads are screaming, quite impressive out of that little case. I'll be happy to inch over 2800 fps for now once I'm done fire forming.

For those of you that were loading for this type caliber for a while what brand brass where you using? I've got all Lapua but I'm assume some of you use Hornady or both. Was there a significant difference in longevity or accuracy?

I'll be sizing cases today and tomorrow for most of the day after I get some chores done around the house. Should get a few hundred done and ready to shoot outdoors next week. I'm gonna get some dope on the fire forming loads and shoot a match on the 4th Saturday of this month with the fire forming loads.
 
Fried Chicken Blowout said:
Steve,

I think I saw another post about the barrel extension coming loose when I was doing my initial research. I would assume it was a freak occurrence unless it was related to the super hot loads. Those loads are screaming, quite impressive out of that little case. I'll be happy to inch over 2800 fps for now once I'm done fire forming.

For those of you that were loading for this type caliber for a while what brand brass where you using? I've got all Lapua but I'm assume some of you use Hornady or both. Was there a significant difference in longevity or accuracy?

I'll be sizing cases today and tomorrow for most of the day after I get some chores done around the house. Should get a few hundred done and ready to shoot outdoors next week. I'm gonna get some dope on the fire forming loads and shoot a match on the 4th Saturday of this month with the fire forming loads.
Click to expand...

The problem with the barrel extension is guys trying to tighten them with a hand torque wrench. 9 times out of 10 they will spin in the vice and not have enough torque on them.
An impact torque wrench is the only real way to get them tight enough that they don't work loose.
 
Been shooting a 6 RAT since Greg came up with the round, think mine was one of the first 10, some time in 2010 I think. Tried a lot of different bullets and powders and settled on 105 Amax over 28.5 gr. of 8208 @ 2740 fps, using Wolf SR mag primers, oal 2.265. The barrel is a 22" 1 in 7.5 twist Krieger, contoured .820 under the handguard, .750 gas block, .720 to muzzle. The Berger 108 target was a close second. Haven't tried the Berger 105 hybred in this rifle yet, expect it will be a great combo.

I would parrot ERUD in praise for this cartridge (not much to add as he covered it) out to the 600 to 800 yd area, still usable past this range but it is slowing enough to give up wind to other rounds. I've got some brass that have upwards of 15 loadings on them, never had to trim. The Alexander Arms mags work the best for me, never an issue with them.

Shot a lot of 87gr. V-max until I just decided to stick with the 105 for everything. Works well for comps and yotes. Both of my uppers shoot the same loads accurately and I have an extra barrel ready to go when the time comes to retire a worn out barrel. If I could only have one AR it would be a 6 RAT.
 
Nice write up. I've had Lee do a couple of service rifle uppers for me and they were both shooters. He is a small shop, but im guessing that if people here realize how well these Fat Rats do and how easy it is to deal with Lee (he answers his phone!) that he will be building a ton of them. He is one of the few gun builders I know (besides John Holliger) who actually shoot often and well in completions. Aside from that Lee runs all the Highpower Matches at the Des Moines club. Can't say enough about this guy... Thanks again for all the photos and detail in your thread.
 
Hey guys thanks for the additional replies to the thread with your experiences. After hearing from you all I sold off a few other bullets that I got samples of and decided to just shoot out the rest of the Nosler 105gr that I have and then treat the fire forming loads more serious. I've got the remaining 200 Nosler bullets are all loaded up and ready to roll.

On another thread I was educated to why the gas block was not closing off as much gas as I expected. The adjustment screw threads needed to be chased with a tap to thread the gas tube in order for the set screw to enter into the gas tube area of the port. I hadn't had to do that with a previous JP as I assume the gas tube must have had an over sized port which allowed for the screw to enter. I'll be going to adjust the gas system down at the indoor range on Friday and then I'll be headed to the outdoor range to get dope on Monday. My first steel match will be in two weekends from now and I'll be using the Nosler fire forming loads for that. - BTW this match never happened. It was cancelled for some reason.
 
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Got a chance to hit the 100 yard indoor range today and get the gas system adjusted and adjust the zero for the load I decided on for the remainder of the Nosler bullets. Ended up with 29.4gr of Reloader 15 with the 105gr Nosler BTHP at 2.29 which is a huge jump to the lands at 2.365 for the last 200 of the Nosler bullets. Went to the range and started shooting with a 10 shot group without adjusting the zero. The big hole you see high in the target is the very first 10 rounds shot. Then I messed with the zero till I had a dead center hit and was done for the day. As other's have stated, even the fire forming loads are pretty good. I'll hit the outdoor range and get dope to 550 yards on Monday.



Untitled by FriedChickenBlowout, on Flickr
 
Oooh... That must mean he has bolts heads back in stock. I'm suppose to be getting a backup bolt head when they arrived.

How long did it take for your barrel to get done? I'm already thinking about ordering a 22" barrel for matches that require a shorter barrel.
 
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