A friend of mine just gave me a Krieger AR15 blank that is 6mm with 1-8" twist and rifle length gas. For those shooting the 6mm AR or 6mm Fat Rat, is the rifle length gas system going to tie me to the 6mm AR? I had planned on the Fat Rat with +2" gas but now I have this barrel.
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You'll probably be just fine with rifle length gas, although you didn't mention the barrel length which is much more important for gas system length than whether it's a 6mm AR or Fat Rat.
It's a 27" blank so it'll be whatever I decide. To me the port location does have something to do with powder choice which might affect my chamber choice. I'm certain it'll be fine with a 6mm AR/243 LBC but I'm wanting to know if anyone here uses a Fat Rat with rifle length gas. Everyone I know shooting them uses +2".
Yes I have a Fat Rat with Rifle Length Gas, built by Lee Wells. What would you like to know?
Your gas port has nothing to do with powder selection, most common powders for 6mmFR are R15 and H4895
There are only two types of chambering for the FR, FR Standard made for Single loading and FR Varmint designed to be used for magazine length cartridges.
You can however change the throat to accommodate a specific projectile, which I would not advise because the Fat Rat Varmint chamber shoots anything from a 95 grain TMK to a 105 hybrid perfectly
There are only two types of chambering for the FR, FR Standard made for Single loading and FR Varmint designed to be used for magazine length cartridges.
You can however change the throat to accommodate a specific projectile, which I would not advise because the Fat Rat Varmint chamber shoots anything from a 95 grain TMK to a 105 hybrid perfectly
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The FR-V is what I'm looking at but wanted to know how long a barrel you used with rifle length gas? What sort of MV are you getting and with what bullets? I will shoot 95-107gn bullets and if this works out I am probably going to ditch my AR-10 for PRS Gas Gun and 3-Gun Nation LR.
I ask because I know with the 243 LBC a popular powder is 8208-XBR and I wouldn't use that with a long barrel and rifle length or extended gas. I think with rifle length gas that about 22" is what is perfect for length with 24" being the top end. After that the port needs to move and I think it allows you to change powder choices some. For example I get better performance from 8208-XBR in mid-length gas at 18" than with slower powders and better luck with rifle length and 20" with RL15 and 2000-MR using .223 and 77gn bullets than I do with 8208-XBR. I can't help but think a 6mm might play similarly. I guess port location and length and powder is something we will likely just have to disagree about.
All, I really want to know is if you have a gun that is working and would you have done anything differently in order to get better performance. Is Lee who you recommend?
I ask because I know with the 243 LBC a popular powder is 8208-XBR and I wouldn't use that with a long barrel and rifle length or extended gas. I think with rifle length gas that about 22" is what is perfect for length with 24" being the top end. After that the port needs to move and I think it allows you to change powder choices some. For example I get better performance from 8208-XBR in mid-length gas at 18" than with slower powders and better luck with rifle length and 20" with RL15 and 2000-MR using .223 and 77gn bullets than I do with 8208-XBR. I can't help but think a 6mm might play similarly. I guess port location and length and powder is something we will likely just have to disagree about.
All, I really want to know is if you have a gun that is working and would you have done anything differently in order to get better performance. Is Lee who you recommend?
Like a said above, YOUR GAS PORT LOCATION HAS ABSOLUTELY FUCK ALL TO DO WITH ANY OF THE STUFF YOU MENTIONED ABOVE.. muzzle velocity variation will come from barrel length, type projectile and powder you have selected.
Any barrel length from 20" to 26" is ideal for rifle length gas system, you can go + 2 if desired but it's not necessary just get adjustable gas block. Yes cLee Wells quite literally design the Fat Rat so yes he is who you should go to, maybe he can get some of this info to sink into your head
Any barrel length from 20" to 26" is ideal for rifle length gas system, you can go + 2 if desired but it's not necessary just get adjustable gas block. Yes cLee Wells quite literally design the Fat Rat so yes he is who you should go to, maybe he can get some of this info to sink into your head
If you're done yelling in response to what I thought was a reasonable reply, I'm still looking for approximately what MV you are getting, from what barrel length, and if you think the FR-V is worth the effort over a 243 LBC. I'm primarily a bolt gun guy and only shoot gas guns at work and now in matches because there are lots of gas gun matches.
I thought I'd ask here first before bothering Lee if I want going to commit to this project. I also know he's not the only guy who chambers for things like the 6mm AR, Fat Rat, AR Turbo, etc.
I thought I'd ask here first before bothering Lee if I want going to commit to this project. I also know he's not the only guy who chambers for things like the 6mm AR, Fat Rat, AR Turbo, etc.
Thanks. What barrel is that because that seems like a reasonably attainable MV compared to the numbers some BHW users post? None of my Krieger have been particularly fast or slow.
KP,
I understand the three groove BHW barrels have less resistance. I was quite surprised to find mine shooting over 2600 with 123's out of a 18" mid length gas, 6.5G. The rifling style supposedly imposes less resistance.to the bullet.
And, FWIW, the port position is one factor that allows faster or slower powder. Which in turn can increase velocity.
One, the pressure at the port needs to be reduced to a level the rifle can handle. The shorter the port distance the faster the powder needed.
Two, that means you can't use slow powders as they wont reduce pressure enough at the port, if that distance is too short for the powder burn.
Three, pressure bleeding off from behind the bullet back through the port essentially ends acceleration of the bullet down the barrel. Length of barrel is less important than length of gas path.
Four, because of #3 it means no matter how long your barrel is, you won't get more velocity with a shorter port distance. How much barrel there is past the port, only need be long enough so that you have enough 'dwell' time for the gas to reach the action. Again, though, the bullet won't be accelerating. ADDED: K_4C is doing the best overall option by adding a "superlative" adjustable gas block. This will allow you to shoot everything from 55's all the way up to what your barrel twist will handle.
So, IMO, you ask a good question. If I could I would run the +2". But, if what you have is rifle length, it will do you well enough to get what you need.
I understand the three groove BHW barrels have less resistance. I was quite surprised to find mine shooting over 2600 with 123's out of a 18" mid length gas, 6.5G. The rifling style supposedly imposes less resistance.to the bullet.
And, FWIW, the port position is one factor that allows faster or slower powder. Which in turn can increase velocity.
One, the pressure at the port needs to be reduced to a level the rifle can handle. The shorter the port distance the faster the powder needed.
Two, that means you can't use slow powders as they wont reduce pressure enough at the port, if that distance is too short for the powder burn.
Three, pressure bleeding off from behind the bullet back through the port essentially ends acceleration of the bullet down the barrel. Length of barrel is less important than length of gas path.
Four, because of #3 it means no matter how long your barrel is, you won't get more velocity with a shorter port distance. How much barrel there is past the port, only need be long enough so that you have enough 'dwell' time for the gas to reach the action. Again, though, the bullet won't be accelerating. ADDED: K_4C is doing the best overall option by adding a "superlative" adjustable gas block. This will allow you to shoot everything from 55's all the way up to what your barrel twist will handle.
So, IMO, you ask a good question. If I could I would run the +2". But, if what you have is rifle length, it will do you well enough to get what you need.
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Careful sandwarrior or bigdick83 is gonna jump on you and tell you that you don't know shit.
Acceleration. The bullet won't gain speed once it's past the port.
I'd like to see some evidence of that claim.
Here's a good place to start. Keep reading until you get to the dynamic flow part as that is what pertains to a bullet going down a rifle barrel:
https://www.witpress.com/Secure/elibrary/papers/AFM98/AFM98004FU.pdf
Also, keep in mind I said "accelerate". Not that gasses have stopped pushing altogether on the bullet. As the bullet passes the port, the pressure has to have dropped enough so that it won't be overbearing on the rifle. (see 'first', and 'second' above) But, you still need to pull enough gas off the system to make the rifle work.
In the case of K_4c and the adjustable gas block, it's there so as to adjust to a wide range of bullets and powders, that may not be optimal for running in his gas length of rifle. Over/under pressure at the port. It's still for the operation of the rifle, not trying to gain velocity. Unless, it's completely shut off, and you have rounds specifically for that scenario.
If it's open enough to run the rifle, the bullet won't be accelerating beyond the gas port.
https://www.witpress.com/Secure/elibrary/papers/AFM98/AFM98004FU.pdf
Also, keep in mind I said "accelerate". Not that gasses have stopped pushing altogether on the bullet. As the bullet passes the port, the pressure has to have dropped enough so that it won't be overbearing on the rifle. (see 'first', and 'second' above) But, you still need to pull enough gas off the system to make the rifle work.
In the case of K_4c and the adjustable gas block, it's there so as to adjust to a wide range of bullets and powders, that may not be optimal for running in his gas length of rifle. Over/under pressure at the port. It's still for the operation of the rifle, not trying to gain velocity. Unless, it's completely shut off, and you have rounds specifically for that scenario.
If it's open enough to run the rifle, the bullet won't be accelerating beyond the gas port.
Sounds like some gross misunderstandings of internal ballistics going on here, along with completely ignoring (or misunderstanding, again) how port size and/or gas block adjustment affect this stuff. The barrel length stuff you're saying is completely untrue.
KP, you're kinda overthinking this a bit. There's not that much difference between the 6mm Grendel-based variants that you need to worry about different powders and burn rates for setting up your barrel. Also, 8208 works great in a 24" rifle length 243 LBC; I think some of your estimates on that stuff is a bit off, or you're thinking the little details matter more than they really do.
Seriously, just pick whichever chamber you want and build it. Make the barrel length whatever you want, but if you're not sure, it's a lot easier to start long and shorten it till you're happy. Tune the gas with an adjustable block that does not bleed off, and enjoy shooting.
Yep, This thread has gone Full Retard.....
So you're saying my chronographed velocities from a host of carbine length, mid-length, and rifle length gas paths, showing mostly slowest to fastest in that order, are wrong? Why aren't we getting the same velocities out of Mk 262 from an M4 as a full length A2?
You are right though, it is overthinking it. The OP's friend gave him a Krieger. He could just cut it the way he wants it and shoot it. FWIW, I never said there was a lot of difference in the 6mmAR-.243 LBC. etc. I said the gas block gives you a lot of lattitude in what you can load for the rifle. But, if you think gas path length doesn't matter, go get a 24" 6.5G and drill a carbine length gas port in it and see if it's satisfactory for you.
A 1970 Army study on this exact issue:
https://www.witpress.com/Secure/elibrary/papers/AFM98/AFM98004FU.pdf
Without calling anyone out, here is a fairly good test of a superlatine arms gas block. It shows the velocity impact of unrestricted gas setting, restricted adjusted setting and bleed off settings. You can draw your own conclusions as to if velocity is impacted by the length of barrel after the gas port.
https://m.youtube.com/watch?v=UwHA9pvkgYA
https://m.youtube.com/watch?v=UwHA9pvkgYA
I stand corrected:. I thought K_4c was saying Superlative as an adjective. I did not realize it was a company.
Whatever you're data is, it's pretty clear you've misinterpreted what it means.
Why do you think your question about the M4 vs A2 relates to the discussion? Obviously the shorter barrel is slower, duh. Your claim that the barrel length after the gas port doesn't accelerate the bullet is completely wrong, along with most of the other stuff you said too.
Have you ever shortened an AR barrel and compared velocity? If you had, you'd see lower velocity with the shorter barrel in most cases. That tells us the bullet is still accelerating in the last few inches past the gas port. There is plenty of data showing this online.
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Inch by inch barrel cut down test.
https://rifleshooter.com/2014/04/223...friends-rifle/
You will see in the tables velocity gain or reduction is dependant on the load.
https://rifleshooter.com/2014/04/223...friends-rifle/
You will see in the tables velocity gain or reduction is dependant on the load.
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I've worked with both 6 HAGAR & 6 RAT rifles for several years. My application was originally XC HP matches, so went with 28" bbls in both chamberings, with +2" gas system. More recently, I built myself a 24" 6 RAT w/rifle gas system for DMR/tactical matches. I bought four straight 1.050" dia Krieger 1-8tw blanks, then contoured, chambered, & drilled gas ports to work with the RAT. I drilled the port at rifle length with a #50 drill, and kept enlarging the port until it would lock the bolt (LMT Enhanced) back on an empty mag. Wound up at .086"/#44 port, which locked the bolt back with 87gr Hornady BTHP bullets over 29.9grs of RL15 & 28.9 of 8208. These were fireform loads. I did the remaining three bbls the same as mine, and all were sold to customers. This was back in 2011, and since I never got any negative feedback from the three guys the bbls were sold to, I'm going to assume that the gas port diameter worked as well for them as it did for me.
I have to push the 24" RAT too hard to suit me to get 2800fps with 105s, so settled on 2750fps using RL15.
Since LMT no longer catalogs the enhanced 6.5 Grendel AR15 bolt, I've been using JP Hi Pressure bolts with good results. I don't do 6 RAT bbls without the sale of one of these JP HP bolts - have heard too many stories about broken bolt lugs on mil spec 6.5 Grendel bolts to be comfortable selling a RAT bbl w/o the best quality bolt I can find.
I have to push the 24" RAT too hard to suit me to get 2800fps with 105s, so settled on 2750fps using RL15.
Since LMT no longer catalogs the enhanced 6.5 Grendel AR15 bolt, I've been using JP Hi Pressure bolts with good results. I don't do 6 RAT bbls without the sale of one of these JP HP bolts - have heard too many stories about broken bolt lugs on mil spec 6.5 Grendel bolts to be comfortable selling a RAT bbl w/o the best quality bolt I can find.
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My post above relates to gas operated semi-automtic rifles. Not bolt action rifle.
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Sorry, duplicate post
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It's possible you've done that and got that result, so I'm not calling complete BS, but it's very unlikely and definitely load dependent, and rare enough that you should have realized the result you got was unusual. Frankly, you're flat out wrong on this statement.
Try cutting another barrel down and testing a few different loads. You'll see most lose velocity. For example, cut a 16" carbine gassed 5.56 barrel down to 10.5"; you'd have to be completely ignorant about this stuff to expect velocity to remain the same. I've shortened a bunch of AR and other barrels in different calibers, and velocity is almost always lost unless the barrel is already too long for the cartridge.
And, once again for the third time, you need to explain why you don't run carbine length gas tubes on your 20"-24" barrel. Then again, you probably do and just change the port size and load.
Because there's no need for carbine gas systems on anything longer than 12.5". AR's have come far enough in the last few years that nobody wants an unnecessarily overgassed system any more. Velocity has nothing to do with it. By your theory my 16" rifle gas barrel should have the same velocities as my 22" rifle gas barrel. I assure you thats not the case.
There are several facters that would impact velocity after the gas port:
1) load (bullet weight and burn rate of powder)
2) open, vented or adjustable gas block (unresticted vs restricted)
3) dwell time (gas system length, load, gas block or vented carrier system, buffer weight and spring all impact)
Blanket statements are just ignorant.
1) load (bullet weight and burn rate of powder)
2) open, vented or adjustable gas block (unresticted vs restricted)
3) dwell time (gas system length, load, gas block or vented carrier system, buffer weight and spring all impact)
Blanket statements are just ignorant.
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Agreed, blanket statements are ignorant. Saying gas path distance has no bearing on anything is just flat wrong. I'm also looking at it from a standard rifle configuration with standard ammunition. So, it seems like we are talking in circles.
Most of us custom load. So, there may well be changes to velocity after the port. But, I can't think of a single one of us that if we seriously wanted more velocity would attempt to do it building a long barrel and a short gas path.
I have always found though, that once you have a system in place, loads can only do so much to increase your velocity. Yes you want to maximize your load for your system. The only way to optimize that is to install an adjustable port. That way you can use a slower powder and crank down the port to get more push down the barrel. But, I'll still maintain most of your velocity is coming before the port, and adjusting the port down is to keep the rifle from getting overgassed is more the reason than getting extra push after the port. As, even with the port cranked down you are taking at least one third of the gas.
That is not what I was speaking about. Don't falsely attribue something I wrote to cover your misstatement.
The original post in this thread was specifically about gas path length. Since you lose about 40% of your gas past the port, you are not getting any meaningful acceleration. At least not as much as a longer gas path would give you.
The two cartridges he asked about are not different enough that either would top the other. Both would benefit if he traded for a rifle length +2" gas system.
And, if you note in my first post before jumping in and splitting hairs I said an adjustable gas block is preferable. But that is still mostly so you can load the rifle up and not slam your action to pieces.
This is the comment that I was addressing. Patently false as stated. There are caveats, but as written it is a false statement.
You forgot to add the standar rifle configuration. But, by your post, the caveats are the rule. And the blanket statement stands as you yourself even acknolegded gas path length is a factor. So much a factor in fact, that if it wasn't, you'd all be shooting your 24" barrels with carbine length gas tubes. Oh, wait! That's why we have LONGER gas tubes. Which is the MAIN factor.
BTW, this is the post I was addressing:
Got anything to say to that? I mean it is about the original post. Or do you just want to go back and forth arguing your point that your chosen factors matter and the real one doesn't?
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Sure; big jake is correct. By regulating the gas properly the location of the gas port becomes less of a factor. Further there is a meaningful increase in velocity between an 18" and 22" barrel with both having rifle length gas systems. That is first hand experience.
Just an observation, as this is not the first time you have just thrown B.S. out there
Sometimes it is better to just read or comment in a constructive way rather than try to put out bad information. I'm not sure why you keep doing this, but maybe you should do a little introspective reflection. It is old and lowers this forum to the ARF.com level.
"By regulating the gas properly" Are you wanting to sell a thousand barrels by drilling each one individually? Or, would it make more sense to drill them all one way, so it will work from the get go?
Your meaningful increase from 18" TO 22" means nothing as the OP asked about a 24" barrel using the rifle path he has now or trading for a barrel with a +2" gas path. There's a reason the Recon and SBR variants are 18" with rifle length gas paths. Because you don't lose velocity with a standard load.
So, you are right, do it your way. I've tried the different load method. There's only so much latitude. It's not as easy as you make it sound. Gas ports: once they're in they're in. Unless you want to take the whole rifle apart and re-tune it to another load. I've watched people trash their upper receivers doing what you say is perfectly okay. Not everyone wants to spend their time away from shooting doing major fixes on their rifle to get it to work right. They just want to shoot it with a load that works. So, why not start with the right gas path length?
By the first line in your reply you ought to make your next build with a 24" barrel and a carbine length gas path...cause you are amazing and the gas length doesn't matter
As to throwing BS out there, you are still in denial. I said you had a good cartridge. The issue was feeding from an open stagger feed magazine, much like you find on standard rifles all over the place. You don't seem to have a problem because you are feeding from a center-feed magazine. After the whole thing got said and done all that was needed was a modification to the follower. Nothing wrong with the cartridge. But, you won't listen. Apparently you're still butt hurt over someone pointing out an issue with you're fabulous invention. I'm sure as hell not going to recommend your cartridge seeing as you don't think feedback is acceptable. And, $250 for dies? Tell me again, how much I'm gaining?
If any of you Guys would be interested in a MK12 MOD 0 Upper Chambered in 6mm Fat Rat with the best parts money can buy send me a PM.
She pretty little thing..
She pretty little thing..
By the first line in your reply you ought to make your next build with a 24" barrel and a carbine length gas path...cause you are amazing and the gas length doesn't matter
Never said that. You sem to be very liberal with your interpretation, or your reading compthension skills are lacking.
You have a history of making comments on matters of which you have little or no understaning, not to mention no first hand expirience with. So butt hurt? No just tired of internet experts that dispence their wisom on forums to bolster their feeling of self worth. The problem that I have with that is: individuals that do not know any better will act on these "experts" advice and end up wasting their hard earned wages because of some hack... I put you in the hack catagory.
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I can't believe this nonsense is still going.
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