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6mm fat rat/ turbo 40 ar

Forward543

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Feb 14, 2017
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Is anybody running these? If so hows your accuracy and reliability? Why the side charging upper? What is the barrel life? If you can really run the 105/108's @ 2900 fps, thats a very attractive setup. Any experience is appreciated. Looking to use this setup for presicion rifle.
 

supratt96

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Dec 22, 2010
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I've been running a Turbo 40 for several years. Accuracy is excellent. 1/2 moa is easy with occasional groups sub 1/4 moa. The side charging option is more of a pain than a benefit since you have to remove the charging knob to pull the bolt. I took mine off and just use the standard rear charging lever. Mine has a 24" barrel. I get mid 2800s with 105s, mid 2900s with 95s and 3000 with 87s. All shoot very well and the rifle has been very reliable. As with any AR, make sure you bump your shoulders by at least .003" when sizing your brass. A longer barrel will of course give higher velocities. I have about 800 rounds through mine now, so I can't give any real insight to barrel life. I would expect at least 2000 rounds under normal use. Pretty easy to load for too. Seems to shoot well with just about any premium bullet from 70gr to 108. Powders that have worked well include RL-15, H4895 and Varget. Probably any powder in that speed range will work well.
 

Jibnast

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Feb 11, 2017
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I have a 24 inch Fat Rat and with the 105's I'm getting 2756 with AR Comp. Barrel life for me has been a crapshoot with on going to around 2200 and the other one to 1700.
 

steve123

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2900 fps with either cartridge is too hot of a load with 105's unless maybe you have a 30" barrel. My 6mmART40 with 26" going that fast was too hot. 2850 - 2875 fps, yes, but still a warm load.

Since I rarely shoot my 6 FatRat past 800Y I'm trying out the 95 grainers soon. A little less BC, a little faster, less recoil, with wind drift the same and less intrusion or compression on the powder. Plus I can keep my precious 105 hybrids solely for the bolt gun.

My FatRat is at 2780 fps with 105's at 22".
 

Forward543

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So if i run super long i could get 2850? Maybe better go 22" -24" and get 2775ish. Or go 22 predator with 80's
 

Erud

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I get 2780-ish with 105's out of 26" barrels in the 6mm AR Turbo 40. If I push them much faster than that the brass doesn't last, not worth it. I've put just over 10,000 rounds through 3 barrels in NRA HP competition, and have gotten a little over 3k of top accuracy out of all 3. Around that number, x-count starts to drop off at 600 yards. 2 Bartleins and 1 Pacnor.
 

steve123

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So if i run super long i could get 2850? Maybe better go 22" -24" and get 2775ish. Or go 22 predator with 80's

I haven't tried a 22 cal version off the grendel case but it makes a lot of sense. I did try a 22 wildcat off of 6.8 and liked it the most so far but all the work to form and trim (more to it than that in this case) isn't something I want to do.

Like ERUD mentioned, above 2800 fps is a warm to hot load in the 6mmART40, even so I still got 6-7 firings out of Lapua brass, though a longer barrel will help with FPS. I've settled on H4895 but trying some of the newish powders could give the extra velocity too, especially with a longer barrel. A 28" barrel should give approx 45-50 fps more alone.
 

Blazin

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Blazin figure I can use my 6.5 grendel sizer, what are you using as a bullet seater.

Still collecting the reloading supplies but I plan to use a Redding 6.5 Grendel Bushing resizing die with a 268 bushing, and a Hornady 044103 6mm seater. I hear this cartridge really likes Sierra 95 MatchKings.
 

tsu45

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What is the favorite out of all the 6mm ar15 frame cartridges? I mostly want one for shooting steel. Being able to shoot the heavier bullets at decent velocities is first priority followed by brass convienence (not having to fireform, turn necks, etc.)
 

shanem81

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My vote would be the 6mmar/243 lbc.just finished one am doing load work up. I went that route because I didn't feel it was worth forming brass for a ar. I'm still playing with loads but a 22" is getting 2900-3000 with 95 Bergers. Haven't gotten out to try the 105s yet but guessing it will be hard to beat the 95s.
 

flatland1

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My 1st 6 RAT was on a 28" Bartlein 1-7.8tw bbl by WOP, in an upper with the side charge set-up so I could use a WOP buttstock w/adjustable cheekpiece. The rifle was set up as for use in across the course HP matches, and was very reliable - don't recall ever having an alibi. I sold it after getting into bolt guns with Gary Eliseo's tubegun setup, so have no idea how long that Bartlein would've lasted. However, my friend (who designed the 6 RAT & had John Holliger doing our barrels & Hornady making dies) is still shooting his original RAT AR bbl, with over 3000rds through it, and is still happy with the accuracy. I believe he's running RL15 or perhaps IMR 8208.

I bought a reamer after selling my RAT upper so I could do a few barrels for myself & others, and have used it to build myself a 24" AR15 for use in some DMR steel & paper matches we ran down at the Hutch club a few years ago. Longest distance we shot there was 600yds, so I bought some S95MKs and loaded them to magazine length with RL15 for just under 2800fps, and get very nice accuracy out of them at that level. Have also done a couple of CZ 527 carbines in the RAT - they make a sweet little walking varmint rig, and I wouldn't be afraid to take one out after deer with the right bullet.
 

Yondering

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Dennis, what size neck does your reamer cut?

I considered trying to use a 6 PPC reamer (just running it in deeper) and then throating as necessary, but everything I've found available for rent cuts a .262" neck, and I want at least .271-.274". PTG does sell several of the 6mm Grendel-based wildcat reamers though so that's always an option.
 

flatland1

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Yondering - My reamer print shows a .275" neck dia. I'd bet that the guys shooting point blank BR with the Grinch are doing a .262" neck & turning necks on their brass. They must be doing something like that, because I've read some glowing reports of BR results with this Grendel-based Grinch.
 

Yondering

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.275 sounds right for a nice no-turn neck. I'm sure you're correct about the point blank BR shooters; I just don't want to do that in an AR.
 

Blazin

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I just picked up a 6mm Fat Rat upper from a guy on 6.5 Grendel forums, and he has three left, link below.
 

bigjake83

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  • May 19, 2013
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    Just contact Lee Wells if you want a 6mm FatRat, He invented the FatRat so you can't get any better then that. I know he has Krieger Barrels in stock, and maybe some Bartleins.

    You can pick up a brand new Complete Upper with a Krieger Barrel for a couple hundred more and built by the man himself..

    http://www.accurateandreliablerifle....OUR-UPPER.html

    My 6mn FR was built by Lee with a 22" Bartlein Barrel 1-8 twist, 5R, Medium Varmint Contour. As a complete MK12 MOD 0 Upper.

     

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    steve123

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    Finally tried the 95 gr SMK with the pointed tips, glad I did. Wanted the TMK 95's but my bud who I went in with on the order got the SMK not understanding the difference. Previously I have been using the Berger 105 hybrids which shot okay but not great in my 6mmFatRat upper with Wilson barrel, barrel just didn't like them too much???

    Well the Wilson barrel shot the 95 SMK fantastic, really waking it up. High node was 2870 fps/22" barrel and with small vertical at distance. Recently put a Witt brake and combined with going 10 grains less bullet weight the felt recoil is almost like a 223.

    I was hitting a 5" plate at 550Y, 10" at 675Y, 12" at 810Y and engine block at 1122Y with multiple hits in a row in 4-8 mph winds. YAY, bout time. Functioned perfectly as well.
     

    bigjake83

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    Finally tried the 95 gr SMK with the pointed tips, glad I did. Wanted the TMK 95's but my bud who I went in with on the order got the SMK not understanding the difference. Previously I have been using the Berger 105 hybrids which shot okay but not great in my 6mmFatRat upper with Wilson barrel, barrel just didn't like them too much???

    Well the Wilson barrel shot the 95 SMK fantastic, really waking it up. High node was 2870 fps/22" barrel and with small vertical at distance. Recently put a Witt brake and combined with going 10 grains less bullet weight the felt recoil is almost like a 223.

    I was hitting a 5" plate at 550Y, 10" at 675Y, 12" at 810Y and engine block at 1122Y with multiple hits in a row in 4-8 mph winds. YAY, bout time. Functioned perfectly as well.

    I've had excellent results with the 107 SMK and the 95 TMKs..
     

    Niles Coyote

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    Still collecting the reloading supplies but I plan to use a Redding 6.5 Grendel Bushing resizing die with a 268 bushing, and a Hornady 044103 6mm seater. I hear this cartridge really likes Sierra 95 MatchKings.

    Some data points for you.
    Seating depth to lands measurements with my Hornady tool on the ARP barrel.

    95 Sierra Tipped MK= 2.778/2.363
    95 Berger Hunting VLD= 2.755/2.343

    Hornady 105 BTHP= 2.750/2.250
    Hornady 105 Amax= 2.750/2.272
    Berger 105 Hunting VLD= 2.748/2.334
    Berger 105 Hybrid= 2.750/2.343

    I fired some shots to check for pressure and velocity using Hornady new brass and CCI #41 primers:

    105 Hornady BTHP seated -.014 with H4895
    26.5=2601fps
    27.0=2705
    27.5=2745 (way over pressure and blew a primer)

    The rest all use 95 grain TMK's seated 2.250

    Varget
    29.0=2802
    30.0=2908 (very light ejector swipe)

    H4895
    27.0=2747
    28.0=2857

    Ar-Comp
    27.0=2824
    27.5=2813 (primer appeared to have failed on the radius)

    All round failed to cycle the bolt at to this point and one thing I had noticed was the gas port was smaller than my other rifle length ports at around .084"

    So I opened the port up to .093" and went out again. This time with an eye on loads that should put me in the 2700-2800fps range using 95 grain TMK's and my low mass JP carrier.

    Varget
    28.0=2711
    28.5=2759
    29.0=2797

    After seeing perfect funtion I switch the low mass carrier with a full mass milspec m16 carrier and fired two more of 28.5 grains of varget and got 2774 & 2768

    Ar-Comp
    26.0=2712 (Failed to lock back)
    26.5=2776 (locked back but on the carrier not the bolt)
    Both of these loads showed very faint ejector swipes so I dont think AR-Comp is going to work in this barrel.

    Varget and H4895 appear to be where I need to look.


    At my 200 yard range.
    I tried 95 grain tmk's loaded to 2.250" (that has them jumping a lonnnnng way) and shot groups using H4895 and Varget and my best group was about .75 moa or 1.5" with most at or just over 2"... after which I bought some 95 SMK's and they are doing much better. I also tried 105 berger hybrids but those were not any better than the TMK's.
     

    steve123

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    I've had excellent results with the 107 SMK and the 95 TMKs..

    All my other 6mm barrels have shot the hybrids just awesome. Figured it was just that the Wilson barrel wasn't a good one ??? After reading Niles post I'm glad I got the 95 SMK, gonna stick with it. 95's seem well suited for the case, barely compressed vs crunching powder. No difference in wind compared to the hybrid since it's going 100 fps faster.

    I forgot to order the new Hornady 108 to try, no matter now.

    My load is 29.3 H4895 in lapua brass, has slight ejector smear but CCI 450's are not flat, it's a warm load. 2.245" OACL. Upper is more reliable with this load for whatever reason???

    I tried the Berger 95 VLD in my old 6mmART40 but couldn't get them to shoot well. SMK's back then had the big meplat and lower BC so didn't try them. 105 Amax became my go-to at the time, shot well and were cheap. Warm load too but shot that load the best of all I tried.

    I was kinda pissed at this current upper, almost gave up on it. I lucked out with the 95 SMK!

    Still want to try a 22 cal version.

     

    flatland1

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    steve123 - I've not done any shooting recently with my 24" Krieger barreled 6RAT (the original version w/.275" neck), but have used the same reamer in a Bartlein 8tw light Palma 5R blank finished at 24" for a Howa Mini action. I know Greg designed his 6RAT reamer for gas gun use, but have been getting good accuracy with it in a couple of bolt gun barrels. I'm stoked on these Mini actions, and have also done a 20 Tactical on another one, which turned out real well. Next project will be a 22 Grendel for another Mini - need to get a barrel blank ordered ASAP, and will then order the finish reamer from PTG, which has a .256" neck & .110" freebore. I've had really good accuracy with Berger & JLK 90VLDs out of a couple of 1-7tw Kriegers in 223AI, so will probably go with another 7tw as opposed to something with a faster twist.
     
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    steve123

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    Mar 16, 2008
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    Do me a favor!!! Try out 22PPC in your HOWA Mini so I can be vicarious. Factory brass is available! Performance should be slightly above 223AI but no fireforming.
     

    Rade1MOA

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    Has anyone tried the 115 dtacs in these 6mm grendel variants? I know the twist would have to be right, although Tubb says a 1:8 will stabilize them....
     

    stalwart300

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    Any of you running a 22 Grendel? I like the idea but I'm not sure if it's worth getting into another caliber. Thoughts?
     

    flatland1

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    I wouldn't be considering doing a 22 Grendel build if it weren't for the Howa Mini action being available with the correct boltface. I've got a nice 24" Krieger bbl'd AR15 in 22 PDK, so am not interested in going the gas gun route with the 22 Grendel. But a nicely proportioned bolt gun, with a decent trigger & in a McM Game Scout stock - well, I'm looking forward to getting one built & doing some range work with the new Hornady 88s as well as Berger, JLK, & Sierra 90s. Probably going to be several months, since I've already looked at most of the places that carry Bartlein & Krieger blanks but haven't found anything yet. I'm not interested in using another 1-6.5tw bbl, as I had problems with the last one I had on an AR15. Since I've had excellent results out to 1400yds with the 90s in a couple of 1-7tw bbls chambered for the 223AI, I see no need to go with a faster twist. Something like a Bartlein #3 or even #2B would be ideal for what I'm after.
     

    Forward543

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    Any of you running a 22 Grendel? I like the idea but I'm not sure if it's worth getting into another caliber. Thoughts?
    I just put together a 5.56x42. Its shooting the 75 eldm at 3005 fps easily in a 20" barrel. The accuracy appears to be pretty good (pretty solid .5 moa so far, but needs volume testing). I am going to run it in a couple prs style matches and see what goes down ive ran the numbers to check the 80grn or 88's, and it does not seem to matter as far as 1k dope.
     

    Mr.BR

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    Oct 5, 2017
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    Old thread but here goes nothing

    I am fidgeting around with mini bolt action feeding from Ar15 mags , and am interested in something with more umph than 6ARC and it seems that 6 Fat Rat and 6mmAR Turbo Improved are just about the top end of Ar15 mag feed 6mm chamberings

    So if anyone has a reamer print of either caliber and is williing to share it would be great
     
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