6 Fat Rat and RL17?

[mclarenross]

I finished my new "tactical" AR a few weeks ago and am looking for some advise on loads for it. Ive searched and read and searched some more for all the info I can on the 6 Fat Rat, 6 AR, 6 AR Turbo and 6 AR Turbo 40 and everyone seems to be using either RL15 or 8208. Im using RL15 and 105 Hybrids right now and its working well but like everyone Im looking for a little more if possible. I know that RL17 in 308 gives a fairly good jump in FPS without excessive pressures so I ran the numbers in QuickLoad and it seems like RL17 is a good option for Fat Rat too. Any opinions on this? One thing driving this is I have a friend with a jug of RL17 he bought by mistake and he will sell it to me for a deal if I want it.

Cartridge : 6 mm Fat Rat
Bullet : .243, 105, Berger Hybrid G7 #24433
Useable Case Capaci: 30.828 grain H2O = 2.002 cm³
Cartridge O.A.L. L6: 2.275 inch = 57.79 mm
Barrel Length : 27.0 inch = 685.8 mm
Powder : Alliant Reloder-17
Predicted data by increasing and decreasing the given charge, incremented in steps of 2.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !
Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms
-20.0 79 23.61 2175 1103 24074 5425 88.4 1.801
-18.0 81 24.20 2230 1159 25612 5614 89.9 1.754
-16.0 83 24.79 2286 1218 27253 5797 91.2 1.709
-14.0 85 25.38 2341 1278 29004 5973 92.5 1.665
-12.0 87 25.97 2397 1340 30877 6141 93.7 1.621
-10.0 89 26.56 2454 1403 32879 6301 94.8 1.579
-08.0 91 27.15 2510 1468 35020 6451 95.8 1.538
-06.0 93 27.74 2566 1535 37315 6590 96.7 1.498
-04.0 95 28.33 2622 1603 39773 6719 97.5 1.454
-02.0 97 28.92 2678 1672 42413 6835 98.2 1.412
+00.0 99 29.51 2734 1742 45247 6939 98.7 1.372
+02.0 101 30.10 2789 1814 48294 7030 99.2 1.333
+04.0 103 30.69 2845 1887 51578 7107 99.6 1.296 ! Near Maximum !
+06.0 105 31.28 2900 1961 55120 7169 99.8 1.259 ! Near Maximum !
+08.0 107 31.87 2955 2035 58944 7217 100.0 1.224 !DANGEROUS LOAD-DO NOT USE!
+10.0 109 32.46 3009 2111 63082 7249 100.0 1.189 !DANGEROUS LOAD-DO NOT USE!


Here is the rifle for those who want to see.

27" Hawk Hill barrel with +2" gas system
Lancer Carbon Fiber 16.25" Handguard
LuthAR butt stock
Billet 80% lower and Mega side charge upper

 

[boltfluter]

Sorry no help on loads. Just wanted to say very cool rifle. 8)

Regards, Paul

www.boltfluting.com

 

[tonysnoo]

We have 3- 6 fatrats and 3- 6ar turbo40s in our group. Tried 4895, rl15, Varget, 414, 380, lever revolution, v140, didn't have rl19 so we tried 4350. Five of the six rifles are now shooting cfe223, 1 still using Varget.

Best velocity and case life with CFE223. Coated 108s at 2850 in 24" turbo and 2880 in 26" rat. About 8 firings on our first cases and still shooting good and holding primers very well....annealed about 3 times. The 87 berger hunting run about 3025 and accuracy and range will shock you.

Good luck...excellent looking rig!!

PS anyone know where any CFE might be available..please PM me...may not make it through our match season without....thanks.

 

[mclarenross]

Good information Tony. I appreciate the data. Unfortunately I havent seen and CFE223 on the shelf since about 2012ish. lol. All of those powders a just a little faster than RL17 on the burn rate chart but not excessively so. I guess Im gonna have to buy a pound and try it out.

Boltfluter, thanks for the compliments on the rifle.

 

[Recko555]

I have a 6Rat with the neck opened up a bit because of pressures. I shoot H4895 and get around 2750 FPS on a 26" barrel with no pressure signs. I used to use RL15 before that but wanted a powder that was more temperature stable. If I try to get more speed, it started showing pressures signs. By the way I used non-coated bullets.
I am happy with its accuracy, so I concentrate on marksmen ship now.

 

[rminut]

MR2000 has a good chance of meeting your demands. it's a little slower than RE15 but faster and more stable than RE17. I had the same accuracy as RE15 in my 6AR turbo.

 

[TBeghtol]

Just tested 28.3 gr 8208 behind a 105 Berger Hybrid .020 off lands.
2790 fps ES 8 SD 2.
Measured just over .6 for ten shots.
Tula KVB223M primer, AA case, 26 inch barrel.
Went to 28.5 just the beginning of pressure signs (slight ejector hole/extractor swipe) and only made 2810 fps with decrease in accuracy.

 

[tonysnoo]

MR2000 has a good chance of meeting your demands. it's a little slower than RE15 but faster and more stable than RE17. I had the same accuracy as RE15 in my 6AR turbo.

Hah hah...always looking for a better mouse trap...I may have to give that a try. I've seen it available quite often this last year. Was is any faster or easier on brass than rl15?

 

[Michaël T]

hi, any of you guys using a 28" barrel with 14" gasport?

thanks Michael

 

[mclarenross]

Interesting suggestion for the 2000-MR powder. I might look at some of that too. I wanted to run it through Quickload but apparently thats not a powder in the database.

MTSK Im running a 14" gas system with a 27" barrel.

 

[mic2377]

I would give 2000 MR a shot. It has been easier on brass compared to RL15, at least in my 308. It is very dense, very high energy, and seems to build pressure more slowly. It also seems to be less temp sensitive than other ball powders, but this is likely anecdotal as I have not done a true scientific test.

 

[mic2377]

Also, very neat rifle. I had considered a 6 mm AR-15 variant but had ended up building a 6.5 Creedmoor large-frame AR.

 

[243Mendoza]

Interesting suggestion for the 2000-MR powder. I might look at some of that too. I wanted to run it through Quickload but apparently thats not a powder in the database.
...

How did you get Fat Rat cartridge data into Quickload?

 

[mclarenross]

There is a feature to add a cartridge into the database. You enter all the case dimensions and the weight and it calculates the capacity for you. Came up with 38.06gr of H2O capacity.

 

[Ksmirk]

Sure am glad to see more info on this round as I'm gathering the remainder of parts as pennies become available, going to scope it so it may be awhile before it gets totally complete but at least there is some real world results out there to compare too.

Probably be shooting mainly 107's since I've got a mess but anyone point me in the right direction for some of the lighter bullets? as this rifle may make a trip to the p-dog field Later,

Kirk

 

[243Mendoza]

How is this done with quick load. Do you use this popup:
https://plus.google.com/u/0/photos/114169314448113695428/albums/6132242041311761153/6132242044505703554?pid=6132242044505703554&oid=114169314448113695428

 

[TikkaSporter]

I'm also running a 6mmAR Turbo 40, 25" Krieger, 1:8 twist... My loads are :

- 105 gr Hybrid, 30.3 gr Varget, CCI BR-4, 2790 fps
- 105 gr A-Max, 30.3 gr Varget, CCI BR-4, 2823 fps
- 87 gr V-Max, 31.0 gr Varget, Rem 7 1/2, 2975 fps

The 87 gr load is a hammer on coyotes, the 105 AMax load hammer's deer and antelope, and the 105 Hybrids are something new I'm trying. They seem to group slightly worse at 100 yards than the other two, but slightly better at 500+ yards... Or maybe I'm just imagining that part . All of them consistently print groups in the 0.3 - 0.6 MOA range.

I also tried RE-15 and H4895... Those powders shot well too, but not as well as the Varget... I still use 28.0 gr of RE-15 with the V-Max's for fire forming, which shoots rather nicely too.