6mm Rat vs Fat Rat

[10at6]

Wondering if any of you are shooting the above with 105-108 class bullets? Does the Fat rat offer any significant advantage? What are you loads. velocities, and results?
Thanks
10

 

[Tireguy]

I am shooting a FATRAT and love it! I believe the difference is the FATRAT had the neck opened up .002 over the RAT which allowed for an increase in velocity.

I shoot the 107 smk's and RL15 and I am getting just a hair over 2900 fps and I can reload the cases 5-6 times before the primer pockets loosen up. I played with N540 and got some great speed and tight groups but the brass was trashed after 1 firing. I am now running a carrier weight which dramatically improved case life.

I had Lee Wells at Accurate&Reliable Rifles put my rig together with a 28" Krieger and a thick walled billeted upper. I have shot out to 1000yds with it and as long I was on top of the wind, I really didn't feel I was at a disadvantage. I am planning on putting a 6BRX together in the near future and I plan on using Lee again.

Jon

 

[Shooterman]

I was under the impression that the neck was opened up in the Fat Rat so that non-neck turned lapua brass could be used.

 

[Tireguy]

Yes...if I remember correctly, some folks were having trouble attaining some decent speeds and had to turn the necks in order to achieve those speeds. So the resolution was to open up the neck about .002 in order to avoid having to turn the necks.

Jon

 

[GWY]

I've been shooting the Rat/Fat Rats for about 2-3 years using H4895 and 107SMKs. Getting around 2750fps out of 26" barrels. I could probably push them faster, but accuracy is so good that I decided accept it. I plan on trying out the Berger 105 Hybrids soon, as I think this may be an even better combination than the Sierras.

A big benefit of this cartridge is that the 107s can also be seated to magazine length which works great for windy days on the 300 yard line. For the 200 yard line, I use 90 Berger BTs.

 

[Hal]

What are the 6mm Rat and the Fat Rat ??

Hal

 

[mao0720]

HAL, the 6mm Rat and 6mm Fat rat are both cartridges based on a 6.5 grendel case necked down to 6mm. Very similar, if not the same (im not sure) as the 6mmAR designed by Robert Whitley. They were designed for High power Across the Course matches, to be used in an AR15. The 6mm bullet gives you much better ballistics in a package that still fits in an AR magazine. I just picked up a 26" Barlein 6mmAR barrel and I got to shoot it for the first time yesterday. Man, this is one accurate rifle! If the 6mm Rat is even close, its got to be a good shooter.

 

[Hal]

Ma

Thanks for the info.

Hal

 

[infantrytrophy]

HAL, the 6mm Rat and 6mm Fat rat are both cartridges based on a 6.5 grendel case necked down to 6mm. Very similar, if not the same (im not sure) as the 6mmAR designed by Robert Whitley. They were designed for High power Across the Course matches, to be used in an AR15. The 6mm bullet gives you much better ballistics in a package that still fits in an AR magazine. I just picked up a 26" Barlein 6mmAR barrel and I got to shoot it for the first time yesterday. Man, this is one accurate rifle! If the 6mm Rat is even close, its got to be a good shooter.

Yes, correct, with one clarification. The 6RAT and FatRat are very similar to Robert Whitley's 6mmAR Turbo40 Imp. As mao0720 said, the 6mmAR is a 6.5 Grendel necked down to 6mm. The Turbo40 Imp and the 6mmRAT (and FatRat) are modifications that move the shoulder forward to allow more powder capacity, compared to the 6mmAR. The shoulder is moved forward by fire-forming in a 6mmAR Turbo 40 (or 6RAT/FatRat) chamber. This is analogous to the 6mmBR vs. the 6BRX or 6Dasher.

The fire-forming step is very easy and not wasteful of components (powder, bullets) since the fireforming rounds can be shot in matches - very accurate.

The whole point of this, as Robert Whitley points out in his 6mmAR.com web site, is that this family of cartridges is just about the maximum that can be handled in the AR platform, in terms of cartridge dimensions and pressure, without modifications to the upper receiver, bolt and barrel extension.

Those of us wanting to shoot a 6mm cartridge in the AR have some great choices:
6mmAR http://www.6mmar.com
6mmAR Turbo40 Imp http://www.6mmar.com/6mmAR_Turbo_40_Improved.php
6mmRAT or 6mmFatRat http://www.accurateandreliablerifle.com/products.html
240 Tomahawk http://www.keystoneaccuracy.com
6HAGAR http://www.keystoneaccuracy.com, http://www.creedmoorsports.com/shop/6mm-HAGAR/, or http://www.whiteoakprecision.com/uppers-match.htm

Another choice would be the 6BR or 6BRX. These are more extensively modified. Link: http://www.bratrifles.com

Randy