So You Want To Make 

Your Mouse 

Space Gun Roar!

by Scott Medesha

        Most Service Rifle shooters seem to be happy with the performance of their .223 ARís, for the

most part anyway. Clever shooters keep coming up with better, heavier bullets; faster twist barrels and higher energy powders to boost performance.

        This is great when your shooting against M14ís that arenít nearly as accurate as the AR has

become. But those of us that shoot in the Match Rifle Category often find ourselves out-gunned by bolt action .260ís and 6mmXís (or one of itís other variants). In some parts of the country, where ranges are protected by tree lines, or the wind just doesnít blow much, a .223 works fine. But, if you live in the West, Southwest or if you frequent places like Raton, NM; Phoenix, AZ; or even Camp Perry, Ohio, you know that the .223 is a bit lacking. Many of us have looked at AR10ís, but find them too large; heavy; poorly balanced; and expensive (though there are some less costly ones being offered these days).

        Realistically, we will be hard pressed to match the performance of these larger cartridges. As the AR15 platform is just to small to accommodate the powder volume that the larger rifles can, without totally redesigning major components of the gun along the way. But we can get much closer


So what can we do to increase 


Drift in a 10 MPH Crosswind


Bullet & Muzzle vel.

300 yds

600 yds



80gr.MK @ 2800fps




6mm BR

107gr.MK@ 2700fps





107gr.MK@ 2900fps




6.5 Grendel

107gr.MK@ 2800fps




6.5 Grendel

123gr.Lapua @ 2600fps




6.5 Grendel

130gr.Norma@ 2500fps




260 Rem.

142gr.MK @2800fps




308 Win.

175grMK @ 2700fps




308 Win.

190gr.MK @2600fps




       Iíve been trying to find the answer to this 

question for the last 8 years. Iíve tried .22 &

6mm PPCís, and found both of them lacking. Either will out perform the .223, but they wonít keep up with the bigger guns. Along with the inadequate performance, they also had magazine problems. None of the factory mags would feed more then 3 rounds reliably without being modified heavily. This may not be a problem anymore. There are some new magazines coming out soon that should end this problem.

        After those experiments I went to shooting an AR10. First in 6.5-08 (.260Rem.) then followed by a 6mmX. Iíve had very good results with both cartridges and recommend them to anyone that is willing to shoot an AR10. Although I am quite happy with the AR10, I have found that most shooters arenít comfortable shooting this larger rifle.

        So I turned back to the AR15 platform. There are 3 cartridges that show performance that far

surpasses the .223 and comes up much closer to the full sizes bolt guns. The first is the 6mmBR. this is a little brother to the 6mmX, that can push a 107 grain Matching within 300 fps of its larger sibling (see above chart). Iíve been playing with this for a couple of years, and it performs very well out to 600 yards. It does have a couple of drawbacks though, first the rims must be turned to the same diameter as a 7.62x39 (or PPC if you prefer). (I have rim cutters for a lathe available, or I will turn the rims for a small nominal fee.) The other problem is again magazines, but it is not as big a problem. Thermold 30 round M16 magazines can easily be shortened and made to work. Also, in late 2004 I should have magazines designed for the BR case available.

        Perhaps the most promising of the bunch is the 6.5 Grendel. This is basically a PPC case with the shoulder blown forward about .070Ē. This gives you 15% more powder volume over the PPC case. The cartridge was developed by Bill Alexander, of Alexander Arms and Arne

Brennan, of Competition Shooting Sports, as an AR15 hunting round, with possible military considerations. As you can see from the performance chart, it does considerably better than a .223, and is right up there with any of the other cartridges that are usable in the AR15

platform. The Biggest advantages may be the factory brass and magazines that will be

available for it. That means no rim turning, no modifying .223 magazines, all this has

already been taken care of.

        I havenít had a great deal of time to play with this one yet, as the brass and magazines are just hitting the market. Hopefully by the end of the year they will be readily available. The little testing Iíve done, did show it will push the Norma 130 grain Match bullet at 2500 fps, atop 28.0 grains of 4895. This will provide very good 600 yard ballistics.

        The last of these cartridges is the 6.5mm BR. This is very similar to the Grendel,

holder about 3.5 grains more powder. Thus, it should give slightly higher velocities and

performance. The drawbacks though are the same as the other BR cartridges; no magazines yet and the rims need to be turned.

        This should give you a better idea of what can be done with your AR15 to increase performance. Having shot a 6mmBR for a while now, I can honestly say it performs very

well. I would think the 6.5mmBR should perform equally, if not better. If you donít mind

the special rim turning and playing with magazines, one of these may be the way to go. But,

if you would rather have Lapua made brass, out of the box, ready to go, as well as having

factory magazines, Iíd recommend the 6.5mm Grendel.


Competition Shooting Sports, Alexander Arms &

Medesha Firearms offers the

6.5 Grendel Ultra-Match Upper Assembly

Built around Alexander Arms New Proprietary 6.5mm Grendel Cartridge

These Medesha Firearms Assembled Uppers use

Alexanderís Specially produced Bolts; Carriers; Barrel Extensions; & other parts.

Lothar Walther 28Ē . 1-8Ē twist stainless steal Match Barrel

Medesha Firearms Products:

Vented Cantable Handguard w/ Handstop

Adjustable Rear Sight Base & New Ladder Type Front Sight

Adjustable Gas System

1- Special 10 Round Magazine



Other Products from Alexander Arms

Grendel 10 round Magazines $32.00

Lapua Manufactured 6.5 Grendel Brass $40.00/100


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Last modified: May 04, 2009

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