What is usually valued most for gas guns is having a case with a hard head so the rims won't tear off or bend during the rapid extraction they produce. Two years ago, member Bobcat45 tested a series of factory-new never-loaded-or-fired bulk cases I sent him with a 500 gram micro Vickers hardness tester, preparing the brass and applying it to the head and neck and taking photomicrographs of the work. The heads were done in two places. The average head hardness result is listed below:
So that makes LC and Starline look like the best candidates. However, since those tests, a new player has appeared called
Atlas Development Group. They make their brass specifically for handloaders, for which they make it with a little less powder capacity and more brass where the pressure ring thins for extra reloading life, and they double-strike their heads, which is how heads are made extra hard (like Lake City). So this is another good gas gun brass candidate. They have put extra effort into controlling the internal capacity of their cases. You get a little bit of brass weight variation (I measured 172.51 grains with SD of .58 grains and ES of 2.40 grains in a 30 piece sample; they claim 172.3 grains average), but it is difficult to find more than a tenth of a grain extreme spread in their 54 grain case water overflow capacity, and that's small enough to make me doubt the precision of the measurement. Pressure and velocity will be about as tight as case influences can encourage them to be. Neck wall runout had an ES of 0.002" in my samples, which is the only place the Lapua and Norma I have can beat it (both about 0.001" neck wall runout ES in my lots of .308 W and 6.5-284), but with most common match bullets that's going to amount to a group spread on the order of about 1/8 to 1/4 MOA in an otherwise bughole-shooting gun, depending on the bullet. Since group error SD adds as the square root of the sum of the squares of the contributors, the difference between the two runout levels would change a ½ MOA group by something on the order of 0.05". So, for any but a benchrest shooter, it is likely to be an error source lost in the noise (though individual guns can present some funny circumstances where that might not be so; as always, you can only try something to be sure of it).
The ADG cases are not inexpensive, running about what Lapua costs, but their extra durability compensates some for their initial price and the hard heads for gas guns is a plus. They can be purchased in small quantity (50) directly from ADG, where they are available either polished or with annealing stain intact (the latter resist corrosion better, but are harder to find in the grass) or in 100 piece bags from
neconos.com, though Neco sells only the stain-intact finish.
Anyway, if I were looking for super brass for a gas gun, I would give ADG a try.
T. O'Heir said:
"...Primed with CCI #34 Primers..." Geez. I wonder how Midsouth determined that {?}
You can tell from the photo. The primers are the original crimped-in, brass-colored primers the military put into the cases originally: a military Number 34 primer.
Number 34 is a standard military primer designation. It did not originate with CCI. They borrowed it to mean the CCI #34 commercial primer has the same ignition sensitivity as the military #34, which they obtain by modifying the anvil in what is otherwise identical to the CCI 250 magnum primer. An actual CCI 250 is more sensitive than a CCI #34. The top drawing number on this list is the drawing above and is the sensitivity spec met by CCI's commercial version.
The heights listed are for a standard height test (H-test) in which a primed case is placed in an upside-down shell holder with a floating firing pin resting on top of it and the pin is struck by dropping a 3.940-ounce weight onto it from the heights listed in the specification.
