I haven’t been able to find any decisive reviews of Gemtech’s 42gr .22LR subsonic ammunition. I finally picked some up under $4/box and decided to wring it through my Feddersen-barreled 10/22.
Since my last precision testing of 10/22 rifles, I have also refined a testing process capable of higher sample volumes, so I decided to compare the Gemtech to these other subsonic flavors presently abundant in my stockpile. (Of course, since Gemtech’s ammo is supposedly optimized for use with a suppressor, this test was conducted with an AAC Element II screwed to the muzzle of the 16″ Feddersen match barrel.)
One thing that has made precision testing much easier is this universal machine rest I developed: After every shot it returns the gun to the exact same position (which can be confirmed by the 32x scope on top), so it’s easy to shoot a string quickly and with zero shooter error.
I’ve also become a little more disciplined with respect to fouling the barrel: When shooting a clean barrel, or changing ammunition types on a fouled barrel, I ignore the first five shots. Different rimfire ammo uses different lubricants, and it takes some number of shots before the bore is consistently coated in the new lubricant. Five shots isn’t really adequate to fully stabilize the bore. (A good bolt action rifle will show that ten or twenty shots are required for it to settle in.) But at the level of precision one can get out of an autoloading rimfire, five shots seems “good enough.”
At 50 yards (the test distance shot here), muzzle velocity variance doesn’t really come into play. But it certainly does at 100 yards and beyond. It was easy to prop a chronograph in front of the machine rest and record the velocity of every round fired during the testing.
Another thing that helped streamline analysis was OnTarget’s TDS software. It can’t (yet) auto-detect multiple shots on a single target, but it does auto-detect the points of aim, and it makes marking the shots and groups fast and easy.
I took advantage of the latest statistical tools available from ballisticaccuracy.com. The aggregated data and analysis are in this Excel workbook.
Summary results, here linked to TDS-marked targets, show that (in this gun) Gemtech’s ammunition is better than Aguila but worse than CCI SV:
||CEP Radius (MOA)
||fps Standard Deviation