Over the weekend I was finally able to get my OSS flash hider installed on the BG MK1 rifle. After two attempts and soaking in water for 24 hours, heating with a blow torch and a solid crack from a brass hammer I finally got the Rocksett to give up. The OSS flash hider is supposedly self-tightening and the suppressor mounts to the muzzle device with reverse threads, so I installed with Vibra-Tite on the threads and gave it a good hand tightening with a wrench. I hoped this would apply minimal tension to the barrel and hopefully improve accuracy slightly. I did all my shooting today with the suppressor mounted and will at a later date shoot a few groups with just the flash hider installed.
I started out shooting by checking zero at 50 yards with some cheap PMC 55 grain FMJ... The group I shot was probably one of the best of the day surprisingly (first group last picture). I then adjusted the scope 2 clicks right and 1 click up for the rest of groups shot today. This minimal point of impact shift with a new muzzle device and suppressor mounted I find nothing less than impressive. I usually use this suppressor on my SCAR 17 and it always performs exceptionally well, while usually only lowering POI 2 MOA at 100. Not only is this set-up the quietest 5.56 rifle I have ever been around, I also did not notice any increase in recoil or blow-back out of the ejection port. The ejection pattern of the brass also stayed right at 4 'O Clock, just like it was shooting with the SureFire flash hider.
I fired two sets of 5 shot groups today with 3 types of ammo in each group. The first set of 3 I did not include any pictures of as they were 1.5-2 MOA across the board. The ammo used was Hornady Frontier 75, 68 and 55 grain ammo. I would really like to attribute the lackluster accuracy mostly to me still getting use to the High Speed DMR trigger and perhaps the rifle settling in with the suppressor installed. Either way the next set of 3 groups improved and that is what I have posted pictures of below..
I'd like to blame myself for the accuracy of the Hornady compared to the Federal Gold Medal Match, however I felt very confident with every shot here. Based on only two different range secessions it would appear the rifle prefers the Federal GMM Sierra 69 Grain BTHP round.. If you exclude the top flyer from this group accuracy works out to sub .5 MOA... I'd love to hear your guy's thoughts on the Federal GMM and if you've had a chance to compare it to other loads out there. I plan on testing others in the future and will keep posting if you guys are still interested in these results.