I spoke before about taking a gas piston upper receiver, chambered in 6.8x43mm SPC, out for a few test drives. Stag Arms has a great setup here, complete with flip sights, comfortable foregrip with lots of room for small accessory rails, a full length rail on top, and a gas piston setup, which makes cleaning a breeze. It’s not cheap, but I’ve lusted after a 6.8SPC gas piston setup for a while.
The first time, I had some real issues, in that the rifle refused to rechamber a round when the trigger was pulled. Stag was very helpful, but they confirmed that more or less this was not going to be the upper receiver’s fault, since they test fire them at the factory, and it worked fine.
I did recall that I’d installed a new adjustable Magpul ACS adjustable stock on my lower, which is a wonderful cheek weld. So maybe I got the wrong length spring? Rifle instead of carbine? Turns out nope. Tiring of the entire process, I purchased a captive recoil spring by JP Enterprises instead. That fixed the short-stroke problem right up.
Which brought me to the next issue: after boresighting the rifle, mid-way through my second range session, I totally lost the sights in the scope. I mean, I was hitting as much as six inches high and left at only 46 yds, the range maximum. I left feeling frustrated, not sure if it was my scope, my upper, or poor marksmanship. The funny thing was, though, was that when I put the laser boresight back in, it was dead on.
Was I really jerking the trigger that much?
I chatted with some friends who also shoot, and I came up with one of two theories. The first was yes, I was in fact yanking on the the trigger. Depressing, but possible. The other was that somehow, the rifle was able to be loose in the grip somehow, and when fired, the recoil impulse drove it to a new home. Careful shooting showed that five rounds aimed as carefully as I could shoot them gropued into a one-inch square . . . six inches high and left. I decided that there was no way I was that precisely yanking the trigger.
What could be going wrong? Again, I came up with a hypothesis. As Buddy the T-Rex says, “an idea we can test.” I thought maybe that I’d adjusted the ACS stock to get a better sight relief, but perhaps I’d not fixed the secondary clamp. What secondary clamp, you say?
The one right in front of the hole in the stock. When you depress the lever inside the hole to move the stock, the clamp opens up. The stock noticeably rattles around on the buffer tube in that case, and as it turns out, that was the problem. Clamping that down, the rifle stayed true to center for an entire firing session. I’m still only shooting 2-4 MoA with it at best, so I have some work to do in that department. On the flip side, my spread doesn’t grow that much firing fairly fast. The 6.8 remains a very pleasant cartridge to shoot, and the piston/stock combo provides a good sight picture not ruined by pulling the trigger.
No photos of targets with holes in them today, but problem solved. Now I can hit the range and worry only about where my bullets are going, rather than if my expensive upper receiver is a lemon. It’s not.