Originally Posted by Spider!
I've never had an SMG in my hands. However, before I did anything to the gun, I would put a caliper on the stripper clips and make sure they are the right width and not varied, especially if the marker worked fine before.
Well, I only have 1 stripper clip. Running Riot gave me one with the gun so I could get measurements if I couldn't find original clips and had to make some. So far, I haven't been able to find any. No surprise.
Obviously, before any permanent modification I am going to mock up something to test.
Originally Posted by russc
What barrel size is it using? SMGs tended to have massively overbored barrels at the breech, and it would taper down after about an inch or two.
RR mentioned earlier that it came from .684 ID tube. I'd have to get my calipers to measure the bore at the breach though to gt an idea on the taper/transition.
The issue is either due to the breach block being milled a hair too wide or the barrel not having enough of a taper at the beginning. Everything stems from this: Since the pawl holds the stripper clip at one point near the back surface and the mag spring presses on the end of the clip, you get a torque on the clip. For the frist 3 rounds in a clip, it isn't a big deal since the magazine/breach prevents too much angle. However, by the last round, the angle is significant enough to possibly cause alignment issues with the barrel. See my crude CAD mock ups below.
Two ways to fix it:
1. Reduce the slop between the clips and the breach. Either make the breach tighter or the clips larger.
2. Increase the ID of the barrel breach/taper.
Shimming the breach seems to me to be the easiest given the minimal tools I have available. But I might also be able to use a hand drill to hone out the barrel breach a touch.