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pdraigh
February 06, 2009, 16:08
I have a STG58 that I built on a Century receiver. The problem I'm having is the apparently common problem of the bolt riding over the round without stripping it out of the magazine. It works most of the time, but not reliably.

The receiver had the relief cuts that roughly matched the mag feed lips, but were still over the lips. So, I scribed the mag contour on the underside of the receiver and dremeled away to the scribe line. Filed it and it's nice and smooth and not hanging over the mag anymore. It fails to feed a little less often, but still does. I closed the gas port a click and it helped a little. (Maybe giving the bolt a little more rearward travel and a little more oomph coming forward.)

I suspect the magazines are still causing some of it because once a magazine is loaded, it's pretty hard to just strip a round out by hand without the mag in the gun. A lot harder than any other magazine I've ever used. Is that normal?

I was thinking new recoil springs; maybe it needs a bit more power on the forward stroke.

Besides the "shouldn't have used a Century receiver," what other things should I look at doing?

Thanks!

brownknees
February 06, 2009, 16:11
What does the front of your bolt look like?
Particularly the bit that comes streight down in a square section at the bottom.
Is the bottom corner sharp, or rounded, & if so by how much.

pdraigh
February 06, 2009, 17:39
The bottom of the bolt is pretty sharp. There's a ramp in the bottom, but that's the way it was machined, not worn down. The kit was in very good condition without much wear anywhere, so I don't think it has been rounded off any.

ggiilliiee
February 06, 2009, 18:16
spred the lips on the mag a bit in the rear profile ...up and out 1/16..(use smoothe dykes.....lips should be touching rails bottoms ... see if that does it ..mag should fit to top of stroke too, no wobble front to back

jwaters
February 06, 2009, 19:22
Don't spread the mag lips. Not a solution.

Check the bolt that it is sharp on the bottom. Also, the mag catch could be worn. Can you push up on the mag and it push up more into the receiver?

I had this problem once, and I try new bolt and new mag catch, problem solved.

I will say I have never had this problem with an IMBEL or DSA receiver.

My Century was OK as well.

ggiilliiee
February 06, 2009, 19:42
spread em .....spread em ....hehehe ....:wink:

pdraigh
February 06, 2009, 20:18
The mag is about as tight as it gets when it's in. I can't see how it could be any tighter. I'll keep tinkering. I've done two builds on a Century and I sold the one that was absolutley reliable because I liked the STG58 coolness. It's being a challenge, though.

tac-40
February 06, 2009, 20:41
Assuming that your mags are all okay and function correctly in another FAL, then:

In most cases when the bolt rides over the rounds in the mag it is because of one or two problems. The first is the bolt cannot engage the back side of the round and push it from the mag. The second is the bolt isn't going back far enough to catch the round in the mag.

To check for the second problem, all you need to do is close off the gas and fire off the rounds. If it works reliably, then slowly adjust the gas until it doesn't, then close it down 2 clicks.

The first problem has several causes: the mag doesn't sit high enough in the mag well or it may be canted (classic Century problem), the front of the bolt is worn and not square, the receiver rails may be out of spec. To check if it is a mag problem, insert a loaded mag and chamber a round. Use the mag as a forward grip, pulling it backward to seat it fully upwards, then test fire. If it works then look for a longer mag catch. The worn bolt is checked by swapping out bolts for one that is known to function. And hopefully it isn't the receiver rails cause that means a lot of work.

One last thing. Check to see which side of the mag feeds from when the malfs occur. This can help you pinpoint the problem.