View Full Version : Why would a gas piston bend?
September 20, 2002, 21:17
My StG58 was shoting VERY poorly my last trip shooting. I took it apart and discovered that the gas piston was into a "v" shape back near the carrying handel. The spring looks a little mangled also. Thanks.
September 20, 2002, 22:39
what was your gas setting?
were you shooting handloads,or factory ammo?
did you have the rifle apart prior tp your shooting, and if so was gas piston taken out?
September 20, 2002, 22:47
mangled springs usually mean the rearward velocity (or compression stroke) is way to fast and hard. You might want to look at the lower receiver to see if the carrier and bolt show extreme evidence of slaming hard into it.
Same sort of thing happend with the FAL 45acp coversion project.
September 20, 2002, 22:48
The gas seting was in the middle of the range and I was using South African surplus ammunition. The only prior dissasembly was removing the bolt and carrier to clean. Could the piston bend because it hadnt been cleaned? I had only shot around 120 rounds through it.
September 20, 2002, 22:55
What sort of signs should I be looking for?
September 20, 2002, 22:57
was it linked ammo? and i'm leaning toward rhineland's statement. a high rearward velocity, or your recoil spring, located in the buttstock is/was binding thus not allowing enough travel for the gas piston/bolt, bolt carrier.
September 20, 2002, 23:09
The bolt and carrier can return all the way. The ammunition was not linked and I had only shot around 5 rounds per magazine. initially the carrier failed to completely close over the bolt during cycling. After that the rounds failed to eject and were hard to eject manually. The first two times I had the gun out it worked great but from the first shot this last time out there was trouble.
September 20, 2002, 23:19
is gas plug turned to grenade setting by chance? did you shoot same lot# ammo before this last time?
and when the carrier didn't close over the bolt. what chain of events took place? tell us what you did. EG put mag in rifle ,pulled charging handle to the rear etc. etc.
September 20, 2002, 23:23
The gas plug wasnt in the grenade setting and it was the same batch of ammo as previous. When the carrier failed to close over the bolt I ejected the magazine and would load a single round and have to cycle it a few times for it to close all of the way. However, with no ammunition loaded the carrier always closed over the bolt.
September 20, 2002, 23:32
the first thing you need to do is verify that there is nothing in the chamber, left over brass,dirt etc. second verify headspace is still OK. look at your gas setting, can you see the hole, or is the hole covered by the gas nut?
September 20, 2002, 23:37
The chamber is clean, the gas port is only half way covered. I dont know how to set or check the headspacing. I had the gun assembled by Entreprise Arms and have only put about 120 rounds through the gun. Could the headspacing have come un-adjusted that quickly? By the way thanks for all your help.
September 20, 2002, 23:43
i was thinking that you have some hot S.A. MG ammo causing the damage, but you mention enterprise arms did the assembly, that might be the problem. who's receiver?
September 20, 2002, 23:51
The receiver is an Entreprise I forget which one, but it was the cheaper of the two. When I load up a magazine, dont fire any rounds, and cycle it manually it works flawlessly. I'm gonna try and clean it up real good. Ive put my old foreign piston back in using the same spring. I'll give it a try next weekend and get a hold of a new piston and spring. I'm gonna call it a night so thanks again for your suggestions, I really appreciate the help.
September 20, 2002, 23:58
open up your gas setting all the way and work in until rifle starts functioning correctly, and try using different ammo. also check your recoil spring for binding by removing it, and cleaning it. also do a search for headspacing and 2 rods method this will tell you if your rifle is barreled correctly.
BTW your welcome.
September 21, 2002, 01:21
Make sure the gas piston doesn't over-extend. If it does, the bolt carrier will contact it and not fully close; when chambering, it will impinge on the piston, slamming it into the gas plug. This ain't good for any part involved. Good luck.
September 22, 2002, 16:44
I had the same exact problem with an Entreprise built rifle recently. With work being a pain, and everything considered I just haven't sent it back yet. I guess I need to though.
Check the size of the gas hole going into the barrel, mine is drilled out way to big, I think this is causing my problems. I don't know who drilled out the gas hole, it's like 150 thousandths.
September 22, 2002, 17:53
Describe your piston.
- Two-piece or one?
- shape of piston head?
- length (as best you can determine)?
- size of gas port?
- short or long gas tube?
- whatever else you think is relevant
- What is this SA MG BS?! The SA use the GPMG/MAG/M240, and their 7.62x51 ammo has no 'MG' set. Rumors and MORE rumors I tell you.
September 22, 2002, 19:08
As best as I can say the head of the piston is flat, then about half an inch down there are three sunken rings. Next about 3/4inch tapered then 1/4 in raised then 1in tapered then 1/4 raised. then about 8.2in tapered. Overall the piston is about 12in long. The gas tube is approximately the same length as the piston, maybe a little longer. Should the piston make contact with teh bolt carrier because there is a circular spot on the carrier. Does the gas piston strike the carrier and send it back? Thanks.
September 22, 2002, 22:01
settle down ted i am not a expert on different countrys ammo, some nato ammo is/was loaded a bit hotter for MGs and no i don't remember where i read or saw that , and it may be fiction. like i said i'm not a expert.
now to address hatehondas question. yes the gas piston is supposed to engage the bolt carrier, this helps the rifle to cycle/reload itself. in other words yes to your last question.
with your piston having the 3 rings, that means it is a US made part, and could be to soft, like i stated earlier your problem could be the manufacturer. as enterprise arms seems to have quality issues. try contacting enterprise arms to see what they have to say. also try using the search function on this board and type in bent gas pistons, this may give you a better idea of what is going on. but the mangeled spring says to much gas or not assembled correctly. just my .02. hope this helps.
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