Which locking piece are you using? If you have the wrong locking piece, even with the correct bolt gap, that can cause problems because the locking piece controls the timing of when the bolt head is allowed to move.
Hi all... I've been lurking around for a while, but this is my first post. Thanks for having me :)
Anyways, I have recently completed my first build of a G3/91 clone. I didn't go the kit route, but bought everything pieces & parts from Gunbroker, RTG Parts, etc, over the course of time. The build went well and I finally have a "working" rifle. My bolt gap is right around .018, and the rifle shoots decent groupings. I am able to cycle the bolt & carrier manually via the cocking handle without an undue amount of effort.
But here's my problem: after firing a round, 90% of the time the spent casing will not eject. Most of the time when this happens I am able to eject the casing manually without difficulty, but sometimes it is very difficult to pull the cocking handle back to eject the casing. In either of these cases, the bolt is visibly out of battery, so I know it's not a matter of the rollers still being locked up.
The casings ejected in this manner all have visible "indentations" from the barrel flutes. It's almost like the pressure from firing the round has expanded the casing to fill the flutes. I have tried 7.62 NATO as well as 2 different brands of 308 , and all exhibit this characteristic. I have shot these same rounds in a CETME with no problems at all. Based on these casing deformations, I believe that perhaps the spent casing is not being ejected because it is expanding into the flutes & "putting the brakes on" the bolt from cycling correctly..?
btw - I tried spraying a little gun oil on the rounds before firing them, and this does seem to help the extraction problem a bit.
I don't know if this is just a matter of the rifle needing to be broken in, or if I have a real and serious problem here. I hope I've given enough info to be of use. If anyone has any ideas on what the problem could be, or advice on how to solve it, I would greatly appreciate it.
To answer the last couple questions...
The trunnion is HK off a demilled rifle. I had thought the barrel was PTR but am now not so sure. It could be real HK91. I got it off of gunbroker in this auction, if the pix tell you anything: http://www.gunbroker.com/Auction/Vie...Item=124775395
The locking piece was purchased new from RTG, labeled as 91/G3 part. The only marking that I can see is a "10/90" date code.
I also didn't think that HK was still using actual date codes by the 90s, everything should be date coded by then. But they may have still used actual dates on parts made for other contracts or something.
While I am indeed having an issue with my rifle, my intent was to seek assistance from those who have more experience in this department. It was most assuredly not to be seen as being ignorant.
Sorry about that Scott. Some people offer help at a "price." Sometimes the price is humiliation. Most of us here on HKpro are not that way.
First big question I have, is whether you have assured that the flutes have been well cleaned. Often that will cure any failures to extract issues you may have. Second question is one that Aviator Dave pointed out, that the locking piece, if incorrect, can cause these issues. --Oil in the chamber can cause issues with extraction, so keep it dry if you can. Lastly, the extractor may be hurting, or binding in its groove in the bolt head. -- See if you can remove and clean that thing really well, as a lot of detritus collects around and in the extractor seat or groove that the extractor rides in.
Are your spent cases really sooty and marked with black striation lines? The sooty part is important, as it is combustion gases which "float" the case in the chamber to enable reliable extraction. If they are not sooty, and all other "usual suspects" don't cure the problem, I would wonder that perhaps the flutes were not cut far enough into the neck area of the chamber to allow for reasonable venting of gases.
That barrel at auction has different contours than my PTR barrel, which is straight out to the muzzle from the front sight base, until it is reduced diameter at the part which is threaded to accept the muzzle device.
Last edited by stubbicatt; 04-24-2009 at 01:15 PM.
"A man is generally what he feels himself to be."
Hey stubbicatt... Thanks for all the info, and I appreciate the disclaimer ;)
So here's an update: When I got home tonight I scrubbed out the flutes again and made sure that the chamber was bone dry. I removed the extractor from the bolt & cleaned everything in that assembly (it was really nasty under the extractor). I applied some Dow 33 grease to the rollers and carrier rails. I then reassembled the rifle and test fired 3 shots. All 3 failed to extract/eject correctly :(
The spent casings had soot lines from the flutes, as well as impressions around the neck of the casing as if they had been pressed right into the barrel flutes.
More part info, if it's of any worth:
The barrel has 12 flutes and is rifled, not polygonal as advertised in the auction.
The bolt carrier is marked "FMP 6/69" on the top and "1E" on the butt end. The bolt has a single "G" on it.
The locking piece is indeed marked "HK 10/90" and was new-in-package. Bolt gap is 0.16 with this locking piece.
I have another, used, locking piece that came with the above bolt & carrier. To my eye, it is identical to the new HK locking piece, except the little "nub" that locks into the carrier is marginally wider across the radius of the shaft than the new HK piece. The only marking that I can discern appears to say "03G" on both sides of the flat, but it's very difficult to make out. This older piece exhibits the same behavior as the new one, but has a .012 gap.
The receiver is an FA-PSG1. And yes, I already know that aluminum receivers have a bad rap. ;)
The recoil rod / stock end assembly is new PTR.
The trunnion is demilled HK.
I think that's all the parts that may have something to do with this problem. I hope that somebody has a brainstorm on what might be causing it, because I'm up against the wall on this one.
Looks like a Korean barrel, they were blued and back in the day were noted for having problems. I would call up Jason at Investment grade firearms and ask his opinion on the barrel and wether it can be tweaked to work. Some guys used to say if you took a jewelers file to the flutes to clean them up it would help with extraction. I would email the guy you bought it from and try to strike a compromise on the cost. Good luck.
I'm thinking that the flutes in your barrel are cut wrong. Likely too wide. When a case is really hard to extract as you say, it can be because of tar/soot build up, or because the casing is spreading out into the flutes. That can happen with thin brass and higher loads usually found in commercial ammo. However, since you're also having the problem with surplus NATO, I'm blaming the barrel.
As stated, I'd scrap that receiver, and barrel, and start anew. The aluminum has a bad rap for a reason. RTG has lots of flats available right now, as do other suppliers. I don't know what it's like to get a "in the white" receiver right now, but that would be the easiest option. For barrels, the PTR pieces seem to function well enough, although there are better barrels available. An original HK barrel is what you'd prefer I'm guessing.
If I spot anything that looks good, I'll pass it on. If you check in the parts for sale section, I bet you might find something within a week or two. Don't be afraid to post a thread in the Want to Buy forum either.