I'm getting light primer hits in my HK91 with a PSG1 group in it. I've had the rifle since the 70s, and the trigger group since the early 90s, and I've never had any sort of malfunction with it until now. The ammo is Malaysian surplus I've had forever, also never a problem with it and I've gone through several thousand rounds of it.
I did recently put a #17 locking piece in the 91, and have been shooting it suppressed, and hadn't cleaned it in awhile so was really, really extra filthy.

It's all clean now, but I can't get to the range for a few days to see if the problem persists.
Could the dirt have caused the problem? It would fire the first round chambered by the charging handle, then just "click" and leave a very light mark on the primer.
Could it be something else? Anybody else ever had the same problem?

maybe the grime? firing pin spring ? hammer spring? is the bolt going all the way into battery?

clean the piss out of it. Check the bolt gap with a set of feeler gauges (get em at Pep boys, napa, autozone etc). Your looking for .010-.018 as optimal range. If for some reason the new LP caused the gap to go up over .020 that could be your source of light primer strike.



Also make sure the trigger housing your using for the PSG-1 back isn't sitting low.



 

Thanks, I'll check the gap as soon as I find my feelers. It is a factory HK locking piece. But if the gap was too large, why would a round chambered with the charging handle fire?

I'm using the same housing the rifle came with, and it worked perfectly with the PSG1 pack for about 20 years. How do I check if it's sitting low, and can it just suddenly do that?
The powder residue was really thick in there, and I probably hadn't cleaned it for about 2k rounds, about 1k of those suppressed. (The suppressor forces a bunch more crap back into the action than normal) Hopefully the filth was the problem.

Another attmpt in the guessing game is that the PSG1 pack is sitting up too high, slowing the carier down enough that the bolt isn't closing all the way.

When you get to the range put a pencil mark on the bolt along the front of the ejection port with it properly closed on a round.  Fire that one out and see if the pencil mark has returned to the proper place on the self-fed 2nd round.

But how could it suddenly be sitting up too high?
I've had it in the rifle for 20 years with no problems, and it only fits in there one way. Just in case there is a misunderstanding, this is a factory HK91 that I got in 1977, not a homebuild or a clone and I've never had even a failure to feed/eject. No problems whatsoever until last weekend. I haven't changed anything except that locking piece, or taken the trigger pack out out of the housing since I put it in there way back in the 90s.

I misunderstood your first post, sorry.  My mind read it as your problem started after you put the PSG1 group on the rifle. So does the problem cease if you put the old LP back in?

I didn't try putting the old locking piece back in yet.

It sounds like it is not locking properly, if you just ease the bolt down on the first round youget the old click with no bang so it sounds like something may be slowing down your bolt.