Failure to fire with my FA91 (HK G3 clone)

[Woda]

On my last trip to the range I was sighting in a new scope on my FA91 when I started to experience failures to fire. The primers had very slight dents in them indicating a bolt seating issue. I stripped the rifle and saw some carbon build up on the bolt face and in the chamber where the bolt seats. So I decided to stop shooting the rifle for the day so I could clean it.

I cleaned the rifle so there is no carbon build up ANYWHERE.

Yesterday I went back to the range to sight in my scope. This time it would not fire at all and there isn't the slightest dent on the primers.

The firing pin is not broken. The hammer appears to be working just fine.

Any suggestions or if there is a gunsmith in the greater Boston area that specializes in G3 type rifles that someone could point me toward I would be very appreciative.

Thank you in advance.

 

[atilla]

did the firing pin break? break down the carrier and bolt and inspect.

 

[dnepro-mike]

oversized rollers?
did you check bolt gap?

 

[Bob Palermo]

oversized rollers?
did you check bolt gap?

This.

These rifles wear on the rollers and they need to be replaced. The bolt gap will tell you that. That is the one thing I do not like about these rifles.

 

[not new guy]

HK91 G3 Rollers and Retainer for HK 91 HK21 PTR91 V51 CETME, HK +2 +4 Roller, RTG Gun Parts

 

[Woda]

Atilla - no as I said in the original post the firing pin is not broken. That was the first thing I checked at the range.

Mike/Bob/new guy - Sorry if this is a dumb question, but how would a worn roller be over sized? Wouldn't a worn roller be undersized and therefore have the problem of an unsafe chamber pressure and not afailure to fire issue?

In any case I'll check the bolt gap.

Also, I have put 300ish rounds (all from the same lot of ammo) through the rifle with the rollers that are currently in it, if they were oversized, would that be possible?

 

[PATRON]

Check gap,it should be .010-.018. Things that could cause your problem,firing pin,dirty rifle, but they do tend to run dirty, bad bolt gap,that can be fixed by replacing rollers.One problem that some people don't know is the trigger pack.Make sure it is set right.

 

[2A_Esq.]

but how would a worn roller be over sized? Wouldn't a worn roller be undersized and therefore have the problem of an unsafe chamber pressure and not afailure to fire issue?

The bolt gap is measured between the bolt and the bolt carrier. As the rollers wear, the gap between the bolt and the bolt carrier shrinks. This would mean that the bolt would not lock far forward enough and could reduce the headspace of the bolt at the trunion.

G3 Experts: Wouldn't this make the "effective length" of the firing pin longer, though, since the bolt/bolt carrier group is now shorter?

EDIT: I think I'm wrong on the headspacing thing.

 

[not new guy]

What kind of ammo? Wolf?

Is your receiver steel or aluminum? There were issues with the aluminum received FA91s not going fully into battery because the rails got dented and/or cracked.

 

[Woda]

2A_Esq. - Thank you for the explanation, that I can wrap my head around.

new guy - German 7.62 Nato like this stuff: German .308 FMJ NATO (7.62x51) 200rd Battle Pack. Aluminum receiver, by rails do you mean the surface of the reciever that the BCG rides on? I will check that too, but I didnt notice anything funny while cleaning it last week before the range trip.

I still haven't takene another look at it, I will have a chance tonight if nothing comes up.

 

[not new guy]

new guy - German 7.62 Nato like this stuff: German .308 FMJ NATO (7.62x51) 200rd Battle Pack. Aluminum receiver, by rails do you mean the surface of the reciever that the BCG rides on? I will check that too, but I didnt notice anything funny while cleaning it last week before the range trip.

I still haven't takene another look at it, I will have a chance tonight if nothing comes up.

That's good ammo.

Maybe bad news if you have an aluminum receiver. It's never a good sign when they have to use epoxy to glue metal parts together. You can google FA91 aluminum receivers and hunt around yourself, but these posts from a user by the name of bladeworks123 sort of sums it up, and tells you how to check for one specific problem:

There are probably many FA91's out there that function OK, but they have had a rather bad reputation for reliability. The main thing is that you know what to watch for in bolt gap. Maybe your problem with failure to fire is the ammo, but no firing pin marks in primers is a good indicator that something is interfering with the bolt closing into battery. That could be a magazine problem, a bent or binding ejector, a bent or misaligned recoil spring guide rod, or just some extra crud hiding out somewhere. You might try dry cycling the action numerous times with the magazine out, turn the rifle upside down and make sure that the bolt is locking up every time you slap it closed. If you don't see any problems with the bolt locking up correctly, and you continue to have good gap, you're probably safe to shoot, and continue to try and find or eliminate the FT fire problem.

If you had failures to fire with no firing pin marks on the primers at all then the bolt is probably not locking fully into battery...... a problem experienced by some with the aluminum receivers.... the bolts do not stay properly aligned, and the rollers try to set prematurely. Look for signs of that on the rails just about 1/4 inch behind the trunnion. You should see dents in the rails, that will eventually lead to cracks. My opinion,,,, save your money and buy a steel receivered rifle.

Fa91 ????


See also: http://www.militaryfirearm.com/Forum/showthread.php?21960-Federal-Arms-FA91

 

[Woda]

So I finally got around to measuring the bolt gap and inspecting the receiver for damage.

The bolt gap is about 3/16"; thats right WAY above 0.020" maximum. So what is keeping the bolt from moving forward? I have no idea. I can't find any debris, cracks, dents, nothing.

Again if anyone knows of a reputable gunsmith who knows the G3 platform well, I would greatly appreciate you pointing me in his/her direction.

 

[Woda]

Sorry to dig up an old post; but I thought I should put an ending on the story in case someone is looking in the future for a solution. I fixed it months ago and forgot about this thread....

The problem was extremely simple and quickly diagnosed by a new friend knowledgeable about HK rifles.

The spring (http://www.robertrtg.com/store/pc/HK91-93-SPRING-FOR-COCKING-HANDLE-SURPLUS-72p1994.htm) that keeps the cocking handle forward had broken and was just enough of an obstruction to not allow the bolt to fully go into battery, but appear as if it was. Replacing it wasn't too difficult either, and I think it cost $3.

 

[not new guy]