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View Full Version : PTR-91 problem... any advice?


DK
January 14, 2009, 15:41
I scored a pretty sweet PTR-91 at a great price, the 16" bbl one. NIB from my dealer (he ordered it for me from CDNN). Took it to the range and it ran through a 20 round mag of West German NATO 7.62 without a hiccup. I loaded up mag #2 and slapped the charging handle down, chambering the first round. First round fired fine, ejected fine, next round hadn't chambered and the trigger hadn't reset. Worked the rest of the mag like a bolt action, pogo'ing the empty out and manually chambering the next round. Finished that mag and moved on to something else.

Went back to the range today (after a careful cleaning from the prior trip), and had the same issue right off the bat (same ammo). Had to maually cycle the rifle every time. It seemed like the bolt wasn't quite going into battery after the rifle would fire (shortstroke).

Any ideas? It's a brand new rifle. My FAL's ate the ammo w/ no problems (naturally ;) )

The thing that has me puzzled is that the PTR ate the initial mag just fine. After that first mag every subsequet round had to be manually cycled.

:?

DK

M2MG
January 14, 2009, 15:57
1. Pull a round apart and look for any sealer on the bullet and case. HK style guns can get the flutes plugged real fast with sealer that some surplus ammo has on the bullet base.

2. If the flutes are clean, try a different flavor of ammo and see if you have the same problem.

good luck

M2MG

chromestarhustler
January 15, 2009, 10:16
FAILURE TO FEED
(bolt moves forward without feeding cartridge)

1) Check that magazine is being held tight by magazine catch. If loose, replace magazine catch spring.
2) Check for deformed magazine lip. Replace magazine if defective.
3) On non HK produced G3 clones, check to verify the front of the magazine mates to the small trunion extension protruding from the rear face of the trunion in the magazine well. If it does not, gunsmithing work will be required.


FAILURE TO CHAMBER
(bolt does not fully close - cartridge is not fully seated)

1) Check for broken or weak recoil guide rod spring. Replace if defective.
2) Check for carbon or gunk residue buildup in cocking tube and trunion recesses. Clean if required.
3) Check barrel chamber for remnants of previously fired ammunition casings or debris build up in chamber flutes. Remove if found.

gunplumber
January 15, 2009, 11:54
I'd first look at the trigger group and recoil assembly - check bolt carrier movement with the trigger group off.

Did you notice an increase in the recoil impulse? I am thinking there is something wrong with the trigger group height that is retarding the bolt carrier, or the recoil spring -Is there a kink?

DK
January 15, 2009, 12:21
The NATO ammo has some type of sealer (blue/green) around the primer, though it doesn't seem excessive. The rounds were packed loose in a large ammo can. Pulled one down, and I don't see any lacquer around the bullet or case. The cases however do feel slightly "tacky". Not sticky, no gunk, nothing like that, just slightly tacky.

I flushed out the chamber and bbl w/ brake cleaner.. I don't have a chamber brush.. I didn't notice an inordinate amount of fouling.

The bolt carrier travels smoothly in the receiver; it slams home and locks into battery just like you'd expect it to when it's empty. The mags are exc. to new, and don't exhibit any damage. The trigger housing is the "Navy type", and the hammer is made by PTR. I can't see enough of the other internals to tell if they are US made.

There aren't any discernable kinks in the recoil spring and it seems to operate as it should.

As for the recoil, I didn't have enough of a chance t shoot it normally bfore it started acting up to pay attention. What baffles me is the first mag went without a hitch. It shot a quarter sized group (about 6 rounds) at 25 yds, and knocked out several dirt clods out at 100yds. Went to reload and it became a single shot.

I'm going to try and slip out to the range in a few and try some different ammo.

DK

DK
January 15, 2009, 16:29
Well, fired some factory commercial .308 this afternoon and no joy. Same problem. When it fires, the bolt carrier comes back just enough to reset he trigger, but not far enough to eject the spent cartridge. It just slams back forward coming to rest slightly out of battery. Hand cycle, repeat.

Something did occur to me while at the range: the first time I fired the rifle I had 2 stocks with me. The factory fixed stock and a surplus G3 sliding stock. I can't remember which stock I had on it when it did fire, but I know for certain it hasn't worked these past two range rips with the fixed stock. It's a PTR fixed stock w/ surplus end cap, and I assume it's surplus spring and rod. Just holding the 2 stocks up against each other the sliding stock seems to have a slightly shorter rod. Action hand cycles fine with both stocks.

I'll try to make another trip tomorrow with the sliding stock and see if that makes a difference.

DK

ggiilliiee
January 15, 2009, 16:41
things id look at ..cocking assy location

headspace ..recheck

roller size

impingement from ejector on bolt under fire ....

chamber slop

gunplumber
January 15, 2009, 16:41
I wonder if you have an "HK 51" spring in the fixed stock. It is shorter.

should be 12-3/4"

Also - wouldn't hurt to check the bolt gap.

DK
January 15, 2009, 17:05
Originally posted by gunplumber
Also - wouldn't hurt to check the bolt gap.

Mystery terms Mark... How does one check the gap of one's bolt? (I'm basically a FAL and AR type of guy.. ;) )

DK

p.s quick check of the recoil spring rod lengths... looks like I was wrong.. both the same and right at 12 3/4"....

gunplumber
January 15, 2009, 17:17
headspace doesn't work on roller delayed blowback systems. instead, you measure the gap between the bolt head and the bolt body with the bolt closed on an empty chamber. Spec is 0.1-0.55 mm, but ideal starting is around .018-.020"

Also, there needs to be a gap between the cocking handle extension and the bolt carrier when closed. should be a minimum of "can just wiggle it" to a max of .022" (box cutter blade). If it is bottoming out, that will give you a false bolt gap as the cocking tube becomes the bolt-return impact surface instead of the chamber face.

DK
January 15, 2009, 17:35
ok, we have wiggle room..... and the bolt gap measured as described looks like .015" on my feeler gauges...

Anything there?

DK

gunplumber
January 15, 2009, 18:29
those are good - which tends to rule out the construction of the gun.

Can you wiggle the grip frame any when the gun is assembled? If the shelf on the grip frame and receiver are off its possible to have undue tension on ejector,

So far though it sounds like everything is correct, which brings us back to the ammo - you say west german? Never heard of it being imported. Are you sure its german?

DK
January 15, 2009, 20:30
Yeah, the ammo came from Dan- "7.62x51 NATO headstamp MEN -Maschinenfabrik Elisenhuette, Nassau - 1980s Berdan 500rds packed loose in GI ammo can."

Like I said it worked beautifully for the first 20 rounds, then the PTR became a single shot :? . I tried the same stuff in my Argy FAL when the PTR went down and the Argy ate it like a fat kid eats potato chips.

I tried some brand new Federal 150grn FMJ this afternoon with the same results- single shot city.

I'm handling the rifle now.. fully assembled, (tried it with both buttstocks), absolutely solid grip frame. Zero wiggle.. :confused:

DK

DK
January 16, 2009, 14:00
Friday update:

I think it's been narrowed down to something wrong w/ the A2 fixed buttstock. I put the G3 sliding stock on today and took it out to the range. Sure enough, it went bang every time and cycled just fine.

I don't see any obvious problems with the recoil spring and/or guide rod on this buttstock. The spring looks new, the guide rod looks new, the little rubber doughnut on the end looks fine. I'm guessing the metal bits on this stock are G3 surplus as there is a 3 digit number stamped below the retaining pin holes; the plastic stock body is new PTR-91 and has their logo stamped at the sling point.

Anything I can check that isn't obvious?

DK

DK
January 16, 2009, 14:04
Can it be lubed too much? It isn't dripping or anything but there is a nice sheen of oil on the A2 guide rod. The sliding stock's guide rod looks more "dry".

Grasping at straws I suppose....

DK

gunplumber
January 16, 2009, 14:13
Originally posted by DK
Friday update:

I think it's been narrowed down to something wrong w/ the A2 fixed buttstock. I put the G3 sliding stock on today and took it out to the range. Sure enough, it went bang every time and cycled just fine.

I don't see any obvious problems with the recoil spring and/or guide rod on this buttstock. The spring looks new, the guide rod looks new, the little rubber doughnut on the end looks fine. I'm guessing the metal bits on this stock are G3 surplus as there is a 3 digit number stamped below the retaining pin holes; the plastic stock body is new PTR-91 and has their logo stamped at the sling point.

Anything I can check that isn't obvious?

DK

Ok, I've seen this on the Speshul Weapunz/Vector 9mm and .223s, and on the 51s, but not on a PTR with a GI stock. But look at it anyway because effects are the same.

Assuming the spring guide is straight , is there a gap around the stock ferule at the top? I've seen some of the crappy US made ones so loose here that the stock cants downward, which binds the spring on the inside of the carrier.

Maybe spray the spring with some dykem and see if its binding - maybe one coil is oversize and thats preventing the full use of the spring.

Also manually bush the bolt carrier down on the spring guide. Should catch the nylon and trap the spring w/the guide passing through