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Author
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Topic: PTR91 BOLT GAP?
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derf
Member
Member # 3609
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posted April 22, 2006 13:59
I wanna talk about other things.
Fishing should be getting hot soon.Did you do the "HK Slap" when you chambered the round? His 0.018 is still in spec, although the gap should be measured on an empty chamber.
Check the obvious:
Pull you bolt head out and stick a round in it and see if it seats correctly.
Check the chamber. The round shouldn't protrude from the chamber more than the recess in the bolt head, I would think. I check all my bolt gaps on empty chambers, including the PTR, and don't worry about what the gap is on a loaded chamber. I am not exactly sure what it should be so I am looking forward to the answer to your question, too. Also, did you try on a live round? Or, just the go gauge? Did the go gauge have the same rim as a live round? Maybe your extractor was not fitting just right on the go gauge? OK, enough gab, gotta get to the gunshow. [ April 22, 2006: Message edited by: derf ] -------------------- Turkish: "What's that for?"
Tommy: "Protection."
Turkish: "Protection from what, ze Germans?"
Posts: 1065 | From: Southern, by Grace | Registered: Feb 2003
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FMJBTHP
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Member # 4910
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posted April 23, 2006 16:56
Another thought: Was the chamber clean for the test? Some small metal shavings or other debris could also cause measurements to be a little off. A brand new rifle could very well have a little "junk in the trunk" left over from the manufacturing process. Mike -------------------- "Helping others to find the products they need, from sources other than Joeken since 2005"
Posts: 359 | From: Peoples Republic of Kalifornia | Registered: Jan 2005
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derf
Member
Member # 3609
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posted April 24, 2006 01:12
quote:
Originally posted by KENNY HART:
derf,
This is a new rifle, so wear is not a factor in this case. The thing I was trying to get at is also Head Space. If the chamber is not cut deep enough and you put in a live round your bolt gap will increase because the round isn't going in the battery far enough and the rollers aren't fully locking into the trunion. I still would like to see what other PTR91 rifles are getting for measurments.
I didn't say anything about wear. Does the base of the gauge exactly match the base of a live round? Is there a similar rim on both? Some gauges just have an angled base and not a rim for the extractor to fit into.
By design, if the carrier doesn't get into full lockup, the firing pin should not be able to ignite the primer. There may be cases of out of spec parts and/or the occasional out-of-battery ignition. But, in general, if you don't have lockup you probably won't have ignition. Most of the out-of-battery ignitions I've hear about (Vulcan, you had one recently, right) were not catastrophic because the gun was so close to being in battery that the system still functioned, i.e. it didn't blow the mag to pieces and shred the receiver, etc. Two things to remember:
The HK system is designed to use pressure to fire the bullet and recock the weapon.
If the round is ignited too far out-of-battery then the pressure will be allowed to drop sooner than if it were in battery. It is like shooting shotgun shells in the primer with a BB gun. (Don't try this) You can get ignition, but the explosion is less intense because the chamber was not focusing the blast to force the load down the barrel. I would like to see what happens to an HK G3 after so many rounds that the system fails. I wonder what would happen? I suspect it would stop cycling long before any dangerous ignitions took place. I wonder what a live round fired into a fouled barrel would do. Probably kick like a mule but not otherwise injur the shooter. -------------------- Turkish: "What's that for?"
Tommy: "Protection."
Turkish: "Protection from what, ze Germans?"
Posts: 1065 | From: Southern, by Grace | Registered: Feb 2003
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FMJBTHP
Member
Member # 4910
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posted April 24, 2006 01:56
Ok, I got curious and decided to check the measurements on my parts kit. Turns out it is short chambered by .010". Using a Black Hills match round, there is a definite gap between the bolt face and the breach when the round is seated into the bolt. I'm sure this would have an affect on bolt gap, most likely a sizable increase. This also means that nearly any round chambered in this weapon would be at zero headspace, which could explain why this design is so inherently accurate. I'm not sure if the short chamber is standard or not, perhaps one of the more knowlegable guys can chime in here. Mike -------------------- "Helping others to find the products they need, from sources other than Joeken since 2005"
Posts: 359 | From: Peoples Republic of Kalifornia | Registered: Jan 2005
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Vulcan Raven
Member
Member # 2882
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posted April 24, 2006 11:26
quote:
Originally posted by derf:
By design, if the carrier doesn't get into full lockup, the firing pin should not be able to ignite the primer. There may be cases of out of spec parts and/or the occasional out-of-battery ignition. But, in general, if you don't have lockup you probably won't have ignition. Most of the out-of-battery ignitions I've hear about (Vulcan, you had one recently, right) were not catastrophic because the gun was so close to being in battery that the system still functioned, i.e. it didn't blow the mag to pieces and shred the receiver, etc.
Yep, I had one with my PSG-1 clone not too long ago. I was letting a buddy of mine shoot the rifle. He recalled from memory that I told him to never let a bolt or slide slam on an empty chamber, so, he had eased the charging handle forward (never load an HK-type weapon like this....always do the "HK slap") While it is true that slamming on an empty chamber will accelerate wear on internal parts, the same is not true for a loaded chamber, because the brass casing acts as a buffer. So, anyhow, when it fired out of battery, I got a case head seperation, which left most of the shell casing stuck in the chamber. This can be removed with a shell extractor of by a tight fitting bronze brush. I used a bronze brush. There was no damage done to the rifle....but a lesson well learned. Do not let inexperienced people shoot expensive rifles. Two things to remember:
The HK system is designed to use pressure to fire the bullet and recock the weapon.
If the round is ignited too far out-of-battery then the pressure will be allowed to drop sooner than if it were in battery. It is like shooting shotgun shells in the primer with a BB gun. (Don't try this) You can get ignition, but the explosion is less intense because the chamber was not focusing the blast to force the load down the barrel.
I can't say I never did this when I was a dumbass kid. No wonder they say God watches out for fools. He sure watched out for me for several years.
I would like to see what happens to an HK G3 after so many rounds that the system fails. I wonder what would happen? I suspect it would stop cycling long before any dangerous ignitions took place. I wonder what a live round fired into a fouled barrel would do. Probably kick like a mule but not otherwise injur the shooter.
I wish we could have the auto sear, just the auto sear.....so that the gun could NEVER fire out of battery. But, the opinion is that if your semi-auto contains just one full auto part, it is a machine gun. So, unfortunately, we are stuck with using weapons that are less than safe by their original design. Thanks, ATF. I'll be sure to send the E.R. bill to you when my rifle blows half my face off from firing out of battery.
-------------------- " It's better to be hated for who you are....than liked for who you are not. " Van Zant
Semper Vigilo et Paratus
Raven
(designated sniper of worthless trolls)
Posts: 2961 | From: Somewhere on NOAA Chart 11534 | Registered: Feb 2002
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Vulcan Raven
Member
Member # 2882
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posted April 26, 2006 12:24
.002" in 100 rounds?! WTF? Something isn't right with these rifles. I've shot about 550 rounds out of my PSG-1 clone, and my bolt gap is still right between .018" and .020" A rapidly diminishing bolt gap means something is wearing down as the rifle is fired. Probably improper hardening procedures on the trunnion.-------------------- " It's better to be hated for who you are....than liked for who you are not. " Van Zant
Semper Vigilo et Paratus
Raven
(designated sniper of worthless trolls)
Posts: 2961 | From: Somewhere on NOAA Chart 11534 | Registered: Feb 2002
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bspring
Member
Member # 286
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posted April 28, 2006 15:19
Any delay blow back rifle new will have a bolt gap decrease during break in; sometimes as much as .005". Ask any Century Cetme/G3 owner.Bill -------------------- Ask me about HK, Cetme, SKS and AR-15, FAL trigger work.
Posts: 165 | From: cos,co usa | Registered: Feb 2000
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Vulcan Raven
Member
Member # 2882
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posted April 28, 2006 18:33
Well, I guess my rifle must be an rare, one in a million kind of rifle.....as I have put over 500 rounds through it without even a .001" decrease. Somebody else stated they had one (A PTR-91 to boot) that had over 800 rounds and his bolt gap was still at .014"....same as when new. I reckon the two of us just got lucky, and we don't have a bolt gap issue. I wonder how many rounds my rifle will ultimately fire before I do see a change. I keep a logbook, so, I'll note it in there when it happens. -------------------- " It's better to be hated for who you are....than liked for who you are not. " Van Zant
Semper Vigilo et Paratus
Raven
(designated sniper of worthless trolls)
Posts: 2961 | From: Somewhere on NOAA Chart 11534 | Registered: Feb 2002
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ginmaster
Member
Member # 5577
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posted May 05, 2006 01:45
quote:
Originally posted by Vulcan Raven:
Well, I guess my rifle must be an rare, one in a million kind of rifle.....as I have put over 500 rounds through it without even a .001" decrease. Somebody else stated they had one (A PTR-91 to boot) that had over 800 rounds and his bolt gap was still at .014"....same as when new. I reckon the two of us just got lucky, and we don't have a bolt gap issue. I wonder how many rounds my rifle will ultimately fire before I do see a change. I keep a logbook, so, I'll note it in there when it happens.
Still at .015 here.
Posts: 65 | From: MO. | Registered: Nov 2005
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Vulcan Raven
Member
Member # 2882
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posted May 05, 2006 18:44
I'm not understanding why some of the rifles are OK, and others are not. It would be interesting to compare (partial) serial numbers, to try and figure out date of manufacture, and see if the older rifles, or the newer ones are having problems. Either they had problems early on, and they changed to better parts....or the original rifles were good, and JLD broke the old rule of "if it ain't broke, don't fix it" and decided to change something, perhaps went with cheaper parts to save money. I don't know....but it sure as hell is strange. ![[spin]](graemlins/spiny.gif) -------------------- " It's better to be hated for who you are....than liked for who you are not. " Van Zant
Semper Vigilo et Paratus
Raven
(designated sniper of worthless trolls)
Posts: 2961 | From: Somewhere on NOAA Chart 11534 | Registered: Feb 2002
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