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PTR 91 36 degree Locking Piece issues

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Greetings, I picked up a PTR 91 a couple of months ago. I have owned a PTR 32 (7.62X39) for a few years and it's one of my favorite rifles. The PTR 91 I purchased from a private owner. First time at the range it ran great, but recoil was a little excessive and I'm not very recoil sensitive. Every shot it would take me off target. My first upgrade was an enhanced buffer spring and piston from Springfield. this helped but rifle was still jumping around but ran well with no failures. I also put a limbsaver on. I was reading about swapping out the locking piece for a 17/36 locking piece. I ordered one from RTG and replaced the stock PTR locking piece which is stamped PTR. At the range it would fire one shot and then malfunction. Appears it is not going fully into battery. I would either get light primer strikes or no strike at all. If I cycled it a few times it would fire and then go back to not going into full battery. I am running standard 149 grain M80 Nato ball ammo. I swapped the original locking piece back in and the gun ran perfectly. With the original locking piece in I measured the headspace at 0.12 inches. When I put in the 17/36 locking piece I racked the rifle pulled the trigger and headspace measured at 0.17. I measured several times and the headspace kept changing. Highest reading was .026 lowest 0.17. Most all of them were above 0.20. As of now I have the original locking piece back in but wonder if anyone had any ideas of what could be causing these issue with the 36 degree locking piece installed. Seems everytime the rifle was charged the headspace would change. Thanks for any info that can be provided
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Does the original locking piece gap measure 100% consistently at .012"? (I'm assuming it's not 0.12" and that's a mistype)

Assuming it does, then there's something about the RCM locking piece you got from RTG parts that is introducing that bolt gap inconsistency.
I'd look carefully at the front edges of the locking piece for excessive or visible wear from the rollers, and also check the rollers themselves. You may need some 'minus' sized rollers to get the bolt gap right, but until you can get a consistent bolt gap measurement with the 36* locking piece, you'll be chasing your tail on different roller sizing.


Edit - what kind of lubricant are you using, if any? Sometimes a return-to-battery problem is simply insufficient lubricant.
 

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I would also make sure you are checking the bolt gap using the proper procedure and the entire area is clean.

I have a PTR91 with the standard locking piece and a modified buffer, and it's pretty tame with 168gr FMJs.

If using a suppressor, it's best to change the stock LP, but without it may just cause issues.
 

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Discussion Starter · #4 ·
Does the original locking piece gap measure 100% consistently at .012"? (I'm assuming it's not 0.12" and that's a mistype)

Assuming it does, then there's something about the RCM locking piece you got from RTG parts that is introducing that bolt gap inconsistency.
I'd look carefully at the front edges of the locking piece for excessive or visible wear from the rollers, and also check the rollers themselves. You may need some 'minus' sized rollers to get the bolt gap right, but until you can get a consistent bolt gap measurement with the 36* locking piece, you'll be chasing your tail on different roller sizing.


Edit - what kind of lubricant are you using, if any? Sometimes a return-to-battery problem is simply insufficient lubricant.
Hi and thanks for the response. Yes the original locking piece consistently measures .012. Visual inspection of the original locking piece and rollers show no excessive wear. I believe the previous owner did not put to many rounds down the tube. I'll have to look closely at the RTG locking piece for wear marks. Not many rounds through the rifle using the RTG part because of failure to go fully into battery. Sometimes I get a light primer strike and then after manually racking in another round I might no even get a primer strike. Luckily the rifle runs well with the original PTR locking piece. I did notice a design difference between the original PTR locking piece and the RTG piece. They both lock into the bolt carrier with no issue. I usually use Lucas products for lubrication and also Red Hawg grease on the carrier. Been around long enough to know proper lubrication is a must.
 

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Discussion Starter · #5 ·
I would also make sure you are checking the bolt gap using the proper procedure and the entire area is clean.

I have a PTR91 with the standard locking piece and a modified buffer, and it's pretty tame with 168gr FMJs.

If using a suppressor, it's best to change the stock LP, but without it may just cause issues.
Hi thanks for the reply. Yes I cleaned up the bolt and my work area is clean. I am using the procedure from the HK91 armorers manual using a Craftsman feeler gauge set. Also measured the cocking gap and it is in spec. I do have a modified buffer using the Bill Springfield enhanced spring and piston. The original PTR locking piece works well with the enhanced buffer setup. I dont run a suppressor. I have been looking for a compensator, right now it just has the HK style flash hider on it. 15x1 RH compensators are few and far between but found one at a relatively decent price from CNC Warrior and it is secured with a jam nut.
 

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Hi thanks for the reply. Yes I cleaned up the bolt and my work area is clean. I am using the procedure from the HK91 armorers manual using a Craftsman feeler gauge set. Also measured the cocking gap and it is in spec. I do have a modified buffer using the Bill Springfield enhanced spring and piston. The original PTR locking piece works well with the enhanced buffer setup. I dont run a suppressor. I have been looking for a compensator, right now it just has the HK style flash hider on it. 15x1 RH compensators are few and far between but found one at a relatively decent price from CNC Warrior and it is secured with a jam nut.
I believe a PTR barrel will have standard Imperial-Inch threads, and not metric - but I'd confirm.
 

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I believe a PTR barrel will have standard Imperial-Inch threads, and not metric - but I'd confirm.
My older PTR 91 has the metric threads. This was common when the company was actually called PTR91 and not just PTR. Back then they used all German new or excellent parts for constructing the 91 guns on their own rolled flats.
 
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This is what I ordered from RTG; RCM HK21E G41 LOCKING PIECE #17, 36 DEGREE (RCM-LP-1736)
I went through the same thing. The #17 locking piece has a smaller barrel diameter than the PTR or standard HK91 locking piece and was not designed for the G3, HK91 or PTR 91. It was designed for the HK21E. Compare the two together and you will see what I mean. Distributors say it can be used but HK experts will say that you are making design changes. The standard locking piece or unmarked is 45 degrees. The best bang for the buck as others have said is get a muzzle brake and nice stock. Big difference. I tried the #17 years ago and it did not work on my HK91, HK41 or HK21 without using a suppressor but then again your forcing the gun to do things it was not designed to do. I got rid of it.
 

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Discussion Starter · #14 ·
My older PTR 91 has the metric threads. This was common when the company was actually called PTR91 and not just PTR. Back then they used all German new or excellent parts for constructing the 91 guns on their own rolled flats.
Hi, yes I noticed many parts were HK stamped. With the original locking piece in the gun runs superbly. Accuracy is great with standard ball. I've shot steel out to 400 yards with it.
 

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Discussion Starter · #16 ·
I went through the same thing. The #17 locking piece has a smaller barrel diameter than the PTR or standard HK91 locking piece and was not designed for the G3, HK91 or PTR 91. It was designed for the HK21E. Compare the two together and you will see what I mean. Distributors say it can be used but HK experts will say that you are making design changes. The standard locking piece or unmarked is 45 degrees. The best bang for the buck as others have said is get a muzzle brake and nice stock. Big difference. I tried the #17 years ago and it did not work on my HK91, HK41 or HK21 without using a suppressor but then again your forcing the gun to do things it was not designed to do. I got rid of it.
Thanks very much for the info appreciate it. Well right now I'm only out 50 bucks for the RCM piece. I am going to fire off an Email to RTG and RCM and see what they can do about it as far as returning the part. Worth a try even though I don't think they will. Going to order the 15X1 RH compensator from CNC Warrior, I've purchased AK parts from them and they make quality parts. Do you have any recommendations regarding a stock? I'm running the factory stock with a modified Limbsaver and a Voodoo tactical cheek rest since I'm running a scope on it. You can definitely see the difference in the design of the stock 45 degree and the 17/36 piece. They list it for the HK21E but are also marketing it for the G3/HK91/PTR. Bolt gap is all over the place with the RCM piece anywhere from 0.18 to 0.26. Comes in consistently at 0.12 with the stock 45 degree piece and the enhanced buffer spring and piston. Thanks again.
 

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Discussion Starter · #17 ·
PTR made a bunch of bad bolts for the x39.

Make sure your belt is sound.
Hi, the PTR32 I have I purchased new about a year and a half ago. I got about 1K rounds through it and the rifle has ran excellent. Last time I broke it down all the internals looked very good and the rifle is lubricated generously, I like to run them on the wet side. Seen to many people at the range with malfunctions on their AR's only to pull the BCG out and see it was bone dry.
 

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Discussion Starter · #19 ·
Most likely the bolt is fine. The bad bolts are several generations ago. Ask me how I know.
Lol, okay going to use my critical thinking skills, your X39 PTR had a defective bolt! I hope they replaced it free. I have a Palmetto KS47, its a hybrid AR and takes standard AK mags like the PTR 32. At about 600 rounds the extractor cracked. PSA knew it was an issue, they came out with a new TCE extractor with a higher Rockwell rating. I went back to them since they have a lifetime warranty and asked for a new extractor. Oh no, you have to send in your whole rifle, not just the Bolt but the whole rifle. Needless to say I declined and purchased the new version of the extractor for $24.00. After putting in the new extractor I had issues with light primer strikes every 2 to 3 rounds. Got on the KS47 forum and they recommended going with an enhanced firing pin and enhanced trigger spring, Before the extractor broke the rifle ran great with the stock firing pin and I had replaced their trigger with a Rise Armament drop in 3 lb flat trigger. So I purchased the enhanced firing pin and enhanced spring from Black River Arms for 25.00. After putting those 2 parts in the gun ran flawless again. Weird issue, all I can think of is PSA's new extractor is slightly out of spec just enough to cause the light primer strikes.
 

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I like the 21E wide butt pad for my G3 types. Snaps right on a factory type stock and looks/is an original HK part.
However, I do have a Limbsaver on my SPUHR stock, which is basically and AR stock adapted to the G3 back plate.
Concerning your locking piece problem, I'd ditch the #17 and move on with life. The rifle may be being damaged while trying to figure out why something that's not really supposed to be in there won't work. If you don't see signs of problems like roller dents, personally, I wouldn't worry about it. You say your rifle won't stay on target when it's fired and that recoil is too much, well, it's a G3 type. These things recoil way more than your 32 and I've never shot a G3 type that stayed on target from shot to shot. And I'm talking point of aim, not the target board. Address the recoil pad/butt pad, install your ordered brake, enjoy your rifle. But please stop asking it to do things with parts it's not intended to use.
 
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