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Thread: #17, 36 Degree Locking Piece & Recoil Management for PTR 91

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  1. #1
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    #17, 36 Degree Locking Piece & Recoil Management for PTR 91

    Hello,
    I have been doing some reading and came across an article that talks about making some modifications (basically (4ea) items; not necessarily all of them but (1) or a combination of them) that would help manage recoil.
    One of the items was to:
    * Remove the flash hider and install a good muzzle brake.
    * Remove the existing buffer assembly and install an "enhanced buffer assembly"
    * Remove the existing butt Pad and install an HK 21 type rubber butt pad.
    * remove the existing 45 degree angle locking piece and install a #17, 36 degree locking piece.

    Upon further reading about the locking piece, most descriptions say the different locking piece is primarily for using a suppressor or heavier loads through the rifle.

    Has anyone ever tried these modifications and what results did you get? Are any of these mods (aside from the butt pad) harmful to the rifle's operation and reliability? I'm especially curious about the different locking piece. The rifle functions very well and I didn't want to fix something the "aint broke"
    I am guilty of installing a Precision Armament M4 72 muzzle brake on the PTR and there is a substantial difference. I decided on this one because of the results I got installing one on my AR-10. Recoil is that of an AR-15.





    " If Clemenza can figure out a way to plant that gun, then I'll kill them both. It's nothing personal Sonny. It's strictly business".... Michael Corleone

    "Stick to your gun if you believe in something
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    Than loved for someone you're not. Oh, and try to help someone out." Van Zant

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    holescreek's Avatar
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    I've swapped LPs out on a single rifle and determined that the difference in felt recoil is negligible. Swapping buffers is meaningless if the rifle runs right.

    If you really want to tame recoil and its a bench gun (like all of mine ) just fill the plastic stock with weight. Lead shot ought to be great. My 17 pound target cetme is a pleasure to shoot.

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    holescreek's Avatar
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    Now that I'm at a real keyboard I'll expand my comment about the locking pieces. The shoulder angle of the LP merely provided leverage for the rollers to press against to push the bolt carrier rearward so the rollers can move inward enough to clear the inside of the trunnion.
    A larger shoulder angle (like a 50 degree) provides more leverage and lets the action open quicker and a smaller shoulder angle (like a 36 degree) makes the action open slower.
    Larger shoulder angles are used with shorter barrels or weaker cartridges.
    Smaller shoulder angles are used with long barrels or hot cartridges.

    The point of changing the locking piece angles is to allow the majority of gas pressure follow the bullet out while keeping enough back pressure to cycle the weapon. That difference is measured in milliseconds and therefore probably not easily detected by felt recoil.

    Will it hurt to change the LP? No. Will you feel the difference? I doubt it.

    I typically advise shooters to change their bolt pawl spring before changing anything else because it is what provides the drag that the locking piece has to overcome. The stronger the pawl spring is the slower the action opens and more gas pressure goes out with the bullet. Be advised that Apex's pawl new springs are about 40-50% weaker than a real HK/Cetme spring so buy it someplace else. I have more information about this in my C308 evaluation thread. Look at you pawl hook as well.
    Last edited by holescreek; 04-18-2017 at 07:19 PM.

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    Senior Veteran The Great 308's Avatar
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    Quote Originally Posted by holescreek View Post
    I've swapped LPs out on a single rifle and determined that the difference in felt recoil is negligible. Swapping buffers is meaningless if the rifle runs right.

    If you really want to tame recoil and its a bench gun (like all of mine ) just fill the plastic stock with weight. Lead shot ought to be great. My 17 pound target cetme is a pleasure to shoot.
    holescreek, I will definitely defer to you when it comes to locking pieces. However I am confused about the statement concerning recoil buffers. Could you please explain what you are referring to? Your statement is contradictory to my experience with several different Cetmes, PTR91s and custom built HK91 clones. From my experience the standard HK91 buffer is not nearly as good as the Heavy 2 stage HK buffer or the HK MSG90 buffer. I noticed a very big difference in felt recoil when switching recoil buffers. I also noticed a huge difference when I rebuilt my Cetme buffer with new internals. The bolt carrier does make contact with the recoil buffer on a correctly running in-spec rifle, otherwise it would not be there. Also both the MSG90 buffer and HK heavy two stage buffer stick farther into the receiver and therefore engage the bolt carrier sooner. These rifles would beat themselves to death without a recoil buffer. From what I have read roller marks in the receiver are caused by both double buffering and under buffering.

    As far as the HK21 butt pad goes that is also a huge improvement for felt recoil. Not only are these much softer but they also distribute the recoil to a larger area. There is also a slip on after market recoil pad made by E&L manufacturing that is not as nice looking but does just as good a job for less money.

    https://elmfg.com/store/hk.html#pad

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    I really appreciate all the information! It helps going forward. The rifle is basically new and only has 100rounds through it....
    " If Clemenza can figure out a way to plant that gun, then I'll kill them both. It's nothing personal Sonny. It's strictly business".... Michael Corleone

    "Stick to your gun if you believe in something
    no matter what;
    cause it's better to be hated for who you are
    Than loved for someone you're not. Oh, and try to help someone out." Van Zant

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    Senior Veteran The Great 308's Avatar
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    RTG has a really good price on a contract HK21 butt pad. The HK heavy two buffer and MSG90 buffer are both very expensive but there is a PCS improved buffer that is affordable but sold out right now. Also Bill Springfiels makes a very affordable upgrade kit for both the standard HK buffer and the Buffer for the collapsible stock.

    http://www.robertrtg.com/store/pc/HK...S-181p1957.htm

    http://www.triggerwork.net/hksbuffer.html

    http://www.triggerwork.net/hkbuffer.html

    http://www.hkparts.net/shop/pc/viewP...idcategory=114

    http://www.hkparts.net/shop/pc/viewP...idcategory=114

    http://www.hkparts.net/shop/pc/viewP...idcategory=114


    http://www.robertrtg.com/store/pc/HK...AD-25p1863.htm
    Last edited by The Great 308; 04-18-2017 at 09:29 PM.

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    I put both the HK21 butt pad and the PCS improved buffer from RTG in my PTR stock. Have not tried them out yet though. Soon, I hope.
    14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer

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    Quote Originally Posted by The Great 308 View Post
    RTG has a really good price on a contract HK21 butt pad. The HK heavy two buffer and MSG90 buffer are both very expensive but there is a PCS improved buffer that is affordable but sold out right now. Also Bill Springfiels makes a very affordable upgrade kit for both the standard HK buffer and the Buffer for the collapsible stock.

    http://www.robertrtg.com/store/pc/HK...S-181p1957.htm

    http://www.triggerwork.net/hksbuffer.html

    http://www.triggerwork.net/hkbuffer.html

    http://www.hkparts.net/shop/pc/viewP...idcategory=114

    http://www.hkparts.net/shop/pc/viewP...idcategory=114

    http://www.hkparts.net/shop/pc/viewP...idcategory=114


    http://www.robertrtg.com/store/pc/HK...AD-25p1863.htm
    I ordered a butt pad and the enhanced buffer from Mr. Springfield. I figured after all your information, teaming those with the brake will help a lot.
    " If Clemenza can figure out a way to plant that gun, then I'll kill them both. It's nothing personal Sonny. It's strictly business".... Michael Corleone

    "Stick to your gun if you believe in something
    no matter what;
    cause it's better to be hated for who you are
    Than loved for someone you're not. Oh, and try to help someone out." Van Zant

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    holescreek's Avatar
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    You're right! I've been thinking of it all wrong. On a good running rifle (no issues like I found on the C308) the carrier shouldn't make contact with the standard buffer. I guess I failed to take into consideration that the heavy buffers (after looking at a photo of them) protrude further towards the chamber which causes the carrier to strike them all the time right? I've never owned one so I'm guessing there is a two stage spring assembly to slow the carrier down.

    I'd assumed they were the same length as a standard buffer but with a different spring setup. The extra length would make a difference. Maybe someday I'll get to test one out.

    Is one company's heavy buffer better than anothers?
    Last edited by holescreek; 04-18-2017 at 09:18 PM.

  10. #10
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    Quote Originally Posted by holescreek View Post
    You're right! I've been thinking of it all wrong. On a good running rifle (no issues like I found on the C308) the carrier shouldn't make contact with the standard buffer. I guess I failed to take into consideration that the heavy buffers (after looking at a photo of them) protrude further towards the chamber which causes the carrier to strike them all the time right? I've never owned one so I'm guessing there is a two stage spring assembly to slow the carrier down.

    I'd assumed they were the same length as a standard buffer but with a different spring setup. The extra length would make a difference. Maybe someday I'll get to test one out.

    Is one company's heavy buffer better than anothers?
    I only have experience so far with the HK MSG90/PSG1 buffer and the HK two stage heavy buffer. I have two of the heavy buffers and one MSG90 buffer. They are both really nice and a big improvement over the standard buffer but I am not sure that either one is better. At the time I was getting parts together for my builds there were no other options for enhanced buffers. However since then I have heard really good reviews of the PCS improved buffer and the Bill Springfield buffers. If they had been offered at the time I would have tried one of these more affordable versions. Both the PCS improved buffer and the MSG90 buffer are longer than standard buffer but have the same outer diameter so they can be used in the HK plastic stocks with no modifications. The HK heavy two stage buffer is longer than a standard buffer but also has a larger outer diameter. I modified my PRSII stock for the HK heavy two stage buffer and my other heavy buffer came from HK in my SG1 stock. I put the MSG90 buffer in an FMP OD buttstock.

    One thing that is cool about the ones Bill Springfield offers is that it is new internals for the standard buffer so you can use it in wood stocks with no modifications. He also makes one that I am going to get which is upgraded internals for the buffers used in the G3 collapsible stocks (this is the only option for an upgraded buffer for these stocks). The new internals include a new (longer?) and different rate spring as well as an extended piston that protrudes farther into the receiver.

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