RCM 28/80 Degree Locking Piece
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Thread: RCM 28/80 Degree Locking Piece

  1. #1
    AWH
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    Default RCM 28/80 Degree Locking Piece

    Has anyone had issues with RCM's MP5K 9MM #28/80 degree LP putting the bolt gap way out of spec? Just curious for feedback. I don't see any other alternatives available right now.

    RCM has added this to their product description:

    "******* IMPORTANT MESSAGE ********** PLEASE READ BEFORE BUYING *******

    RCM strives for the highest quality parts and has been for over 20 years. That’s why we don’t cut corners on material selection, manufacturing processes, Q/C standards and customer service. We don’t try to compete with other US made parts. We compete with genuine German Parts. That’s how high we set the bar for ourselves. There seems to be some confusion with swapping out one locking piece with another and not expecting the bolt gap to change. Well it does! This particular locking piece is for a PDW/K platform with a suppressor mounted on the end of the barrel or heavier loads. Your bolt gap will change and it seems to vary on the brand of the gun and the quality of all the parts that were used in the assembly. You can take a brand X gun that has part tolerances all over the place and when you press and pin the barrel then set bolt gap with brand X parts it will most likely perform. How good? That’s hard to say. Now you swap out the 110 degree locking piece with the 80 degree and some will perform with a larger bolt gap. Some will use different rollers to bring it back to nominal. Some will see such a huge gap that even -8 rollers won’t help. Now your cussing out RCM for an out of spec locking piece because your bolt gap is way off the charts. Well folks now your seeing the flaws in the build and in the parts. Now if your trying to figure out how to resolve this issue you only have one choice. Repress the barrel using either a German Bolt Group or a RCM Bolt Group. BUT take this in consideration. Even in our German guns the bolt gap changes when we change out the 110 locking piece with the 80 degree and both are factory locking pieces. There are so many variables to consider on every piece that makes this gun work. Every part has a tolerance and think of all the parts that create the bolt group. Stack all those tolerances up and if it exceeds the smallest roller size to adjust for it then you will have issues. RCM is not perfect in any regards but focuses on idiot proofing the process to prevent out of print parts getting through. If you feel that something isn’t right give us a call."
    Last edited by AWH; 05-22-2020 at 06:40 PM.

  2. #2
    Tug
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    I did a write up on my experience. Its on here somewhere.

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    Tug
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    I did a write up on my experience. Its on here somewhere.

    here it is copy and past

    FYI. Purchased a AA89 a few years ago. Shot it just a few times and put it away. Now have a little time to work it up.

    It came from the factory with a gap of .017. I put a #28 RCM locking piece in it. Bolt gap increased to about .028. I installed HK -8 rollers. Gap returned to about .020.

    Removed the AA89 plastic lower and installed a HKParts net clipped and pinned HK SEF lower. Dropped my sear pack in it.

    It will not reliably shoot the 115 steel case Wolf without a suppressor. I think this ammo is just too weak to have reliable extraction. With any of my cans, it is reliable. Just enough back-pressure to get it over the hump.

    124 Win Nato is reliable with or without a can.

    158 IMI is reliable with or without a can.

    I think I have $225 or so in HK parts in an AA89. Will sell the AA89 lower which should reduce the cost a little. I am happy with the gun because it was inexpensive to start with and came with FA bolt and 3 lug. Its fun to shoot. Will check into heavier than 115 gr bullet steel case ammo.

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    AWH
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    Quote Originally Posted by Tug View Post
    I did a write up on my experience. Its on here somewhere.

    here it is copy and past

    FYI. Purchased a AA89 a few years ago. Shot it just a few times and put it away. Now have a little time to work it up.

    It came from the factory with a gap of .017. I put a #28 RCM locking piece in it. Bolt gap increased to about .028. I installed HK -8 rollers. Gap returned to about .020.

    Removed the AA89 plastic lower and installed a HKParts net clipped and pinned HK SEF lower. Dropped my sear pack in it.

    It will not reliably shoot the 115 steel case Wolf without a suppressor. I think this ammo is just too weak to have reliable extraction. With any of my cans, it is reliable. Just enough back-pressure to get it over the hump.

    124 Win Nato is reliable with or without a can.

    158 IMI is reliable with or without a can.

    I think I have $225 or so in HK parts in an AA89. Will sell the AA89 lower which should reduce the cost a little. I am happy with the gun because it was inexpensive to start with and came with FA bolt and 3 lug. Its fun to shoot. Will check into heavier than 115 gr bullet steel case ammo.
    I appreciate the response! I have seen some reviews of the RCM locking piece, but couldn't find anything posted recently.

    I understand switching the LP will change the bolt gap, but just wanted to ask for some input before purchasing.

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    Tug
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    Even if you bought a OEM HK locking piece, you would still need to check gap. I got a $20 bill and an IPA on my desk that says it would change the gap a little too. Good luck. Let me know if you need anything.
    GregAB and gsyoung54 like this.

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    ^^^^^^ What Tug Said ^^^^^^

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    I’ve seen a bunch of folks post about seriously big changes in the bolt gap with this latest run of RCM 28/80’s. Mine went from .016 to .018 going from the 110 to 80. But, like Tug said, change the LP and the BG changes. Same thing happens on my 5/10. I go from the 24 to 25, it widens a bit. Some of the moves people are seeing are crazy. RCM’s statement seems to make a lot of sense to me. 🏼

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    AWH
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    Quote Originally Posted by Tug View Post
    Even if you bought a OEM HK locking piece, you would still need to check gap. I got a $20 bill and an IPA on my desk that says it would change the gap a little too. Good luck. Let me know if you need anything.
    Quote Originally Posted by GregAB View Post
    ^^^^^^ What Tug Said ^^^^^^
    Quote Originally Posted by Rdrdr90 View Post
    I’ve seen a bunch of folks post about seriously big changes in the bolt gap with this latest run of RCM 28/80’s. Mine went from .016 to .018 going from the 110 to 80. But, like Tug said, change the LP and the BG changes. Same thing happens on my 5/10. I go from the 24 to 25, it widens a bit. Some of the moves people are seeing are crazy. RCM’s statement seems to make a lot of sense to me. 🏼
    Thanks guys! I appreciate the responses. Seems like the RCM pieces are not an issue.

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    I put an RCM in my PTR 91GIR with zero change in bolt gap. Put an RCM in my PTR 9KT and the first one wouldn't even fit in the bolt. Had to send it to PTR, who replaced the entire firearm because of several issues. Put the same locking piece in the bolt and had to use -8 rollers to get it back in spec. Added an HK locking piece to my PTR G3K clone and had zero change.

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