Mp5SD cone issues

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  • Sev89

    Dreams about cheese
    Nov 4, 2010
    2,106
    Anatomy Park
    Got a question I'll post here for the sake of it. Have a PTR 9R that was SBRd/converted into an SD clone. I finally got it back from paint earlier in the week, but I'm experiencing some problems with it. With the hammer dropped, the action will cycle like butter 99% of the time. Every so often however, the moment you pull the charging handle, it'll stiffen up, and take noticeably more force to cycle. On top of that, it sometimes has trouble going fully into battery on both semi, and full auto. For this second issue, I've tried different mags, namely KCI, and some HK mags. Sometimes I can get it to empty a mag or two without issue, then it starts getting a case of the ass and doesn't want to fully go into battery. I've also got a couple of the magpul drums, it wouldn't reliably feed, and with the drums, would stove pipe, and fail to go into battery with these as well.

    Anybody have trouble shooting suggestions?
    Here's the culprit in question
    IMG_1882.jpeg
     

    cms81586

    Member
    Feb 8, 2018
    54
    Tolerance stacking with a paint applied too thick inside the receiver? I have about 20-30 MP5 mags if you wanted to try more of a variety to troubleshoot and are near Frederick/Hagerstown. All HK varying from used to never loaded.
     

    outrider58

    Loves Red Balloons
    MDS Supporter
    Tolerance stacking with a paint applied too thick inside the receiver? I have about 20-30 MP5 mags if you wanted to try more of a variety to troubleshoot and are near Frederick/Hagerstown. All HK varying from used to never loaded.
    For the life of me, I do not understand people painting the insides of receivers. Same thing with dips. It's not super tricky to avoid. A little wadding, a little tape...

    I have dealt with this stupidity before. No excuse(if this is the case).
     

    Sev89

    Dreams about cheese
    Nov 4, 2010
    2,106
    Anatomy Park
    Tolerance stacking with a paint applied too thick inside the receiver?
    This was my initial thought. I've spent the better part of a week just cycling the action. I don't really think it's made much of a difference. Appreciate the mag offer, unfortunately I live several hours out of state.
     

    Sev89

    Dreams about cheese
    Nov 4, 2010
    2,106
    Anatomy Park
    For the life of me, I do not understand people painting the insides of receivers. Same thing with dips. It's not super tricky to avoid. A little wadding, a little tape...

    I have dealt with this stupidity before. No excuse(if this is the case).
    I was shocked when I found out about it myself. I thought the painter was just going to paint the outside of the receiver. Found out they made no attempt to cover up the locking area, they just put an earplug in the chamber. I'm really hoping it's just a case of paint getting where it shouldn't be.
     

    Sev89

    Dreams about cheese
    Nov 4, 2010
    2,106
    Anatomy Park
    Didn't take the time to shoot it. I sent it out for paint just as soon as it came back from being converter, as the front half of it was in the white, and already starting to rust. I've kicked myself enough times for not having shot it before hand.
     

    outrider58

    Loves Red Balloons
    MDS Supporter
    Didn't take the time to shoot it. I sent it out for paint just as soon as it came back from being converter, as the front half of it was in the white, and already starting to rust. I've kicked myself enough times for not having shot it before hand.
    There are plenty of experts on that gun. I am not, but it sounds like it is gummed up with paint. It will worsen as the gun warms up. Cerekote? The mags you are using are not bad or questionable mags, AFAIK.
     

    rouchna

    Defund the ATF
    MDS Supporter
    Nov 25, 2009
    6,003
    Virginia
    This was my initial thought. I've spent the better part of a week just cycling the action. I don't really think it's made much of a difference. Appreciate the mag offer, unfortunately I live several hours out of state.
    Where do you live? I’m in Loudoun county, VA and I also have a ton of MP5 mags.
     

    smdub

    Ultimate Member
    MDS Supporter
    Nov 14, 2012
    4,770
    MoCo
    What paint? Something like cerakote is so thin it won't make a difference

    The SD uses a cut open cocking tube. All sorts of gunk (paint) could have gotten in there from the bottom as they were trying to coat the handguard cage. It can also cause it to warp when welding or have a burr.

    Some SD suppressors are larger than the orig and you need a different machined cocking support to clear.

    Or it could just be a crappy cocking tube (or welded crooked.) I recently bought a PTR51 and it had horrible machining marks in the tube. I'm not even sure why as it isn't supposed to be machined. The cocking support hung up on all the ridges - some of them pretty severe. I smoothed some of them out reaching in w/ riffler files and it runs now but I'm trying to figure out how to run a ball hone up in there w/o tearing up the cocking slot. Might try a flap disc instead. Anyway, it was cheap so I could replace the tube and still be ahead but its BY FAR the crappiest made PTR I have. Had lots of other small issues too.
     

    4g64loser

    Bad influence
    Jan 18, 2007
    6,957
    maryland
    What paint? Something like cerakote is so thin it won't make a difference

    The SD uses a cut open cocking tube. All sorts of gunk (paint) could have gotten in there from the bottom as they were trying to coat the handguard cage. It can also cause it to warp when welding or have a burr.

    Some SD suppressors are larger than the orig and you need a different machined cocking support to clear.

    Or it could just be a crappy cocking tube (or welded crooked.) I recently bought a PTR51 and it had horrible machining marks in the tube. I'm not even sure why as it isn't supposed to be machined. The cocking support hung up on all the ridges - some of them pretty severe. I smoothed some of them out reaching in w/ riffler files and it runs now but I'm trying to figure out how to run a ball hone up in there w/o tearing up the cocking slot. Might try a flap disc instead. Anyway, it was cheap so I could replace the tube and still be ahead but its BY FAR the crappiest made PTR I have. Had lots of other small issues too.
    Flap sanding drum with an extension. Ball hone is not gonna do it as it will.get banged up in the cocking slot.
     

    outrider58

    Loves Red Balloons
    MDS Supporter
    What paint? Something like cerakote is so thin it won't make a difference

    The SD uses a cut open cocking tube. All sorts of gunk (paint) could have gotten in there from the bottom as they were trying to coat the handguard cage. It can also cause it to warp when welding or have a burr.

    Some SD suppressors are larger than the orig and you need a different machined cocking support to clear.

    Or it could just be a crappy cocking tube (or welded crooked.) I recently bought a PTR51 and it had horrible machining marks in the tube. I'm not even sure why as it isn't supposed to be machined. The cocking support hung up on all the ridges - some of them pretty severe. I smoothed some of them out reaching in w/ riffler files and it runs now but I'm trying to figure out how to run a ball hone up in there w/o tearing up the cocking slot. Might try a flap disc instead. Anyway, it was cheap so I could replace the tube and still be ahead but its BY FAR the crappiest made PTR I have. Had lots of other small issues too.
    I'm not saying you are wrong, but I have personally dealt with(internally) painted uppers in ARs that were complete shit. Talk about your tollarence stacking. When it comes down to it, Cerakote is nothing but paint. It comes with all the encumbrances that all other paints do.

    These were "professionally" painted parts. Not some random in his garage.
     

    smdub

    Ultimate Member
    MDS Supporter
    Nov 14, 2012
    4,770
    MoCo
    I'm not saying you are wrong, but I have personally dealt with(internally) painted uppers in ARs that were complete shit. Talk about your tollarence stacking. When it comes down to it, Cerakote is nothing but paint. It comes with all the encumbrances that all other paints do.

    These were "professionally" painted parts. Not some random in his garage.

    Cerakote goes on under a thou. I can literally use a thimble full in the airbrush and spray a M11 upper. Its nothing short of amazing how little is required compared to other paints. To match the gloss on a HK it likely has to go on a little thicker. But there is still nothing in the cocking tube area or any other part of the HK receiver that has that level of tolerance. I have built several. The stamped sheet metal has pretty forgiving tolerances if it was built correcly (which is in question here.)

    No doubt some other paints can be globbed on. Just saying its difficult to screw up cerakote that bad.

    I've sprayed their anti-friction stuff in & on some internal parts. I have some Aero uppers that came w/ it from the factory inside.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,126
    Elkton, MD
    I disagree with those who say Cerakote does not cause dimensional or function issues.

    I see a lot of guns that go from working to not working and the only factor is Cerakote. It's a problem and Cerakote applicators often claim it's not.

    May not be the case here, but it's a serious issue to consider for those reading.

    Applicators spray inside the gun because gun owners for the most part are about "show". They want looks and don't consider function.

    Imagine having an engine builder paint the cylinder bores and bearing surfaces. Not good.

    The coating may not be the issue here but it's a possibility. There are a lot of checks that would need to be done to see what is the culprit.
     
    Last edited:

    outrider58

    Loves Red Balloons
    MDS Supporter
    What paint? Something like cerakote is so thin it won't make a difference

    The SD uses a cut open cocking tube. All sorts of gunk (paint) could have gotten in there from the bottom as they were trying to coat the handguard cage. It can also cause it to warp when welding or have a burr.

    Some SD suppressors are larger than the orig and you need a different machined cocking support to clear.

    Or it could just be a crappy cocking tube (or welded crooked.) I recently bought a PTR51 and it had horrible machining marks in the tube. I'm not even sure why as it isn't supposed to be machined. The cocking support hung up on all the ridges - some of them pretty severe. I smoothed some of them out reaching in w/ riffler files and it runs now but I'm trying to figure out how to run a ball hone up in there w/o tearing up the cocking slot. Might try a flap disc instead. Anyway, it was cheap so I could replace the tube and still be ahead but its BY FAR the crappiest made PTR I have. Had lots of other small issues too.
    That means you are doing it right.

    I've had uppers and lowers that would not close due to heavy Cerakote on the edges. I sanded it off, and the halves went right together, just as they did before being sprayed. I've also had uppers that I couldn't even get the BCG into from heavy Cerakote buildup.

    I've painted several of my own guns with Duracoat with zero issues because I took the time to protect the insides from over spray.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,126
    Elkton, MD
    I'm not saying you are wrong, but I have personally dealt with(internally) painted uppers in ARs that were complete shit. Talk about your tollarence stacking. When it comes down to it, Cerakote is nothing but paint. It comes with all the encumbrances that all other paints do.

    These were "professionally" painted parts. Not some random in his garage.
    Yep
     

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