M&P45 threaded barrel rubbing?

This is a discussion on M&P45 threaded barrel rubbing? within the Defensive Carry Guns forums, part of the Defensive Carry Discussions category; I just got my threaded barrel for my M&P45 with high aspirations of suppression some day soon. When I first installed it, the slide would ...

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Thread: M&P45 threaded barrel rubbing?

  1. #1
    Distinguished Member Array RKM's Avatar
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    M&P45 threaded barrel rubbing?

    I just got my threaded barrel for my M&P45 with high aspirations of suppression some day soon.

    When I first installed it, the slide would lock back.... but without any aid of the slide lock. The barrel was dragging. I could barely pull the slide back enough the engage the lock. When I did get the slide lock engaged, when I'd release it, the slide would stay locked. I realized it was the sides of squared chamber area (don't know the technical term) rubbing against the inner walls of the slide. After some heavy oiling and excessive racking of the slide, I've gotten it to loosen up quite a bit. It no longer locks open, but is still a bit stiff. Now, if I load a snap cap in a full mag and pull the slide back it will chamber a round. When I first installed it, it was just stuck rearward, unless I gave the rear of the slide a smack.

    Is this normal, and will it eventually wear in? I got it to the point that I think it'll run, but I'm just not too sure, it may still cause a hang up. I guess I'll just have to shoot it and break it in. I'm hoping when the barrel heats up and expands it won't cause problems.

    Just seeing if anybody else has come across this. I couldn't find anything with Google. Just one guy saying he sent his back to S&W and they didn't fix it. Mine seems to be wearing in just from racking it over and over.

    I replaced my USP with this M&P45. As much as I loved my USP, the DA trigger was just horrid and there were a bunch of thing I didn't like about it that I tried to ignore, because I love it so much. And since I've had a hankering for an M&P, I went for it. This is supposed to be my nightstand gun so I hope it runs reliably. I haven't had a chance to get to the range yet, so my G30 has been keeping my safe both home and away from home.

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  3. #2
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    "I guess I'll just have to shoot it and break it in. I'm hoping when the barrel heats up and expands it won't cause problems."

    The universal law that metal expands when it heats up is not going to make an exception for your firearm.
    If it's tight already and just barely not binding then it's very likely that your firearm will lock up either when the barrel heats up or when the gun gets dirty enough.
    Be aware of the fact that "drop in" parts seldom just drop in.

    If you do not have a suppressor yet for your firearm then you're better off putting your original barrel back in for now.
    Especially if this is your carry gun or night protection gun.

    You will eventually need to hand fit that new barrel to your slide or have a qualified smith do it.
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    Don't worry, I haven't even fired this gun yet. It's destined to be my night stand gun, but as I said, until I shoot it and put rounds through it, threaded barrel or not, My G30 is being used for home defense and carry. The M&P won't get carried. My G19 slide and barrel are off at Fail Zero getting some EXO treatment, my J-frame only sees pocket use Mon-Fri and my 1911, well.... that sits in the safe and is a range "toy". So it's just my G30 for carry and HD right now.

    I was wrong, it's not the sides, I believe it's the top.

    This is supposed to be a factory S&W barrel. I'm not sure why the shape of the top of the barrel is inconsistent. I hit it with a very fine file and it seemed to have made a difference. It's still a little tight but not as tight. I do believe it needs shot and worn in, and I do think heat my play a factor until it breaks in.

    Threaded barrel on the left, original on the right.

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    You should be seeing wear marks on the new barrel where metal is bearing against metal. Check everywhere on the new barrel because sometimes a new part is not actually binding exactly where you think it is.
    Sometimes a tolerance difference someplace else on the barrel may be causing it to bind in a completely different location.
    Ideally you should Mike the original and the replacement everywhere and compare specs & that will tell you a lot.

    Where you need to be careul when you shoot it is that if the barrel is not properly fit you could potentially split your frame rails.

    I hear you that it's a S&W part but, drop in Colt parts made by Colt often do not drop right in either. You would think that they SHOULD but, they don't.
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    I've been looking for wear marks. I can find anything. Unfortunately, I do not have a micrometer here at home, but I do at work.

    I have it to the point where it's not super tight anymore. Just "snug".

    You know how when the slide is locked back, you can shake the gun and the barrel rattle around? Well this doesn't rattle with ease, but it you physically grab the barrel, you can move it around. So there is a bit of play, as I think me messing with it is wearing it in. However, I fear it wear the slide there for making the original barrel too loose, if that's possible.......

    It's to the point where I do think it'll run, and if it wasn't 9:40 at night and I didn't have to work tomorrow, I'd be able to get to the range and try it. It's not so tight that it would split the frame rails. Maybe at first it would have.

    The slide operates with ease, just like factory up until the last 1/4" or so when it get just slightly tighter. When released, it has no problem loading snap caps into the chamber.

    Like I said, what I'm mostly worried about is this barrel wearing in, and then causing too loose of a fit when I go back to the original barrel. Can it be too loose? I'm assuming all it will affect is long range accuracy. I rarely shoot my pistols more than 25 yards.

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    and then causing too loose of a fit when I go back to the original barrel. Can it be too loose?

    That shouldn't be an issue.
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    I know it's not your hands and you can't actually feel what's going on, but here is some good visual aid. It's better than pictures.

    IMG_1067 | Flickr - Photo Sharing!

    You can see it gets snug toward the end of the travel, but it's not like I have to beat it out with a hammer or anything.

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    I found where it's rubbing. I've done some very light filing on the barrel, around the squared edges of the chamber area and have really loosened it up. Not as loose as the original barrel, but I feel pretty confident in it. It's looser than in that video above^^^ I think worse case until/if it wears in is that it will just cause feed issues (which I honestly think it will run fine). If it does have problems, I can always swap in the original barrel and have a real gun smith fit the threaded barrel.

    I'll find out in a few days when I get out to the range.

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    I'd degrease the slide and the barrel. Lightly smoke the barrel with some candle soot - slowly/carefully insert it - move it - and then carefully remove the barrel and see where that soot is rubbed off.

    If it's the flats on the sides or the top of the barrel - you don't want to file them.

    Take a piece of flat glass - mist a coat of spray adhesive onto the back of a sheet of ultra fine 3M "Wet or Dry" Silicon Carbide paper - Stick it to the glass - put a couple of drops of oil on the 3M paper - lay the barrel flats down on the 3M and you can lightly oil polish the metal on the flats without really removing any metal & that should cut that friction down if that is where the problem is.
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    Candle soot? I never thought of that. Sounds like an old trick.

    I'm not sure what all that stuff is you mentioned in your 3rd paragraph. Could I possible just wet sand the sides with 3000 grit sand paper? Maybe even buff the sides with some buffing compound and a dremel (with a soft, cloth wheel of course). I've worked on cars for a big part of my life, so if this was a car part, that's what I'd do. But it's a gun... not a car part.

    I'm slowly, ever so slowly getting this thing worked in. Tomorrow morning is the moment of truth. Going to take both barrels to the range and fire away. The barrel has really loosened up, so much that it takes almost no extra effort to slide the barrel all the way through the slide. I think simply from this point, putting rounds downrange will polish it out all the more it needs to go.

    I'll report back with what happens, good or bad. Kaboom or no kaboom. Going to feed it a few mags of 230gr +P HST and mostly just 230gr FMJ.

  12. #11
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    Well, four stitches on my right eyebrow and a few minor cuts on my right hand later.......................

    Just kidding. It ran flawlessly. What I did to work the barrel in must have worked. After shooting it, it feels even better. No hang ups, no kabooms. POA/POI are the same as far as I can tell between the barrels. This gun is super accurate as long as I do my part.

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