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Thread: J Frame Issues

  1. #1
    Boolit Buddy 12DMAX's Avatar
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    J Frame Issues

    I recently purchased a NEW M&P 340 and am experiencing a problem where after firing 15-20 rounds the cylinder when swung open does not rotate freely, it develops some excessive drag.

    I removed the cylinder and discovered flakes of lead are accumulating in the yoke bore causing the binding. I scrape them off with my fingernail, lightly lube everything and GTG until the next 15-20 rounds.

    What I did notice is my cylinder gap is all out of whack. Measured with a feeler gauge the driver side is .010 and the passenger side is .007. My gauge is too wide to pass through. This seems not only excessive but why the difference? Something bent? Not aligned correctly? I will call S&W tomorrow and see if there is anything they can do.
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  2. #2
    Boolit Mold cas's Avatar
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    You could/should check barrel to throat alignment with a range rod, assuming you can come up with something the right size that will work.
    Former cylindersmith.

  3. #3
    Boolit Master

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    I have a m&p 340 PD. Well, it's my 2nd one. S&W replaced the first. I had an issue with the B/C gap wider at the bottom than the top, but the main problem was the cylinder would slip past the stop on the frame when I tried to eject the cases. Not a good thing on a SD handgun.

    Hope they take care of you, mine was replaced about 2007 +/- , it's been a while. They issued a prepaid shipping label and I got back a new frame with my barrel. They squared the barrel and it is still in spec. It was very close to touching at the top.

  4. #4
    Boolit Master Outpost75's Avatar
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    At S&W they apparently still face off barrels by hand with a file, instead of using statistical.process control to produce parts which assemble and fit within tolerance. Cannot believe they are still in the 19th Century...
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  5. #5
    Boolit Master
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    That S&W J-frame needs to go back to S&W.

  6. #6
    Boolit Master tazman's Avatar
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    I have an older model 60 in 38 special which will gum up around the cylinder axle making it harder to turn. It takes a lot more than 15-20 rounds though and none of the problem is lead chips.
    I can go a range session without problems. Usually 50-100 rounds and then do a good cleaning when I get it home. I just have to take the cylinder off the gun and make sure it is clean.
    Mine has very tight throats at around .356. Fortunately the barrel is at .355 so it all works out well for accuracy and no leading.

  7. #7
    Boolit Buddy 12DMAX's Avatar
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    It definitely is going back. I am going to tear it down one more time and take pictures. Shoot it again to gum it up and ship it back. Should of done that the first time ( pictures)
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  8. #8
    Boolit Buddy 12DMAX's Avatar
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    Well, seems I no longer know how to add photos?
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  9. #9
    Boolit Master
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    You're right to send the gun back to S&W for the BC gap issue. The yoke barrel and bore interference may well be related to excess combustion byproducts escaping as well. However, I have found that oil will cook in this area and cause difficulty. The solution I've found most reliable is to clean with WD40, and reassemble without any further lubrication. The residual WD40 supplies sufficient lubrication, and does not cook and gum. Cylinders turn freely much longer. Don't be concerned about the old wives tale of contaminated ammunition; the tiny amount of WD40 here won't migrate to your chambers.
    Last edited by Tatume; 10-08-2018 at 07:14 PM.

  10. #10
    Boolit Buddy 12DMAX's Avatar
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    Quote Originally Posted by Tatume View Post
    You're right to send the gun back to S&W for the BC gap issue. The yoke barrel and bore interference may well be related to excess combustion byproducts escaping as well. However, I have found that oil will cook in this area and cause difficulty. The solution I've found most reliable is to clean with WD40, and reassemble without any further lubrication. The residual WD40 supplies sufficient lubrication, and does not cook and gum. Cylinders turn freely much longer. Don't be concerned about the old wives tale of contaminated ammunition; the tiny amount of WD40 here won't migrate to your chambers.
    It most definitely is lead, I am trying to figure how to add a photo.

    Aaaah, got it! Size to big.
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    Last edited by 12DMAX; 10-08-2018 at 08:17 PM.
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  11. #11
    Boolit Buddy
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    I have a 340CT.....be careful with the buildup. I had a chunk come loose and cut a gash in my cheek. It drew blood and a bunch of it.

    I now only shoot with shooting glasses....bb gun or 454 Casull.

  12. #12
    Boolit Buddy 12DMAX's Avatar
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    Quote Originally Posted by birch View Post
    I have a 340CT.....be careful with the buildup. I had a chunk come loose and cut a gash in my cheek. It drew blood and a bunch of it.

    I now only shoot with shooting glasses....bb gun or 454 Casull.
    I have no build up anywhere else, all down inside the cylinder yoke. I measured everything again tonight, I borrowed some narrower feeler guages. .007 will pass snuggly through from the passenger side, .010 from the driver side will only pass through until it finds the .007 side.

    The bushing is not shown in the pictures.
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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check