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Gunsmiths (Dan?) or RKIs...

Would there be any improvement in M&P45 accuracy w/tighter slide-to-rail fit?

Is something like this readily accomplishable on M&P 45s? Would this best involve adding material to the frame rails, or inside the slide rail grooves instead?

Reasoning behind the madness:
  • M&P45 slide feels looser than either of my other 45 autos & way looser than buddy's P220;

  • my soon-to-be former G21 + my stock regular 1911s, in absolute formal-stance shooting;

    "range accuracy" are a twinge better than my M&P using bulk ammo (WWB/UMC 230gr FMJ);

  • a tad of this is due to trigger/user getting used to each other + break-in;

  • most dispersion related to "1st round flyer" due to difference in manual vs cycled chambering;

    (no flinch: regular 45ACP is easy for me to shoot controllably and isn't harsh like 40S&W);

  • for real-world shootability above's somewhat irrelevant: M&P45 wins hands-down on

    ergonomics & pointability - fast shots & natural pointing are great, comfortable etc.

    • Bill Wiese

      San Jose CA

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4,366 Posts
I am not a gunsmith and in fact the mere thought of taking a file to the guts of a pistol makes me woozy.

However, I can tell you that frame-to-slide tightness has very little to do with the accuracy of guns using a locking mechanism such as found on SIGs, Glocks, M&Ps, etc. The sights are on the slide and the barrel locks to the slide so it's slide-to-barrel lockup that really matters.

Most SIGs get rattle loose after 10k rounds or so but I can tell you from long experience that it doesn't impact accuracy. There is actually a modification a gunsmith can make to the barrel of a "worn in" SIG to stop the frame/slide rattle but it does nothing to improve the gun's performance.

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1,509 Posts
Also not a gunsmith.

Unless you are moutning a sight on the frame, the frame to slide fit is almost irrelevant. It's the slide to barrel fit that matters. That is unless you are shooting form an index rather than using the sights. Then the consistancy of your index and the rellative concistancy of the slide to the pistol frame, and thus your hand, matters.

For some reason bar-sto was previously going to offer M&P aftermarket barrels. Now they don't offer ANY S&W barrels on their site. No word on anyone else stepping up to offer barrels that might be fit tighter.

Short of the old "squeeze it in a vice" appraoch, I have no idea how you would go about tightening the slide other than maybe tig welding on some material to the frame inserts and cutting them back to an exact fit. The former souns like an exercise in fultility that likely will decrease reliability. The latter sounds very expensive and time consuming.

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1,481 Posts
Todd & Raz-0 are right on the money there is really no accuracy to be gained by tightening up the slide to frame.

Getting the barrel to fit the slide tighter is where there could be some improvement.

I should have the first prototype aftermarket barrel in my hands in the next two weeks, so they are coming fairly soon.

Just for giggles I am planning on tightening one up, I have been waiting to do this on a new Pro model when it comes out. I was planning on welding up the frame block then milling them down for a good fit. It is really the vertical fit I will be trying to get tight, as that is what brings the barrel up in to the slide consistantly. Most M&P are already pretty good in the vertical but like I said I will see what happens if for no other reason to than just to find out.
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