M745 off-center primer hits

[EPVegas]

Hello all. I took my recently acquired 745 to the range, and ran into a problem. Looks like the firing pin is hitting off center, which misfires the LPP .45 about one in 8 times. The SPP ammo does fire reliably.

It also looks like the firing pin "hole" in the breechface is oblonged, with a small lip of metal at the bottom.

Does this look like a bent firing pin, that could be resolved with a part replacement? Or is this a more serious issue, that might need a bushing (?) or more drastically fix and need to sent out?

 

[armorer951]

Could be a damaged firing pin or spring. (or both) The drag mark on the primer indicates there is a lot of build up on the perimeter of the firing pin hole in the breechface. This could be just shooting debris and copper, or damage to the cavity itself. The slide may not be closing completely. The barrel chamber may also need a good cleaning.
Have you considered disassembly of the slide, and a thorough cleaning/inspection of the parts and the internal f.p. cavity?
A really good cleaning with some solvent and stainless or brass brush may solve the issue. If you decide to do the inspection and cleaning, be sure not to put any lubricants on the internals or f.p. cavity when re-assembling.


Carter

 

[EPVegas]

Have been out of town, haven't had a chance to disassemble yet. There is a lip of metal at the bottom of the FP hole, probably causing the drag mark. Will perform a thorough cleaning asap and see what I find, thanks!

 

[WR Moore]

What was said above. I can recall reading about bushing the breech face to restore firing pin location, but have never done it. Besides a very thorough cleaning, how about a new recoil spring? Oh, what ammo? If reloads, your loads might not be a good fit for the chamber. Try a plunk test.

 

[Outpost75]

Mil Standard is that FP indent must not be off center more than half the diameter of the striker point. In M1911 can be affected by shallow barrel lockup, caused by incorrect slide stop fit on barrel lugs and / or link length.

 

[-BTM-]

That firing pin hole (is there a term or that?) doesn’t look right, at all.

 

[bigggbbruce]

Egg shaped. Needs a qualified gunsmith try and save the slide.

 

[EPVegas]

Egg shaped. Needs a qualified gunsmith try and save the slide.

Was afraid of that. Any idea what would cause it?

 

[WR Moore]

I went downstairs and looked at my 1006. The 745 DOES NOT have a barrel link. The barrel is returned to it's position by the cam surface on the bottom of the barrel riding on the slide stop pin. It's lowered by the action of the angled lugs on the sides of the barrel under lug acting on the angled sections of the frame.

Have you plunked your ammo? IIRC, there's two recoil springs for a 745, one target ammo and one duty/hardball ammo.

 

[stansdds]

Egg shaped. Needs a qualified gunsmith try and save the slide.

I agree. As to why the firing pin hole is oval is a good question. I cannot see normal use causing this, the steel in the breech face is pretty thick. I'm thinking either a manufacturing defect or someone was trying to fix something, maybe they were attempting to fit an aftermarket barrel and maybe they did not fully understand how to fit a barrel and ended up with the barrel chamber being lower in the slide at lock up and the firing pin was hitting too far off center for reliable ignition. With a used firearm, you usually don't know the rest of the story.

 

[bigggbbruce]

As mentioned lock up is cam action, as are most semi-auto these days. Could be bad machining of the barrel might be the firing pin channel. Weld up and machine work is the best course. Difficult, costly though. And finding the right one to do the work.

A temporary fix would be to peen the metal back. A punch "new" 5/16 or so. Long enough to protrude out the muzzle end. Small hammer 4 oz. With very light strikes move the metal very slowly. To hard will shear the metal and you'll be doing the other repair. Soon.

 

[steelslaver]

This is a case where I would let the factory have first crack at fixing it

 

[stansdds]

This is a case where I would let the factory have first crack at fixing it

If S&W will still repair it.

 

[steelslaver]

If S&W will still repair it.

If not rather than a weld up I would suggest a machinist go in with a long 1/4 or 5/16" end mill and cut down about 5/16 then make a bushing from something like a drill bit shank. I would put some taper in the rear of the firing pin hole to guide the pin in. Make it slightly over sized, stick it on dry ice, warm the slide up to say 300f then pick the bushing up with a piece of round stock with fair sized magnet stuck to the other end, that will hold the bushing to the other end especially if you put a pin in the bushing end of the rod. Quickly place the bushing in the hole, remove the magnet and give the rod a solid tap to make sure the bushing is seated. If you recessed the edge of the bushing face a bit you could also stake the area of the slide around it. Works for in revolvers for 44 mags etc. should work for a 45acp in a semi

 

[WR Moore]

Check with the factory first to get that out of the way. If nothing else, you might find out who bought up S&Ws obsolete parts. If no other slide available, check with Alex Hamilton at Ten Ring Precision. If he can't do it, he might be able to suggest someone. Or, one of the gents here on the forum.

ETA: I checked a couple of parts sources, barrels yes, slides no. Couldn't recall the length of a 645 slide, appears to be too short.

 

[stansdds]

As far as I know the 645 and 745 slides are dimensionally identical, the difference is that 745 slides are carbon steel and had different rear sights. Jack First might have some parts, he seems to have S&W parts that no one else has.

 

[stansdds]

If not rather than a weld up I would suggest a machinist go in with a long 1/4 or 5/16" end mill and cut down about 5/16 then make a bushing from something like a drill bit shank. I would put some taper in the rear of the firing pin hole to guide the pin in. Make it slightly over sized, stick it on dry ice, warm the slide up to say 300f then pick the bushing up with a piece of round stock with fair sized magnet stuck to the other end, that will hold the bushing to the other end especially if you put a pin in the bushing end of the rod. Quickly place the bushing in the hole, remove the magnet and give the rod a solid tap to make sure the bushing is seated. If you recessed the edge of the bushing face a bit you could also stake the area of the slide around it. Works for in revolvers for 44 mags etc. should work for a 45acp in a semi

I don't know if there is enough breech face thickness for this, but back when the M1911 was put into service, breech face, barrel bushing slot, and slide stop notch durability issues surfaced. At that time, the technology and technique for fully heat treated slides was not yet available, so Colt spot treated the front of the slide and stop notch. Their solution for the breech face was a threaded bushing. So if there is ample thickness in the breech face of the 645/745 slide, perhaps it could be drilled and tapped for a threaded bushing.

 

[EPVegas]

For the record, all the ammo was factory new, Federal or Speer. I'll swing by Nelson Fords shop with it next time I am in AZ, and also reach out to S&W. Will let you all know what I find. Thanks for all the responses