A chambered round "should" not make a tighter "Lock-up"

[bad_man_ one]

FWIW,
The ANSI/SAAMI specification for a chamber dimension designates that there is always clearance to the chambered round.
i.e. - the 10 m.m. chamber tolerance for the depth is .922" min to 1.004" max.
Where as the tolerance on the bullet is .922" max length down to as little as .822", so there could be as much slop as .022" or as little as zero.

Then add in the standard tolerance of statistical quality control of a +/- 3 sigma limit ("Bell curve").
Then 99.7% of the parts and chambers will never see the extreme ends of the tolerance limits.

Then add in the clearance specified in the Smith & Wesson pistol armorer's course manual
for the breech face to the barrel chamber hood locking lug to be at .002" - .008" clearance.

The chambered round will not make a firearm that has been made to the proper tolerances, lock up any better.
If it does, then something in those areas was not made to ANSI/SAAMI specification .

Sorry for the rant,
this is a subject that I pay very close attention to in the production of my conversion barrel project.
Regards,
BM1

[KurtC]

You are correct, it "shouldn't" make a difference. Unfortunately, it does make a difference in many production pistols. Things seem to tighten right up with a loaded mag and a cartridge in the chamber.

[bad_man_ one]

KurtC, Yes Sir,
I agree with you 100% that it shouldn't make a difference.
I have seen some terrible tolerances being held,
or I should say - not held by some of the gun manufacturers and also the after market barrel manufacturers.
Regards,
BM1

[Shadow1006]

BM1, when I had to fit my Bar-Sto 40S&W & 9x25 Dillon barrels to the slide the barrel hood was the part which kept them from fully dropping into locking lugs of the slide. With careful polishing of the end of the barrel hood it continued to get closer and closer. The Bar-Sto 9x25 Dillon conversion actually needed the side of the barrel hood trued up a very little. As we talked about before the 9x25 chamber actually needed to be cut a little deeper for proper head spacing.

The other area that needed adjustment was the area where the barrel slides over the slide stop pin. Here again a few strokes with a honing stone, to the flat area that rides over the slide stop pin, allowed the slide to achieve proper lockup.

I didn't take any measurements but it wasn't much metal removed.

Chambered rounds didn't increase or make the the lock up any tighter...

Best regards!

[Rock185]

Hello Bad, very interesting and glad to see I'm not the only guy with an interest in this stuff. I've measuered quite a few .45 ACP and 9MM headspace dimensions, but just one 10MM. Wish I'd have thought to measure headspace on the other seven or eight 10MM Smiths I've owned. The headspace dimension on my current 1026 is 1.001" and the hood to breech face on mine is .006",so I guess it's within the spec. BTW, do you mean .992" on the 10MM minimum dimension?

[bad_man_ one]

Originally Posted by Rock185

Do you mean .992" on the 10MM minimum dimension?

Rock185,
The dimension for the 10 m.m. case (Brass) is .982" to .992" and the dimension for the chamber depth is .992" to 1.004" in depth.
Regards,
BM1

[Rock185]

Thanks bad. I didn't say it as well as I could/should have. I meant minimum chamber depth, not minimum case length.

[VTHokiesDuckHunter]

This is what these forums should be all about! Great info and discussion guys.

As a Mechanical Engineer, shooter, and someone with a background in TQM/statistics I found this thread to be one of the best of the week.

I wish my knowledge of gun building and mechanics was half as solid as some of you.