how is it that many 45ACP handgun frames can handle the 10mm round given the significant discrepancy in pressure? Were they just initially "overbuilt?" Could the HK USP 45 handle a 10mm conversion?

I may be WAY off base but I'll try.

I think the number one reason .45 is more common is dimensions dealing with cartridge length.

You can beef up any gun part but you can't cut it in half and add dimensions easily.

I'm sure there are many other factors and WAY more knowledgeable people will step in to better answer your questions.

I’m pretty sure a usp could handle a howitzer round if it would fit

Chamber pressure and recoil spring weight are the determining factors, after it's decided that the pistol is large enough to physically fit the round.

Polymer frames such as the Glock flex (a lot). With metal frames, cracking and fatigue would be the only issues, largely mitigated by the proper weight (and placement) spring, and by design.

Pressure takes place in the chamber. SAAMI max chamber pressure for the 10mm is less than 9mm+P, and slightly more than 9mm standard pressure.

Slide velocity is the only other real concern, which comes back to spring weight, and the structure to support it, and of course, a structure big enough (long enough) for the cartridge. It turns out that a pistol large enough for 45 acp, dimensionally, is in the same ballpark for 10mm.

My USP 10mm conversion seems to be holding up OK. At least no cracks that I can see.

All depends on how you do it I’d guess.

10mm conversion barrel on a 45 upper.
10mm conversion on a 40 upper/lower.
Or what I did with a 40 upper reamed to 10 on a 45 lower.

quote:

Originally posted by fullmann:
My USP 10mm conversion seems to be holding up OK. At least no cracks that I can see.

All depends on how you do it I’d guess.

10mm conversion barrel on a 45 upper.
10mm conversion on a 40 upper/lower.
Or what I did with a 40 upper reamed to 10 on a 45 lower.

Where did you go to have this done and how much? I’d love to have something like that

Glock was smart. They made a 10mm and then changed it to a 45 Auto.

Other manufacturers converted a 45 Auto to a 10mm.

It was up to me to convert them to .38 Super.

10mm, being smaller in diameter than 45, means there's more metal left over, thicker chamber walls.

quote:

Originally posted by .38supersig:
Glock was smart. They made a 10mm and then changed it to a 45 Auto.

Not really. The conversion to the higher diameter cartridge and resulting movement of the feed ramp caused the 45 barrels to have truly awful chamber support that they didn’t get fixed for a good 10 years.

quote:

Originally posted by limblessbiff:

quote:

Originally posted by fullmann:
My USP 10mm conversion seems to be holding up OK. At least no cracks that I can see.

All depends on how you do it I’d guess.

10mm conversion barrel on a 45 upper.
10mm conversion on a 40 upper/lower.
Or what I did with a 40 upper reamed to 10 on a 45 lower.

Where did you go to have this done and how much? I’d love to have something like that

Ran across a complete USP 45 lower on the interwebs and nabbed it, bought a low mileage 40 and harvested the slide and recoil spring, sold the barrel, lower and mags.

I contacted RCM and got a 40 tactical barrel and sweet talked them into sending it to me pre-nitride. Had it reamed to 10mm and sent it back for nitride.

The 40 upper drops right on the 45 lower

I ordered a other recoil assembly and then swapped to an 18# and a 20# recoil spring to allow for ammo differences.

I’m using MK23 mags for the longer feed lips, swapped to USP baseplates. I still need to tweak the feedlips a little more to get them to feed a little better.