View Full Version : 40 cal in a 10mm ???

mold maker
06-06-2008, 09:22 PM
I read in another forum that some folks are shooting .40 cal. S&W ammo in 10mm hand guns. Is this a safe practice? Is there not damage to the 10mm throat? Will the extra 1/8" boolet jump change the pressures, and velocity? Don't both head space on the case mouth?
I'd never seen this before and am plum full of questions.:-?

06-06-2008, 10:23 PM
I think few do it knowingly and most brag about how smart it is, never about damages.

The major issue I have about it is that the extractor has to hold the shorter ammo, and it is not a headspace control or cartridge holding part.
Excessive headspace will allow the case to move forward before being slammed back against the breech, which sounds like extra stress on the locking lugs (these can wear very quickly when the barrel itself is poorly fitted between breech and lugs, I have that much experience with the problem).

So considering extractors and barrels prices, I wouldn't do it.

A better solution is, I think, to reduce the depth of the chamber by inserting a ring of steel in it. The operation was reportedly quite popular when various European 9mm "longos" were imported in the 50's, and such rings were available commercially.
Major Nonte wrote about cutting sections of steel cases and inserting them in some of his guns. No welding/gluing was needed, only a tight fit (some shooters will feel safer with an epoxy bond).

Of course the process has been criticized for various reasons.
My major issue is that the conversion is pretty much a permanent one, as you don't want the little thing to move easily, and I would have to try it to see if leading and errosion are a concern.
Pressurewise, the long jump/throat should then ease things up.


06-07-2008, 02:49 AM
One of the crew on the job needed several sticks of dynamite, so he headed for the shack. When he got inside, he turned on the light, but the bulb blew, leaving him in darkness. He took out his trusty zippo and, lighting it, fished what he needed out of the open crate, grabbed a length of fuse off the shelf, and went on his way.

A fool would conclude that since nothing happened, it must be safe to do it again.

Need I say more?

06-07-2008, 05:35 AM
they are probably doing it in a revolver with moon-clips.
it is like shooting 38 in a 357 mag.
s&w does make the 610 in 10 mm.

mold maker
06-08-2008, 01:21 PM
No, we are discussing regular .40 cal ammo, being fired in a Colt Delta Elite 1911 style semi auto. This of course is not like 38/357 or 44 special/44 mag. which are all rimed ammo.
The purpose was to save money with the cheaper .40 cal ammo. The Colt Delta Elite 10mm, of course is no longer available, and rapidly rising to collector status.
It was being discussed on a reloading/gun forum. Almost no negatives were discussed. I think there would be a great danger of damage to the weapon, and even a possible safety issue. The unsupported EXTRA 1/8" free bore jump might first erode a ring in the 10mm chamber, change pressure peaks, and place undue wear and strain on the extractor.
I too am faced with the high cost of 10mm ammo, and would welcome the opportunity to save 25% on factory ammo. but not at the expense of damage to a superb handgun.
Thanks to all who have addressed the issue. Thats exactly why I joined this forum.

06-08-2008, 11:22 PM
I forgot the most obvious, along with the price of ammo: Colt, Auto-Ordnance and Armscor/RIA/etc sold their barrels for less than $100 a while ago (see their websites and parts lists). Just stay away from Roto barrels at $35.

Any 1911 .40 S&W bbl should have the same hood dimension as a 10mm (about ...10mm if memory serves), and you should be able to drop one in your gun or have an oversized one fitted. The mags might even work well enough for target purpose.

it would then be a matter of choosing which barrel you would sight the gun for.

Or ..... have you kept your empty brass so far :wink:?