.40 in a 10mm chamber

[kneelingatlas]

I've been playing with a 10mm Hunter, dreaming of the ultimate 6" Limited Tanfo and wondering: has anyone had any issues shooting .40 out of a 10mm chamber? I know in theory the round could slip in front of the extractor and slide into the chamber, but has anyone had that happen? I haven't had any issues, but I've only fired maybe a box of ammo though it, does anyone else shoot this way and have some experience to share?

[Steve RA]

I remember back when the "Short and Weak" first hit the scene that was a fairly common question. I had a couple of friends who had 1911 10mms that tried and then shot quite a few .40s thru their guns without problems.

Now I'd say, give it a longer try and see if any problems develop. As I remember, they used to load the .40s as long as practicable.

[56hawk]

I've also shot a few rounds of 40 in my 10mm. Apparently it can cause problems though:

http://www.thegunzone.com/10v40.html

[jmbaccolyte]

Atlas- As you point out its a headspace issue, maybe the extractor will serve to locate the cartridge. I've been doing the opposite- loading .40 cases to 10mm lengths and shooting them in a .40 barrel (with 10mm mags), which in my Tanfo Match has worked perfectly.

[kneelingatlas]

Hmmm

[wscottstewart]

Atlas- As you point out its a headspace issue, maybe the extractor will serve to locate the cartridge. I've been doing the opposite- loading .40 cases to 10mm lengths and shooting them in a .40 barrel (with 10mm mags), which in my Tanfo Match has worked perfectly.

You can load your 40 loads long and use 10 mm magazines to make this feed in your 40. But those are NOT 10 mm OALs.

[wscottstewart]

Hmmm

I know you probably forgot more about tanfoglio than I know. Is there some rule about using the 10mm ammo in competition or is it just about the load?

If you reload, you can make 10 mm the same as 40 PF

[chaosshooter00]

I bought a gun that had a barrel marked .40 and it was actually cut to 10mm. I put 30,000 rounds through it before a gunsmith caught it after I broke an extractor. Never skipped a beat, also, wasn't a Tanfo.

[kneelingatlas]

Hmmm

I know you probably forgot more about tanfoglio than I know. Is there some rule about using the 10mm ammo in competition or is it just about the load?

If you reload, you can make 10 mm the same as 40 PF

The brass is much harder to come by and since I get all the .40 I want for nothing, it's infinitely more expensive; Starline 10mm brass cost more than I spend on the entire loaded .40 round .

[wscottstewart]

Yes cases are .20 but once you have it, then reloading costs the same.

[kneelingatlas]

Where I shoot the majority of my matched the brass recovery rate is very low, just ask the 38 super duper guys

Besides, if I were interested in keeping track of my brass I'd be shooting a 38 Open gun, but I'm not which is why I shoot 9 Major

[jmbaccolyte]

Atlas- As you point out its a headspace issue, maybe the extractor will serve to locate the cartridge. I've been doing the opposite- loading .40 cases to 10mm lengths and shooting them in a .40 barrel (with 10mm mags), which in my Tanfo Match has worked perfectly.

You can load your 40 loads long and use 10 mm magazines to make this feed in your 40. But those are NOT 10 mm OALs.

I load to 1.23" O.A.L. (over all length) with 180 grain bullets, not 1.135" O.A.L. I realize that 10mm OALs are more like 1.26" OAL, next I will try loading 1.26" OAL.

Your mileage may vary, perhaps because your gun is different. Best wishes.

[kneelingatlas]

In the article 56hawk posted the problem was the 40 round being touched off in front of the extractor... Maybe if the loading long the bullet would hit the rifling before it got that deep...

[jmbaccolyte]

Start with mild loads if you're writing what I think you're saying.

[kneelingatlas]

I'm not too concerned, but I'm trying to get my hands on a .40 barrel anyway, just for piece of mind.

[dirty whiteboy]

Shot thousands on 40's out of a 10mm Glock, bought an extra extractor to have "just in case", but never needed it.

[Steve RA]

It's somewhat the same as shooting 9mm in a .38 Super chamber.

[kneelingatlas]

I feel more comfortable with 40/10 than 9/38 because the only difference between 4/10 is the length whereas 9/38 have different necks and bases

[jmbaccolyte]

...Maybe if the loading long the bullet would hit the rifling before it got that deep...

I think you're right that a long enough loaded .40 round with the bullet touching the rifling would correct the headspace problem, but I've heard that causes pressures to jump. I'd start with a mild load and work up while watching for pressure signs.

Let us know what you decide to do on this latest project.

[kneelingatlas]

I didn't intend to load so long the bullet touched the rifling during normal cycling, just long enough so that if if were to jump in front of the extractor for some reason it wouldn't go into battery.

[peterthefish]

Never one to let a bad idea stand in the way of an ill thought out response, I wonder if you could cut and polish a .140" section from the end of a piece of 40 S&W brass and put it in the chamber, essentially reducing the chamber to .40 length?

Not sure how long it would last (and if you'd be able to get it out once it got good and dirty and swaged) but thought I'd throw out what came to mind.

[Nealio]

I would think reliability would be an issue shooting .40 in a 10mm because you are head spacing on the extractor.

[Steve RA]

If you have a normal length chamber and get a slightly short case you may be doing that already. That could be in any caliber.

[kneelingatlas]

If you have a normal length chamber and get a slightly short case you may be doing that already. That could be in any caliber.

Exactly, because of case variations I believe every .40 has a slight gap from the front of the chamber, I just haven't had a chance to test that theory yet.

[Steve RA]

Easy way, run a bunch of empty cases thru the chamber and note the difference compared to some point you pick on the barrel hood.