# 10mm auto vs 40 S&W



## Richard686

I never learn unless I ask questions, so here goes...

"I" thought 10mm auto was the same as 40 SW but when I bought a sack of 10mm brass, I find them much longer than 40 SW.
Now my question...

I also bouight some 10mm auto bullets.
Says they are .400
Is that the same as 40 Smith and Wesson bullets? Just the brass is different?
My reloading book..which I must replace does not list 10mm or 40 SW


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## NDTerminator

The 10MM is to the 40 S&W roughly what the 357 Magnum is to the 38 Special. Same caliber & diameter bullets are used but the 10MM is much more powerful than the 40 S&W.

I've always been at kind of a loss why it didn't catch on bigger. The FBI adopted it back in the 90's and when they take somethiong on it usually goes big with the rest of the LE & civilian shooting world. I suppose it was that the 40 S&W was easier to control with less muzzle blast while having enough oomph to be a fairly reliable one shot stopper...


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## People

The FBI had problems with too much penetration. They still use the 10mm in their MP5-10s.
Other than that it is just like what NDTerminator said.

If, by some incredible space-time paradox, Chuck Norris would ever fight himself, he'd win. Period.


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## Brad from ND

Same bullet, longer case. You can trim the 10mm brass down to 40 SW length. Trim to length for 40 is .845 and for the 10mm is .982. Do not trim less than .845 because the case headspaces from the case mouth. Hope that clears it up for you.


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## Richard686

Brad from ND said:


> Same bullet, longer case. You can trim the 10mm brass down to 40 SW length. Trim to length for 40 is .845 and for the 10mm is .982. Do not trim less than .845 because the case headspaces from the case mouth. Hope that clears it up for you.


Fine idea,trimming the cases, thanks...except..
How safe is it tii trim with the primers in? Pop'em out? Never done that before..can they be reused?


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## Brad from ND

I wouldn't try trimming them with primers in em. I wouldn't try popping them out either. I didn't realize you primed them already. I would find someone with a 10mm and have them single load them and shoot the primers out. Then resize and trim. Or you could just go get a new bag of brass, now. :lol: It sounds like a lot of work!


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## iwantabuggy

Richard686 said:


> Brad from ND said:
> 
> 
> 
> Same bullet, longer case. You can trim the 10mm brass down to 40 SW length. Trim to length for 40 is .845 and for the 10mm is .982. Do not trim less than .845 because the case headspaces from the case mouth. Hope that clears it up for you.
> 
> 
> 
> Fine idea,trimming the cases, thanks...except..
> How safe is it tii trim with the primers in? Pop'em out? Never done that before..can they be reused?
Click to expand...

Shouldn't be that big of a deal to trim with the primers in. There is nothing in my trimming setup that would set off a primer. My suggestions would be to:

1. Make sure you do it away from any powder residue.
2. Wear eye protection (which should be doing anyway).
3. Make sure you get all the shavings out of the case when you are done.


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## dakotashooter2

Case thickness may be an issue if you trim them. I think some 10 mm cases are a bit thicker to accomodate higher pressures. My Lee book shows the 10mm OD to be .001 more than the 40. That may be on account of the extra thickness but I'm not sure. Also some cases tend to get thicker as you get nearer to the base so if you cut them down you may be seating a bullet into the thicker area of the case. If your gun has a tight chamber the extra thickness may be enough to cause them to hang up. Besides trimming is gonna be a pain. I have been trimming about .135" off .41 mag cases to make .41 special length, about the same amount you'd have to trim. Lets just say the trimmer blades don't seem to stay sharp long enough

I have no doubt you could easily swap that 10 mm brass for some 40, though it may not be primed. Maybe even 2 for 1. I know I sent some 
10 mm range brass to a guy on this site a while back. Post it in the classifieds

If you use a lath type trimmer the primers shouldn't be an issue. You won't be able to use a lee hand trimmer with the primers in.

Get a new loading manual. If yours doesn't have the 40 or 10mm most likely the powder choices and data are out of date. If you don't want to spend the money on a new manual Hogdon publishes an "annual" that is usually available on the newsstands for $7-$8 and covers quite a bit. The LEE manual is kind of generic and a bit cheaper than those from the bullet manufacturers. Most of the powder companies have free booklets available at most sporting goods stores and loading data available online if you go to their sites. With those resources there is no excuse for outdated data.


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## Brad from ND

I noticed in my book that there was a .001 difference in diameter, too, but I didn't think it would be a problem since the 10mm and 40 S W are the same die sets. I could be wrong.


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## CV-580

Trying to convert 10mm cases to .40 S&W is a very bad idea!

From previous posts on this thread it appears nobody is aware that the 10mm uses large primers and the .40 S&W uses small primers.

Although trimming cases to length may be easily done it is time consuming.

Once cases are trimmed the INSIDE of the cases must be reamed out. Again very time consuming. Also, good luck finding a reamer made for doing this. Would likely have to be custom made, in other words very expensive.

After wasting all of this time on ruining 10mm cases you still end up with cases that have the WRONG size primer pocket.

This will (obviously) require you to have different loading data for cases with small and large primers.

You will also have to make sure you keep cases with different size primer pockets segregated or you will have total chaos while trying to reload.

The 10mm brass is more valuable. Why would you wany to turn it into junk. Why not sell or trade your 10mm brass and buy .40 brass.

Wouldn't that be cheaper, faster and make more sense???

For the original poster...

If you "never learn unless you ask a question", why don't you ASK THE QUESTION FIRST???

Why go out and do something you obviously have no business doing then ask your question?

If you are incapable of understanding or fiquring out the difference between 10mm and .40 brass until after you make the mistake, how do you expect to reload?

You can't make that type mistake when powder and primers are involved.

CV


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## dakotashooter2

In defense of the original poster, many reloading dies are marked 
40 S&W/10mm. In looking at the dies, someone of limited knowledge could easily assume they are one in the same. Though I agree that the FIRST purchase any new reloader should make is a loading manual which should be thoroughly read before buying anything else.


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## Ruthless

Richard686,

Just wondering what gun you are reloading for. I've read that Glocks hate .40 S&W reloads and they have been know to "kaboom" because of the high pressures that the .40S&W puts out and the fact they don't have a fully supported chamber. Make sure whatever gun you are reloading for has a fully supported chamber otherwise I would not reload for that gun.

Also, I would spend a lot, and I mean a lot of time reading about reloading .40S&W before I ever reloaded one round.

When I started reloading I spent months researching all the info I could find. That is how I learned not to reload for my Glock .40.

I would also recommend starting at the bottom powder levels and get used to reloading before ever moving into high amounts of powder.


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