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Old January 14, 2013, 01:44 PM   #1
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10mm case trimmed to 40 S&W

noobie question here

I was at the range the other day and saw a bunch of 10MM cases on the ground. I am wondering if it is O.K. to trim these cases to .845 ish and run them through my 40 S&W?

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Old January 14, 2013, 01:56 PM   #2
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ONLY IF YOU ARE WILLING TO CHANCE the 40's tabbing the large primer on a 10MM cartridge. GO back and check the history of why S&W went with SP primers in their 40S&W.
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Old January 14, 2013, 02:23 PM   #3
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unless you have the skill to work up a custom load, that probably isn't a good idea. Look inside one and compare it to your 40. Trim one to length and then compare the volume it has versus the volume of an actually 40 S&W shell. Besides, do you really want to monkey with small primer vs. large primer when you can buy once fired for so little money? You could probably sell the 10 mm if you have enough to offset a lot of the cost.

If you have a speer reloading manual, read their section on 357 sig. Same applies to 40 S&W from 10mm.

Now, I have no experience with the 10mm. But it seems to me that if the 10mm has a beefier base and someone did have the skills to create a custom round to chamber in 40 S&W, he might have a round that wouldn't bulge so bad in an unsupported chamber. A rube-goldberg solution to a non-issue? Quite possibly.
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Old January 14, 2013, 03:41 PM   #4
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I wouldn't chance cutting those things down.

I'd be happy to reimburse your postage and recycle those cases properly
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Old January 14, 2013, 05:38 PM   #5
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I'd put them up to swap for what you need. I picked up a bunch of .357 sig. that the game wardens shot at their range. I put them in brass traders on a couple different forums and ended up with some .9mm and .40 s/w.
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Old January 14, 2013, 06:44 PM   #6
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You could probably sell the 10 mm if you have enough to offset a lot of the cost.
I can find .40 brass on the ground at the ranges I frequent, and would gladly trade them 2-for-1 for 10mm brass.
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Old January 14, 2013, 06:57 PM   #7
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Do not trim down 10 mm brass. People that reload 10 mm would be glad to trade for .40 S&W brass. Most likely two for one.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.
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Old January 14, 2013, 07:06 PM   #8
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Lots of decent replies...

...but, I have to ask...what is "tabbing" a primer?

In a nut shell, you would need to trim and check volume. One of your issues would likely be the thicker stronger case mouth.

It would be a challenge to get a half decent load. It is also basically a sin to destroy more expensive brass to make cheaper and more plentiful brass.
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Old January 14, 2013, 07:09 PM   #9
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for the time and effort you would need to spend
you could simply SELL the 10mm, buy .40 once fired and walk away with a profit... and be MUCH further ahead time, equipment, and effort (not to mention money wise)

Oh, and the LP in .40 had issues with being struck on the truncated nose of the bullet behind it, usually only a problem in tube guns, but it was an issue, I forget why, in .40
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Old January 14, 2013, 07:17 PM   #10
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I've done it and it did not result in any real advantage.
I had 7.0 gr of unique with a 155 gr bullet.
Pressure went up and the cases started to show a little stress.
I have a barrel in 40 S&W for my universal receiver So I have the ability to measure pressure.

I will be glad to trade brass though

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Old January 14, 2013, 07:56 PM   #11
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Don't do it.

Should be an easy trade to someone looking for 10mm.

Besides, I think I recall something about the webb being a little thicker, which would reduce capacity and result in increased pressure. That would explain the results edward5759 observed.
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Old January 14, 2013, 10:08 PM   #12
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Thanks for the replies! Really wasn't sure with it using a large pistol primer.
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Old January 14, 2013, 10:41 PM   #13
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I am another who would be happy to trade .40 brass for 10mm brass...two or more for one.
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