This is a discussion on Cartridge Profile: Reloading the 10mm Automatic within the Reloading forums, part of the Defensive Ammunition & Ballistics category; History first. In 1983, Jeff Cooper and some friends were fed up with the lack of power in the 9mm and 45 Auto cartridges for ...
History first. In 1983, Jeff Cooper and some friends were fed up with the lack of power in the 9mm and 45 Auto cartridges for self defense. They set out to make a better cartridge.
They started with a 40 caliber bullet, as it splits the difference between the 35cal 9mm Luger and the 45 cal 45 Auto. It was first designed to fit in the same size gun as the 9mm Luger. The testing and performance angered them even more. It just wasn't up to what they wanted. So they went up and worked with the next larger auto pistol action, the 1911 whose cartridge was 1.260" OAL. If you were paying attention, you just realized they designed the 40S&W cartridge before Winchester and S&W did, and the 10mm team thought its performance wasn't up to their standards. So they went back to the drawing board and, using the previous .30 Remington case, cut a little less off than previous arriving at a case length of .992".
So arriving at this new OAL of 1.260", they were raising their eyebrows. This is what they wanted. They called this new cartridge the 10mm Automatic. Bullet diameter: .400" (borrowed from the .38-40). Overall length: 1.260" (borrowed from the 45 Auto). Maximum operating pressure: 37,500psi. Initial load for which the cartridge was developed was a 200gr FMJ bullet at 1200fps from a 5 inch barrel generating 640fpe at the muzzle. Quite a handfull.
They chambered this cartridge in a modified CZ75 marketed by the (now defunct) Dornaus & Dixon, which they called The Bren Ten. The gun failed but the cartridge lives on. It was adopted for use by the FBI after reported failures during the infamous 1986 Miami Shootout. They adopted a lighter recoiling loading which projected a 180gr JHP at 950fps. This was later used as the basis for the shortened 10mm called the 40S&W and is very similar to the prototype Jeff Cooper and associates worked with during the development of the 10mm Auto.
Now on to handloading. Handloading the 10mm Auto is pretty straight forward and it is a straight walled pistol cartridge, meaning carbide sizing dies can be used and case lubrication is optional rather than necessary. There are many brands of cases out there, Federal, Remington, Hornady, Norma, Starline, Winchester, PMC. There are also nickel plated brass, which some claim to split sooner than brass cases. I have not found this to be true. I have loaded over 50K rounds of 10mm and they all wear out at about the same point.
There are plenty of commercial bullets available in weights from 135gr Nosler JHP up to the fabulous Hornady 200gr XTP. Cast bullets are widely available and the nominal size is .401". Some of my favorites are:
135gr Nosler JHP
155gr Hornady XTP
165gr Speer Gold Dot
180gr Remington Golden Sabre
200gr Hornady XTP
In lead bullets the middle weight 170-180gr bullets have done very well. The SWC type bullets are pretty good for targets, the truncated cone (TC) profile will feed in most any gun. Some of the round flat point (RF) bullets intended for the .38-40 do well for hunting. A wide meplat is necessary for deep penetration.
Powders are a fun topic. If you look at the burn rate chart, pretty much anything between IMR 800X and Acccurate Arms #9 will work well in the 10mm Auto. I have personally used HS6, Blue Dot, WSF, W571/HS7, Unique, and Longshot in my 10mm loads.
For magnum, high velocity loads, 800X, Blue Dot, and AA#9 are the ones to use. For medium-heavy loads Blue Dot and W571/HS7 are great. For medium loads HS6 and Longshot will do great. Light loads and lead friendly loads are reserved for Unique and WSF.
Primers are normal large pistol primers. Nothing fancy. Magnum primers are NOT needed. There is some data out there using magnum primers with 800X. One note about Winchester WLP primers. These are dual purpose primers. They can be used with either standard or magnum loads. I have used CCI 300, CCI350, and WLP primers in 10mm with no measurable differences.
These are some loads I have used in my guns with the powders I mentioned my use above. The data is in the following manuals. The characters in  reference the source in the data below. Data in bold is listed max load. DO NOT EXCEED.
Lyman #48 [L48]
Hornady #7 [H7]
Hodgdon 2004 [H2004]
Nosler #5 [N5]
Sierra #5 [S3]
135gr Nosler JHP 11.5gr Blue Dot 1308fps [N5]
135gr Nosler JHP 12.5gr Blue Dot 1459fps [N5]
135gr Nosler JHP 10.5gr HS6 1345fps [H2004]
135gr Nosler JHP 11.0gr HS6 1410fps [H2004]
150gr Sierra JHP 8gr Unique 1250fps [L48]
150gr Sierra JHP 9gr HS6 1162fps [L48]
155gr Hornady XTP 12.5gr Blue Dot 1400fps 4" [H7] Note: manual indicates 1425fps from 5"
155gr Hornady XTP 11.0gr HS6 1325fps [H7]
180gr Hornady XTP 9.2gr Longshot 1246fps [H2004-lists Sierra bullet]
180gr Hornady XTP 9.4gr HS6 1127fps [H2004]
200gr Hornady XTP 6gr Unique 1050fps [L48]
200gr Hornady XTP 9.6gr Blue Dot 1148fps [L48]
175gr LSWC 6gr WSF 1050fps [L48] Note: listed starting load is 6.2gr. Operates 1911, very easy shooting load, no leading.
I run two loads with my custom 230gr SWC, one with WSF and one with Blue Dot. No leading in either. These two loads were SWAGs (scientific wild ass guess) I worked up for my business offerings. No pressure sign. I won't post the data here as I have no pressure testing to support my findings. They both feel like a heavy 45 Auto.
There you have it. 10mm reloading in a nutshell.
"The pistol, learn it well, carry it always ..." ~ Jeff Cooper
"Terrorists: They hated you yesterday, they hate you today, and they will hate you tomorrow.
End the cycle of hatred, don’t give them a tomorrow.
Founder of the BDA Pony Club
Thanks Tubby for the article. Very nice read.
I always sorta liked the idea of the 10mm but have never gone down that road. I'd even like to play with the .40 S&W through hand loading. I kinda recall when the 10mm came out and Cooper and Co. writing about it. Seemed like a neat idea. I sure snapped up the various 10mm/.40 bullets as they became available to try in my .38-40. I've only fired other's 10mm and .40 S&W guns. Perhaps I'll get around to one of my own.
You really like hand loading. You ought to continue to post your thoughts on cartridges you play with.
Tubby45, good info. Thanks for sharing. I recently ordered some .40 components to try my hand at reloading it from Midway. Have been doing 9mm and it is going ok, but I keep checking here to see what else you posted, seeing maybe I can get a nugget or two of good info. Thanks again.
PM me your address and I'll send you a 40S&W present. Don't worry about shipping. Next time you see [hear] one of those bell ringers outside a store, think of me and toss in a few bucks.
PM sent, is really not necessary. I already give to those bell ringers every chance I get. It is the season after all. Thank you