My hunting and defensive pistol cartridge of choice is the 10mm Auto, and my every day carry gun is a Glock 29SF 10mm with factory 3.77” barrel. For dangerous game defense I carry a Glock 20 with either the factory 4.60” barrel or, more commonly, a Lone Wolf 6.00” extended barrel. Both of those pistols, and all three of those barrels, were used in testing for this article.

Longshot works best with high sectional density bullets (for 10mm Auto) like the SIG SAUER 165-gr. V-Crown, Sierra 180-gr. jhp and Hornady 200-gr. XTP used in testing.

SAAMI maximum operating pressure for the 10mm Auto is 37,500 p.s.i., but most published data for high-SD 10mm bullets runs at pressures 2,500 to 7,500 p.s.i. below the SAAMI maximum. There is no SAAMI +P pressure rating for the 10mm Auto. The 10mm got off on the wrong foot after being adopted by the FBI. It was too much gun for most agents, so they downloaded it to reduce recoil (a/k/a the “FBI load”). Even though the FBI eventually dropped the 10mm, most commercial 10mm ammo available today approximates the FBI load.

DoubleTap and Buffalo Bore load their 10mm ammo to substantially higher velocities, and the rumor is they use Longshot to do it without exceeding SAAMI maximum pressure. With this in mind, I decided to carefully experiment with Longshot and mid- to high-SD bullets to see what I could get for velocities without creating any signs of over pressure.

Extreme overpressure can destroy your gun and kill you in the process. Signs of modest overpressure are flattening of primers and more than normal case head expansion. My plan to avoid mayhem was to use Hodgdon’s published maximum charge weights—which I’ve been safely loading for years with 165- to 200-grain 10mm bullets—and work up in 1/10th grain increments until any signs of overpressure were detected, then back down a tenth of a grain. All powder charges were weighed on a RCBS Charge Master 1500 dispensing scale, since metered charges can vary substantially.

Even though Longshot meters well, we used an RCBS charge Master 1500 dispensing scale to weigh every charge. When working at the edge of the pressure envelope, metered charges are simply too variable for safety.

For testing we used new Starline brass cases—top-shelf stuff that was dead-on SAAMI spec in all dimensions right out of the box. For bullets we used Hornady’s venerable 200-grain XTP, the legendary Sierra 180-grain JHP and Sig Sauer’s new 165-grain V-Crown (made by Sierra for Sig Sauer).

After firing each round during load development, the case was inspected under magnification for signs of over pressure, and the case head diameter and length were measured with an electronic caliper. As soon as any sign of overpressure appeared—usually a flattened primer—testing stopped, the powder charge was reduced by 1/10th grain and that became my maximum load for that bullet brand and weight. Sixty rounds were loaded with each bullet at its respective maximum charge weight, and twenty rounds were fired with each of the three barrels to obtain velocities and test for functioning. All fired cases were again inspected and measured for signs of overpressure, but they all looked fine, with no issues observed. No malfunctions of any kind occurred during testing.

The following chart shows the average muzzle velocities in f.p.s. and muzzle energies in ft. lbs. obtained with each load, fired from each barrel, as measured with an Oehler Model 35P chronograph.

                                              3.77” Barrel             4.60” Barrel                 6.00” Barrel
Bullet                                 Velocity/Energy       Velocity/Energy        Velocity/Energy
165-gr. SIG V-Crown JHP ….. 1,334/649                1,405/723                        1,492/813
180-gr. Sierra JHP …..           1,265/640                1,315/687                        1,406/784
200-gr. Hornady XTP JHP ….  1,221/661                1,271/716                        1,344/798

The velocities obtained are virtually identical to the velocities for the same 10mm bullet weights and barrel lengths as those manufactured by both DoubleTap and Buffalo Bore.

Loaded rounds (left to right): Hornady 200-gr. XTP, Sierra 180-gr. JHP and SIG SAU er 165-gr. V-Crown JPH. Disregard the cannelure on the V-Crown as it is for .40 S&W seating depth.

Our derived maximum charge weights of Longshot have not been included in the table. That’s not an oversight­—it’s an intentional omission in the interest of safety. There are simply too many variables involved for us to publish these charge weights, including pistol and barrel quality and condition, chamber dimensions, barrel rifling type and depth, bullet design, jacketed vs. lead bullets, bullet jacket alloy, cartridge case quality and condition, primer selection and handloader experience.

To publish our derived maximum charge weights would imply they are safe to use in any 10mm pistol. Well . . . they’re not. They’re safe to use only in these two pistols and three barrels when loaded with the same brands and lots of bullets, primers, cases and powder used to develop these loads. We recommend that handloaders always begin load development at the recommended starting charge weights and work up from there. It’s a fun and safe project when you do it as outlined above.

For more information on the components used in this article, contact:

Hodgdon Powder Co.
Tel.: (913) 362-9455
Web: www.hodgdon.com

Hornady Manufacturing
Tel.: (800) 338-3220
Web: www.hornady.com

Sierra Bullets
Tel.: (888) 223-3006
Web: www.sierrabullets.com

Starline Brass
Tel.: (800) 280-6660
Web: www.starlinebrass.com