45 GAP Brass expansion

[Russell Lang]

Have any of you G-37 users measured your fired brass vs. unfired? My curiosity comes from measuring my 40 S&W from my G-23( .422 unfired, and .432 fired, for .010" expansion) Since the 45 GAP operates at higher pressure than the 45 ACP, I was wondering if the chamber dimension allows for slightly larger expansion. Just curious!;d

[petej88]

I should be able to answer your question within a week or so when I start reloading for the 45 Gap.

Because of the massive expansion with Glock 40's, I always used a good third party barrel.

Since the 45Gap brass has a fairly mellow pressure compared to a 40, and since it is more beefed up than standard 45ACP brass, I don't expect to find anything alarming. We will see.

[petej88]

I look forward to having some fun and testing this new caliber this winter.

Here's a comparison of new and once fired 45Gap brass expansion:

New factory Speer 200 gr flat points:
diameter of case base: .472
diameter of middle: .470
diameter of mouth: .471

Once Fired Speer 200 gr flat point brass:
diameter of case base: .4725
diameter of middle: .4765
diameter of mouth: .4725

Reloaded cartridge specs (using above fired brass):
diameter of case base: .472
diameter of middle: .4705
diameter of mouth: .471

I was pleasantly surprised that case expansion was in very decent tolerances, even with full power factory Speer 200 grain ammo, which is rated at 950 fps (Power Factor of 190). It's a handful to shoot.

The beefed up brass alone makes me like the 45Gap a lot, especially in the Glock pistol format (nice security since the G37 and G21 have about the same amount of exposed brass at the 6 o'clock chamber opening). Note: The max standard pressure for the 45ACP is 21,000 psi. The maximum pressure for the 45ACP & 45GAP is 23,000 psi -- not a huge difference.

I should be able to easily create some mellow USPSA/IPSC loads at aprox 169 Major Power Factor (845 fps), which is more than 100 fps SLOWER than the Speer 200 grain GD factory round. Note: the U.S. Major Power level is set to 165 at 825 fps with a 200 grain bullet. I'm hoping some of the Ammo Companies coming online with the 45Gap will produce some factory loads for competitive shooters. This could actually help make the 45 Gap more popular and a fairly flexible round.

While some folks have stated that the 45 Gap 185 grain GD load is not significantly better at all than the .40 180 grain version, David on ammolab.com thought the difference was quite significant. You can read about it at his forum group. Just think what the 45 Gap will offer when it matures.

You can already buy 45 Gap ammo for $10 - $13 even though it's brand new on the market. The 45Gap has a full complement of 185 to 230 grain loads now. Note: I remember paying $36 for a box of 357 Sig ammo when it first came out!

Lots of ammo companies as well as strong rumors of at least a few other big firearms companies working on 45 Gap means this new round has made decent inroads during its very first year of life.

For those interested in the security of using beefed up brass, making a big hole even if the JHP doesn't expand, using lower pressures than most other duty calibers, as well as being able to cram 10+1 45 rounds into a Standard Sized Grip, the 45 Gap might just prove itself despite the Church of Naysayers & Other Calibers.

;c