Police Sergeant Pontificates on .40 vs 9mm "cartridge ignition pressures"

The public often look to police for firearms expertise. Unfortunately, some police feel the need to demonstrate their lack of knowledge.  When asked about a trade-in of Glocks, Sergeant Michael Grennes is reported as giving this response. From nwitimes.com:

The difference between the 9mm and the .40-caliber guns, he explained, is one of cartridge ignition pressures. The 9mm has a long, low, smooth ignition impulse, while the .40 has a short, sharp, abrupt ignition impulse.

That recoil caused cracking of the frame in the .40-caliber guns, especially ones that had been used often over four to five years, he said.

There is no significant difference in pressure levels in Glock .40 caliber and Glock 9mm pistols.

SAMMI pressure limits for the 9mm = 35,000.   For the .40 cal = 35,000.

Given the abysmal ignorance of most reporters about firearms, it is possible the Sergeant was misinterpreted.

The Sergeant’s information carries a bit of truth. Early Glock .40s used the same recoil spring as the 9mm, which allowed the .40 to recoil more sharply. The .40 caliber has more energy, so there is more energy in the recoil impulse. With high round counts, a small number of frames suffered hairline cracks.

The Sergeant may have confused internal pressures with external mechanics.

In the early generation 3 Glocks, starting about 1998, the frames were reinforced with an  extra pin in the frame, that also offered a stress relief hole to stop the rare cracking of the Glock .40 calibers. As the pistols the Sergeant is referring to are only 4-5 years old, they are not subject to the cracking problem.

It appears there is a current trend to go from .40 caliber Glocks to 9mm Glocks. It may offer the opportunity to pick up some inexpensive, but excellent Glock .40 calibers as police trade ins.

Reinforced frames have 2 pins instead of 1 pin above the trigger, so they are easily noted.  The Generation 5 Glocks have gone back to 1 pin, but are only offered in 9mm.

©2018 by Dean Weingarten: Permission to share is granted when this notice and link are included.

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