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

Gun Watch ^ | 9 September, 2018 | Dean Weingarten

[marktwain]

Two police departments in Michigan are trading in police guns for new ones.

The Valparaiso police department is trading in .40 caliber Glocks that are a few years old for 9mm Glocks that are new. The trades should happen this year, in 2018.

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.

Gun Watch

[dangerdoc]

I used to frequently shoot hundreds of rounds in a session, usually takes about a hundred rounds to settle in. I only shoot S&W revolvers now, after a hundred rounds, I stop and make sure no screws have backed out and use a brass brush on the front of the cylinder and wipe down the back of the cylinder, if I don’t it will bind.

[dangerdoc]

Or a backed out cylinder pin.

[CodeToad]

“I know of no one that loves their hammer.”

Then you don’t know very many people.

[CodeToad]

“How about firearms that are over 100 years old that still work just fine?”

I have a few century arms, and they work great.

[Blood of Tyrants]

When they make a 17 round mag fed revolver, I’ll consider one.

[Blood of Tyrants]

The sergeant sounds like a gun shop ninja. If he knew squat about guns he wouldn’t use made-up terms like “cartridge ignition pressures”. A better, more understandable explanation would be cheaper ammo allows more range time for officers, higher cap magazines allows more shots in a high-stress situation where 80-90% of shots are misses, and lower recoil allows quicker follow up shots.

[Blood of Tyrants]

One guy said his wife carried a revolver in her purse. A loose coin jammed in between the cylinder and frame somewhere. He had to use a small punch to get it out.

[Blood of Tyrants]

Less recoil, quicker follow up, more rounds for the same weight.

[Mr Rogers]

“I only shoot S&W revolvers now, after a hundred rounds, I stop and make sure no screws have backed out and use a brass brush on the front of the cylinder and wipe down the back of the cylinder, if I don’t it will bind.”

Check your cylinder gap. I had (still have) a S&W 22 LR that did that. Bought it new in the 70s. Had a 0.006 cylinder gap on one side and 0.001 on the other. Filed it even and it hasn’t had a hiccup in the 40 years since. And it is the only revolver I’ve fired hundreds of rounds thru at a sitting - and 22 rounds are notoriously dirty!

If I was worried about a strain screw backing out, I’d use Locktite on it. But mine has now gone 15+ years without budging. I don’t mind shooting 100-150 rounds at a time thru my J-frames, 38 special only for that, but they have never had a hiccup of any kind. The day one malfunctions on me, it will be a first.

When I CCW, I start with a clean gun. I don’t expect to ever shoot into double digit counts defensively. Besides, if I carry a reload of my J-frame, it is in the form of my Beretta Pico.

;>)

[dangerdoc]

After a few hundred rounds either crud or cylinder pin back off will lock my revolvers up tight where my government models, Glock and other models keep firing.

[ought-six]

I have several revolvers, as well.

[Envisioning]

The public often look to police for firearms expertise.

Maybe the uninformed public....

[Celtic Conservative]

S&W was sued, and settled out of court confidentially. The next generation of S&W guns changed their design enough to avoid patent issues.

CC

[sarge83]

The Taurus was my brothers. But that being said I do own one Tarus a TCP .380, nice piece. Revolver wise, Colt’s S&W’s, Rugers, Rossi.

[1_Inch_Group]

I’d take parts from 3 previously working .40 pistols in the hope of making one usable one.....

In place of a working 9mm.

Too fast, not enough mass.

[gundog]

Bullet weight, powder burn rates and bore diameter all influence the pressure curve of a fired round. The first two can be varied to affect internal pressures. Sounds like the officer just found a new way to say “I want a new gun,” and baffle those that would say he can’t have one. Try it on the wife.