Glock 20


New member
I carry a 10mm Glock 20; I practice with the same pistol only using 40 cal ammo for costs reasons.
It appears to me there is no real difference between the two in shooting at targets. I do shoot enough of the 10’s to be comfortable with the firearm.
Is there something I am not seeing and should be aware of?
The old saying is if do don’t see it with your own eyes there not a problem. To many times I have gone by that found out latter on I was missing something.


New member
The 10mm is a longer round that the 40cal. It can cause issues in the barrel of your pistol, weak spot.


New member
Thank you, As much as I shoot I probably have some damage already.
I know I have shot 300 rd a week for several weeks, might look for some new parts and then purchase a 40.
Thanks again.


New member
Get a Lone Wolf barrel. Also get a 20# spring for that thing. Unless you are rich, 300 rds a week means you will be reloading. I blew a 20 up with a reload. The Glock barrel allows the case to expand over 0.018 inch, and the light 17# spring lets the slide release and extract the shell with a heck of a lot of pressure still in the chamber. The combination has caused (and certainly did cause in my case) case head separation and the resulting issues associated with it. Since going to a Lone Wolf barrel and Wolff 20# spring, I have had no issues with anything I have shout out of my 20SF.

Providence Ranch

New member
My concern would be headspace. The chamber for a 10mm is a bit longer than the 40 S&W. This makes a difference as both the 10 and the 40 headspace on the case mouth. Your extractor will keep the round from floating forward when using 40 ammo, but that leaves a small gap between where your case ends and your actual barrel begins. There's a lot that could go wrong here, from accuracy problems to excess pressure buildup.

My question would be, does your owners manual state that it is ok to fire 40 S&W from your 10mm? My guess is no. If not, buy a new barrel specifically clambered for 40 S&W. You're asking for trouble otherwise.


Active member
If you want to fire both 10mm and 40S&W ammo from the same pistol, you should get a revolver like the S&W 610. 40S&W ammo should NOT be fired from a G20 or any other 10mm semi-auto.


New member
Being that I haven’t heard anything positive about using my 20 with 40 cals I am going to stop.
Am going to a get Sig silver elite P229 40. I have a 9mm and I love it. But I have a lot of 40 rounds so it’s a good reason for another firearm.

Thanks again for reading my thread and providing answers.

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