First rounds on target with the Deltapoint Pro optic on my G40 MOS... This is actually 2 separate groups, the 5 rounds farthest to the left were some old stray 40 S&W rounds (155 Silvertips) I had left over from back when I carried the Beretta 96, they fed and fired fine in the 10mm Glock... The other 5 rounds were handloads I threw together with 7 grains of Power Pistol powder under a 200 grain XTP.
All rounds fired from 50 yards, sitting, using shooting sticks.
Looks like it needs to be adjusted a little to the right, and up a click.... I want it sighted for 75 yards, that gives me a point blank range of just over 100 yards, which is about as far as I care to shoot a pistol at a game animal.

First, thanks for this thread and the info that it has generated.  Haven't reloaded anything past 180gr, yet.

Second, Did I understand you correctly when you said you fired 40 S&W thru a 10mm barrel?  I thought the cases used the case mouth to set in the chamber which would make the round set too deep for the firing pin.  I'm not looking to run out and buy 40S&W vs. just curious.

In this case the extractor tension holds it against the breech face. But, you are correct.

Quote from: PCFlorida on May 14 2017 08:55:56 AM MDT
In this case the extractor tension holds it against the breech face. But, you are correct.

Thanks, makes since now.  It should be noted that I do not plan to partake in this activity and will continue to only run 10mm thru my G20.

Yes some firearms can hold the 40S&W back against the breech face and allow them to fire from the 10mm barrels.
Here is what you all should know;  The end of chamber cut is about 1/8" away from the end of the 40S&W case mouth, this allows carbon fouling to deposit and will need to be cleaned before using 10mm cartridges otherwise you risk a failure to full go into battery.  There is excessive blowby until the bullet enters the bore to seal it.
Another issue is that the bullet can be shaved by the edge of the end of chamber cut and leave a deposit rolled up against this area and it can be difficult to remove, this can also cause wear to that area.

So while it can work, having an aftermarket conversion barrel chambered for the cartridge (reasonably priced) is the safest route to get the most out of your shooting pleasure. 

Quote from: The_Shadow on May 14 2017 10:56:58 AM MDT

So while it can work, having an aftermarket conversion barrel chambered for the cartridge (reasonably priced) is the safest route to get the most out of your shooting pleasure.

I think this should be discussion of (40SW  in 10mm) closure right here. It's the policy I follow and to consider and use a 10mm barrel for .40SW, when the .40 barrel is just not that expensive. In fact, groupthink or 10mm-firearms.com should not be seen as recommending .40SW in 10mm barrel, especially when doing it correctly is so inexpensive.

I agree.... There is no good reason to habitually? fire 40 S&W in 10mm barrels... For all the above reasons.

But, I had a specific reason for doing it...I wanted to see if they cycled the action, that's the only reason I did it.

Why? The fact that they functioned fine tells me the G40 comes with a spring that it too weak for the loads I plan on shooting.

Glock should ship it with a 20# dual spring... Currently, nobody even offers a 20# dual spring, but that is what the G40 needs.

To each his own, but I never understood running 40 S&W (or 40 case loaded long with heavy bullets) through a 10mm barrel.

As Shadow pointed out there's at least the possibility of inconvenience, no to mention what can go wrong from firing the wrong cartridge.

Pablo hit the nail on the head, go guy a conversion barrel for $90 and do it right!

Edit: Was typing a general reply, wasn't aimed at you Ridgerunner

Notice the timestamps.... This is me having this discussion on Facebook yesterday and earlier today.

No harm, no foul guys.... Just wanted to make sure everybody was clear.... I don't agree with it as a normal practice either.


But if the world ever came to an end and there was no more 10mm ammo...

Hell I don't even fire 38 Special in my 357 Mag.....I load some pretty weak loads in it, but I use 357 brass.

Quote from: Ridgerunner665 on May 14 2017 12:08:09 PM MDT
Hell I don't even fire 38 Special in my 357 Mag.....I load some pretty weak loads in it, but I use 357 brass.

Same here.  I download all the time, but always use brass that is the right dimension.

The revolvers and rifles chambered for the 357, 44 and others have a smooth tapered section that guides the bullets through the transition using shorter cased ammo like 38 Spl and 44 spl.  However the shorter casings still allows some carbon deposits which can hamper chambering of the longer casings if not cleaned.  The semi auto chambers have a end of chamber cut which is squared up.  They can accumulate all sorts of particulate, lead, copper and carbon fouling even with the proper length cartridges.  Use of shorter casing ammo like the 40S&W in a 10mm just accelerates the issues.

Think of those 410 revolvers, 2 1/2" and 3" chambers which also will utilize the 45LC and some the 45ACP.  Drastically different lengths of cartridges.

I have shot many 38's from mt 357 mag revolvers and rifle, but it became the reason I carried a range box with cleaning supplies to clean things up before leaving the range.  That insured my then carry pistol was not going to have any chambering issues.
Now I carry my 10mm firearm and want to add to my skills using 40S&W ammo, 357Sig and 9x25 Dillon, I just switch out barrels...DONE! 

Got the G40 sighted in today.

From a solid rest I can reliably hit a 12"x12" steel plate at 150 yards...I honestly didn't expect it to come that easily.

I'm confident I can take game with it at 75 yards, maybe even a bit more.

I fired 50 rounds of full power 10mm reloads (200 grain bullets at over 1,300 fps)... I now understand very well why the FBI watered the 10mm down... It's not brutal, but a 9mm it is not!

I'm looking at trigger options... The trigger itself (the part you pull) is uncomfortable to me, my finger is sore after those 50 rounds. The trigger won't be a problem for hunting but it makes it less than ideal at the range.

The trigger pull... Is hard to work with... You try to do a slow steady squeeze and it starts and stops 2-3 times before it goes bang....I don't much like that, looking at spring combos that might help there.