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Old September 19, 2011, 08:37 AM   #1
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Reliability of 10mm conversion in Glock 21?

Considering getting a Glock 21 so that I can shoot the normal .45 acp and and a 10mm conversion barrel and mags for it.
Anyone have experience with this setup and its reliability?

Do you need to change out the extractor for the case difference?
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Old September 19, 2011, 10:20 AM   #2
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Have not done that conversion myself. Here is a link
to an excellent forum that covers this topic.
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Old September 19, 2011, 11:00 AM   #3
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There is another way to do the conversion of the G-21 to 10mm, that is with a entire slide assembly, either the complete stock 20 slide or say the Lone Wolf Long slide & barrel setup! That way you just swap the top ends with the correct extractor & geometry for the cartridge and magazines. The 10mm will require some stronger springs than those of the 45.

I currently have the G-29 with several conversion barrels but I have thought of doing a G-21 to have 45 and Long Slide for 10mm!
The "10mm" I'm Packin', Has The Bullets Wackin', Smakin' & The Slide is Rackin' & Jackin'!
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Old September 19, 2011, 01:18 PM   #4
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I just purchased a new complete G20 upper for my G21. It was pretty expensive but still cheaper than another pistol. Conversion barrels exist but rounds may not extract properly.
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Old September 19, 2011, 05:22 PM   #5
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You may also want to consider that the ejector (which is in the frame) in the Glock 21 that was designed for the 45, may not be the optimal size or in the optimal position for the 10mm cartridge.
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Old September 19, 2011, 06:03 PM   #6
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FWIW, I stuck a 10mm G20 barrel (Lone Wolf) in my Glock 21, inserted a 10mm mag with subsonic 10mm loads, and it worked just fine. I was not sure if I needed or wanted a heavier strength spring for use with the 10mm, so I refrained from shooting any full house 10mm ammo. I think your conversion will be every bit as reliable as a regular G20.
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Old September 20, 2011, 09:28 AM   #7
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The ejector/trigger housing is the same part in 20s and 21s. Extractors are different, but the extractor should have enough range of motion to swing in and grab the 10mm rim.
G-20 slides are heavier that 21 slides, but as long as you're not shoot top end 10mm loads, and most commercial loads are not, that should not be a factor.
I would highly recommend KKM conversion barrels, both of mine have dropped in perfectly, the fit is indistinguishable from the stock barrels. Rifling is perfectly smooth, best I've seen, better than My Freedom Arms. The only rifling that I've seen that is that smooth was with a well worn Sig P226 barrel.

I wish someone would build a .40 conversion barrel for the G-21/G-30. If the 10mm works, I don't see why a .40 wouldn't. .40 has plenty of power to cycle a G-20 or G-29, I've had both of those conversions, and if the extractor and ejector work with 10mm, it should work with .40 as well. >40 feeds just fine from 10mm mags.

I would think a .40 conversion would be more popular than a 10mm conversion as well.
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Old September 20, 2011, 09:56 AM   #8
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Thanks to everyone for their responses so far.
HH, I had a KKM barrel for my glock 17, and it was really nice. But my brother wanted it more than me, so it is gone.

Why are the g20 slides heavier than the g21. Aren't they the same szie and dimensions, except for the barrel hole?
Would a heavier spring compensate for the difference for hotter 10mm loads.

I shot some medium 10mm loads out of my glock 29 but never got a chance to shoot the BB or hotter stuff.

They do make a .40 conversion barrel for the Glock 20.
Im looking at the 10mm conversion so that I could use the same gun for pernal and woods/hunting. Of course I could just use 10mm for both as well and just get the g 20, but I really like the .45 acp format as well.
From the sweet grass to the slaughter house; From birth until death; We travel between these two eternities........from 'Broken Trail"
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Old September 20, 2011, 03:28 PM   #9
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The 21 slide is heavier because it needs more mass than the 20 slide to efficiently function with the much higher pressure 10mm Auto.

I was going to do that too, but opted instead for the GLOCK 20SF. I will miss not being able to shoot 45ACP, but I think the versatility of the 20 will make up for it. Maybe one day I'll save up enough to get a 21 also! Whatever you end up doing, have fun. The 20/21 GLOCKs are my favorites!
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Old September 20, 2011, 04:46 PM   #10
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Why not skip the 10mm conversion and just get some 45 Super ammo? I'm a big 10mm advocate, but the 45Super really levels the playing field.
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Old September 20, 2011, 05:15 PM   #11
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The Glock 20 was designed specifically for the 10mm and released prior to the G21. It has a heavier slide for a reason. I know people post about converting G21's to 10mm and I'm sure it can be done. I just wouldn't do it. I did get a 40 S&W conversion barrel for my G 20 and it works fine with the factory mags and recoil spring.

Heavier springs don't compensate for proper design. Too heavy a spring will lower reliability and batter the gun from the slide slamming forward.

There is an article I'm sure you can find on the web regarding tests with a 1911 using various spring rates and finally with no recoil spring to deteremine the rate of battering and damage to the gun.

As with all locked breached pistols once the proper functioning spring rate for reliability was found, the spring rate made very little difference. And even with the very light spring rates there wasn't the damage you'd expect to see after reading the web.
"Iwoke up this morning and got myself a beer. The future is uncertain and the end is always near."

Last edited by FALshootist; September 20, 2011 at 05:23 PM.
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Old September 20, 2011, 09:33 PM   #12
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Actually the 20 was under development as a .45acp when the 10mm lite came out for the FBI trials. Glock quickly changed the 20 to 10mm to get it on the market ASAP. The .45acp version became the 21 and was introduced later.

The slide on the 20 is thicker in some areas than the 21, IIRC, the holes in the end of the slide are the same size. A heavier spring with 10mm hunting loads would be a good idea. 20 or 22 pounds are normally used.

Last edited by Hammerhead; September 21, 2011 at 03:56 PM.
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