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Old 08-19-2013, 20:36   #1
VBVAGUY
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Gen 4 Glock 21 10mm conversion >>>>>>>

I am sorry if this has been already covered, but I am considering purchasing a Gen 4 Glock 21. Am I correct in that I can purchase a Glock 20 slide and barrel and that it will work with the Glock 21 frame ??? Also am I correct in that I should be able to purchase a .357Sig / .40S&W conversion barrels and use it in the Glock 20 slide. Please let me know if this is correct. Thank you for any info. God Bless
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Old 08-19-2013, 21:02   #2
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Yes. Although I regularly run a non conversion G-20 Stormlake barrel in a G-21 slide along with G-20 mags in my G-21 frame with no issues.
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Old 08-19-2013, 21:08   #3
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Originally Posted by PBRLite View Post
Yes. Although I regularly run a non conversion G-20 Stormlake barrel in a G-21 slide along with G-20 mags in my G-21 frame with no issues.
Did you have to modify the extractor? Two very different casing sizes.
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Old 08-19-2013, 21:08   #4
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Quote:
Originally Posted by PBRLite View Post
Yes. Although I regularly run a non conversion G-20 Stormlake barrel in a G-21 slide along with G-20 mags in my G-21 frame with no issues.


Thanks for confirming. The Gen 4 G21 looks like this would be a nice all-around gun to have with the different slide and conversion barrels, etc. God Bless
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Old 08-19-2013, 21:23   #5
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Did you have to modify the extractor? Two very different casing sizes.
No mods to the extractor.

This guy has been proving you can do it for years:


Last edited by PBRLite; 08-19-2013 at 21:36.. Reason: Added content
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Old 08-19-2013, 21:26   #6
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Originally Posted by PBRLite View Post
No mods to the extractor.
And your brass ejects normally? I might have to try this too.
I heard it can lead to premature extractor failure when you use a barrel and slide of two different diameter calibers.
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Old 08-19-2013, 21:38   #7
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Quote:
Originally Posted by VBVAGUY View Post
I am sorry if this has been already covered, but I am considering purchasing a Gen 4 Glock 21. Am I correct in that I can purchase a Glock 20 slide and barrel and that it will work with the Glock 21 frame ???
The lower frames of the G20 & G21 are completely identical.
Look for a Gen 4 G20 slide for the right fit.
You don't even need to replace the RSA, they are both the same. You install the G20 slide assembly on the frame, you use a 10mm mag and you are good to go.
I've done it, no issues, simple to convert.
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Old 08-19-2013, 21:45   #8
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Originally Posted by Roger G23 View Post
And your brass ejects normally? I might have to try this too.
I heard it can lead to premature extractor failure when you use a barrel and slide of two different diameter calibers.
I've shot several thousand rounds, and the majority of them were my nuclear hand loads and I have not seen any extra wear to the extractor. Hell, I've even shot a few thousand rounds of .40 S&W from a G-20 barrel in a G-21 slide as well.
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Old 08-19-2013, 23:55   #9
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The G20 & G21 frames are identical ..including internals. The slides are different. G21 has a larger breach cut on the breach face, a larger firing pin safety, different extractor ...I've heard of people firing a 10mm barrel out of the G21 slide but the breach face is wider so the 10mm barrel doesn't lock up very well...breach end moves side to side.
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Old 08-19-2013, 23:59   #10
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Quote:
Originally Posted by PBRLite View Post
No mods to the extractor.

This guy has been proving you can do it for years:

http://youtu.be/Df4YQevQFYY
This video is not of the topic we're discussing here.
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Old 08-20-2013, 00:00   #11
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Quote:
Originally Posted by PBRLite View Post
I've shot several thousand rounds, and the majority of them were my nuclear hand loads and I have not seen any extra wear to the extractor. Hell, I've even shot a few thousand rounds of .40 S&W from a G-20 barrel in a G-21 slide as well.
The G20 & G21 frames are identical ..including internals. The slides are different. G21 has a larger breach cut on the breach face, a larger firing pin safety, different extractor ...I've heard of people firing a 10mm barrel out of the G21 slide but the breach face is wider so the 10mm barrel doesn't lock up very well...breach end moves side to side.
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Old 08-20-2013, 00:04   #12
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Quote:
Originally Posted by nraman View Post
The lower frames of the G20 & G21 are completely identical.
Look for a Gen 4 G20 slide for the right fit.
You don't even need to replace the RSA, they are both the same. You install the G20 slide assembly on the frame, you use a 10mm mag and you are good to go.
I've done it, no issues, simple to convert.
The recoil spring weights are the same for the G20 and G21? Huh? How could that be possible? The vast difference in pressures, etc... Doesn't make sense.
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Old 08-20-2013, 06:29   #13
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My bad. I was laying in bed and didn't listen to the video. Same guy has done a vid shooting a G-21 with a stock G-20 barrel. Can't seem to find it at the moment.
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Old 08-20-2013, 07:40   #14
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Quote:
Originally Posted by Roger G23 View Post
...I've heard of people firing a 10mm barrel out of the G21 slide but the breach face is wider so the 10mm barrel doesn't lock up very well...breach end moves side to side.
Below is a photo showing the relative accuracy of various 10mm barrels in the G21SF slide. The upper left target is a factory G20 10mm barrel in the G21SF slide. The upper right is a LWD G20 10mm barrel in the G21SF slide. The lower left is a KKM 45-10mm conversion barrel in the G21SF slide. See the photo notes below for the source. I think Desertscout is the same guy that made the video to which PBRLite is referring above.

The effect on accuracy resulting from minor differences in barrel hood and breechface dimensions is inconsequential. It's not surprising that PBRLite gets good results with the config he is running.

Suggested additional reading: Converting the Glock 21 to 10mm Caliber

General Glocking
Photo posted by Glock Talk member Desertscout on 12-3-2008 in GT thread titled "Glock 21 conversion to Glock 20?" Desertscout wrote, "The first pic is all G21SF with various 10mm bbls in it. They are listed on the targets. We had a couple of Type II malfs out of the KKM bbl and the LWD bbl but it was not too bad. Altogether, about 50 rounds were fired. The center and lower right targets were shot with a stock G29 bbl in G30. It shot well and zero malfs. I think the amount of shadow in the late PM attributed to some of the point of impact variations."
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Last edited by GRT45; 08-20-2013 at 08:22..
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Old 08-20-2013, 07:44   #15
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Originally Posted by Roger G23 View Post
The recoil spring weights are the same for the G20 and G21?
Yep, Glock, Inc. installs the same 17-lb RSA in the G21 and G20 at the factory:

Gen4
30077 Recoil Spring Assembly dual (marked 0-7-2) - fits G-21Gen4- G20Gen4
Gen3
SP 05586 Recoil Spring Assembly - fits G20-G20SF-G21-G21SF (marked 5600 on end of recoil spring guide)
Ref: Glock, Inc. Parts Order Form (Certified Armorers Only), FRM-72-26 / Rev 68 / 07.15.13
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Last edited by GRT45; 08-20-2013 at 08:54..
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Old 08-20-2013, 08:06   #16
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Looks like the stock barrels were more accurate than the others, including the KKM!

AK

Last edited by Arnold Kuhl; 08-20-2013 at 08:07..
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Old 08-20-2013, 23:17   #17
Roger G23
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Quote:
Originally Posted by GRT45 View Post
Below is a photo showing the relative accuracy of various 10mm barrels in the G21SF slide. The upper left target is a factory G20 10mm barrel in the G21SF slide. The upper right is a LWD G20 10mm barrel in the G21SF slide. The lower left is a KKM 45-10mm conversion barrel in the G21SF slide. See the photo notes below for the source. I think Desertscout is the same guy that made the video to which PBRLite is referring above.

The effect on accuracy resulting from minor differences in barrel hood and breechface dimensions is inconsequential. It's not surprising that PBRLite gets good results with the config he is running.

Suggested additional reading: Converting the Glock 21 to 10mm Caliber

General Glocking
Photo posted by Glock Talk member Desertscout on 12-3-2008 in GT thread titled "Glock 21 conversion to Glock 20?" Desertscout wrote, "The first pic is all G21SF with various 10mm bbls in it. They are listed on the targets. We had a couple of Type II malfs out of the KKM bbl and the LWD bbl but it was not too bad. Altogether, about 50 rounds were fired. The center and lower right targets were shot with a stock G29 bbl in G30. It shot well and zero malfs. I think the amount of shadow in the late PM attributed to some of the point of impact variations."
Good stuff. I think I'm being converted into believing.
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Old 08-20-2013, 23:18   #18
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Quote:
Originally Posted by GRT45 View Post
Yep, Glock, Inc. installs the same 17-lb RSA in the G21 and G20 at the factory:

Gen4
30077 Recoil Spring Assembly dual (marked 0-7-2) - fits G-21Gen4- G20Gen4
Gen3
SP 05586 Recoil Spring Assembly - fits G20-G20SF-G21-G21SF (marked 5600 on end of recoil spring guide)
Ref: Glock, Inc. Parts Order Form (Certified Armorers Only), FRM-72-26 / Rev 68 / 07.15.13
Wow. OK Thank you.
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Old 08-20-2013, 23:19   #19
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Originally Posted by PBRLite View Post
My bad. I was laying in bed and didn't listen to the video. Same guy has done a vid shooting a G-21 with a stock G-20 barrel. Can't seem to find it at the moment.
No sweat bro. I think you're right. Wow. I love education.
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Old 08-21-2013, 09:38   #20
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Quote:
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The recoil spring weights are the same for the G20 and G21? Huh? How could that be possible? The vast difference in pressures, etc... Doesn't make sense.
Quote:
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Wow. OK Thank you.
I read that the G20 slide weighs more than the G21, that would give it more inertia.
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