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Old 03-15-2015, 11:19   #1
USMC Riflecoach
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Problems with G21 to 10MM conversion

Hello , I recently bought a KKM Precision drop in 10mm conversion kit for the Glock 21 and installed all parts according to instructions with no problems. This was a new 10mm barrel made with a larger OD to fit the slide of the 45acp, a new extractor, and a new spring loaded bearing. I am having about a 40 percent rate of failure to feed. I am using this factory load from Double tap:


http://www.midwayusa.com/product/252...ProductFinding

I really want to run this load and have little to no interest in running a 10mm load that is below the original Norma standard for the 10mm.



I tried the stock Glock 16lb recoil spring and a ISMI 20 lb spring and ISMI captured guide rod. Nothing seems to do work, failure to feed about 40 percent of the time.



I am using brand new Glock 20 mags.

Gunsmithing


Any ideas? Any suggestions are appreciated. Thank you
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Old 03-15-2015, 13:07   #2
WeeWilly
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Can you hand cycle them through without the failure?
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Old 03-15-2015, 13:18   #3
USMC Riflecoach
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WeeWilly, Yes I can cycle them through by hand without a hiccup, just went and did it to verify. Also maybe this tidbit of info will help, this gun runs fine with the rather anemic Rem/Umc 180 MC factory load with either the stock 16lb spring or the 20lb, makes no difference. I should have stated such in my initial post. I am still scratching my noggin here.
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Old 03-15-2015, 13:25   #4
WeeWilly
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Originally Posted by USMC Riflecoach View Post
WeeWilly, Yes I can cycle them through by hand without a hiccup, just went and did it to verify. Also maybe this tidbit of info will help, this gun runs fine with the rather anemic Rem/Umc 180 MC factory load with either the stock 16lb spring or the 20lb, makes no difference. I should have stated such in my initial post. I am still scratching my noggin here.
I think I would maybe try doubling up on mag springs for a test. The G21 slide is lighter than the G20 slide (the G20 Slide has less meat milled away). Your slide could be out running the mag springs. Just a guess.

You won't be able to get a full capacity test with dual springs, but at 40% failure, you probably don't need a full magazine to determine if you are going in the right direction.

If that helps, I would play with some Wolff extra power mag springs to get full capacity and eliminate the failures.

Good luck.

PS - I run a 22lb ISMI flat spring on a stainless guide rod for my G20SF (Gen 3). It will cycle my lightest 40S&W loads and yet keep the slide from banging the frame on my nuke loads (i.e. 1300fps+ 180gr jacketed).
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Old 03-15-2015, 13:49   #5
USMC Riflecoach
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So WeeWilly, pardon me here if I am a little slow but I am confused. In your post you state I should try double mag. springs, as in "magazine", but in the PS you mention running a 22lb ISMI recoil spring. I agree the slide is out running the mag springs, so perhaps I need to look at increasing spring weight of the recoil sling and the magazine springs? Is this correct?
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Old 03-15-2015, 13:57   #6
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Originally Posted by USMC Riflecoach View Post
So WeeWilly, pardon me here if I am a little slow but I am confused. In your post you state I should try double mag. springs, as in "magazine", but in the PS you mention running a 22lb ISMI recoil spring. I agree the slide is out running the mag springs, so perhaps I need to look at increasing spring weight of the recoil sling and the magazine springs? Is this correct?
Sorry, TMI in a single post.

I suggested doubling magazine springs (2 stock springs) as a test. If the double magazine springs eliminate the problem you can try some extra strength Wolff magazine springs, these may be all you need.

In addition, I would run at least the 20lb recoil spring as I think it should cycle anything you want to shoot. I have found I can run 22lb ISMI springs and not affect the reliability. I think the ISMI flat springs are a little lighter than the round wire springs from companies like Wolff, so 22lb round wire might challenge the feed reliability on lighter loads.

WW
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Old 03-15-2015, 14:02   #7
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Willy that is very clear and and appreciate very much your expertise and help in this matter. First chance I get I will try the double mag spring test and see how it goes. Thank you!
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Old 03-15-2015, 14:57   #8
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Let us know how it is going, it helps all of us get a beaten path where one didn't exist prior.

Good luck.
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Old 03-15-2015, 17:36   #9
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With my work schedule it might be awhile before I get range time again but when I do I will let ya'll know.
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Old 03-16-2015, 01:27   #10
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I feel sorry for you trying to put the floor plate back on with two springs but I too am interested to know if it works. I've never seen that done but it sounds like a decent test. I'm impressed willy.
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Old 03-16-2015, 09:26   #11
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I feel sorry for you trying to put the floor plate back on with two springs but I too am interested to know if it works. I've never seen that done but it sounds like a decent test. I'm impressed willy.
Thanks, hopefully we shall see, it is just a guess.

I have seen extra power springs work in applications where guys are pushing slide velocities beyond where a gun was designed to operate. The G21 slide is lighter, so I would expect it is moving faster than a similar G20 might with equal loads.

While Double Tap is not as hot as others like Underwood or most guys home loads, it is still stout ammo.

I have seen heavier springs help feed in the G21 when loading hot 45 Supers and frequently when guys do a 460 Rowland conversion and the comp selected is less than perfect.

Doubling the stock spring is just a cheap way to see if a stronger spring will help the symptom. Definitely not an optimal permanent solution. Not sure how many rounds get sacrificed but I suspect at least one or two.

Definitely don't want to spend the money on heavier magazine springs until he gets an indication it is going to help.
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Last edited by WeeWilly; 03-16-2015 at 09:30..
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Old 03-20-2015, 08:51   #12
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Well I was ordering a bunch of stuff from Midway anyway so I picked up a Wolff 10 percent mag spring and a 22lb ISMI recoil spring. I thought this will do the trick for sure.... well kinda, had same issue but only about 1 out of 10. Sooo I guess its on to a 24lb recoil spring and if that does not work I think I got an expensive boat anchor.

I have a stock G20 that stuttered occasionally with the same Double-Tap load and I put the 20lb spring in it and now it runs flawless. I hope the 45 converted to 10MM with the KKM barrel will work out as it is much more accurate. However if I can not get it to feed 100 percent, well then the accuracy advantage is not worth it.
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Old 03-20-2015, 10:20   #13
WeeWilly
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Originally Posted by USMC Riflecoach View Post
Well I was ordering a bunch of stuff from Midway anyway so I picked up a Wolff 10 percent mag spring and a 22lb ISMI recoil spring. I thought this will do the trick for sure.... well kinda, had same issue but only about 1 out of 10. Sooo I guess its on to a 24lb recoil spring and if that does not work I think I got an expensive boat anchor.

I have a stock G20 that stuttered occasionally with the same Double-Tap load and I put the 20lb spring in it and now it runs flawless. I hope the 45 converted to 10MM with the KKM barrel will work out as it is much more accurate. However if I can not get it to feed 100 percent, well then the accuracy advantage is not worth it.
Bummer, I was hoping the 10% springs would get you over the hump. It does sound like it took you in the right direction. The 24lb spring will also slow things a little, at least in one direction , but hopefully that will be all you need to get things in tune.

The only negative the 24lb spring does to me is little higher felt recoil and I have to swap it out when I am shooting 40S&W level loads.

It is amazing what a little weight does to slide velocity.
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Old 03-20-2015, 11:24   #14
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One other thought, if you want to ensure the difference in slide weight is at the root of the difference in reliability you are seeing, you can add weight to the G21 slide.

The G21 slide weighs 22 grams less than the G20 slide, with all that weight in the front half of the slide. You could tape 2 nickels to each side of the slide in the front half of the G21 slide and you would have essentially eliminated the weight difference.

The comparison is not exactly apples for apples as the barrels weigh differently as well (smaller hole, more metal), but the above will get you close.
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Old 03-20-2015, 14:13   #15
USMC Riflecoach
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Funny you mention that, I was thinking about that this afternoon and was wondering how I could weight the 2 slides I have to find the difference. I did not think my digital powder scale could weigh that heavy. But you solve that part 22 grams... lets see that converts to 339.51 grains. I was wondering if the 24lb spring did not work could I polish the inside front portion of the slide to remove the finish and start adding spot welds with my mig to make up the weight... we are talking almost an ounce of weld. If I go turn the amps down and go slow and keep the slide from heating up to much... just thinking out loud here.
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Old 03-20-2015, 14:31   #16
WeeWilly
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Originally Posted by USMC Riflecoach View Post
Funny you mention that, I was thinking about that this afternoon and was wondering how I could weight the 2 slides I have to find the difference. I did not think my digital powder scale could weigh that heavy. But you solve that part 22 grams... lets see that converts to 339.51 grains. I was wondering if the 24lb spring did not work could I polish the inside front portion of the slide to remove the finish and start adding spot welds with my mig to make up the weight... we are talking almost an ounce of weld. If I go turn the amps down and go slow and keep the slide from heating up to much... just thinking out loud here.
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I think I would test with taping the nickels or maybe a stick on wheel weights (11 grams of lead on either side won't be very big), before I went to welding on the slide.
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Old 03-21-2015, 14:33   #17
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Of course a test would be in order but if the test was a success, then I would be looking for a more permanent solution, unless I wanted to go around with a bunch of change glued to my slide,lol!
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Old 03-21-2015, 16:40   #18
WeeWilly
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Of course a test would be in order but if the test was a success, then I would be looking for a more permanent solution, unless I wanted to go around with a bunch of change glued to my slide,lol!
I think if a little added weight with some taped weight worked, I might look into something like nickel silver brazing of additional material. It would put less heat into the slide, maybe preserve the heat treating a little better.

If you have access to a mill, you could braze some on the inside and then mill it back so everything cleared.

I agree that super gluing nickels on the outside, while definitely adding a certain bling factor, might be misconstrued by some, not to mention the difficulty in finding a holster that might work.
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