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Posted: 7/26/2009 10:56:26 AM EDT
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I really liked the idea CMMG had of adding a set screw to their 22LR conversion adapter collar. Holding the feed ramp in a fixed position on the chamber stub to help prevent any feeding problems makes a lot of sense.
So today I decided to try it. I pulled the upper from my most recent project and removed the optic. This is a Model 1 Sales dedicated 22LR barrel and chamber adapter collar. I used a ceiner kit I got from MidwayUSA when they still had them for $139.95. I measured the adapter collar thickness and determined a 8-32, 3/16 set screw would work just fine. I clamped the entire upper (it was a flat top upper receiver) to my drill press, and while pushing the ceiner kit all the way forward, I drilled a hole through the collar. I set the depth so that I only dimpled the chamber stub to help the set screw hold the collar in place. I took the collar of off the ceiner conversion and tapped it. I went ahead and pulled the barrel off, mounted the collar, and used the dremel to polish the chamber and feed ramp as one piece. I think it made it much easier to see if everything fit right. For the price of a set screw and a little of my time, this may be something really worth doing. I won't get a chance to test it out until week after next. YMMV, Dave 
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Quoted:
I really liked the idea CMMG had of adding a set screw to their 22LR conversion adapter collar. Holding the feed ramp in a fixed position on the chamber stub to help prevent any feeding problems makes a lot of sense. LOL That set screw is a fix for some sloppy machine work. If they would have machined the adapter collar and barrel to match nice and snug in the first place then a screw would not be needed. . |
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I think a ball detent would be better. So you need an allen wrench to pull out your bolt? No thanks!
This would help an issue I've discovered with .22 uppers on Cavalry Arms uppers, the rear of the lower is a little too long, leaving a gap between the upper and lower at the rear. .020-.030 too much gives light hits and misfires. I've actually bedded the rear of my lower with JB Weld. |
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The dpms lopro upper fixes the cavarms lower/upper gap right up. There is a very slight gap in mine. You bedded a cavarms lower with JB weld? Interesting. I don't run the buffer stop in my cavarms. I haven't noticed any problems. I have some FTE's but never any light strikes. |
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If the chamber adapter is machined to short then the whole 22 bolt/kit will be to short or if the barrel is machined to deep
were the collar/chamber adapter fits up against, then the whole 22 bolt/kit will be to short. When you put your 22 bolt/kit in the upper it should be a flush fit not a sunk in fit. it should look like this 
. notice the tab on the top of the 22 kit, that tab should be up against the lower receiver when closed and will keep the 22 kit snug against the barrel so it wont move when you pull back the charge handle, only the 22 bolt will move not the rails or the chamber adapter. 
The other problem is when the chamber adapter is bored out to big ID or the barrel is lathed down to small OD, then you get a sloppy fit. . If the barrel or extension is machined to short between these two lines then this can cause the 22 kit to be loose. 
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Just looked at my kit in my cavarms and the gap is definitely there. The lopro fills it at a bit better than a regular upper but it doesn't fix the bolt being able to move a bit back and forth. I put a couple small pieces of stovepipe tape on the top back of the bolt and that snugged it up. I wonder if it will make my occasional stovepipe go away. |
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notice the tab on the top of the 22 kit, that tab should be up against the lower receiver when closed and will keep the 22 kit snug against the barrel so it wont move when you pull back the charge handle, only the 22 bolt will move not the rails or the chamber adapter. Okay so I put three layers of stovepipe aluminum tape on that spot. I shot a ton of rounds today and not one FTE. 100% with 6 different types of ammo. Thanks for the heads up that really has made the gun a ton more reliable. |
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Quoted:
notice the tab on the top of the 22 kit, that tab should be up against the lower receiver when closed and will
keep the 22 kit snug against the barrel so it wont move when you pull back the charge handle, only the 22 bolt will move not the rails or the chamber adapter. http://i197.photobucket.com/albums/aa166/redtazdog/AR22kitfit17w.jpg Okay so I put three layers of stovepipe aluminum tape on that spot. I shot a ton of rounds today and not one FTE. 100% with 6 different types of ammo. Thanks for the heads up that really has made the gun a ton more reliable. Good for you!  sometimes a small mod can make all the difference.
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