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Posted: 11/10/2013 8:25:00 AM EDT
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I bought a CMMG 22 LR Upper at the Knob Creek MG Shoot last month. It has the SS bolt assembly and a plastic fwd bolt assist/ anti-bounce thingie. I put it on a Plum Crazy lower I have with a rifle buffer tube and A1 stock. I also installed a polymer plug in front of the buffer that is supposed to help keep forward pressure on the bolt. The next weekend I went to the range and had so much trouble I didn't even use an entire 25 rd mag in it. I had noticed when I cleaned it that the fwd bolt assist thing tended to make the action less than smooth so I just toke it out. I already had 3 CMMG Mags (made by Black Dog for CMMG I think, and I picked up 2 Brownwell's 25 rd Black dog mags. All of the mags seem loose in the magwell....alot of fore and aft movement. Friday morning I went back to the range. I brought several different types of HV .22Lr (Speer AR Auto Match (plated), Fed Auto Match (unplated), Rem Golden Bullet (HP), CCI Mini mag (Round Nose). The rifle worked much better without the bolt assist thingie in it. Still had alot of failure to chamber resulting in bent tips, ect. The Rem HP's failed to feed every 3 to 4 rounds. CMMG recommends round nose ammo for best results but I had them and tried them anyway. The CCI Mini mags were the biggest surprise. I had numerous failure to fully seat rounds. I had to work the charging handle 2 or 3 times to get the bolt to close maybe 8 or 9 different times for 2 mags of 20 rds each. On one of my last mags (not the CCI MIni mag rounds) I either had a slam fire where it fired out of battery or the rim blew off the round. Quite a surprise. We managed to get the casing out of the chamber and as there was no apparent damage to the upper I fired off the rest of the mag and one other. The rifle did not fire a complete mag without some kind of failure to feed throughout some 250 to 300 rds fired. The most I fired without a failure was 18 from 1 magazine. I did relube it about halfway through the session.
Any thoughts on getting better reliability? I thought so putting some duct tape on the mags to get them to fit-up tighter. |
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2nd post in two days about failure to chamber on CMMG uppers.
Makes me wonder if the chambers are off. Make sure you are not resting the rifle on the mags. It will change the angle of the feed lips if the mags are loose. Check the chamber for burrs. Oh, and Black Dog would never build mags for CMMG 
Dave N |
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Well Bob, it may very well be a chamber issue but I don't think that's it.
I'm thinking something much simpler that I have experienced with CMMG Barrel Collars. Easy test. Remove the upper from the lower so there is no chance of the hammer falling. With the ejection port cover open and the bolt held to the rear, ease a round into the chamber. I use the blue proof of action dummy rounds but a live round will work just as well - keep the muzzle pointed in a safe direction. Now look closely at the ramp. Is it too high, thus keeping the rim from going to the breech face? Sometimes the collar's ramp is too high and the cartridge can't go all the way into battery. There should be no - zero - gap between the cartridge rim and the breech face. This gap will cause the rim to be too close to the bolt and cause OBD's and/or a case bulge directly forward of the cartridge case rim. It is an easy fix, with patience and using the dreaded Dremel Tool, or a jeweler's rat tail file, lower the "U" at the top of the ramp being very careful not to remove too much material. It is easiest to perform this task with the bolt/collar assy held in a vise, accessing the "U" from the front of the collar. Stop every so often to test, if the rim clears the ramp and is tight against the breech face, you're done. This is an easy test you can do in about ten minutes. If this isn't it, well, then you lost ten minutes. Hope this helps, Ted |
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I count myself lucky - almost all my conversions work well with good ammo - mostly CCI MiniMag and SV.
The CMMG left hand dedicated upper I bought has not issues - other than the backing plate weld cracking and unreliable ignition with target triggers. The Kuehl and Spikes dedicated uppers also have no feeding issues. Loose mags in my uppers and conversions seem, in my experience, to feed better. I'm talking the Ciener type conversions. Ciener steel, CMMG and BD mags - all feed better when there is a little play. I once tightened the Ciener steel mags - the sheet steel can be bent to make a nice, snug fit in the magwell. Feed problems galore. I bent the sides back in to loosen things up and functioning was 100%, YMMV |
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Quoted:
Well Bob, it may very well be a chamber issue but I don't think that's it. I'm thinking something much simpler that I have experienced with CMMG Barrel Collars. Easy test. Remove the upper from the lower so there is no chance of the hammer falling. With the ejection port cover open and the bolt held to the rear, ease a round into the chamber. I use the blue proof of action dummy rounds but a live round will work just as well - keep the muzzle pointed in a safe direction. Now look closely at the ramp. Is it too high, thus keeping the rim from going to the breech face? Sometimes the collar's ramp is too high and the cartridge can't go all the way into battery. There should be no - zero - gap between the cartridge rim and the breech face. This gap will cause the rim to be too close to the bolt and cause OBD's and/or a case bulge directly forward of the cartridge case rim. It is an easy fix, with patience and using the dreaded Dremel Tool, or a jeweler's rat tail file, lower the "U" at the top of the ramp being very careful not to remove too much material. It is easiest to perform this task with the bolt/collar assy held in a vise, accessing the "U" from the front of the collar. Stop every so often to test, if the rim clears the ramp and is tight against the breech face, you're done. This is an easy test you can do in about ten minutes. If this isn't it, well, then you lost ten minutes. Hope this helps, Ted Thanks Ted....the round I had the slam fire with exhibited a bulge just in front of where the primer was before it got nearly blown clean off. |
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That is typical of the cartridge not fully seating in the chamber. There are
several causes: 1) See my posting re: ramp 2) The chamber is tight. 3) Head space is bad. 4) Extractor is too long or the "cut" is too shallow. 5) Extractor is binding on the walls of the cut. 6) Someone over chamfered the breech face causing the cartridge rim to not be supported 360 degrees. The case will bulge in the area where the edge of the breech face has been removed. 7) Remove gunk or carbon from bolt face and under extractor hook. If it is a tight chamber the "buzz" may help remove any burrs. Head Space issues? Don't shoot it, take it to a gunsmith, same for extractor issue. Improper breech face issues, again gunsmith. Other than that, without seeing your gun I'm afraid I'm out of options. Ted |
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