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Posted: 11/2/2009 7:09:27 PM EDT
First off I want to thank SpecOps-13 for mentioning in a thread that the CMMG bolt/barrel collar was .460 compared to Spikes barrel collar being .500. I pulled out my Dedicated DPMS M-4 dedicated upper and measured the bolt collar opening. My DPMS bolt collar opening measured .460 and the barrel extension inside the upper measure .450. I called CMMG technical and they answered a couple of questions for me in regards to their dedicated uppers. I decided to order a CMMG collar and received it today. Just as I expected the collar fit my barrel just like it was made for it expect for the cut in the side of the barrel for the extractor. As soon as I can enlarge the extractor cut on the ejection port side of my barrel I think I will be able to test fire my DPMS dedicated upper using a Ciener/CMMG conversion bolt. This is a simpler solution than trying to make a spacer to work with a Spikes bolt with collar. I really like spikes nickel plated bolt but this is a very easy fix to enable a shooters to use the high capacity mags with their DPMS dedicated uppers. The price of the collar is a few cents less than $50 including shipping but that is still cheaper than several high capacity mags if they are ever produced for the DPMS/Colt conversions. Since I already had numerous BDM high capacity mags and a Ciener conversion kit this worked out great for me. I had been planning on trying to adapt my DPMS dedicated upper for some time to use a Ciener pattern bolt but hadn't done it. Thanks again SpecOps-13 for the valuable info. AR15.com has come through for me again! One other thing to mention, if anyone else would consider this mod, remember to back out the set screw on the bottom of the CMMG Collar so the collar will slide on the barrel extension. With this set screw I feel sure this would help compensate if the original DPMS barrel extension was a little smaller than mine. The feed ramp on the CMMG collar appears to line up perfectly with the chamber on my DPMS barrel so hopefully I'll get to test this modification this week.
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| I had time to modify the extractor groove on the ejection port side of the barrel to accept the Ciener bolt. The DPMS uses two extractors and the one on the the ejection port side is at about the 2 O'clock position. The Ciener extractor sits at the 3 O'clock position so you need to modify the side of the barrel for the Ciener extractor claw to rest. I put some duct tape on the side of the upper so I wouldn't mar the finish. I used a flat file and a large flat round disc on a dremel tool to remove the steel. I cleaned the upper then conducted a test fire. The modification works like a charm and was close to 100% reliable with Federal bulk. I had a couple of failures to fire but I don't think this was because of the modification. Extraction was brisk and the bolt seemed to go completely into battery. This firing pin has many thousands of rounds on it and may need replaced. I could see no change in point of aim or accuracy. For anyone who has a DPMS dedicated upper and would like to use a higher capacity mag this is very worth while modification. If a person didn't have a Ciener or CMMG conversion kit a person can order a CMMG conversion bolt with the barrel collar. I didn't have time to get pics but the only technical part was enlarging the cut out for the extractor claw. As long as you go slow its not that difficult. Being able to use the BDM with BHO follower is another plus. I see no reason why I could not switch back and use the DPMS bolt if I so desired. I am one very happy dude! Thanks again for the info SpecOps-13! |
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There have been people doing this mod for some time now, but it required them to make their own barrel adapter. It sounds like a good thing for you that the CMMG adapter was pretty much GTG as is and should make it easier for those that have a DPMS kit to update it to use BDM/Ciener style mags.
I'm not sure why Spikes didn't go ahead and offer DPMS adapters when this topic came up months ago. |
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Quoted:
Because it requires a barrel modification which, although not at all difficult, is beyond the manufacturer's control. So some meatball screws up his barrel and blames the guy who made the part. That's the reality of product liability in the US today. Funny how many manufacturers have been selling "gunsmith fit" 1911 parts for a long, long , long time now and you don't hear the stories you describe... Maybe there's just more "meatballs", as you say, in the .22/9mm AR world 
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Looking at CMMG's on-line catalog I foound this part. Is it the one I need?
.22 Dedicated Chamber Adapter For the dedicated .22 upper or barrel. Allows our .22 conversion kit to fit the dedicated .22 barrel. Set screw holds kit in place. Chrome-Moly. SKU Number:22-170 Price: $39.95 |
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Quoted:
Looking at CMMG's on-line catalog I foound this part. Is it the one I need? .22 Dedicated Chamber Adapter For the dedicated .22 upper or barrel. Allows our .22 conversion kit to fit the dedicated .22 barrel. Set screw holds kit in place. Chrome-Moly. SKU Number:22-170 Price: $39.95 Your correct, sku # or part number 22-170 price $39.95 shipping $10 total $49.95. I ordered mine on line Thursday IIRC and got it on following Monday. The collar was shipped via UPS in a padded envelope. Hopefully I'll get to the range this week and run a few hundred more rounds through my DPMS using the Ciener conversion with CMMG collar. I think my DPMS is going to see a lot more use.
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Quoted:
Just to be sure I have this right as I really like my DPMS dedicated M-4 upper. I have a CMMG conversion that I use in a 5.56 AR. I just need to buy a CMMG collar and then fit in the extractor. Is this right? Thanks, John Yes the CMMG collar should fit your DPMS barrel but you will need to enlarge the ejection port side extractor claw groove. Its simple to measure the opening of your DPMS barrel collar. Mine measured .460 and the barrel measured .450. I would have done this sooner but I thought all the barrel collars were the same size of .500(which is more difficult to accomplish). For whatever reason CMMG went with the smaller barrel diameter which is great for those with DPMS uppers. Let me know if you need anything further. |
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I took my DPMS upper to the range today and had no extraction or feeding problems but I got a couple of failure to fire. I pulled the bolt out and disassembled it. I pulled the firing pin and the tip which the firing pin spring slides on had broken from the firing pin barrel. I replaced the firing pin and it runs like a top now. I guess its time to order some new firing pins from BDM. I figure the last pin had 15,000 rounds on it. I know this rifle is going to get a lot more use now. I should have done this mod a long time ago.
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Quoted:
I took my DPMS upper to the range today and had no extraction or feeding problems but I got a couple of failure to fire. I pulled the bolt out and disassembled it. I pulled the firing pin and the tip which the firing pin spring slides on had broken from the firing pin barrel. I replaced the firing pin and it runs like a top now. I guess its time to order some new firing pins from BDM. I figure the last pin had 15,000 rounds on it. I know this rifle is going to get a lot more use now. I should have done this mod a long time ago. Glad you got this done. I modified my DPMS upper to run on a Ciener Kit a year ago - I converted an old Ciener chamber adaptor for mine. I have since used my DPMS upper a lot more than I would have had I left it "stock". Enjoy! Brad |
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