Steve in Allentown PA Posted March 20, 2014 Share Posted March 20, 2014 (edited) In putting together a new rifle I've discovered that the CMMG bolt catch is too short to reliably engage Magpul magazine followers. Military issue mags do engage the bolt catch 100%. I'd like to get the Magpul mags to work 100% The pictures below illustrate the problem: As you know, the circled area in the picture below engages the magazine follower. This is a Colt bolt catch. This is a closer view of the engagement lug. Below is the same lug but upside down. It measures .27" from the body of the bolt catch to its tip. The CMMG is right around .265". Does anyone know where I can get a bolt catch where the lug protrudes from the body of the bolt catch more than this Colt? I'd be happy to get one that is 0.290" or longer and file it to fit. Edited March 22, 2014 by Steve in Allentown PA Link to comment Share on other sites More sharing options...
reptoid Posted March 20, 2014 Share Posted March 20, 2014 You might want to look very closely at your Magpul mags. I had 3 brand new 10 rounders (mod 3) that had a small burr on the molded follower which caused the follower to hang up right at the top of it's travel. All rounds would feed but it wouldn't lock back reliably and if I racked the bolt slowly by hand it would never lock back. I pulled the follower's and sanded the molding burr off at the very back , reassembled, and viola they all work perfectly. Link to comment Share on other sites More sharing options...
Steve in Allentown PA Posted March 21, 2014 Author Share Posted March 21, 2014 I had 3 brand new 10 rounders (mod 3) that had a small burr on the molded follower which caused the follower to hang up right at the top of it's travel. I considered this at first but it's not the issue here. I held the bolt back as I looked down through the ejection port while I slowly inserted the magzines. The Magpul followers would just barely engage the tip of the bolt catch lug then slip past it. I can pin the blame on the the mags for not being mil-spec but the easiest fix is to install a bolt catch with a longer follower engagement lug. My problem is I have no idea which, if any, manufacturer makes a lug the length I need. Obviously, since I have one example of each in hand I know the Colt lug is longer than the CMMG, But I don't know about any of the others that are out there. Link to comment Share on other sites More sharing options...
MickB Posted March 21, 2014 Share Posted March 21, 2014 Is it possible your lower is out of spec in the bolt catch area? Mick Link to comment Share on other sites More sharing options...
Steve in Allentown PA Posted March 21, 2014 Author Share Posted March 21, 2014 Is it possible your lower is out of spec in the bolt catch area? Certainly could be. All the other pin holes and mag catch holes are fine so I'd be happy to only have to find a longer bolt catch lug. I'm getting the feeling that this is pretty much a non-issue with the guys here. Link to comment Share on other sites More sharing options...
reptoid Posted March 21, 2014 Share Posted March 21, 2014 You should have .050" to .070" overlap where the tip meets the mag follower; at least all of mine do. If the follower is able to slip past the bolt release on the front side you've got other issues. Either the follower is not being held in postion or the lower is not locating the bolt release properly. Most bolt releases are between .260" and .270" for the dimension in your photo. If you don't get the above overlap, I don't think it's the bolt release. Link to comment Share on other sites More sharing options...
Steve in Allentown PA Posted March 22, 2014 Author Share Posted March 22, 2014 Either the follower is not being held in postion or the lower is not locating the bolt release properly. Most bolt releases are between .260" and .270" for the dimension in your photo. If you don't get the above overlap, I don't think it's the bolt release. I managed to put the decimal in the wrong place in the picture. The measurment is actually 0.270". Assuming 0.270" is of the correct lug length then the receiver is out of whack. Oh goodie. Too bad nobody makes a longer than spec lug to allow an for an easy fix for an out of spec bolt catch recess. Link to comment Share on other sites More sharing options...
BBJones Posted March 22, 2014 Share Posted March 22, 2014 Who made the lower? Most companies will assist you if they made/sold a bad lower. Link to comment Share on other sites More sharing options...
Steve in Allentown PA Posted March 22, 2014 Author Share Posted March 22, 2014 (edited) Who made the lower? Most companies will assist you if they made/sold a bad lower. In fact I sent an e-mail with pictures to the company a few hours ago. I'll post the results of that communication. Edited March 22, 2014 by Steve in Allentown PA Link to comment Share on other sites More sharing options...
Steve in Allentown PA Posted April 15, 2014 Author Share Posted April 15, 2014 (edited) Who made the lower? Most companies will assist you if they made/sold a bad lower. In fact I sent an e-mail with pictures to the company a few hours ago. I'll post the results of that communication. Here's my update as promised. The company is in the process of making changes in their manufacturing process to address this issue and will swap receivers with me when the new ones come out. In the meantime I went ahead and modified a RRA 9mm bolt catch which works perfectly. See the pictures and write-up below. I substitutued "xxx" in place of the company name. No need to trash the company since they are new and working out the kinks inherent in a start-up operation. ------------------------------------------------------ I put together a lightweight AR using a BCM upper on a 3rd generation xxx lower and had no serious issues until I got to the bolt catch. The one that came in the CMMG LPK would not engage Magpul followers. So I pulled the bolt catch out of a Colt and put it in the xxx. Still no go. You can see the problem below. So I picked up a Rock River 9mm bolt catch, shortened the engagement lug and beveled the area where the one bolt lug hits it after the last round is fired. Worked like a charm. The rifle functions perfectly. The picture below shows the difference between the modified RRA and the stock Colt. "B" in the picture below shows the shortened follower engagement lug. "A"is the area that needed to be beveled. Before cutting the bevel as I hand cycled the action the bolt would be stopped by one of the lower bolt lugs engaging the bolt catch as the bolt moved rearward. The picture below is of the stock Colt bolt catch showing the streak where the bolt lug runs across the top after the last round is fired. The picture below shows how the modified RRA 9mm bolt catch engages a Magpul follower. The engagement lug does not interfere with the rounds but is long enough to engage the follwer correctly. I tested Colt, Magpul, and GI mags straight out of the arms room. All worked perfectly with this modified bolt catch. Edited April 17, 2014 by Steve in Allentown PA Link to comment Share on other sites More sharing options...
StarvinPilgrim Posted April 16, 2014 Share Posted April 16, 2014 Nice fix Steve. And good job on the write up & pics! Link to comment Share on other sites More sharing options...
tacticalCOWBOY Posted April 17, 2014 Share Posted April 17, 2014 This is a awesome thread this is great info. Thanks for all the pics Link to comment Share on other sites More sharing options...
Mark Gale Posted April 19, 2014 Share Posted April 19, 2014 Not trying to piss in the OP's Cheerios but... There is a reason the ramp highlighted in red is a part of a 5.56 bolt catch and not its 9mm counterpart. This fix for poor quality lower receivers has been tried many time over the years. Like all those who came before him, the OP is going to find out fast it won't last. Parts designed for a specific platform shouldn't be used in another. Link to comment Share on other sites More sharing options...
Steve in Allentown PA Posted April 20, 2014 Author Share Posted April 20, 2014 Not trying to piss in the OP's Cheerios but... Mark, Thanks for the heads-up. I totally agree with your thoughts. When I swap out this receiver for one of the new batch I'll let everyone know if they've corrected the problem. Link to comment Share on other sites More sharing options...
Steve in Allentown PA Posted May 19, 2014 Author Share Posted May 19, 2014 As promised, here's my follow-up report. The new 4th generation receiver that I swapped for my 3rd generation version has solved the problem of the bolt catch. Seems the recess in which the bolt catch sits was too wide which allowed the catch to rotate enough on its pin to be pushed out of engagement with the Magpul magazine follower. I've got a standard 5.56 CMMG bolt catch in there now and even though its magazine follower lug is slightly shorter than the Colt's, it's working correctly. FYI, the company making the receivers is Tennessee Arms Company and, as with any start-up operation, has had to work through teething issues. They post regularly on the Lightfighter forum where the members act as Beta testers. Looks like they've got everything squared away. I now have a soft shooting, mid-length, 16" barrel, less than 6lb carbine that runs like a raped ape. Wish I could have had one of these to hump through the boonies back in the day. Link to comment Share on other sites More sharing options...
bowhunt24 Posted February 7, 2020 Share Posted February 7, 2020 Hi Steve, are you still active on here? I know it's 6 years later, but I'm about to attempt this fix and had a couple questions. Cheers! - Evan (evan.e.moore@gmail.com) Link to comment Share on other sites More sharing options...
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