BayouBob Posted October 11, 2012 Report Share Posted October 11, 2012 Am I overlooking something? My CMMG Mark 3 has an A2 stock and buffer assembly. (One of CMMG's fruitless attempts to correct the overgassed issue.) I put an adjustable gas block on the rifle and am now able to regulate the action for my chosen load. The buffer spring CMMG put in the stock must have come off the shock absorber for a 3/4 ton truck. It binds against the bolt catch so hard it takes both hands to push the release. The catch already has a groove worn in it from the pressure of the bolt coming to rest on it.Since I can tailor the amount of gas and therefor the violence of the bolt carrier movement shouldn't I be able to use a lighter power spring to relieve some of the pressure on the bolt catch? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 11, 2012 Report Share Posted October 11, 2012 I'd say, just get the Armalite spring and run it. Just make sure it's the AR-10 spring. <thumbsup> Quote Link to comment Share on other sites More sharing options...
washguy Posted October 11, 2012 Report Share Posted October 11, 2012 Hi bob I'm liking the tubbs spring it fits either a2 or cars wash Quote Link to comment Share on other sites More sharing options...
survivalshop Posted October 11, 2012 Report Share Posted October 11, 2012 I'm running a Tubbs( Superior Springs ) spring in my 16" AR 308 with collapsible stock ,with no problems. Its a little fun to get in there the first time ,but works & I think works well. Some say they don't last ,but it seems smoother running than the stock DPMS carbine spring I had in there. It was just a trial set up & I kept it in there & am continuing its testing . Stock DPMS carbine buffer is still in there also . Quote Link to comment Share on other sites More sharing options...
BayouBob Posted October 12, 2012 Author Report Share Posted October 12, 2012 Have you guys noticed an unusually heavy pressure on your bolt catch? Quote Link to comment Share on other sites More sharing options...
washguy Posted October 12, 2012 Report Share Posted October 12, 2012 Have you guys noticed an unusually heavy pressure on your bolt catch?Hey Bob Nope none of mine have any unusual pressures :) Wash but whats up with yours? Quote Link to comment Share on other sites More sharing options...
BayouBob Posted October 12, 2012 Author Report Share Posted October 12, 2012 To release mine it takes what feels like 30 or 40 pounds of pressure on the release. It has been that way both when it had the carbine stock and even worse with the A2 stock. I have put high temp bearing grease on it to smooth it but it helps very little. The bolt catch actually has a groove worn in it from the bolt hitting it. I've got around a thousand rounds through it and it still feels like it is trying to tear itself apart. The only solution to the heavy release effort I can think of is a lighter spring. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 14, 2012 Report Share Posted October 14, 2012 There;s definitely something up with that spring you have - it certainly shouldn't take that much force to release the bolt. Quote Link to comment Share on other sites More sharing options...
BayouBob Posted October 14, 2012 Author Report Share Posted October 14, 2012 CMMG seems to think it is no big deal. I have owned 11 other AR's in various calibers (This is my first 308.) and Uncle Sam let me play with M1's, M14's and M16's. I have never seen a bolt catch that was under pressure remotely like this. I am going to put a standard A2 spring in it just to see if it is only the spring that is the cause. The adventures sure do continue with this rifle. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 14, 2012 Report Share Posted October 14, 2012 I am going to put a standard A2 spring in it just to see if it is only the spring that is the cause. 5.56 A2 spring? Don't do that... Quote Link to comment Share on other sites More sharing options...
survivalshop Posted October 14, 2012 Report Share Posted October 14, 2012 5.56 A2 spring? Don't do that... Yes, I would not fire the rifle with a std A2 ,AR 15 spring in it , but to see if it truly is the spring pressure making it so hard to release the bolt stop , go ahead , just to test it. Ya never know , it could be a bolt stop fitment problem . I have seen it before .There is definitely a difference in the two types of springs ( AR 15 & AR 308 ) Quote Link to comment Share on other sites More sharing options...
BayouBob Posted October 14, 2012 Author Report Share Posted October 14, 2012 What is interesting is that CMMG says all their 308's are like that. I may also replace the bolt catch. Does anyone know if the bolt catch is a surface hardened part? If it is not, I could try polishing it to see if that is the problem. It could also be a fault in the bolt. Quote Link to comment Share on other sites More sharing options...
BayouBob Posted October 16, 2012 Author Report Share Posted October 16, 2012 Curiouser and Curiouser. I swapped out the spring from my Sig M400 A2 with the spring in the Mark 3. (The Sig bolt catch release is smooth as glass.) The spring from the Mark 3 in the Sig was a little heavier to release but still smooth. The spring from the Sig in the Mark 3 was a little easier to release but still took quite a bit of pressure, much more than when it was in the Sig. That tells me that at least part of the problem is the contact between the bolt and the catch. I guess the next step is to get a new bolt catch and see if that makes a difference. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 16, 2012 Report Share Posted October 16, 2012 Separate the upper and lower - does the bolt catch cycle smoothly? Nothing on it at all, no pressure from a mag, no pressure from a locked-back bolt - is it rough in it's mount in the lower? Quote Link to comment Share on other sites More sharing options...
tg4360 Posted October 16, 2012 Report Share Posted October 16, 2012 Is it possible that the rear face of the bolt catch is rough or has a burr on it?What we need here and across the board is real DATA on buffer spring weights for the various platforms.Knowing what a manufacturer supplies or recommends for their particular rifles and then working from there would go a long way to eliminating the guess work going on.It "feels" like the rifle is doing such and such is not as good as knowing it's right.The original system was to not have an adjustable gas system so they must have figured out buffer weight and spring rates to keep the bolt closed during the time of peak chamber pressure.Knowing this is one thing and I wish I had the time/resources to do the research. Quote Link to comment Share on other sites More sharing options...
washguy Posted October 16, 2012 Report Share Posted October 16, 2012 Hi Tg I believe Slashes buffers has a spredsheet on just what you are looking for...go check it outI dunno why folks have troubles with buffer springs and what not... especially when they buy them new from the mfg?Ive built five mega 308's this last year and have never ever had a buffer/buffer spring problem nor a bolt catch prob...I always just use the plain ol buffer and buffer spring,but on a couple I tried the Tubbs flatwire spring and no problems with that one either. In a lot of cases it seems lack of lube in a rifle and using crap steel cased ammo will give you cycling problems. :) Wash Quote Link to comment Share on other sites More sharing options...
BayouBob Posted October 23, 2012 Author Report Share Posted October 23, 2012 Figured it out. The buffer spring appears to be a standard DPMS 308 heavy spring with 39 coils. The bolt catch was evidently a plain AR-15 catch. The flat part of the catch that sits down in slot of the receiver was just a little thinner than the slot was wide. That allowed it to lean a little bit toward the front of the receiver when the bolt pushed on it with the heavy spring causing the catch to bind and not want to move out of contact with the bolt and causing the bolt to wear a groove in the face of the catch. I replaced the catch with a DPMS purpose built AR 308 bolt catch. The DPMS catch is just a tiny bit thicker than the one that came on the rifle so there is no slop in its fit in the slot. Instantly, without even polishing the face of the catch, the pressure on the button to release the bolt catch dropped by 2/3. It takes just a little more effort to push the bolt release than on an AR-15. I can still tell there is a strong spring pushing against it but it is smooth.I have passed my observation on to CMMG since they didn't seem interested in addressing the issue. Quote Link to comment Share on other sites More sharing options...
washguy Posted October 23, 2012 Report Share Posted October 23, 2012 Way To go Bob! Those nitwitts at cmmg shouldnt be allowed to build a bb gun ! Good for you! :) Wash Quote Link to comment Share on other sites More sharing options...
unforgiven Posted October 23, 2012 Report Share Posted October 23, 2012 Thats great news brother Bob. <thumbsup> Quote Link to comment Share on other sites More sharing options...
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