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Posted: 7/23/2013 6:08:43 PM EDT
| Has anyone had a problem with a .308 bolt catch not holding the bolt back or holding bolt on last round? I have replaced bolt catch and tried a lighter buffer spring. Any suggestions? All else function great. John |
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Yep. Usually a magazine issue.
I'm guessing you are using a bolt release made specifically for .308's? If so, drop a few drops of oil in there with it and make sure it works smoothly. How is the spring tension on it? If that's all good to go, try some different magazines. Shoot one round at a time and see if it locks back. |
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http://www.calguns.net/calgunforum/showthread.php?t=787058 This guy had one break. But it looks like there is a specific .308 catch that isn't always used depending on who made the lower. |
| To Mathecb - No, the bolt won't lock manually with buffer installed. It will without buffer. Perhaps buffer length. Using a Magpul MOE straight rifle stock, Armalite buffer and spring. Going to try a DPMS buffer. Upper is a DPMS on a QD lower and DPMS lr308 LPK. Shoots great, except for the bolt catch issue. |
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Are you using the Armalite spring with the DPMS buffer? If so get the correct DPMS sping too
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Nope. Not the buffer. The bolt catch does not catch the bottom of bolt. Gonna try shimming it. If that works, I'll try and build up the bolt and heat treat it. Unless someone has an oversized one. |
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Don't go messing up your bolt.
You said it does lock back without the buffer? Make sure you're using a 308 specific buffer and spring, not the AR15 ones. The AR10/308 buffers are around 5 1/4" long. The AR15 buffer is almost 6" long. An AR10 buffer spring is around 13.75", with about 34 coils. A DPMS 308 buffer spring is around 12.75", with about 39 coils. The AR15 buffer spring is around 12.75", with about 44 coils. If that's not the problem, check to make sure you didn't use too long of a screw in your stock. If it's too long, it'll keep your bolt from going into the tube far enough to clear the catch. Loosen it up and see if you get the extra travel you need. And if all else fails, you said it's a Quentin Defense lower. Was it an 80% lower? If so, you might want to check how much travel the bolt catch has. Some of the QD 308 80%'s have had a problem with the bolt catch plunger hole not being drilled deep enough, so the bolt catch isn't coming up high enough to catch the bolt. With the upper off, push the bottom of the bolt catch paddle all the way in to lift the bolt catch up. Use a caliper to measure how high the bolt catch sits up from the top of the lower. I don't remember off the top of my head what it is exactly, but IIRC it should be right around 0.50" (1/2"). I'll have to double check tomorrow. Good luck. Hope this helps. |
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Quoted:
Nope. Not the buffer. The bolt catch does not catch the bottom of bolt. Gonna try shimming it. If that works, I'll try and build up the bolt and heat treat it. Unless someone has an oversized one. Don't go jacking with parts, especially no the carrier. Like mentioned above, you have the wrong combo of parts or have a receiver issue. It may help to be a bit more specific. EXACTLY what parts are you using? |
| QD 80% lower built to 100% per specs. DPMS lower parts kit (308), DPMS complete upper, Now with DPMS 308 Rifle Buffer, spring, tube with Magpul MOE fixed stock. Meant to say was going to build up Bolt Catch. Will check on bolt catch movement and depth of spring hole and report findings. Bolt catch presently does not appear to lift high enough to catch bolt when looking thru ejection port. It may be as simple as drilling spring hole deeper. Who knows? |
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Quoted:
QD 80% lower built to 100% per specs. DPMS lower parts kit (308), DPMS complete upper, Now with DPMS 308 Rifle Buffer, spring, tube with Magpul MOE fixed stock. Meant to say was going to build up Bolt Catch. Will check on bolt catch movement and depth of spring hole and report findings. Bolt catch presently does not appear to lift high enough to catch bolt when looking thru ejection port. It may be as simple as drilling spring hole deeper. Who knows? You could have saved me a lot of typing if you had put all this info in your original post 
I measured out 4 different lowers and was getting a bolt catch height of 0.51-0.55". Measured height with empty mags pushing up on the bolt catch was 0.474-0.475". So if you measure anywhere above 0.475", it should work correctly. |
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On some Quintin 308 lowers the dims from the top deck to the bolt catch step and plunger hole are off by .010" to .015"
and will sometimes cause Issues with the bolt not locking back once the mag is empty such as your situation...Check the gap between your upper and lower receivers, it should be around .004"/.007" but not much more than that, if it is then your lower is likely out of spec. |
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Quoted:
Got the specs for the bolt catch spring hole from QD yesterday. Going to measure today. If it's w/I specs, the lower is off. QD said they will work with me on it. I'll post results. Dealt with them on a few custom jobs, great guys, they will take care of you. |
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Quoted:
Got the specs for the bolt catch spring hole from QD yesterday. Going to measure today. If it's w/I specs, the lower is off. QD said they will work with me on it. I'll post results. They had told someone else who had the same problem that the depth was suppose to be around 0.40". But that's not deep enough, it should be closer to 0.50". So what depth did they tell you it should be? |
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Quoted:
.38 but should function .361 to .40. Haven't measured yet. They have to be giving you the measurements for something else. The plunger alone is about 0.422" and wouldn't go in completely at those depths. I'd call them back and ask them again to make sure they weren't thinking you were talking about something else. |
| Okay, here goes. Measured bolt catch spring hole depth. It was 0.40". I increased depth to 0.47" gradually. 0.47 gave me 0.50" rise. Catches bolt as it should using charging handle as well as with both magazines checked empty and with last round fired. I am now a happy camper. Thanks for all of your input. |
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