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+--- Thread: Failure to lock bolt!!! (/showthread.php?tid=9402)
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Failure to lock bolt!!! - martkin64 - 05-25-2015
Hey guys,
I have been reading through these posts for a little bit now. Nice Forum! I have just recently finished building my Grendel. I will be posting pics as soon as I put the bi-pod on. Any way the upper and lower are Mil Tac billet with DPMS lower parts kit.The barrel is A Deadshot barrel from Oregon 19 " with a 2" milled compensator and match bolt, nickel boron carrier.... I will send pics soon.. But I shot the first 20 rounds through it and I had feeding issues, and the bolt would not lock back to the rear. The mag is an AR Stoner 10 rnd. I took it to a trusted gun shop and they found that the gas port was at .91 They stepped it up in increments and shot it until it worked... It did not work until .99 .... I took it it out again and fired 40 rnds... Fed just fine but still did not lock back on the last RND... You guys have any suggestions for me?
I would appriciat your input.
Failure to lock bolt!!! - achristian8 - 05-25-2015
I had that issue with a 6.8 spc barrel from AR perfomance. It also had to be drilled out. The very first thing I would do is check the gas block alignment. If it is fine go over the gas tube and the gas rings on the bolt. I'm sure someone on here can tell you the gas port size for the grendel. It may just have to be bigger. Did you only use one mag.
Failure to lock bolt!!! - martkin64 - 05-25-2015
I did only use one mag... I have a friend coming over this weekend with his, and I am going to shoot that one.. The gas port size is a little big but within the allowable size. The gas block alignment is good now, it was a little out but was test fired after it was fixed.. Still had issues. That's when the port was drilled out. I will check out the rings on the bolt.. Do you have a different mag company in mind? Thanx.
Failure to lock bolt!!! - NugginFutz - 05-25-2015
Well, first I think that you're calling the port diameter incorrectly, because .99 is nearly 4x the bore diameter.
Secondly, even at .099", that's a decent port diameter. I'm not certain what the recommended gas port size is for an 19" barrel, but it seems to me you're right about there. It also depends on what your gas length is... Mid, rifle or custom. It seems to me that at 19", an RLGS would be appropriate.
Before modifying the weapon or drilling any more, I'd try a different magazine. While failure to lock back is usually associated with being under gassed, checking with another magazine is a reversible step, whereas drilling the port bigger is not.
I'd also suggest ensuring your BCG travels without friction or interference. Yes, I see it is NiB, but some coatings are a bit thick and can initially cause binding. (Worse, some cheaper ones flake after a short while.)
I'm sure the rest of the horde has some thoughts on the subject, and will chime in soon.
Good luck!
Failure to lock bolt!!! - martkin64 - 05-26-2015
Thank you NugginFutz!! I am going to try another mag next week... I am sure you are right. Now that the feeding issue is fixed I do not want to drill any more. I'm even been thinking of getting some less expensive wolf ammo and just breaking it in a bit more..
Failure to lock bolt!!! - arnie - 05-26-2015
I don't see where you mention this ,but does the BCG lock back when its pulled back with the charging handle ? Also do you have the stock bolt lock .I have had trouble with a few fancy finger operated bolt lock extensions that for some reason wouldn't let the BCG lock back . Too much mass to move I guess.
Failure to lock bolt!!! - martkin64 - 05-26-2015
The bolt does lock back when I pull the charging handle back and holds oped until I release it. The bolt lock is the one that came with the the kit, DPMS lower parts kit and the Magpul upper parts. I have also read that the buffer spring might play a part in this. But it is a Magpul Stock, so I'm not sure.
Failure to lock bolt!!! - terrywick4 - 05-26-2015
I had this issue and it was because the gas block was not aligned properly with the hole for it in the barrel.
Failure to lock bolt!!! - Keep The Change - 05-26-2015
Checks i would make.
-swap mags. Try an AA mag if possible.
-swap ammo. Are you using good quality ammo?
-try lighter buffer spring or weight
-check fit of carrier and lube up
-check gas block alignment
I hope is an easy solution
-KTC
Failure to lock bolt!!! - martkin64 - 05-26-2015
Keep The Change Wrote:Checks i would make.
-swap mags. Try an AA mag if possible.
-swap ammo. Are you using good quality ammo?
-try lighter buffer spring or weight
-check fit of carrier and lube up
-check gas block alignment
I hope is an easy solution
-KTC
I will get an AA Mag... I am using Hornady A max, I will look into a lighter buffer spring. Carrier and lube are good to go. Gas block alignment are good as well.... I will order an AA mag tomorow... Are they the better mags?
Failure to lock bolt!!! - montana - 05-26-2015
.094 is the recommended gas port size for a rifle length gas system. .076 to .078 is for a 18" barrel MLGS.
Failure to lock bolt!!! - cory - 05-26-2015
You beat me to it Montana. That gas port seems oversized.
Any chance you have your gas block all the way against the shoulder? If not how much of a gap are you leaving? This seems like the gas block is misaligned or there's some debris in the gas tube or block, constricting the flow. What brand gas block and tube are you using?
Before you do anymore machining I'd confirm that your mag isn't the culprit. You should think about listing your location. There maybe someone on the forum that's nearby you that had a mag or two you could try out. Or someone that's intimately familiar with the AR15 and Grendel that could give you build a look over.
Failure to lock bolt!!! - Keep The Change - 05-26-2015
martkin64 Wrote:I will get an AA Mag... I am using Hornady A max, I will look into a lighter buffer spring. Carrier and lube are good to go. Gas block alignment are good as well.... I will order an AA mag tomorow... Are they the better mags?
The 6.5 Grendel is (Bill) Alexander Arms brain child (it's a little more complicated than that) so he makes sure mag suppliers get it right. Basically if he is using it or recommends it for the 65 Grendel then I would listen and use what he is using.
I'd double check make sure the gas block isn't too far back or forward. It maybe aligned vertically but not horizontally. I'd maybe even change gas blocks to insure it isn't that.
Failure to lock bolt!!! - martkin64 - 05-26-2015
Keep The Change Wrote:The 6.5 Grendel is (Bill) Alexander Arms brain child (it's a little more complicated than that) so he makes sure mag suppliers get it right. Basically if he is using it or recommends it for the 65 Grendel then I would listen and use what he is using.
I'd double check make sure the gas block isn't too far back or forward. It maybe aligned vertically but not horizontally. I'd maybe even change gas blocks to insure it isn't that.
The Gas block is ok.. How would you go about cleaning the gas tube out?
Failure to lock bolt!!! - montana - 05-27-2015
Did you check your gas key on your bolt carrier to make sure it is tight and not leaking? Did you check the end of your gas tube button to make sure it is not worn and centered in your gas key?
Failure to lock bolt!!! - martkin64 - 05-27-2015
montana Wrote:Did you check your gas key on your bolt carrier to make sure it is tight and not leaking? Did you check the end of your gas tube button to make sure it is not worn and centered in your gas key?
I just checked the BCG and it looks ok and tight.... But I did notice that there is a little bit of black carbon/ soot...just forward of the gas block itself. I have always shot AR's with black barrels... This one is FDE so I don't know if this is normal.
Failure to lock bolt!!! - montana - 05-27-2015
I have seen carbon behind the gas block where the gas tube enters the gas block but never in front. I would remove the gas block and put some blue loc-tite around the gas port of the barrel to seal the gas block if your getting excessive leakage. Be sure to avoid getting any loc-tite in your gas port. All of the gas blocks I have used have always had a tight seal without using blue loc-tite but yours may need it. Which gas block are you using?
Failure to lock bolt!!! - Keep The Change - 05-27-2015
martkin64 Wrote:I just checked the BCG and it looks ok and tight.... But I did notice that there is a little bit of black carbon/ soot...just forward of the gas block itself. I have always shot AR's with black barrels... This one is FDE so I don't know if this is normal.
Ding Ding Ding Ding!!
I think you found the culprit. The gas block should be sealed up tight to force all pressure into tube.
What brand is gas block?
Is barrel polished at gb location?
Failure to lock bolt!!! - martkin64 - 05-27-2015
Keep The Change Wrote:Ding Ding Ding Ding!!
I think you found the culprit. The gas block should be sealed up tight to force all pressure into tube.
What brand is gas block?
Is barrel polished at gb location?
The gas block is a CMMG and the barrel is cerakoted.
Failure to lock bolt!!! - arnie - 05-28-2015
The magazine is what pushes up the bolt lock to stop the bolt open on last shot . How strong the spring is could make a difference .