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Posted: 6/10/2025 2:26:40 PM EDT
[Last Edit: jwf2874][Edited]
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brand new Grendel Build. While I know some will roll their eyes at this comment it was put together by a VERY good and detailed gunsmith. So i don't think there is operator error on the assembly. It's a 16" ballistic advantage stainless barrel. all components are brands i've used before. nothing off the wall. nothing fancy. standard low profile (not adjustable) gas block rifle shoots lights out accurate but of the 4 ammo's listed below only the Hornady Black locks the bolt back on last round 100% of time. And THAT is after changing to a reduced power buffer spring. Using a "yellow" reduced power spring and a carbine buffer. In the past when i've had similar grendel builds i've used h2 or h3 buffers and they ran fine. we've checked all the normal suspects. not seeing any "gas leaks". confirmed alignment of gas block, etc... I've tried AAC 123gr OTM, AAC Sabre Black tip 123 gr, Hornady V-Match 100gr ELDVT, and the hornady black 123 gr ELD. seems undergassed but can't sort it out. The AAC OTM won't cycle and and partially locks back. Sabre will cycle most of the time but partially locks back. Hornady 100 gr won't cycle or lock back. Hornady Black works 100%. Really wish the AAC 123 OTM would run because the accuracy from it is stupid good in this barrel (and it's cheap!!), but i don't need a single shot AR15. Would you just buy a buncha hornady black and call it a day? Is there an even lighter buffer spring (or buffer) to try than the yellow spring and carbine buffer that might work with the other ammo? Other ideas that don't involve buying another rifle or telling me Grendel is stupid? (i found an old post with a similar question and one of the responses was "tell him to buy a non-gay caliber". ) Help please. Really thought this was going to be the Cat's meow. |
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Need photo of spent case, including sides and spent primer to start with. Hence need to see if problem is chamber or over pressure, or if dealing with under pressure problem due to possible leak in the gas system or gas block passage not correctly aligned with the barrel gas port. On some of the gas blocks, they are made for front hand clip, while some are not, so you have to measure from barrel shoulder to center line of gas port, the same on the bolts, and some cases, the gas block need to be mounted with it slightly off the barrel shoulder to index the two port correctly without blockage. From there, need detail on the build parts, including charging handle pull test, to make sure face of bolt is stopping 1/8"~1/4" in front of back of ejection port back edge, and last inch of pull is the same tension as middle of the pull. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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Could be head spacing off to shoulder from bolt face (too tight), could be that last chamber cut is not deep enough, could be that leade is too short and causing bullet embed at loading, or could be cross wall demensions too tight, or even chamber wall lefts in reamer chatter state; a ll which can cause short stroking problems/will leave tell tell signs on the spent cases in one form or another. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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I had a similar problem with a BA barrel; 12.5” 6.5 Grendel. I finally decided it might be under-gassed, so I measured the gas port. I felt it was really small (sorry I don’t remember the exact measurement, it’s been a while), so I called BA. They said they made the port that size because they assumed it would be ran suppressed. I didn’t have any cans at that time. I drilled the port larger myself, and it ran perfect after that. I’ll see if I can find my notes and post the port sizes before and after. I ran a wooden dowel rod down the barrel and VERY gently drilled the port out. It’s not rocket science, you just don’t want the tip of the bit to touch the bottom side of the bore/rifling. Update, I found my notes. BA said the port should be .055”. I miked it as .050”. I drilled it to .073”. Again, this was on a BA 12.5” 6.5 Grendel barrel. You may have and need different sized port for a 16” barrel. |
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Originally Posted By wideglidejoe: I had a similar problem with a BA barrel; 12.5” 6.5 Grendel. I finally decided it might be under-gassed, so I measured the gas port. I felt it was really small (sorry I don’t remember the exact measurement, it’s been a while), so I called BA. They said they made the port that size because they assumed it would be ran suppressed. I didn’t have any cans at that time. I drilled the port larger myself, and it ran perfect after that. I’ll see if I can find my notes and post the port sizes before and after. I ran a wooden dowel rod down the barrel and VERY gently drilled the port out. It’s not rocket science, you just don’t want the tip of the bit to touch the bottom side of the bore/rifling. Update, I found my notes. BA said the port should be .055”. I miked it as .050”. I drilled it to .073”. Again, this was on a BA 12.5” 6.5 Grendel barrel. You may have and need different sized port for a 16” barrel. VERY helpful. I just reached out to BA and they said for this 16" midlength the gas port should be .073. we will get existing port measured. |
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Drilling gas port, is the last thing that you want to do, after you make sure nothing else is wrong with the rig to start with. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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Originally Posted By Dano523: Drilling gas port, is the last thing that you want to do, after you make sure nothing else is wrong with the rig to start with. <This. Metal once removed, can never be replaced. There is nothing wrong with opening the gas port as a last resort. Have you tried a lighter buffer? Are you sure the gas block is perfectly aligned? Lighter bullets usually have more powder and usually creates more port pressure to run the gun. I've never run factory ammo through my 6.5 G, so I don't have any experience with the various brands. I had a buddy who was experiencing reliability issues, and discovered he had a rifle buffer spring installed in a carbine receiver extension. Probably not your problem, but worth a look. |
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Originally Posted By jwf2874: [...] And THAT is after changing to a reduced power buffer spring. Using a "yellow" reduced power spring and a carbine buffer. In the past when i've had similar grendel builds i've used h2 or h3 buffers and they ran fine. we've checked all the normal suspects. not seeing any "gas leaks". confirmed alignment of gas block, etc... [...] Originally Posted By jwf2874: [...] And THAT is after changing to a reduced power buffer spring. Using a "yellow" reduced power spring and a carbine buffer. In the past when i've had similar grendel builds i've used h2 or h3 buffers and they ran fine. we've checked all the normal suspects. not seeing any "gas leaks". confirmed alignment of gas block, etc... [...] Originally Posted By borderpatrol: Have you tried a lighter buffer? Are you sure the gas block is perfectly aligned? [...] I had a buddy who was experiencing reliability issues, and discovered he had a rifle buffer spring installed in a carbine receiver extension. Probably not your problem, but worth a look. The Springco yellow is a carbine buffer spring, reduced power, presuming that's what OP is talking about. Those first two concerns were fairly well addressed in the first post. |
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Still waiting for photo's of spent cases, to see if problem is under gas, or over gassed to start with, or just a reamer chatter chamber or one that has not been correctly cleaned yet before rig was put into action to start with. If chamber is a shite show, then nothing is going to solve the problem (short of replacement barrel_, since you can slow the bolt unlock way down to try to reduce the residual bore pressure on the spent case before the pull with even heavier buffer so case is not grabbing as much to rough chamber walls on the pull, but all that is going to do is cause the rig to short stroke worse, since not enough gas pressure to cycle the B/C correctly all the way back instead Bottom line, is rig it correct, then should be running without problems on standard buffer and spring (be it full lenghts for butt stock rig, or carbine lengths for telescoping stock instead. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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