6.5 Grendel Pistol Issue

[wideglidejoe]

I've recently put together a 6.5 Grendel pistol upper, using a 12.5" Ballistic Advantage barrel that I purchased from Granite Ridge, along with a 6.5 Grendel bolt & carrier. I already have a 10.5" 5.56 pistol, I'm swapping the two uppers between the same pistol lower. The 5.56 runs perfectly, in all ways. I wanted the 6.5 Grendel pistol to go with my Alexander Arms 6.5 Grendel rifle upper, which I love. I've put maybe 30 rounds thru the 6.5 Grendel pistol upper, with some issues. It fires OK, it ejects the empty brass to 3-4 o'clock, resets the trigger (Geissele S3G) for the next shot, but "short cycles" or whatever you want to call it, without loading a new round. I've tried three different mags, two different 10 rd AA mags, plus a 30 rd E-lander, all three of which work fine in my 6.5 Grendel rifle, so I don't think its the mags. One friend tells me I've got gas issues, either the gas port isn't lined up correctly or gas port isn't big enough, others tell me its a buffer/spring issue. I'm using the standard carbine buffer & 10.5" spring, which works great with the 5.56 upper, even when running very fast with the S3G trigger.

Any suggestions which end to start on? Gas port size, gas block alignment, or buffer &/or spring?

Thanks in advance!
Joe

[Drillboss]

When firing a single round, or the last round, does the bolt lock back on the empty mag? Does the bolt catch hook the bolt face or the bolt carrier?

[wideglidejoe]

Drillboss, thanks for replying, good question...........I don't know. After every shot, it ejected the empty, bolt went forward, I pulled the trigger to see if it had loaded a new round, it hadn't, but the trigger was reset and it snapped, so I used the charging handle to load a new round, to repeat everything again. I never got to the last round in a mag before I changed and tried other mags. I guess I should've went to the last round in a mag, even if I loaded the last round manually, to see if the bolt locked back on an empty mag after ejecting the last empty brass. But, those mags work fine in the 6.5 Gr rifle, locking back on empty mag. I'll check that on next range trip, hopefully early next week. It seems the bolt is cycling far enough back to eject the empty and reset the trigger, but not far enough back to pick up a new round from the mag, or its cycling so fast its skipping over the next round in the mag, if that's possible?

Oh, I didn't mention in my original post, I'm shooting Hornady factory ammo. I'll eventually reload, once I get this pistol upper sorted out and accumulate enough brass. I don't want to add another variable to the mix right now.

Again, thanks for all opinions and suggestions! I'm off to my son's karate tournament, I'll be out of pocket for a while.

Edit; Next trip out, I may try this upper on another lower that I originally built as a pistol, but I'll have to change the buffer tube on that lower back to pistol if I do that.

[BluntForceTrauma]

I've been reading reports on AR15.com the gas ports are drilled on the small side.

[grayfox]

Like Drillboss indicates, load and fire a single round with the original setup, then look to where the bcg winds up.
1. short stroke so much as to not lock back at all, goes back into battery
2. catches on the carrier face
3. catches on the bolt face (this is the desired one)

[Drillboss]

A good first function test for a new build is to load one round in the mag, chamber it, and see if it extracts easily with the charging handle. Then, reload the round and fire it from the hip. Then check to see if anything blew up and also, did the bolt catch hook on the face of the bolt. If it didn't lock back at all or if it caught on the bolt carrier, you probably don't have enough gas. In that case, I'd check for proper alignment of the gas block first.

Another test is to drop a loaded round into the chamber, then point the muzzle up and see if the round falls out. If it has to be tapped out, the bullet could be into the lands or the chamber might be too tight. This test is easier if done before assembly.


Rather than following this advice, I just fought my way through what I thought was undergassed, but turned out to be a snug chamber, aft of the shoulder.

I personally haven't seen issues with buffers and springs. Not to say it doesn't happen, I just haven't had to deal with it yet.

Good luck with it.

[98Z]

Check this first - check your gas port size:

http://www.65grendel.com/forum/showthrea...-port-size

A little more info:

http://www.65grendel.com/forum/showthrea...port-sizes

[wideglidejoe]

To All that have posted replies/comments; Thank you for taking time to do so! I've got some work to do. I've done some of the above, I just didn't go into that much detail in my original post, but I obviously have some more checking to do. Thanks again to all for your suggestions, advice, etc! I'll try to get to the range early next week, then spend some time on the bench with it again checking stuff out.

[Lakeray]

To All that have posted replies/comments; Thank you for taking time to do so! I've got some work to do. I've done some of the above, I just didn't go into that much detail in my original post, but I obviously have some more checking to do. Thanks again to all for your suggestions, advice, etc! I'll try to get to the range early next week, then spend some time on the bench with it again checking stuff out.

Please let us know how it turns out...

Ray

[Lakeray]

Just noticed that three of us (including the op) are from Oklahoma!

[wideglidejoe]

Just noticed that three of us (including the op) are from Oklahoma!

Yep, I noticed the same thing! I'm on the east side of Broken Arrow, in Wagoner county. I'll try to get to the range Wed or Thurs and try the comments/suggestions already listed above, but I'm also getting ready for a spring break ski trip!

I did call Ballistic Advantage today, a tech told me the gas port for this particular barrel is drilled at 0.0595". He also suggested checking the gas block, as Drillboss did, which I may do before going back to the range and trying the other suggestions from above. The tech also suggested running the lightest buffer possible. The buffer I'm using is what I suppose is the standard carbine buffer and 10.5" spring. The buffer isn't marked H1, etc., its unmarked. All other carbine buffers are heavier than the standard carbine buffer, correct?

More to come, I'll post more info and results ASAP.

Thanks to all!

(edited for typo)

[rabiddawg]

I don’t know if this will help but I converted a 16” 223 colt over to a Grendel pistol. I used a Faxon group buy barrel, monster bolt and a pistol buffer tube. Everything else came from the donor rifle.

I looked at the group buy barrel specs but the port size isn’t listed. BFT may know what it measures

I would check the gas block alignment and verify if the port is big enough. Mine has never missed a beat.

[wideglidejoe]

I don’t know if this will help but I converted a 16” 223 colt over to a Grendel pistol. I used a Faxon group buy barrel, monster bolt and a pistol buffer tube. Everything else came from the donor rifle.

I looked at the group buy barrel specs but the port size isn’t listed. BFT may know what it measures

I would check the gas block alignment and verify if the port is big enough. Mine has never missed a beat.

Hey rabiddawg,
Since you said everything else came from the donor rifle, I'm assuming since the donor was 16", that the buffer and spring are/were standard carbine?
Thanks,
Joe

[98Z]

The buffer isn't marked H1, etc., its unmarked. All other carbine buffers are heavier than the standard carbine buffer, correct?

Correct. That would be a standard buffer, if it's unmarked on the buffer face. That is one SMALL gas port... Tell more about that 10.5" spring. That's a little short for a standard AR15 carbine spring. Check the info linked below:

http://heavybuffers.com/reference.html

[rabiddawg]

Hey rabiddawg,
Since you said everything else came from the donor rifle, I'm assuming since the donor was 16", that the buffer and spring are/were standard carbine?
Thanks,
Joe

Mine wasn’t marked either. I simply put the buffer and spring in the pistol tube and rolled with it.

[wideglidejoe]

To 98Z; my 5.56 pistol lower buffer spring is 10.5" with .072 wire and 39 coils. It runs fine with 5.56, both 55 gr and 62 gr green tip. That's the lower I'm going to run the 12.5" Gr upper on.

Sometime back, I found a chart elsewhere on the web, or AR15.com or somewhere, that shows a bracket of 10 1/16" to 11 1/4" for carbine springs, and 11.75" to 13.5" for rifle springs. I have a stock out-of-the-box 16" Colt LE6920, it's spring is 10.5", with .072 wire and 38 coils, and a 16" 7.62x39 that I built upper and lower from scratch, using a 10.5" with .072 wire and 38 coils. Both of them run fine with a 10.5" spring. I see on Slash's chart that he just lists 11.25" with .072" wire and 39 coils instead of a range of length. I'm open to trying a 11.25" spring if it could help my situation.


To All; as far as gas port size, that's what the Ballistic Advantage tech told me yesterday; .0595". He elaborated that they don't have any trouble running suppressed or unsuppressed with that size port.

This morning, I removed my gas block and gas tube from the 12.5" Gr barrel. The barrel gas port measures .0550" with my Dillon reloading calipers. The gas block port is obviously much larger than the port in the barrel. The barrel has a "stain", or residue from firing it, where the gas block port was over the barrel port. The barrel port is centered within that stained area. I blew on the gas tube at the bolt end, it is very clear, unobstructed thru the gas block port.

At this point, I'm thinking my barrel gas port is too small. I tried calling the BA tech back today, but didn't get an answer, I'll keep trying to talk to him again. I'm thinking the gas block & tube are OK, were originally installed OK, and the unmarked standard carbine buffer and 10.5" spring are OK.

I'm going back to look on the AR15.com forum, I'm thinking it was there that I saw a post with several comments that they were taking their barrel port from .060" (or my .0550" port that is supposed to be .0595") out to the upper .060's or even .070".

Thoughts? Opinions?

Thanks,
Joe

Edited for typo.

[wideglidejoe]

I just found another post on this forum where worthen86ford cut down a 16" Anderson 6.5 Gr barrel to 10.5", and he opened up his gas port from .068" to .073" to get it to function reliably.

[98Z]

It certainly won't hurt to open it up. The hole in the gas block is 0.125", and that is the max, due to: That's as big as you can make a hole in a gas tube (the actual 303 stainless gas tube) based on it's diameter. Worst thing that can happen - it's too much gas, and you install an adjustable block to tame it back down.

[Dcommoncents]

I had/am having a similar issue with a 12" Grr pistol, although not quite as severe. I posted here if you're interested: http://www.65grendel.com/forum/showthrea...stol-build

To summarize, I saw an improvement when I more carefully aligned the adjustable gas block, but it's still not 100%. I'm going to try a non adjustable gb for better gas flow. If that doesn't work I'll be opening my gas port too, just haven't decided what diameter. One thing I have going for my build you might want to consider is a noveske flaming pig style muzzle device that I think must add some back pressure to simulate slightly longer dwell time.

[98Z]

I had/am having a similar issue with a 12" Grr pistol, although not quite as severe. I posted here if you're interested: http://www.65grendel.com/forum/showthrea...stol-build

One thing I have going for my build you might want to consider is a noveske flaming pig style muzzle device that I think must add some back pressure to simulate slightly longer dwell time.

Shouldn't be necessary to get a Faxon 12" with carbine gas to function. The Noveske Pig shouldn't be the determining factor in function or not function. There's plenty of pressure in the 6.5G round to operate a 12" carbine gas system, without it.