6.5 Short Stroke? Update: Problem Solved

[Rusty Shackelford]

My most recent 6.5G build has an issue. About half the time it wont pick up a round from the mag. Instead of a bang, I get a click. It also fails to lock back on the last round about half the time. Cycle the bolt by hand and it works just fine.

Same thing happens with 5 different mags from three different brands. ASC, E-Lander and Duramag. Ammo is Hornady 123g Frontier bulk ammo. The mags and ammo run fine in other guns.

The build in question is a PSA 18" SS with rifle length gas.The lower is an A-2 rifle stock and buffer. Standard gas block and BCG.

Am I under-gassed? Is the rifle buffer and spring too much?

My next range trip I will take a carbine stocked lower with a standard weight carbine buffer and spring and see what happens.
I would like to try some different ammo but that is not easy to do right now.

Does anyone see anything I'm missing? What else should I try?

All suggestions are welcome and appreciated.
Thanks, R.

[VASCAR2]

[Rusty Shackelford]

Thanks for the reply.
I built this one. It's a 18" PSA bbl and a BCG that I bought on this site. Standard-non-adjustable gas block. No signs of gas leakage at the gas block or key.
Gas key is tight and well staked. I'm not sure how to check gas block alignment without a borescope.
The block is in line with the gas tube straight down the bbl and into the upper. Tight up against the journal. I have always lined them up this way and never had a problem.
I've built a dozen or so uppers and lowers and never experienced this.
Gonna try the carbine lower tomorrow.
R.

[mtnlvr]

The toothpick or spaghetti method work for installing gas block so it's port is aligned with the barrel's port. The gas block may not want to be engaged with the shoulder in all applications.

[Bonas]

Not all gas blocks are made to be pushed tight to the journal. Some should be set off it. If the block is a set screw style, the port in the block will line up with the rear screw hole. Turn the block over, and use the rear screw hole to determine where the block should go.

[LRRPF52]

[montana]

The fool proof way to check the gas block with the barrel port alignment is with a bore scope. https://teslong.com/collections/rifle-borescopes

Many different ways to skin a cat.
gas block aligner.jpg

gas block genie.jpg

Check your gas tube for cracks, fit in the gas key, worn flange that fits in the gas key.. https://www.brownells.com/gunsmith-t...prod41043.aspx

There is a myriad of areas a rifle can lose gas including the gas key I.D. being out of spec. You need a .180 go pin gauge and a .182 no go pin gauge..https://www.mcmaster.com/

Change the bolt carrier group with one you know works and see if it helps with cycling..It could be your gas port is undersized..A lot of unknown variables..

Do process of elimination to find the solution..

[imaguy3]

compressed air also works to check gas block alignment. I use small piece of hose attached to my air gun... slip it over the gas tube inside the receiver and give it a squirt of air, if you feel air come out of the barrel then you're gtg.

[montana]

compressed air also works to check gas block alignment. I use small piece of hose attached to my air gun... slip it over the gas tube inside the receiver and give it a squirt of air, if you feel air come out of the barrel then you're gtg.

Not necessarily, the ports can be partially offset-blocked creating a smaller gas port diameter and still allow compressed air through ..

[Rusty Shackelford]

Thanks everyone for the tips and suggestions. Here's what I have determined so far.
Changing to a carbine lower with standard weight buffer improved functioning to almost 100%. Only one mag out of the 5 that I tried failed to chamber a round and lock back on the last round. I put it aside for now. My remaining mags ran perfectly.
So, it appears the rifle buffer and spring were too heavy for this rifle. That does not mean it is the only possibility.
The problem may still be in the gas system since I have built rifle length uppers before and they ran fine on this A-2 stocked lower.
Further testing will continue after I get my hands on a bore scope and take a look at the gas port and block alignment.

Also, can anyone tell me where I can find out the proper gas port size for rifle length gas for 6.5 Grendel? If my port is under-sized, as some have suggested, that my be the answer.
Thanks, R.

[VASCAR2]

[SDW]

What about the ejection pattern? What direction ('o-clock') is it flinging the cases and how far now? With the rifle lower and now, with the carbine lower?

FWIW, I'm running a 20" rifle-gas upper, barrel is from Ballistic Advantage, one of their "Premium" DMR stainless versions. I may have mentioned the gas port diameter on this barrel in an earlier thread of mine. I'll try to look. VASCAR2's .094" sounds right to me though. The lower has an A1 stock, standard rifle buffer and spring. Rifle shoots fine with all the 120+ gr ammo I've tried (Hornady Black and my own handloads).

However, it did not cycle the Federal Am. Eagle 90 gr TNT ammo very well. Didn't exactly short-stroke with this stuff as I recall, meaning to the point where it wouldn't chamber the next round. It simply didn't lock back on the last round. I don't recall the ejection pattern. the info on this 90 gr loading is anecdotal since Rusty hasn't even tried this ammo yet in his upper. Just FYI.

A bore scope is nice to have; I got one through Amazon. It was maybe $40? Worth the money. I think you can find cheaper ones too.

[montana]

Thanks everyone for the tips and suggestions. Here's what I have determined so far.
Changing to a carbine lower with standard weight buffer improved functioning to almost 100%. Only one mag out of the 5 that I tried failed to chamber a round and lock back on the last round. I put it aside for now. My remaining mags ran perfectly.
So, it appears the rifle buffer and spring were too heavy for this rifle. That does not mean it is the only possibility.
The problem may still be in the gas system since I have built rifle length uppers before and they ran fine on this A-2 stocked lower.
Further testing will continue after I get my hands on a bore scope and take a look at the gas port and block alignment.

Also, can anyone tell me where I can find out the proper gas port size for rifle length gas for 6.5 Grendel? If my port is under-sized, as some have suggested, that my be the answer.
Thanks, R.

I had to open up the gas port on a 20" 5.56 rifle length Faxon barrel. I called Faxon and they gave me permission to proceed before I sent it back..They were great to work with. I have the correct chucking reamers-drill bits and pin gauges to do it properly.. If you try this, place a steel cleaning rod in the bore before you drill so you won't hit the side of the bore opposite the gas port.. I gradually opened the gas port, while test firing after each increase to get the proper port size..If all things were equal, a standard size gas port would work..Most rifles and ammunition are not equal..Drilling the gas port is the last option I will use..If you over size the gas port, you will have to adjust the gas some where a long the process, adj gas block, adj bolt carrier, adj gas tube, install a new gas tube with a smaller port, etc..

[Rusty Shackelford]

Thanks again.
I just got finished with a bore scope and there is no miss-alignment of the gas block.
It looks like now my next step is to pull the gas block off and measure the port.
If it's under-sized, can I just drill it out with the proper size bit in a drill press. Surely it's not that simple. But I aint afraid to try it.
R.

[Rusty Shackelford]

[QUOTE=SDW;303692]What about the ejection pattern? What direction ('o-clock') is it flinging the cases and how far now? With the rifle lower and now?

I'm not sure of the pattern since I use a Brass Goat to catch my cases. If I keep going with this experiment, I may have to take the goat off and spread out a tarp to see where they land.
If I don't run out of ammo first.
It may be about time to break out the Rock Chucker.
R.