01-25-2023, 12:25 PM (This post was last modified: 02-09-2023, 04:51 PM by LRRPF52.)
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.
The PSA 6.5 Grendel uppers Ive seen ship with an adjustable gas block. There has been confusion on which screw actually adjust the gas, whether side or front. If this is a factory upper sounds like you need more gas. If you assembled the upper and have a fixed gas block then Id check the alignment or look for gas leakage around the gas key on the bolt carrier.
VASCAR2 Wrote:The PSA 6.5 Grendel uppers Ive seen ship with an adjustable gas block. There has been confusion on which screw actually adjust the gas, whether side or front. If this is a factory upper sounds like you need more gas. If you assembled the upper and have a fixed gas block then Id check the alignment or look for gas leakage around the gas key on the bolt carrier.
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.
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.
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.
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..
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.
imaguy3 Wrote: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 ..
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.
01-27-2023, 02:20 PM (This post was last modified: 01-27-2023, 06:56 PM by 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.
Rusty Shackelford Wrote: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..
VASCAR2 Wrote:Ive read .094 gas port diameter for rifle length gas on 18 6.5 Grendel. This size has been posted before for RLGS and I saved it to my notes.
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.
[quote=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?
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.
montana Wrote: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..
Awesome. So it can be done. Thanks for the info.
R.
Rusty Shackelford Wrote: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.
The problem with 18 RLGS in 6.5 Grendel is there isnt much dwell time left in front of the port, and bore volume is a lot larger than 5.56 NATO.
18 RLGS works great suppressed for that reason, because the can acts as an accumulator/additional barrel length.
I would expect to see no smaller than a .094 gas port for RLGS 18, but in cold weather shooting lighter bullets, you might want it opened to .109 (7/64ths bit).
Precision Firearms introduced an Intermediate Length Gas System 18 barrel and gas tube about 10 years ago that addresses this, being between a MLGS and RLGS.
I think thats an ideal length for 18 6.5 Grendel.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
So, measuring the gas port in true hillbilly fashion, I used the shaft of drill bits. An .078" would pass with a little wiggle room. An .094" would not enter. I used it to open the port up to 0.94" then used an .109" to open it a little more.
Preliminary testing firing a few rounds in the back yard shows ejection at 4oclock about 6' away. That's with a carbine stock and H buffer. No hiccups with FTFs or locking back on the last round. I am encouraged.
I'll try to get to the range this week and try it with the rifle lower, but it looks like a rainy week and a full work schedule may get in the way.
Again, thanks everyone for the help. It looks like I'm on the right track now.
R.
01-30-2023, 09:27 PM (This post was last modified: 01-30-2023, 11:38 PM by Harpoon1.)
Quote: 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.
Thats a solid gold tip right there! Thanks.
I got lucky over drilling and touching the other side of the bore but, thankfully it didnt cause any accuracy issues. Not a gunsmith, just shade tree, work on my own stuff, usually in the kitchen, with portable hand tools! If I screw it up, no big deal. I never buy high end/ top tier gun stuff anyway. Same issue with a PSA 223 Wylde, 1/8 Chrome lined 18 FN barrel with a RLGS. Shot lights out but short stroked half of the ammo I had. I opened it up to the next drill bit size and runs like a champ now, and its still the most accurate barrel of any AR Ive ever owned, in any caliber! Thats like 20+ barrels now! It is retarded accurate, for any platform and its chrome lined! It should last forever!
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Scrubbed it down with some JBs and a bronze brush to knock down any high spots and let her rip! Good as new!
I finally got out to the range yesterday and can happily report that this rifle now flows like water. With the rifle stock and buffer back in place it feeds all 4 kinds of ammo I have, plus three different hand loads, from all my mags. Yes, Wolf steel case too. And, it locks back on empty every time.
Ejection pattern with Hornady American Gunner 123g was 7-8 feet away at about 5 o'clock in a neat little pile about the size of your average kitchen sink.
Accuracy aint bad either. With Hornady Black I got a three shot group of 1.2" at 100 yards. I'm no bench rest shooter, so I feel like that's pretty good using a bi-pod rested on the hood of my Jeep. The American Gunner at 50 yards went three shots into a group that I could completely cover with a dime.
Now that I have all this empty brass, can get to work on some more hand loads.
Thanks all, R.
![[Image: ?u=https%3A%2F%2Fwww.precisionfirearms.c...ipo=images]](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.precisionfirearms.com%2Fuploaded%2Fimages%2FArion%2FIMG_1830.JPG&f=1&nofb=1&ipt=22cee492ec9cfae7f2409f4a88edfc93322f3bf4f47f35ecb6c3b54d9c4d42e2&ipo=images)
If I screw it up, no big deal. I never buy high end/ top tier gun stuff anyway. Same issue with a PSA 223 Wylde, 1/8 Chrome lined 18 FN barrel with a RLGS. Shot lights out but short stroked half of the ammo I had. I opened it up to the next drill bit size and runs like a champ now, and its still the most accurate barrel of any AR Ive ever owned, in any caliber! Thats like 20+ barrels now! It is retarded accurate, for any platform and its chrome lined! It should last forever!
