Questions regarding my 6.5 Grendel piston build

[Bret]

I spend this afternoon putting together my latest AR15. It's an Alexander Arms 6.5Grendel receiver set, Alexander Arms 6.5Grendel mid length barrel, Alexander Arms 6.5Grendel bolt, an Adams Arms mid length piston system, a lower parts kit and a carbine stock kit. Everything seems to go together pretty well.

I got near the end and realized that I don't have a cam pin, firing pin nor a firing pin retaining pin to go with the Adams Arms carrier. Would I be correct to assume that all of these parts are the same for 6.5Grendel and 5.56x45?

The video that came with the Adams Arms piston kit showed the first step as removing the bolt gas rings. Interestingly, the written instructions omitted this step. I understand that the gas rings are not needed, but would there be a negative side effect if I didn't remove them? It doesn't seem like they'd interfere with anything, but sometimes I don't know as much as I think I do. If there's no negative side effect, I'd prefer to leave them so as not to make a permanent commitment.

[TomMcC]

I don't see why they would be different. Have you tried to fit them? How it go?

[Bret]

I went ahead and pulled the cam pin, firing pin and firing pin retaining pin out of a new 7.62x39 bolt carrier that I have.

I took it shooting today along with 180rds of Wolf 100gr FMJ 6.5Grendel. I ran 80rds through it using the Alexander Arms lower. I had one double feed when trying a RZE Unimag (runs 7.62x39 100%), so I switched over to Elander 6.5Grendel magazines. Function was 100% after that. Oddly, the spent cases literally ejected only about six feet in to a nice area about two feet in diameter. This was using a regular carbine buffer, so this rifle is definitely not overgassed.

Next, I swapped in my M16A1 lower which has an H2 buffer installed (runs 5.56x45, 223Rem and 7.62x39 100%). Unfortunately, I had five feed to feed due to short stroking. Spent cases were only going three to four feet. I then installed a carbine buffer in the M16A1. The Adams Arms instructions warned that the rifle might experience carrier bounce in full auto if using a carbine buffer. If so, they suggested installing an H2 buffer as a remedy. I already did that and had short stroking, so I gave it a try anyway with the carbine buffer. Sure enough, I had several failures to fire due to carrier bounce. Each time the primer had an indentation, I guess it just wasn't hit hard enough. I do wonder if they would have fired if the firing pin spring Adams Arms supplied had not been installed. Obviously they put it in the kit for a reason, so I left it installed. At this point I'm open to suggestions for how to get this 6.5Grendel build to run 100% in full auto. I guess I'll try a H1 buffer. Perhaps the window between the carbine buffer and H2 buffer will be just right. Another option is to try higher powered ammo that will make it run with the H2 buffer. Anything else that I should do?

BTW, before anyone asks why I decided to do a 6.5Grendel build with an Adams Arms piston system the answer is simple. It's just something different and I like learning. The rifle is surprisingly light.

[richiecotite]

I’d ditch the piston, then try the h2, or drop down to a h


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[TomMcC]

I went ahead and pulled the cam pin, firing pin and firing pin retaining pin out of a new 7.62x39 bolt carrier that I have.

I took it shooting today along with 180rds of Wolf 100gr FMJ 6.5Grendel. I ran 80rds through it using the Alexander Arms lower. I had one double feed when trying a RZE Unimag (runs 7.62x39 100%), so I switched over to Elander 6.5Grendel magazines. Function was 100% after that. Oddly, the spent cases literally ejected only about six feet in to a nice area about two feet in diameter. This was using a regular carbine buffer, so this rifle is definitely not overgassed.

Next, I swapped in my M16A1 lower which has an H2 buffer installed (runs 5.56x45, 223Rem and 7.62x39 100%). Unfortunately, I had five feed to feed due to short stroking. Spent cases were only going three to four feet. I then installed a carbine buffer in the M16A1. The Adams Arms instructions warned that the rifle might experience carrier bounce in full auto if using a carbine buffer. If so, they suggested installing an H2 buffer as a remedy. I already did that and had short stroking, so I gave it a try anyway with the carbine buffer. Sure enough, I had several failures to fire due to carrier bounce. Each time the primer had an indentation, I guess it just wasn't hit hard enough. I do wonder if they would have fired if the firing pin spring Adams Arms supplied had not been installed. Obviously they put it in the kit for a reason, so I left it installed. At this point I'm open to suggestions for how to get this 6.5Grendel build to run 100% in full auto. I guess I'll try a H1 buffer. Perhaps the window between the carbine buffer and H2 buffer will be just right. Another option is to try higher powered ammo that will make it run with the H2 buffer. Anything else that I should do?

BTW, before anyone asks why I decided to do a 6.5Grendel build with an Adams Arms piston system the answer is simple. It's just something different and I like learning. The rifle is surprisingly light.

I'm not familiar with the Adams system...is it adjustable? Nothing wrong with the 6.5 G, it's cool little cartridge. I know it's used for hunting coyotes.

[Bret]

I’d ditch the piston, then try the h2, or drop down to a h

I don't have to run it in full auto, but it would be nice. I have plenty of DI AR15's and just wanted to try something different. Adams Arms' system is not heavy at all.

I'm not familiar with the Adams system...is it adjustable? Nothing wrong with the 6.5 G, it's cool little cartridge. I know it's used for hunting coyotes.

The system isn't continuously adjustable. There are three settings. 12:00 is full, 1:30 is partial (the instructions say for suppressors) and 3:00 is off. It did cross my mind to call and ask if they have gas plug that allows more gas through it.

[Iraqgunz]

https://www.m4carbine.net/forumdispl...eyond-5-56-223

[Bret]

Thanks Iraqgunz for moving this thread.

I spoke with customer service at Adams Arms. The guy I spoke with was very helpful. His first suggestion was trying an H1 buffer. His second suggestion was to enlarge the gas port hole in the barrel. I had thought that the limiting factor for the gas was the internal diameter of the gas plug. He pointed out that in fact it's the gas port hole in the barrel that's the limiting factor for gas flow. He suggested upping it 0.003" to see what happens. I'll give the H1 buffer a try. If that doesn't work, then I'll enlarge the gas port hole on the barrel.