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6.5 Creedmoor build not running until I cut buffer spring?

giannid

Private
Full Member
Minuteman
Mar 20, 2017
145
13
Chagrin Falls, Ohio
So I recently just finished up a 6.5 creedmoor build using all aero components except a 16 inch faxon barrel and superlative adjustable gas block. When I put the aero enhanced 308 carbine buffer tube kit, I noticed the spring was very tight. I dimpled the barrel with a jig to make sure I had proper alignment of the gas block.

Today I went out and shot some test rounds to check function of the rifle prior to load development. With the gas block wide open, the gun would barely eject a round and would not load a second round or stovepipe one in the chamber. Shot a few rounds with a can and it ran fine. After checking and double checking everything, I figured I'd try cutting the spring to see if I could get it to run. Started cutting one coil at a time until I got it to function without the can and end up taking 4 turns out of the spring to get it to run dependable.

Not a big fan of having a cut spring in the gun. I did get it to run reliably but I'm wondering if I should be looking at something else. I haven't built many AR10's and most of my experience building is with the standard AR15's. Comparing the ar10 spring to an ar15 spring, I notice they are very different. I installed a regular ar15 spring in the gun and it seems to close up the bolt fine but I did not try running rounds through it.

Where should I go with this? I'm wondering if I should buy one of the fancy spring kits or just run the cut spring, or something else. One though I had was the gas port isn't big enough but rather not mess with opening it up. This is going to be primarily a thermal hunting rig and I want this gun to run like a sewing machine.
 
Get an A5 tube, regular H2 or H3 buffer, and then choose the appropriate recoil spring. I like the Tubbs flatwire spring or SR25 carbine spring.

I am not a fan of standard carbine tubes and short buffers.
 
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Why a carbine length tube and spring on a large frame gasser?
 
Why a carbine length tube and spring on a large frame gasser?

This is the kit I purchased for this gun. Figured I'd use it as it's all aero components and figured it would work well with it.

You guys think this could be causing my problem? I figured it was the way to go as I wanted an adjustable stock.
 
Could be a multitude of things. You running handloads or factory ammo? Is the ammo underpowered? Sounds like you got enough gas with your can on. It can be a bitch to tune the large frame guns. Ammo, gas port placement and size, BCG weight, buffer length and strength all have to work together.
 
All of the above, and gas guns sometimes just need to wear in for a bit, before you really get a good running gun.
 
I'm running hand loads which are 42 grains of H4350 under a 120 grain sierra bullet. This is a moderate load and on the higher end of the reloading data.

I haven't played around with the large frames AR's before, but both my prior builds ran fine which were 6mm creedmoor builds. Both those used a rifle buffer tube. I'm relatively certain the gun will run as it's running suppressed and with the spring cut. Didn't want to cut the spring but figured it was a cheap fix to see if I could get it to run. I'm just not a fan of modifying stuff and rather it run right without a cut spring.
 
Maynr the gun just needs to wear in all of the mating surfaces.

Maybe the gas port is small.

Maybe it is partially obstructed. Do you have a bore scope? The best use for one that I have found is checking the alignment of a gas block.

If it is running and not damaging anything- like the receiver extension tower, run it for a while. See how it goes.
 
a5/armalite buffer tube or a rifle length buffer would likely help. Dont like the idea of cutting coils on the standard buffer spring, but if it works it works.
 
Hello. I would verify that the spring is correct (rifle sping in a carbine tube ect. Also, the Tubs flat wire spring in my testing would work in the Carbine tube, not the rifle length.
Also+ double check your loads , but the spring does sound like it is a bit too heavy.
I had a AR15 build chambered in a 17Remington. Had to cut coils from spring to get it to function. was using IMR 4198

Switched the powder to Tac, H223, and Varget and ran reg spring, buffer ect.w/o issue The powder was not producting enough gas to operate properly.​

This may or may not help.. It could be many things.... but start simple 1st... hope you figure it out.