260 Remington in the AR platform

Been a fan of 260 Remington for a long time. Longer than 6.5 Creedmore has even been a thing but for some damn reason I can never get it to run in a semi auto.

I’ve tried multiple different guns, different barrel makes, but I can’t get it to cycle reliably. The latest build I tried it in was, and yes I’m gonna be shunned, a Diamondback DB10 that I had swapped the factory 308 barrel for a Ballistic Advantage 16in 308 Hanson Profile barrel. With that setup the gun functions flawlessly and with 168 FGMM ammo it shoots MOA or better from 100 to 400 which is all the distance I have.

I swapped out 2 separate barrel makes (Liberty/Satern Barrels 18in Stainless barrel in 260 Rem and a Shilen 20in Stainless in 260 Rem) and the gun will not cycle. It will do a multitude of things. From Bolt Override of the next round, to locking the bolt and spent cases up tight, to stovepipe and double feed to a combination of multiple of those.

Out of both of those barrels, multiple different types of magazines and multiple different ammo types, I consistently have the same issues, but when I swap back to the 308 BA Hanson barrel, the gun runs flawless.

I’ve tried the barrels on 4 other manufacturers of 308 AR’s as well and have the same exact issues.

Anyone got any suggestions on what could be causing this? I’d really really like to get this 260 Rem AR thing to work.

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Originally Posted by JFArmsCo

Been a fan of 260 Remington for a long time. Longer than 6.5 Creedmore has even been a thing but for some damn reason I can never get it to run in a semi auto.

I’ve tried multiple different guns, different barrel makes, but I can’t get it to cycle reliably. The latest build I tried it in was, and yes I’m gonna be shunned, a Diamondback DB10 that I had swapped the factory 308 barrel for a Ballistic Advantage 16in 308 Hanson Profile barrel. With that setup the gun functions flawlessly and with 168 FGMM ammo it shoots MOA or better from 100 to 400 which is all the distance I have.

I swapped out 2 separate barrel makes (Liberty/Satern Barrels 18in Stainless barrel in 260 Rem and a Shilen 20in Stainless in 260 Rem) and the gun will not cycle. It will do a multitude of things. From Bolt Override of the next round, to locking the bolt and spent cases up tight, to stovepipe and double feed to a combination of multiple of those.

Out of both of those barrels, multiple different types of magazines and multiple different ammo types, I consistently have the same issues, but when I swap back to the 308 BA Hanson barrel, the gun runs flawless.

I’ve tried the barrels on 4 other manufacturers of 308 AR’s as well and have the same exact issues.

Anyone got any suggestions on what could be causing this? I’d really really like to get this 260 Rem AR thing to work.

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The .260 barrels don't work on anything, and the .308 barrels work just fine? That rules out the BCG. You are dealing with a gas issue. Most of you malfunctions sound like under gassed. Bolt overide is usually not enough gas. Cases not ejecting with bolt stuck.. lack of gas, double feed is failure to extract but with enough BCG movement to pick up the next round and jamb it into the fired brass.. lack of gas.

Have you fired one round and see if the rifle will lock back on the empty mag?

Now that you mention it, I have done that and it doesn’t lock back. I’ll try an adjustable gas block

How will an adjustable gas block increase your gas? Won't that only allow you to restrict gas flow more?

An adjustable gas block cannot give you more gas. It can only restrict gas flow, it cannot possibly increase gas flow. Drilling out the gas port to the next larger size, however, will increase gas flow. Do it yourself, or farm it out. But if you are low on gas, this is the answer.

Or, possibly, a lighter buffer and/or action (recoil) spring...

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Originally Posted by JFArmsCo

Now that you mention it, I have done that and it doesn’t lock back. I’ll try an adjustable gas block

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Originally Posted by Rascally

An adjustable gas block cannot give you more gas. It can only restrict gas flow, it cannot possibly increase gas flow. Drilling out the gas port to the next larger size, however, will increase gas flow. Do it yourself, or farm it out. But if you are low on gas, this is the answer.

Or, possibly, a lighter buffer and/or action (recoil) spring...

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Correct. Evidently I fat fingered the post whole time on my phone and deleted the part about wanting the adjustable gas block for use with Suppressor. My dad owns a Wire Drawing Die manufacturinging planet and has check pin gauges in the .0001-4.000 inch range in stupidly small incremental increasing ranges so I’ll check what the port size is and slowly work it up.

Got a PM from another member who was having the exact same issues with same caliber on semi auto guns. He tried a couple things and suggested I give them a shot as well, KAK makes a dual ejector bolt, said he dropped that in along with opening gas port bigger and using an adjustable gas block and no longer had any issues. Worth giving it a shot cause I sold my 260 bolt gun to build this project so I’ve got 2500rds of FGMM 142’s and handloads to the FGMM spec that I’d like to be able to ise

Ran down to the old mans shop. Gas port is .078.

For 260 Remington I’m not entirely sure what is small and what is larger on gas port sizing. Anyone have any info on that?

The port in the gas block is nearly always larger than the port in the barrel. Just start to enlarge the barrel port (.079, test; .080, test; etc.) until you get consistent lock back on last shot. I'd surely go slow, you don't want to go too far too fast. Then maybe go one step larger to account for the occasional weak round. At that point, if you're planning on a suppressor, you can think about an adjustable GB.

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Originally Posted by JFArmsCo

Ran down to the old mans shop. Gas port is .078.

For 260 Remington I’m not entirely sure what is small and what is larger on gas port sizing. Anyone have any info on that?

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Quote:

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Originally Posted by JFArmsCo

Ran down to the old mans shop. Gas port is .078.

For 260 Remington I’m not entirely sure what is small and what is larger on gas port sizing. Anyone have any info on that?

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.078 is right about spec. Has your testing been with handloads or factory ammo. If handloads, go get a box of factory stuff and see what happens.

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Originally Posted by AKDoug

.078 is right about spec. Has your testing been with handloads or factory ammo. If handloads, go get a box of factory stuff and see what happens.

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All shooting has been done without FGMM ammo so far as my handloads I’ve got left over are built around the bolt gun I had in 260 Remington. Thinking maybe open the gas port up slowly until I get complete reliability, then use an adjustable gas block

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Originally Posted by JFArmsCo

All shooting has been done without FGMM ammo so far as my handloads I’ve got left over are built around the bolt gun I had in 260 Remington. Thinking maybe open the gas port up slowly until I get complete reliability, then use an adjustable gas block

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Just out of curiosity, what powder is in your handloads?

Varget in 200 of them and I can’t remember what the rest are. The other powder worked MUCH better in my bolt gun I had, much more consistent than the Varget was. I’ll look when I get back to the shop

Opened gas port to .080

Gun runs 85% now. I get a dead trigger about every 6 rounds. By that I mean the next round is chambered, but I get a “soft click” instead of a bang. Hammer drops but firing pin doesn’t even make a mark on the primer. I didn’t think to check whether the bolt was full locked or not, so I’ll try to do that tomorrow. Occasionally I still get a stovepipe double feed so there’s still some gas issue or an extractor issue. Waiting on the KAK dual extractor bolt to arrive, but I’m wondering if I possibly need a different buffer or spring or combo of both.