Straight pull bolt action AR

[Jlong51454]

I am toying with the idea of building a bolt action AR in 6arc. I know there are dedicated bolt actions for the 6arc. My big question is, would the locking lugs stand up to the 62k pressures of this cartridge long term? In my head, without the rotational force of unlocking they would hold up long term. Input?

 

[patience0830]

AR's are not bolt actions. Either you're building a tactical bolt action rifle, straight pull or otherwise, or an AR. Which is it?

 

[Jlong51454]

AR's are not bolt actions. Either you're building a tactical bolt action rifle, straight pull or otherwise, or an AR. Which is it?

I should have been clearer. I would be building a single shot AR upper. It would have no gas system or an adjustable gas block that I would close.

 

[patience0830]

Doesn't make any sense to me to reinvent the wheel. If you're using a proven system, why the concern about the different cartridge? Is the 6ARC designed to fit in an AR15 action or more suited to the AR10?

 

[Jlong51454]

Doesn't make any sense to me to reinvent the wheel. If you're using a proven system, why the concern about the different cartridge? Is the 6ARC designed to fit in an AR15 action or more suited to the AR10?

The cartridge can be loaded to 55k in a gas gun. In a bolt action it can be loaded to 62k. It is for the ar15 platform.

 

[Squid556]

A while back I did a 300 blk repeater project on a side charging BCA upper. I simply moved my gas block enough forward to block the port, removed the tube, buffer and spring.

So basically I had a gasless, springless, side charging straight pull 300 blk. Thing was super fun and slick to run the action on. I ran somewhere under a hundred rounds through it in that configuration with no issues. Personally I would leave the spring in just to safely ensure you don’t mislock the action.

Mechanically speaking, the AR locking system should equally be able to handle single shot use as it does semi use. The pressure spike has come and nearly entirely gone by the time the system unlocks. It has to otherwise it would have weird ejection issues like some delayed blowback guns (G3, FAMAS) get when they try and eject under high pressure.

In your case… you would still be limited to the gas gun pressure rating because that lower pressure is derived from the strength of the AR bolt head. ARs can run approx 60K on a .378 case head. But that number gets smaller as you use larger cases. Less material, less strength. I seem to remember a variant of the M855A1 being pushed over 60K and lug failures started to happen more often. I think Grendel guys run into that problem as well since brass pressure signs often occur higher than what the Grendel bolt is rated for.

You may already know about these but it’s relevant to the project

UP-15 Complete rifle – Bolt Action AR Uppers | AR-10 & AR-15 | Uintah Precision

***DUE TO ORDER VOLUMES, UP15 BACKORDERS HAVE ABOUT A 2-4 WEEK LEAD TIME*** ***In stock quantities represent components on hand to complete rifles. At this point, due to order volume, orders are being assembled as they are received.*** The UP-15 is a TRUE bolt action AR rifle with a 3-lug...

uintahprecision.com

 

[Leo]

"In your case… you would still be limited to the gas gun pressure rating because that lower pressure is derived from the strength of the AR bolt head. ARs can run approx 60K on a .378 case head. But that number gets smaller as you use larger cases. Less material, less strength."

Squid556 is correct. Pound per square inch times square inches of contact equals pounds of force, Hydraulic principles apply because except for a tiny amount of case to chamber wall friction, all the rest of the pressure is like a hydraulic piston pushing back.

 

[Jlong51454]

A while back I did a 300 blk repeater project on a side charging BCA upper. I simply moved my gas block enough forward to block the port, removed the tube, buffer and spring.

So basically I had a gasless, springless, side charging straight pull 300 blk. Thing was super fun and slick to run the action on. I ran somewhere under a hundred rounds through it in that configuration with no issues. Personally I would leave the spring in just to safely ensure you don’t mislock the action.

Mechanically speaking, the AR locking system should equally be able to handle single shot use as it does semi use. The pressure spike has come and nearly entirely gone by the time the system unlocks. It has to otherwise it would have weird ejection issues like some delayed blowback guns (G3, FAMAS) get when they try and eject under high pressure.

In your case… you would still be limited to the gas gun pressure rating because that lower pressure is derived from the strength of the AR bolt head. ARs can run approx 60K on a .378 case head. But that number gets smaller as you use larger cases. Less material, less strength. I seem to remember a variant of the M855A1 being pushed over 60K and lug failures started to happen more often. I think Grendel guys run into that problem as well since brass pressure signs often occur higher than what the Grendel bolt is rated for.

You may already know about these but it’s relevant to the project

UP-15 Complete rifle – Bolt Action AR Uppers | AR-10 & AR-15 | Uintah Precision

***DUE TO ORDER VOLUMES, UP15 BACKORDERS HAVE ABOUT A 2-4 WEEK LEAD TIME*** ***In stock quantities represent components on hand to complete rifles. At this point, due to order volume, orders are being assembled as they are received.*** The UP-15 is a TRUE bolt action AR rifle with a 3-lug...

uintahprecision.com

Thank you, after I posted the question I nerded out on bolt thrust research and calculations and came to the same conclusion. It might hold for some time but I am not going to risk it. My face is too purdy. I like those uppers but wow are they proud of their stuff. I can buy a nice savage for 600 bucks.

 

[bobjones223]

I like those uppers but wow are they proud of their stuff. I can buy a nice savage for 600 bucks.

I am confused? BCA is one of the cheapest AR uppers you can get into?

I will also state that the one I got from them was very nice. I got a 10.5" 7.62X39 upper for $205.00 with BCG.

With glass on top it will hit Lifesavers all day long at 50yd with cheap steel case crap.

 

[Jlong51454]

I am confused? BCA is one of the cheapest AR uppers you can get into?

I will also state that the one I got from them was very nice. I got a 10.5" 7.62X39 upper for $205.00 with BCG.

With glass on top it will hit Lifesavers all day long at 50yd with cheap steel case crap.

I was referring to the Uintah Precision bolt action action uppers as being proud of their stuff.

 

[Indiana_Jeff]

Thank you, after I posted the question I nerded out on bolt thrust research and calculations and came to the same conclusion. It might hold for some time but I am not going to risk it. My face is too purdy. I like those uppers but wow are they proud of their stuff. I can buy a nice savage for 600 bucks.

I think you have answered your own question. For a one-shot-at-a-time gun, a quality bolt action is hard to beat. Good luck & stay safe!