243 and the 105s to 108s in 1-8 twist

[urbanrifleman]

Does anyone have anything they would like to share concerning the 243 in 1-8 twist? I am getting ready to build an upper for my AR10, and thought I would ask.

Thank you in advance.

 

[Eric Leonard]

an 8 twist 243 with 105s is a lazer beam for sure,,I have one in an AICS chassis and it runs really well with 105`s from the AI mags,,if the AR mags are much shorter than 2.80 you will have to load the 105 class bullets down below the neck shoulder junction or maybe shoot 95`s,,,,myself if I had to load the 243 with 105`s shorter than 2.80-2.825 I would chamber a 6 Creedmoor or the XCII

 

[Zero333]

By seating 105's deep in the case due to ar10 mag constraints you will sacrifice a little speed but no more than 50 fps so it's not as big of a deal in my opinion.

The 6 Creedmoor might indeed be the better option... might be.

 

[HPMike800]

Does anyone have anything they would like to share concerning the 243 in 1-8 twist? I am getting ready to build an upper for my AR10, and thought I would ask.

Thank you in advance.

I had a 243 AR-10 years ago. The problem is slow powders in a gas gun. Don't use factory ammo. You will lose speed because you will need to stick with medium speed powders. If you want to go 6mm, I would choose a case sized for 4895, Varget, N140 etc. That will allow you to run long bullets in a Mag as well.

If you want simple, 6.5 Creedmoor is a better way to go IMHO.

 

[urbanrifleman]

I had a 243 AR-10 years ago. The problem is slow powders in a gas gun. Don't use factory ammo. You will lose speed because you will need to stick with medium speed powders. If you want to go 6mm, I would choose a case sized for 4895, Varget, N140 etc. That will allow you to run long bullets in a Mag as well.

If you want simple, 6.5 Creedmoor is a better way to go IMHO.

What is wrong with slow powders in an AR10 gas gun? What is the effect?

 

[HPMike800]

What is wrong with slow powders in an AR10 gas gun? What is the effect?

Rifle powders slower than say Varget or there abouts increase port pressure and cause the action to cycle early and forcefully. It can do damage and tear the rims off your cases. It depends to some degree on specifics of the rifle, but that's the rule of thumb.

 

[Ksmirk]

Could you not go with an adjustable gas block? Later,

Kirk

 

[urbanrifleman]

Could you not go with an adjustable gas block? Later,

Kirk

Yes. And my new Ar10 will have the gas block an extra two inches out over a standard AR10 rifle length.

I do not see how slow powders would make an action cycle "early". Hard yes. But not early.

 

[HPMike800]

I agree that the "stopwatch" timing won't change much. However powders that are too "slow" for the design of the rifle will have higher pressure in the barrel when the bullet passes the gas port. That means the case is still stuck to the chamber wall when the gun extracts the round. So the action is cycling "early" relative to the pressure curve you have produced with "slow" powders. The result is bent/torn case rims.

Moving the port forward will help some. An adjustable gas will not remedy the problem.

In my factory 243 AR-10 I ended up running H380 at about 2700fps (100gr bullets). Pretty slow for a 243Win. Lighter bullets may help IDK.