I'm looking at having a 16" 6.5 creedmoor barrel made. I understand that a 6.5cm has much more pressure than a 308. I also understand that a longer gas length reduces dwell time, and therefore pressure. I am also aware that if there isn't enough pressure the action will not cycle correctly.

I'd like to run a rifle length gas system if possible. Will this produce enough pressure to cycle the action correctly? Would it be better to go with a mid length system and use an adjustable gas block? (I'm going to use an adjustable block either way) My fear is ordering a rifle length 16" barrel and finding out my action wont cycle properly because it's under pressured.





Note: I understand that 6.5cm is usually used in longer lengths. I am pretty set on 16". With a Hornady 140gr AMAX out of a 16" barrel the 6.5cm will still be supersonic past 1000 yards, which is longer than I need for my purposes. If you play around with a ballistics program you will find that the difference between a 16" barrel and a 27" barrel is actually not that great in terms of distance before the bullet goes transonic (Less than 100 yards extra). My goal is to have a relatively light weight AR10 that can shoot out to 1000 yards if I get a chance to do so; and which can be used for hunting at closer ranges if I get the opportunity to do so. It's my "do almost everything" build.

Barrel will be from X Caliber.

I would advise a rifle length gas system on that. The last 20" I made had a +2" system on it and it works well.

I'm not a big fan of 16" 6.5 CM barrels, though. Those are long inches on that caliber.

Thank you for the advice. I appreciate it.

This one will be a 16". Next build is probably a 22" based on a Howa bolt action. Goal for this rifle as far as distance was to be able to hit 1000 yards if I ever get the chance to shoot that far. 16" is all I need for the purpose of this gun.

Thanks.

I would definitely go RLGS.  I don't know what port you would use, but maybe start with .086" and see if that needs to be opened up.

16" is plenty to reach 1000yds supersonic.  You'll have more drop of course, but drift won't be bad at all.

I would also look at 130gr and 123gr.

Depending on the barrel, it could easily be faster than that too. A lot of the Bartleins have been very fast, with the 24s giving almost 3k fps with 140 class bullets.

I agree .086" is a good starting point, but I wouldn't be surprised if it works best at .0935" or a little larger. Are you planning on putting a can on it?

Not particularly interested in paying for a suppressor at the moment, but if the HPA passes and prices come down I would be open to it eventually. I already have pretty bad bilateral hearing loss from shooting cannons.

That chart is what I used to decide on 16". Putting those numbers in with a 143gr Hornady into Hornady's ballistic calculator results in the following numbers.

16" barrel at 2505 fps velocity will be at 1227 fps at 1200 yards.
27" barrel at 2663 fps velocity will be at 1204 fps at 1350 yards.

An 11" longer barrel gives you a difference of 150 yards before going transonic, and even a 16" barrel is good to 1200 meters. This is with un-optimized factory ammo.

6.5 creedmoor is truly an awesome round.

Those are very low numbers for a 27" barrel.