Creedmoor AR

[DeadeyeChrista'sdad]

Sort of sticking my nose out a little far.
I'm in the beginnings of a nice 6.5 creedmoor build, and already my ADD contaminated brain is already speculating on the next thing.
It occurs to me that everything that makes an AR10 a perfect platform for a .308 also makes it an even better platform for a 6.5 creedmoor.
Upon checking, I find numerous 6.5 uppers available.
So what say you? Good idea? Bad idea? Insufferable redundancy?

 

[DRob]

From what I understand, the 6.5 Creedmoor is everything the .308 wants to be and then some. Traditionalists may cry out in anguish.

OTOH, perhaps your next must-have will be a 6 Creedmoor. It's beginning to gain traction.

 

[Xrage]

I was looking for a 6.5 creedmore weapon last year. For me the AR platform is a high volume shooting weapon system and since the 6.5 creedmore has a relatively short barrel life i bought a Ruger precision bolt action rifle and I love it. I personally dont think 6.5 is a practical caliber for an AR rifle.

 

[BiscuitsandGravy]

Last summer PSA was running one of their 20" SS 6.5CM uppers on sale for $399. I was like you, I wanted to give 6.5CM a try and PSA had their sale so it was a win-win. IIRC there was a thread about them. We reload so we have a couple go-to recipes. One is 140g Barnes Match Burners over 38.5gr of RL17. YMMV.

Link to upper... https://palmettostatearmory.com/psa...djustable-gas-block-bcg-and-ch-516447593.html

Link to lower... https://palmettostatearmory.com/psa-pa-65-6-5-creedmoor-stripped-lower-receiver.html

These are the sku's from last summer.

Take care.

 

[SSE]

I think the AR would be great in 6 or 6.5 CM
With a match grade barrel the AR will shoot with a bolt gun. When I decide on 6 or 6.5, then I will decide on bolt or AR. To me the only reason I might go bolt is it is easier on the brass.

 

[Rookie]

I have a 6.5 and a 6 Creedmoor. The 6 Creedmoor is going to be my new coyote gun when I figure out what load it likes. SSE is right, they're hard on brass.

 

[Areoflyer09]

I think the AR would be great in 6 or 6.5 CM
With a match grade barrel the AR will shoot with a bolt gun. When I decide on 6 or 6.5, then I will decide on bolt or AR. To me the only reason I might go bolt is it is easier on the brass.

I’ve got the Savage MSR Long Range in 6CM. I really enjoy it. It’s a really big softy, very easy to shoot.

 

[VulpesForge]

If you're going to be attempting to drive the rifle out past 600-800 yards consistently then 6.5 creedmoor is your man. Higher BC means it is impacted significantly less by wind at great ranges and outmatches 308 nearing the 800 yard mark, I believe, in terms of retained energy ftlbs beyond that point. Before that extreme distance though, 308 beats 6.5 CM handily for energy on target if your intent is to hunt long range. If you've taken 308 out any significant distance at all you know it's more highly disturbed by wind than 6.5 CM at distance as well. I had this conversation with myself for weeks before I landed on 308 and what really drove it home for me was barrel life and ammo cost. Barrel life for 308 is closer to 5k rounds and you can expect 6.5 to give you between 2k and 3k as far as intended match grade accuracy goes. Yes, both will still handily shoot past 100 yards well past those round counts and most people wouldn't be able to tell the difference, so you have to decide how far you're actually going to be shooting the rifle (honestly) and go from there. Ammunition is another big factor for me, but I reload for both. You could, before the panic, get cheaper wolf or tula 308 for $0.30 or less per round delivered and the cheapest 6.5 CM from S&B was getting down around the $0.60 per round mark. You can effectively double your ammo for the money by going with 308 or you can get higher quality ammunition like surplus or AE brass for the same money as "cheap" 6.5 CM. 6.5 CM is inherently more accurate, but it's more expensive and doesn't preform terminally as well as 308 at ranges less than 800-1000 yards. You also have to consider availability since we just happen to be in one of the panics that seems to occur every 4 years or so. I can't go to my local shops and find 6.5 CM, but even when the real panic was going on they still had 308 stocked and even had different bullet weights in some cases. YMMV on that particular subject, but it is definitely something to take into account if you don't hoard ammo when it's cheap and especially buying a new caliber during a shortage. I say all that with the caveat that I own a 6.5 CM Ruger precision and absolutely adore the caliber. In my humble opinion 308 is the round most people are going to land on if they want a do all rifle that will go farther than most people have the ability (or the glass) to shoot. 6.5CM is an amazing round with lower recoil, but in order to gain meaningfully on 308 it needs to be taken out past 800+ yards in order to see a reasonable retained energy comparison between the two.

Tl;Dr : In terms of AR-10's, 6.5 CM is better for extreme range but costs A LOT more in the long run and is only advantageous you intend to seriously shoot it way way out there. 308 is for everyone not going out past 800 - 1000 yards, is more available locally in the panic times, and saves by almost half if you're running comparable ammunition.

 

[markiemark]

I have been looking at the 6.5 as well but see quite a bit of talk about overgassing with it. From those that have it, is that a problem?

I was concerned and looking at the PWS uppers since they are piston driven. Is it helpful to have a rifle +1 for anything longer than 20” perhaps?

 

[sheepdog697]

If you build one make sure to do the +2 gas system on a 6.5 creedmoor barrel. 22" barrel with +2 gas is what most people think is the ideal setup.

 

[BiscuitsandGravy]

I have been looking at the 6.5 as well but see quite a bit of talk about overgassing with it. From those that have it, is that a problem?

I was concerned and looking at the PWS uppers since they are piston driven. Is it helpful to have a rifle +1 for anything longer than 20” perhaps?

FWIW, the upper we picked up from PSA last summer was way over gassed. Fortunately, since it came with an adjustable gas block, we were able to tune it down very nicely.

 

[Hohn]

I love the creedmoor, but in a gas gun I think I'd go with 7-08. Longer barrel life and will hit a tiny bit harder down range with some loads. That shallower shoulder angle is also more of a help than a hindrance in a gas gun. Plus, it's closer to the .308 that the AR10 was designed around and is less likely to have the gas system issues that so many 6.5 AR guys struggle with (you can assume you WILL need an adjustable gas block if you build a 6.5 AR).

 

[sheepdog697]

FWIW, the upper we picked up from PSA last summer was way over gassed. Fortunately, since it came with an adjustable gas block, we were able to tune it down very nicely.

adjustable gas blocks help with the pressure. Since the 6.5cm is high pressure sometimes these don’t even remedy the situation. However, adjustable gas blocks dont do much for the dwell time. The +2 gas will keep the bolt locked long enough for the bullet to leave the barrel. Accuracy can degrade if your AR is unlocking before the bullet leaves.

 

[Hohn]

adjustable gas blocks help with the pressure. Since the 6.5cm is high pressure sometimes these don’t even remedy the situation. However, adjustable gas blocks dont do much for the dwell time. The +2 gas will keep the bolt locked long enough for the bullet to leave the barrel. Accuracy can degrade if your AR is unlocking before the bullet leaves.

6.5 creedmoor= 62,000 psi MAP piezo per SAAMI.
.308 Winchester= 62,000 psi MAP piezo per SAAMI.

Exactly what do you mean that the creedmoor is "high pressure"? Compared to what?

 

[sheepdog697]

6.5 creedmoor= 62,000 psi MAP piezo per SAAMI.
.308 Winchester= 62,000 psi MAP piezo per SAAMI.

Exactly what do you mean that the creedmoor is "high pressure"? Compared to what?

Good point Hohn, you are referring to chamber pressure. I should have clarified. Im talking port pressure, the pressure of the gas when it comes into the operating system. There is much more space and volume in a .308 bore than 6.5 or .260. Slower burning powders through a tighter bore with 6.5 and .260. The +2 gas system has a lower "port pressure" because it allows for a longer time between ignition and bolt opening. Again, this is simply a recommendation if you're starting from scratch. Avoid issues others have ran into when building a large frame with a .260 or 6.5 chamber. People build them with regular rifle length gas systems, and dont have issues. However, i think there is no argument that a 22" barrel with a +2 gas would be more reliable than an 18" with rifle gas. You dont hear too many issues about people having blown primers or brass getting beat up in the .308 platforms. At least not as much.

 

[Rookie]

Yup, my 6mm Creedmoor is hard on brass and primers even with a +2 gas tube.

 

[Hohn]

Good point Hohn, you are referring to chamber pressure. I should have clarified. Im talking port pressure, the pressure of the gas when it comes into the operating system. There is much more space and volume in a .308 bore than 6.5 or .260. Slower burning powders through a tighter bore with 6.5 and .260. The +2 gas system has a lower "port pressure" because it allows for a longer time between ignition and bolt opening. Again, this is simply a recommendation if you're starting from scratch. Avoid issues others have ran into when building a large frame with a .260 or 6.5 chamber. People build them with regular rifle length gas systems, and dont have issues. However, i think there is no argument that a 22" barrel with a +2 gas would be more reliable than an 18" with rifle gas. You dont hear too many issues about people having blown primers or brass getting beat up in the .308 platforms. At least not as much.

Ah,yes. Absolutely the smaller bore has more port pressure because the volume the behind the bullet is smaller. Burn speed, however, doesn't matter here. If you have the same charge weight and it all burns, you're producing about the same amount of gas (within similar powders-- ball vs extruded, for example).


One common problem with AR gas system tuning is that the gas energy is pressure * volume. And the amount of volume depends on pressure and time. Long story short, simply changing orifice size can't offset the effect of higher or lower pressure. Ideally, you should change the gas system length relatively easily as part of tuning. But right up to the cork time limit, longer gas is better gas.

 

[sheepdog697]

Correct +2 gas meaning +2” it would be an XL gas tube.

Im pretty sure we are saying the same thing.