16” 6.5 Creedmoor barrel worth it?

[pointblank4445]

1) much hype

This is the enemy of every new cartridge.

People were expecting scaled down 6.5CM ballistics down to a 16-18" small-frame AR15 with the 6ARC. Meanwhile you see hype of the 6.5CM being hyped as having a ballistic arc/trajectory to .300WM. We've already seen in this thread the inevitable 6.5G to 6.5CM comparison cause "It's all 6.5mm"...about like a Frenchie and a pitbull are comparable as "terriers".

People always gettin' set up for disappointment making comparisons outside of a straight "apples-to-apples":
A) Cartridge type (magnum vs. short action rifle, intermediate vs. short action rifle, etc.)
B) Platform type (large frame vs small frame vs bolt)
C) Barrel length inconsistency

Ya know what ya don't see much of:
- Here's what a 6ARC is doing out of an 18" AR compared to 77smk out of an 18" AR
- Here's what a 6.5CM is doing out of a 16" SR compared to a 16" 308 SR


For the record, I think there's a better mousetrap to be had in a 6mm AR15...

[drtywk]

What BCG problems have you heard of with the 6mm ARC?

Magazines really are the only downside to 6ARC, but Duramag 6.5 Grendel mags seem to have solved a lot of those issues. And to be honest, Geissele wouldn't have jumped into the game if there wasn't DOD money to be gained from it. Has anyone even seen a G gun or barrel in the wild, that wasn't on YouTube?

[pinzgauer]

What BCG problems have you heard of with the 6mm ARC?

A lot of people don't understand the difference with cartridges like 6.5Grendel and 6mm ARC and the fact that they have to be loaded to lower pressures due to increased bolt thrust.

(PSI x case head area)

Pressure limits on both are well below normal primer/case head swipe levels.

So just like with 6.5 grendel, there is very likely a bunch of people seriously overloading 6 mm ARC. With resultant bolt issues.

There is also the ever popular tendency to try to use a 5.56 bolt opened up to a larger bolt face.

You can't do that, the Grendel standard bolt follows colt's original research when they made their 7.62x39. there is a very specific geometry to both the bolt face depth and the radius of the lugs that has to be followed to shoot reliably at even 52k PSI

I don't know of anyone having bolt issues with Grendel in the last decade who was using a proper Grendel bolt, and my brother and I have been shooting 6.5G for longer than that.

As to 6.5 g versus a short creedmoor, there is a point of diminishing returns with barrel length relative to case capacity.

This is something metallic silhouette shooters learned 30-40 years ago with 7BR versus 7-08 in the same pistol. And we were all about windrift and retained energy at 200 m.

The larger case required significantly more powder to get the same velocity, which significantly increased recoil. Conservation of mass and all that. (Remember your powder also exits the barrel in the form of gases at the same velocity. And has mass. So recoil is determined by the powder weight plus bullet weight)

You can still get nominally just a hair more velocity out of the 7-08 case, but with significantly more recoil. (And fireball)

I know that 14" with a 7mm cartridge the larger case capacity stuff just wasn't worth the hassle and expense.

Back to op, I shoot a 16" 308 on a regular basis and I do not find it objectionable, nor do others. That said I have no doubt that creedmoor would be more effective in the same barrel length, especially down range.

That unless you were doing the slow and heavy route, in which case I think 308 would win.

I don't bother trying to sell people or debate on the merits of grendel. But I will say in an M4 size package it is a very good option. Especially when compared to the weight of a large frame.

[1168]

Geissele wouldn't have jumped into the game if there wasn't DOD money to be gained from it.

Unless of course they thought there was money to be gained by association of their name with DoD.

[turnburglar]

To everyone that says: "Why not go with X caliber that fits into an AR15?"

Simply put; the old racing adage still applies: "There is NO replacement for displacement". The 6.5CM has a 40+ grain case capacity and is already slinging some of the most aerodynamic pills on the market. It is also a very versatile cartridge in being able to load super long 147gr ELDM's or zip 95gr vmax that has the same BC as a 77gr SMK. I shoot a local PRS style match that goes out to 700 yards, and is AR's only. I have spotted for every caliber that fits into a semi auto and can tell you that 6.5 Grendel and 6 Arc are NOT that impressive to watch fly. As a general rule of thumb any cartridge that doesn't start above 2600 FPS is gonna rainbow. If you are actually shooting out to distance you will learn speed matters probably more than BC. You only need like a 0.45G1 BC and SPEED and you can get to 1k easy.

Just as an aside I have that Wilson Combat 16" recon and its a shooter. Needs some help with gas as I said its kinda spicy. I only went from a 18" to a 16" because I have a can in jail and I want to keep the gun handy.

For a true "battle rifle" get a SCAR17.

[drtywk]

Unless of course they thought there was money to be gained by association of their name with DoD.

Hence my entire point. G would not have jumped into this, or their 6.5CM project (MRGG), if there wasn't DOD funding involved in the development, which would also lead to the potential of the "me too" buyers out there helping them recoup their cost sharing portion of the project.

[Pappabear]

Which 16 inch barrel matters a great deal too. My DD Delta 5 bolt gun has a very fast (tight chamber?) barrel for a 20inch gun. It performs like my 24 inch bolt gun.

I bought an MWS 20inch SS barrel to inch out every possible bit of velocity vs my 16 inch barrel and I gained a measly 50 to 75 FPS. Another note, our other shooting buddy often quoted here has an 18inch MWS barrel that he makes consistent hits at 1,360 with 175 TMK's flying at 2630 FPS and its his favorite gun. And he has many many many guns like most of us.

So you can def run 6.5cm out of a 16 inch gassy with success, but dont 100% compare ones guys gun to your build. Just build shoot and learn, that is all you can do.

PB

[Disciple]

Sheared lugs, broken extractors and all the other fun stuff trying to trim off the meat to accept 220 Russian bases into an AR bolt.

That technology was already worked out with the 6.5 Grendel. Use good bolts and don't handload using pressure signs as your guide (which appear much higher than 52,000 PSI) and the problems go away, unless I am badly misinformed.

We've already seen in this thread the inevitable 6.5G to 6.5CM comparison cause "It's all 6.5mm"...about like a Frenchie and a pitbull are comparable as "terriers".

I feel personally called out here, and if so I am being misrepresented. My point was that heavier bullets appear to provide a greater relative benefit from the Creedmoor.

[pointblank4445]

Point noted with the PSI, but tis the nature of the beast to want more and push a bit more, and a bit more. Again, people experimenting to make things what they aren't.

I feel personally called out here, and if so I am being misrepresented. My point was that heavier bullets appear to provide a greater relative benefit from the Creedmoor.

Not a call-out, more just springboarding off that comparison and poking fun at the startling amount of people that put too much stock into bore diameter, and not enough into case capacity and the relationship of BC to MV.

Honestly, I and others have circled the question of short/handy and its relation to performance/capability. I can fill an album with my failed endeavors in this area. It always reminds me of what I call the "CCW Paradox" which is just the boiling frog in gun terms. If y'all will indulge me, it starts like this:

- I should get a Glock 43 to carry
- Perhaps it should be a 43X for capacity
- If I'm going to 43X, might as well G48 since I AWB since the grip size is no different
- If I'm G48, I might as well G19 since it's the same footprint but with better performance capacity
- If I'm G19, what's a fraction of an inch on the grip and barrel to go G17
- Since I got a G17 sized grip might as well just roll G34 and slap on an X300.

Between each step is small but top and bottom are miles apart. Figuring out the nuance of that sweet spot FOR YOU is the hard part.

[markm]

It always reminds me of what I call the "CCW Paradox" which is just the boiling frog in gun terms. If y'all will indulge me, it starts like this:

- I should get a Glock 43 to carry
- Perhaps it should be a 43X for capacity
- If I'm going to 43X, might as well G48 since I AWB since the grip size is no different
- If I'm G48, I might as well G19 since it's the same footprint but with better performance capacity
- If I'm G19, what's a fraction of an inch on the grip and barrel to go G17
- Since I got a G17 sized grip might as well just roll G34 and slap on an X300.

Between each step is small but top and bottom are miles apart. Figuring out the nuance of that sweet spot FOR YOU is the hard part.

I see the same paradox in REVERSE with rifles all the time on the forums. This thread topic is a world class example.

Now I'm not totally unsold on the possibility of the OPs idea, but it is the classic example of wanting big performance in a smaller and/or lighter package.