AR Build - 6mm Arc or 6.5 Grendel?

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Saluki91

Saluki91

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I'm building a funzies AR for club matches out to 500 yards, and possibly eliminating the occasional coyote. In a perfect world, it would also accompany me on some future hog hunts. Finally, value-for-money will be a high priority. The plan is to acquire quality components as I find them on sale. I'm in no hurry.

What say ye... 6mm Arc or 6.5 Grendel? Arc intrigues me, but I wonder about component availability long term. Grendel seems to be well established.

Is there a particular barrel (or two or three) that I should keep an eye on?

Any other words of wisdom?

As always - Thanks!
 
6 ARC were it my money. I’ve been building Grendels long enough that Bill still owes me money, but the ARC better does the things I want to do.

Components are largely the same - as even if 6 ARC brass would somehow become short, it can be formed from Grendel brass in a single pass. Suitable 6mm bullets are typically prevalent, with far more relevant options than the 120 class 6.5mm bullets.

My slant in this favor is heavy enough, I sold my last Grendel a few years ago to build a 243LBC as a wildcat, which is a 6 ARC which hasn’t been watered down as much - same case, same neck down, just without the shoulder pushed back 30 thou. Now that the ARC is available as factory ammo and standard barrels, it’s dead simple.

Proof Research barrel. 20-22” leaving room within 24” for the brake.
 
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Varminterror said:
6 ARC were it my money. I’ve been building Grendels long enough that Bill still owes me money, but the ARC better does the things I want to do.

Components are largely the same - as even if 6 ARC brass would somehow become short, it can be formed from Grendel brass in a single pass. Suitable 6mm bullets are typically prevalent, with far more relevant options than the 120 class 6.5mm bullets.

My slant in this favor is heavy enough, I sold my last Grendel a few years ago to build a 243LBC, which is a 6 ARC which hasn’t been watered down as much - same case, same neck down, just without the shoulder pushed back 30 thou. Now that the ARC is available as factory ammo and standard barrels, it’s dead simple.

Proof Research barrel. 20-22” leaving room within 24” for the brake.
Click to expand...



what he said^^

I have AR’s in both and I’ve got to say the Arc can throw the heavy pills that the Grendel can’t I’d go ARC IF It were me

ymmv
 
Objectively, when we’re talking about AR’s stuck with limited Mag length capacity, the math is all out there. At the muzzle, the 6.5 Grendel has a bit more momentum than the ARC - a 123 at 2550fps versus a 108 at 2700 (neglecting any differentiation for barrel length vs. handling balanced against weight). It is less than a 10% gap, but it’s in favor of the Grendel. Kinetic energy at the muzzle is very similar, with a slight advantage to the Grendel (it’s a larger case with a larger bore area operating at the same max pressure, so yeah, that’s basic physics). But you’ll see about a 10% advantage in ballistic coefficient and about a 5% advantage in sectional density and about 10% reduction in recoil momentum for the ARC...

Not so different than what we see for a lot of cartridges - there’s a tipping point where bigger caliber bullets simply don’t gain enough. 35 Whelen versus 30-06, 338win mag versus 300win mag... pushing up caliber to the point where we start sacrificing too much velocity or especially have to start limiting BC and sectional density because they simply can’t fit heavier, longer bullets into the rifle... yeah... nothing of benefit happens. Going down below 6 ARC doesn’t seem to pan out, as we go back down in ballistic coefficient when we drop to 80-90grn 22cal bullets and again, lower sectional density to boot.

So if you want to think a 6 ARC is in the sweet spot for the Grendel/x39/ppc case with 6mm bullets, all of the above info should help you KNOW why it really IS the sweet spot.
 
As a 6.8 SPC fan boy, ARC. Such an interesting little round. Plan to build one myself at some point when I get done playing with these 6mm Creeds.
 
if you do not reload, forget it. The factory stuff is throttled down on both. Folks want to talk about the 6s at 105 and forget about the 107 SMK in 6.5 in the Grendel that does over 3k. The 120 SMK can be driven to near 3k with an adjustable gas block.
You do not need heavy bullets with the 6 or the 6.5 it ain’t a 30cal.

I shoot cans and the Grendel with 160g subs is quite effective.

If you want to do a 6 you might do he 6x45 or the Mongoose, both are based on the 223 and are single pass with LC bass. The mongoose has a shortened neck, 40 degree shoulder and blown out body to achive the same H2O capacity.
The 1-8 at 18” in SS gives you all of the options for bullet weight and handling. A mid length gas setup, is what you want for the small capacity cases.
 
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I'll take the other opinion and say the grendel. I don't think the arc is going to be around in a few years, and I know it's only a half a mm in diameter difference, but I don't have much faith in anything smaller than 25 cal for hunting anything larger than a coyote.

I reload, so having a dead end caliber isn't the end of the world, but it's annoying. New powders come out and there is not data, brass can be hard to find, etc.

On the other hand, you'll be able to find 6mm bullets easier than 6.5 in a crunch. Stupid creedmoor shooters buying all the 264 bullets so I do t have any for the grendel, grumble grumble grumble..........
 
Saluki91 said:
I'm building a funzies AR for club matches out to 500 yards, and possibly eliminating the occasional coyote. In a perfect world, it would also accompany me on some future hog hunts. Finally, value-for-money will be a high priority. The plan is to acquire quality components as I find them on sale. I'm in no hurry.

What say ye... 6mm Arc or 6.5 Grendel? Arc intrigues me, but I wonder about component availability long term. Grendel seems to be well established.

Is there a particular barrel (or two or three) that I should keep an eye on?

Any other words of wisdom?

As always - Thanks!
Click to expand...



So what are you building?
 
Armorer 101 said:
The 120 SMK can be driven to near 3k with an adjustable gas block.
Click to expand...
What powders are you running that can get close to 3K with the Grendel?

CFE 223, 8208, and leverevolution all ran out of case capacity around 27-2750 using 123 Amax in my bolt gun.... Now admittedly my CZ seemed slow so that could be part of it.

Are 120 SMKs significantly shorter then an A-Max? I've ever used em.
 
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@LoonWulf - I’ve been biting my tongue all day over that one... there ain’t a powder which 1) fits into the Grendel case 2) at safe pressure for the AR which will push a 120 SMK to 3000. Not by 200fps, adjustable gas block or not. That would be pushing pressures in a bolt gun a bit harder than I like, let alone a gasser.

Unless he has a barrel longer than 30”...
 
horsemen61 said:
So what are you building?
Click to expand...
As of today, I have a 17 Designs Lower, and a Magpul MOE stock kit... not much, but it is a start. The plan is to take advantage of sale prices as they present themselves. This hunt for bargains is genetically driven - it isn't necessarily based on need. I don't mind spending $ on components that provide value for that money (barrel, trigger, etc.).
 
I think the decision should be based on what you think your primary function will be for the rifle. Long range percision - 6 mm ARC. Plinking and intermediate target shooting - either. Hunting - 6.5 Grendel. I like hunting with a heavier bullet and the Grendel gives me that ability. Not real heavy but heavier.
 
greyling22 said:
I'll take the other opinion and say the grendel. I don't think the arc is going to be around in a few years, and I know it's only a half a mm in diameter difference, but I don't have much faith in anything smaller than 25 cal for hunting anything larger than a coyote.

I reload, so having a dead end caliber isn't the end of the world, but it's annoying. New powders come out and there is not data, brass can be hard to find, etc.

On the other hand, you'll be able to find 6mm bullets easier than 6.5 in a crunch. Stupid creedmoor shooters buying all the 264 bullets so I do t have any for the grendel, grumble grumble grumble..........
Click to expand...
hornady released the cartridge, to my Knowledge they have yet to drop any round ever. Plus making the arc if needed is about as easy as it gets.
 
For me it would be the Grendel. Simply because of the option for cheap steel cased plinking ammo, in addition to quality factory ammo. I reload, but I like options too.
 
I really want a 6 ARC, but I will probably build my next ar in 6.5 grendel. The availability of ammo, projectiles, brass, and barrels is just favored to the 6.5. In a year or two that might be different, but right now 6.5 all the way. Now a 6 ARC bolt gun though....
 
Saluki91 said:
As of today, I have a 17 Designs Lower, and a Magpul MOE stock kit... not much, but it is a start. The plan is to take advantage of sale prices as they present themselves. This hunt for bargains is genetically driven - it isn't necessarily based on need. I don't mind spending $ on components that provide value for that money (barrel, trigger, etc.).
Click to expand...



which cartridge are you going with?
 
Varminterror said:
@LoonWulf - I’ve been biting my tongue all day over that one... there ain’t a powder which 1) fits into the Grendel case 2) at safe pressure for the AR which will push a 120 SMK to 3000. Not by 200fps, adjustable gas block or not. That would be pushing pressures in a bolt gun a bit harder than I like, let alone a gasser.

Unless he has a barrel longer than 30”...
Click to expand...

Yeah, my Grendel must be particularly slow, at 16" it's pretty comfortable in the low 2,400 fps range with 120/123gr. I've gotten it up past 2,500 fps leaning on it with LVR, but that seemed a little frisky pressure wise.

500-600 fps more out of a barrel of any length is solidly in 6.5 CM range.... Quite a trick.
 
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