AR 15 alternative calibers, what's yours?

[nortac]

The modularity of the AR platform lends itself to a slew of alternative calibers other than 5.56/.223. I'm about to embark on a .300 Blackout build and have interest in the 6.5 Grendel as well. What are your alternative calibers, advantages and/or pitfalls for your choice and did you build it or purchase a complete assembled upper?

 

[Ad Astra]

Very enthusiastic .300 BO fan here. Love that round! Palmetto upper, purchased.

Wanted 6.5 Grendel, since I already shoot, load and cast 6.5x50mm Arisaka. But wanted to use existing AR mags, so.

AA

 

[nortac]

@ Ad Astra, do you use .223 mags or .300 BO specific mags? I understand that some .300 BO loads function better in .300 BO mags, while others function fine in standard .223 mags. Are 6.5 G mags hard to come by/expensive?

 

[nortac]

Very enthusiastic .300 BO fan here. Love that round! Palmetto upper, purchased.

AA

So do you reload for it and what do you use it for? Do you hunt with it or use it/ intend to use it suppressed? This question applies to all respondents and caliber choices

 

[nortac]

Nice list of AR 15 and AR 10 calibers:

List of AR platform cartridges - Wikipedia

en.wikipedia.org

 

[RandyC]

I have a 458 Socom. Have barrels but haven't put together 450 Bushmaster and 357 maximum rimless. I have most of the parts for one, I should probably put one together.

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[OkieStubble]

I wouldn’t mind having a 6.8.

 

[nortac]

I wouldn’t mind having a 6.8.

So why a 6.8 SPC ? Please elaborate!

 

[Ad Astra]

So do you reload for it and what do you use it for? Do you hunt with it or use it/ intend to use it suppressed? This question applies to all respondents and caliber choices

I have dies and cast.30, but haven't loaded any yet. Think I've been to the range twice this year ... Wasting my membership! Its a bad year.

No, can't hunt. No can, either, but shooting subsonic is good for home defence. I never SD supersonic ...

AA

 

[OkieStubble]

So why a 6.8 SPC ? Please elaborate!

Just like the .40 settles the debate between 9mm and .45, the 6.8 settles the debate between AR or AK between .556 and 7.62x39.

The .40 hits heavy like the .45 and fast like the 9mm. The 6.8 SPC hits heavy like the AK round but also shoots fast, flat and with distance like The AR round, but the 6.8 will still have the knock down after it travels that 800 meters.

 

[RandyC]

Back when they both came out there were a lot of comparisons between the 6.8 and the Grendel. At range the Grendel was the clear winner

Then again, as a 2 legged varmint gun out to 300yds the 6.8 is pretty hard to beat. I like the 458 Socom better in that role, for me, even with the minimalist magazine capacity.

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[nortac]

I read a report that basically states the 6.8 and 6.5 are essentially equivalent out to about 500 yds, after that the Grendel's 6.5 bullet has the advantage as it's ballistic coefficient allows it to drop less, be less affected by wind drift and retains energy better at distance.

 

[OkieStubble]

I read a report that basically states the 6.8 and 6.5 are essentially equivalent out to about 500 yds, after that the Grendel's 6.5 bullet has the advantage as it's ballistic coefficient allows it to drop less, be less affected by wind drift and retains energy better at distance.

I think the .556 will soon be obsolete with the rising popularity and promise of calibers like the 6.8 SPC the 6.5 Grendel and even the 6.5 Creedmoor.

While similar, they all have their own individual and specific pro’s in their design parameters without having a lot of con’s. Biggest con I can think of right off the top of my head, is the price of 6.8 ammo which far and away exceeds the price of Grendel ammunition.

However, while the ballistics of the Grendel and SPC are somewhat similar and match well in combat distances of 300-500 yards, the SPC was specifically designed to work better from shorter AR barrels of 16” or less.

While you can shoot the Grendel quite effectively from a 16” AR, I think it’s best suited for 20” barrels and taking advantage of its slightly better velocities and energy coefficients which better increases pin point accuracy at slightly increased longer ranges.

In other words, if I wanted to carry a comparable sized and weighted AR for combat distances, I think I would want a 14” AR with red dot and magnifier for residential and commercial areas chambered in 6.8 and a 20” Scoped AR with some 4 by 12 by 50 magnification in Grendel for more rural areas, IF I didn’t want to lug around a heavier 7.62x51 battle rifle.

I’d rather do Creedmoor in a large scoped bolt over an AR for way downtown stuff any day.

 

[nortac]

I can't disagree with your logic of a 6.8 SPC in a carbine length barrel vs. 6.5 Grendel in a rifle length barrel.
Therefore I need both, in true B&B fashion!

 

[RandyC]

I think the .556 will soon be obsolete with the rising popularity and promise of calibers like the 6.8 SPC the 6.5 Grendel and even the 6.5 Creedmoor.

While similar, they all have their own individual and specific pro’s in their design parameters without having a lot of con’s. Biggest con I can think of right off the top of my head, is the price of 6.8 ammo which far and away exceeds the price of Grendel ammunition.

However, while the ballistics of the Grendel and SPC are somewhat similar and match well in combat distances of 300-500 yards, the SPC was specifically designed to work better from shorter AR barrels of 16” or less.

While you can shoot the Grendel quite effectively from a 16” AR, I think it’s best suited for 20” barrels and taking advantage of its slightly better velocities and energy coefficients which better increases pin point accuracy at slightly increased longer ranges.

In other words, if I wanted to carry a comparable sized and weighted AR for combat distances, I think I would want a 14” AR with red dot and magnifier for residential and commercial areas chambered in 6.8 and a 20” Scoped AR with some 4 by 12 by 50 magnification in Grendel for more rural areas, IF I didn’t want to lug around a heavier 7.62x51 battle rifle.

I’d rather do Creedmoor in a large scoped bolt over an AR for way downtown stuff any day.

ALL of this makes perfect sense.

The articles I'd looked at suggested the dramatic drop off for the 6.8 came after 300 rather than 500 so I've tended to view it as being of somewhat limited usefulness without considering how well it excels in it's niche. That's bad on my part. It says "special purpose cartridge" right in the name...

I reload for everything so ammo costs are pretty evenly matched component price-wise. If I was going to let component prices scare me off 75 cent a pop 458 brass would have already done it. I cast for that as well so the high price of appropriate projectiles isn't a thing as long as I maintain a supply of wheel weights.

I've been thinking of building a 22 or 24 inch AR10 6.5 Creedmoor. Other irons that have been in the fire long enough to start melting.

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[RandyC]

I can't disagree with your logic of a 6.8 SPC in a carbine length barrel vs. 6.5 Grendel in a rifle length barrel.
Therefore I need both, in true B&B fashion!

Yeah, he sold me.

I think I already have a couple hundred pieces of 6.8 brass too. I've bought rifles for lesser reasons...

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[Raissermesser]

I think the .556 will soon be obsolete with the rising popularity and promise of calibers like the 6.8 SPC the 6.5 Grendel and even the 6.5 Creedmoor.

While similar, they all have their own individual and specific pro’s in their design parameters without having a lot of con’s. Biggest con I can think of right off the top of my head, is the price of 6.8 ammo which far and away exceeds the price of Grendel ammunition.

However, while the ballistics of the Grendel and SPC are somewhat similar and match well in combat distances of 300-500 yards, the SPC was specifically designed to work better from shorter AR barrels of 16” or less.

While you can shoot the Grendel quite effectively from a 16” AR, I think it’s best suited for 20” barrels and taking advantage of its slightly better velocities and energy coefficients which better increases pin point accuracy at slightly increased longer ranges.

In other words, if I wanted to carry a comparable sized and weighted AR for combat distances, I think I would want a 14” AR with red dot and magnifier for residential and commercial areas chambered in 6.8 and a 20” Scoped AR with some 4 by 12 by 50 magnification in Grendel for more rural areas, IF I didn’t want to lug around a heavier 7.62x51 battle rifle.

I’d rather do Creedmoor in a large scoped bolt over an AR for way downtown stuff any day.

My guess is that 5.56 will remain popular much the same way other older rounds have remained popular. I don't know which of the newer rounds will become popular, if any. That's not to be contrary: the 5.56 has a lot of user momentum behind it, while the newer rounds don't as of yet.

 

[jkingrph]

I built up three 6.5 Grendle AR's about 8-9 years ago, and finally got a CZ 527 bolt action in that caliber a couple of years ago. I think it's a fantastic little caliber, very mild recoil, and hits steel targets with a lot more authority than a 5.56. I have not tried any of the other calibers, nor plan to do so. When I started factory brass was very expensive and hard to come by, long waiting times, so I picked up a quantity of IMI 7.62x39 brass, resized, loaded and started fireforming. My fireforming loads fed and cycled my AR 15 fine, and gave accuracy good for plinking. The only difference is those cases use large rifle primers, vs small in the standard brass.

 

[nortac]

I have a CZ 550 FS bolt gun in 6.5x55 Swede, I would love to have the 527 in 6.5 Grendel.

 

[RandyC]

I know a guy in New Zealand that built a bolt rifle, uses it for their goats. He really likes it.

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