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Old April 19, 2018, 08:32 AM   #1
Bartholomew Roberts
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Alternate Caliber AR15 vs. AR10

It seems lately that there is considerable effort going into squeezing more power out of intermediate caliber rifles like the AR15. With new bolts, barrels, and magazines, we have some good choices that can increase the effective range over 5.56.

At the same time though, AR10s are getting leaner and meaner. I’ve seen some moderately priced AR10s in the 8lb range. You can pick up a 16-18” AR10 that will weigh less than a 24” AR15, be balanced better, and hit harder because it is chambered in a full-bore rifle cartridge.

So where is the point of diminishing returns when it is smarter to step up to a lightweight AR10 instead of trying to squeeze more out of the AR15?
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Old April 19, 2018, 08:50 AM   #2
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If polymer cases become a reality, that would really help get the weight down on the AR10. With that said, the 270AR and 7mm Valkyrie pack a lot power into a AR15. But forming the 6.5x47 Lapau brass isn't a lot of fun IMO. The TAC6 (6mm 6.8 wildcat) and 6mm Predator (6mm Grendel wildcat) are almost as good. Would love to see one of these wildcats become a SAAMI cartridge. Won't be surprise is the 7mm Valkyrie makes it. And a 6mm wildcat like the TAC6.
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Old April 19, 2018, 11:00 AM   #3
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I dont know where the point of diminishing returns is but im very happy i bought an AR10 in .308. Cant yet speak to accuracy but the larger round just is a lot more fun to shoot - feels real. And in every department other than cost and recoil (depending what round you pick) its gonna beat out about everything that runs through an AR15, at about .50 to .90 a round for brass case depending what you pick.

You can debate tactical advantage, what you really need for stopping power for your application, but kinda like riding a Harley there is nothing like more raw power versus something more engineered and refined.

Personally, my very amatuer view, i think some of the adaptions to make the AR15 support larger caliber or pistol configurations are just compromises to make it work.. An auto loading handgun can often hold 15 rounds yet nearly will fit in your pocket. An AR10 can take rounds where they chose a projectile and matched charge, then made the rifle to fit it versus designing something around what fits in the existing rifle.
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Old April 19, 2018, 11:33 AM   #4
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For me, it comes down to ubiquity. While 308 is used all over the world, the AR10 isn't as strictly controlled as the AR15. The larger calibers in the AR15 aren't nearly as prolific as the military cartridges are. I would be/am willing to sacrifice the ubiquity of the cartridge before sacrificing the ubiquity of the platform.

Besides, there are much more prolific platforms for the 308 a la G3, M14 over the AR10. Granted, the ergos are different, but I like my CETME (kind of wish it had the H&K diopter, but such is the compromise made to buy the inexpensive version), but I also understand that's my personal opinion.
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Old April 19, 2018, 12:07 PM   #5
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I was very tempted to buy an AR10 more recently, but ended up with a AR-15 in 6.5 Grendel. The reason I didn't go AR10 was the lack of part standardization. Too many possible problems matching up if you are assembling your own (even if you are buying completed uppers and lowers).

Also you've got to consider the difference in function at the weights you mention. A 24" Ar-15 will be a heavy barrel meant to shoot really accurately without moving a whole lot because it is quite front heavy (probably varmint rifle), but the AR-10 would be a lightweight, heavier recoiling, less accurate (in theory), pencil-barrel-heating-up-very-quickly rifle that is more maneuverable and balanced. I'm not sure the weight comparison really works.

I've seen fully assembled DPMS AR-10s for under $600. If you just want a higher powered AR-15 that could do a little bit of everything, that's really tempting. It's be a great pig or deer hunting gun as long as it is accurate enough (and it easily should be for reasonable ranges). I do believe at $600 its cheap enough that the price tag isn't an issue at all. It just comes down to what functionality you want.
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Old April 19, 2018, 12:23 PM   #6
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"...a 16-18”..." Those are marketing fad rifles. Far too much velocity loss to bother with 'em. The point of diminishing returns starts with carbine length barrels. And expecting rifle length performance.
"...AR10s in the 8lb range..." A real Armalite AR-10 weighs 7.25–8.9 lbs. with no mag and a 20" barrel.
The Finns bought 5 AR-10s chambered in 7.62 x 39 for testing back in the 50's. Always thought that was a brilliant combination.
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Old April 19, 2018, 03:06 PM   #7
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The OP's initial question is a good one. Consider where things are going recently between an AR10 in 6.5 Creedmore vs AR15 in .224 Valkyrie as a long range platform. Which would you want?
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Old April 19, 2018, 03:22 PM   #8
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I wrestled with this problem last year ..... daughter (age 12 at the time) liked shooting my AR-15, and took a deer with it when she was 11- the deer was small, and the range was short..... and the same rifle and load did not work well at all on bigger deer further out in 2016. So.... I was looking for more gun in a similar package- daughter is pretty slight of build and pretty recoil sensitive. I was pretty set on a 6.8SPC or 6.5G ...... but prices for the guns, bullets, brass and dies were just way too high and/or hard to find...... in addition to the fact that they did not really add all that much advantage in terms of energy ....... I stopped dorking around with the idea of a slightly better AR round and went with PSA's AR-10 in .308WIN ..... worked really well. Much cheaper, brass, bullets, dies and magazines (5 rounders for hunting) were everywhere..... didn't break the bank, either. I like it so much that I might get one in 6.5CM .....
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Old April 19, 2018, 03:29 PM   #9
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The Finns bought 5 AR-10s chambered in 7.62 x 39 for testing back in the 50's. Always thought that was a brilliant combination.
Try as I might, I can't think of anything "brilliant" about that ...... seems akin to putting a tiny inline 4 cylinder gasoline engine in a full sized truck.
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Old April 19, 2018, 06:48 PM   #10
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Quote:
in addition to the fact that they did not really add all that much advantage in terms of energy
jimbob, I'm gonna disagree with you there. Initially, off hand, my thought is: 6.8SPC bullets are heavier and have better ballistic coefficients. Again, off the cuff here. But how much slower are they going compared to a 5.56 was something I did not know. So I looked it up.

The second piece of the story is something that (can be) slightly debated: using kinetic energy (KE) as a unit of measure of effectiveness of a round. Not here to debate that, but it gives an easily comparable number to use, so we'll use it knowing that shot placement is paramount. Chuck Hawks had a good article that really baselined 800ft/lbs of energy minimum for killing a deer cleanly, so we'll use that number.

On Hornady's website they list "appropriate" uses for their bullets, so picking a bullet in 6.8SPC and a bullet in 5.56 that are both 'recommended' for deer and then matching barrel length gives us 2 bullets out of a 16" rifle, useful as you wanted a rifle that was still handy for your daughter. The 6.8SPC retains our minimum energy out to, just under, 400yds. Whereas the 5.56 only retains that energy to just under 200yds. I'd say that's pretty significant and that moving up to an AR10 gives you, potentially, more range (didn't look that one up), however you had to switch to an entire new platform.

Not saying that you didn't pick the best option for your situation, just that I feel that the 6.8SPC DOES give an appreciable gain over a 5.56 without having to go to the AR10.
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Old April 19, 2018, 08:36 PM   #11
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"If polymer cases become a reality, that would really help get the weight down on the AR10"
How can the weight of a dozen brass cases make that much difference?

I own an AR 10 but haven't even scoped it--no real purpose for it at this time. AR type rifles are the "big thing" right now but I see no "magic potion" connected to the AR's. The 6.5G and 6.8 provide the AR platform with medium range medium game capability. Kept in that context, the AR has a place in the hunting tool box.
The AR 10 has big game capabilities within reason but it's a big(ger) package and tends to get heavy. Making the AR 10 lighter comes with compromises as the barrel comprises the major source of the weight.
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Old April 20, 2018, 09:04 AM   #12
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Originally Posted by jimbob86 View Post
I wrestled with this problem last year ..... daughter (age 12 at the time) liked shooting my AR-15, and took a deer with it when she was 11- the deer was small, and the range was short..... and the same rifle and load did not work well at all on bigger deer further out in 2016. So.... I was looking for more gun in a similar package- daughter is pretty slight of build and pretty recoil sensitive. I was pretty set on a 6.8SPC or 6.5G ...... but prices for the guns, bullets, brass and dies were just way too high and/or hard to find...... in addition to the fact that they did not really add all that much advantage in terms of energy ....... I stopped dorking around with the idea of a slightly better AR round and went with PSA's AR-10 in .308WIN ..... worked really well. Much cheaper, brass, bullets, dies and magazines (5 rounders for hunting) were everywhere..... didn't break the bank, either. I like it so much that I might get one in 6.5CM .....
Glad to see your review, been looking slowly at the psa's. Sure wish they, or anybody, made the ar10 in 243. There used to several out there but the supply has dried up.
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Old April 20, 2018, 09:19 AM   #13
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If you like to shoot, cheap caliber for the win.

- 9mm
- 7.62 x 39
- .223
- 12 ga
- .22
- .308

That's my story, and I'm sticking to it. Go on about how 'exotic calibers are so much better'... I don't care
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Old April 20, 2018, 09:24 AM   #14
COSteve
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Or . . . . . take up handloading and all of them are cheaper.
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Old April 20, 2018, 09:32 AM   #15
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Sure wish they, or anybody, made the ar10 in 243.
When I was shopping for the PA-10 that I bought, there were complete uppers for 6.5Creedmore listed (but out of stock right then), and barrels for 7-08 (in stock) .... and there was a .243 R-25 at walmart ..... there's 2 of the latter on GunBroker right now (one is just $500!)..... they are all possibilities.
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Old April 20, 2018, 09:35 AM   #16
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Or . . . . . take up handloading and all of them are cheaper.
+1!

Though if one is happy with crappy ammo, the bulk steel cased stuff is hard to beat for short term cost.......
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Old April 20, 2018, 10:48 AM   #17
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jimbob, I'm gonna disagree with you there. Initially, off hand, my thought is: 6.8SPC bullets are heavier and have better ballistic coefficients. Again, off the cuff here. But how much slower are they going compared to a 5.56 was something I did not know. So I looked it up.......
Actually, the .277" bullets in weights commonly chambered for the 6.8SPC are comparable (usually .24-.27 G1) to the heavier .223" bullets .... the exception to this that I found was the Hornady 120gr SST .... but that bullet can't be launched at much more than 30/30 velocities with the available case capacity offered by the 6.8 and barrel lengths commonly available .... and needs every bit of that velocity to be stabilized by the common 1:11 twist rate of commonly available 6.8SPC barrels .... I've seen claims (on this very forum) of longer custom barrels with tighter twists launching ~120ish (IIRC) grain bullets at 2700+ f/sec ........ believe me..... I checked out the 6.8 and 6.5 AR offerings literally for YEARS ..... what is possible, if you mine the necessary unobtainium, drop the cash and burn the time and everything is tweaked just right and all the stars align just right....... that is all very, very interesting, but even after all of that, it just does not compare favorably to the ft/lbs of energy, ballistics and terminal effects available off the shelf afforded by the extra case capacity and two to three pounds of extra weight of the .308WIN AR10.

Quote:

The second piece of the story is something that (can be) slightly debated: using kinetic energy (KE) as a unit of measure of effectiveness of a round. Not here to debate that, but it gives an easily comparable number to use, so we'll use it knowing that shot placement is paramount. Chuck Hawks had a good article that really baselined 800ft/lbs of energy minimum for killing a deer cleanly, so we'll use that number.

On Hornady's website they list "appropriate" uses for their bullets, so picking a bullet in 6.8SPC and a bullet in 5.56 that are both 'recommended' for deer and then matching barrel length gives us 2 bullets out of a 16" rifle, useful as you wanted a rifle that was still handy for your daughter. The 6.8SPC retains our minimum energy out to, just under, 400yds. Whereas the 5.56 only retains that energy to just under 200yds. I'd say that's pretty significant and that moving up to an AR10 gives you, potentially, more range (didn't look that one up), however you had to switch to an entire new platform.
"our minimum energy" .... that's just it, in a nutshell, and it flies in the face of one of my favorite maxims: "Happiness is having enough, so get plenty to start with." ......

Quote:

Not saying that you didn't pick the best option for your situation, just that I feel that the 6.8SPC DOES give an appreciable gain over a 5.56 without having to go to the AR10.
..... agreed, my situation is not everyones ..... but I think everyone should consider the cost of of what is gained, on both sides of the issue.

..... "having to go to the AR10" ...... I'm trying to figure what the cost of that is ..... certainly less in terms of cost and time ...... 2 to 4 pounds heavier with the AR10's currently available off the shelf ..... but this reminds me of something I said some years ago, at the height of the "Light Rifle" craze in the bolt action hunting rifle market: "It seems to me that people are putting in insane amounts of time, money and effort into making a lighter rifle ..... I think maybe they should work a bit more for stronger arms than a lighter rifle."

OTH, I think it's great what is being done with the various new cartridges.... the work being done with the SPCs, Grendel, Wolverine, PCC, Valkyrie, Creedmores, etc .... keep pushing the envelope of the possible...... good stuff to know.
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Old April 20, 2018, 04:13 PM   #18
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Originally Posted by Bartholomew Roberts
So where is the point of diminishing returns when it is smarter to step up to a lightweight AR10 instead of trying to squeeze more out of the AR15?
Since our state recently allowed straight walled pistol/rifle cartridges for deer hunting, it has less to do with "squeezing more out", but more about finding a round that meets the requirement. 450 Bushmaster meets the threshold nicely.
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Old April 20, 2018, 07:43 PM   #19
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I shoot a 6.8 during antlerless deer season. So far, I haven't found a need for any bullet other than the 90 grain bonded soft point as loaded in the Federal white box ammo.
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Old April 20, 2018, 08:03 PM   #20
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I shoot a 6.8 during antlerless deer season. So far, I haven't found a need for any bullet other than the 90 grain bonded soft point as loaded in the Federal white box ammo.

My favorite is Nosler's 110 gr Accubond. No desire to carry a AR10 for hunting. My 16" .308 AR10 became a safe queen after I built my first 6.8.
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