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Old July 12, 2012, 01:41 PM   #1
jason41987
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AR15 for big game?

hey everyone.. im building an AR15 soon, and well, ill be investing in a couple different uppers for it.. one of these uppers id like to make would be for big game hunting, so id be looking for accuracy, range, and of course a cartridge better suited for the task.. so im thinking 18-20 inch barrel, free floating forearm, maybe invest in a good trigger group as well...

so any suggestions for individual components i should look into, and advice for a good large game cartridge that could fit in an AR-15 mag?... maybe 6.8 SPC, 6.5 grenel, 30 remington AR, 300 AAC blackout to name a few ive thought of
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Old July 12, 2012, 02:04 PM   #2
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How big is your big game?
If you have elk, moose or big bears on the list you'll want to look at a 458 SOCOM or a 50 Beowulf.

If you are going for deer, I'd recommend a 6.8SPC over about any of them.

If you are hunting mostly Pronghorn antelope I might give a nod to a 6.5 Grendal.

I have killed a lot of antelope and deer both with my 6.8 SPC and I find its ok out to about 400 yds, and has been excellent to 300 The Grendal is a bit better past 300 yds, but neither is going to kill super well past 400.

The bullets that fly so well in the grendal don’t perform well on game as a rule. So I am toild by my friends that hunt with them anyway.

The 458 and the 50 are both in the league of the old Sharps rounds, so they have LOTS of power --- but don't shoot flat.

If you must have a lot of power and a lot of range both the AR-15 is not the correct rifle. Look at the browning BARs in the bigger chamberings if you need a 400-500 yard elk rifle in an automatic.
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Old July 12, 2012, 02:12 PM   #3
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300 yards would be about the max limit for what i need.. what size bullets does the grendel use? the 6.8 uses standard 7mm bullets doesnt it?.. since id be reloading often, id want something that uses a common, easy to find bullet
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Old July 12, 2012, 02:52 PM   #4
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For big game, short yardage, it's the .50 Beowulf or the .450 Bushmaster or .458 Socom from the AR platform.

The .300 has decent power with supersonic loads at short distances, but I wouldn't call it "big game".

The 6.5 Grendel (we own one) is unsurpassed for long range ballistics-target shooting- from the AR-15 platform, but not the best choice for your application.

Like the previous posted asked- what's "big game" to you...?
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Old July 12, 2012, 03:11 PM   #5
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well, deer for the most part.. maybe the occassional elk on trips, but mostly just white tail
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Old July 12, 2012, 04:03 PM   #6
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the 6.8 uses standard 7mm bullets doesnt it?..
No, those are .270's in the 6.8 ctg.
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Old July 12, 2012, 04:22 PM   #7
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I'd go Grendel at longer ranges and 300 Blackout for inside 200 yards
http://www.ar15.com/forums/t_1_5/132...CS_POSTED.html

Barnes 110 gr Vortex FTW
http://www.youtube.com/watch?v=9mXa5AiT0r4
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Old July 12, 2012, 06:11 PM   #8
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im reading up more right now on the 6.5mm grendel vs the 6.8mm SPC since these seem to be the front runners in more power and range in the AR15 platform, and the nature of the the 6.5mm grendel with even a slightly smaller diameter bullet is capable of carrying bullets of equal weight but with what seems to be about .100 more in ballistics coefficiency... hard to find a 6.5mm bullet that doesnt have over .500

really seems like it might be turning into a 6.8 vs 6.5 debate for me.. and i think i might have a bit more fun with this upper with some long range target shooting as well as hunting.. seems the 6.5 is the better cartridge ballistically but the 6.8 has a bigger market and more support.. tough choice, ill have to do more research on these
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Old July 12, 2012, 07:19 PM   #9
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The 6.8 SPC is wholly inferior for long range shooting.

Alexander Arms has a couple of 6.5 Grendel factory loads for hunting, but you really need to handload until commercial ammo catches up as this caliber is rapidly getting the respect it deserves since SAAMI acceptance.

If you handload, want whitetail, and the best long range ballistics available from the AR-15 platform, the 6.5 Grendel is the clear choice.

http://www.rifleshootermag.com/2011/...del-evolution/
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Old July 12, 2012, 07:46 PM   #10
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hmm, what size barrel length would the 6.5 grendel be best in?..

im thinking i could build a long range rifle with a heavy, or fluted barrel, free float forearm, quality bipod, stock with adjustable cheek comb, match trigger group and good optics

im also guessing for an absolute sharpshooter, im thinking direct impingement will be better.. i dont think a short-stroke piston would offer me any advantage, actually, i could be wrong, but i think it might decrease the accuracy vs DI
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Old July 12, 2012, 08:50 PM   #11
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In my home state it's illegal to use anything under a 24 caliber 70 grain for Deer, 85 grain for big game. I'd go AR10 platform if you want something for larger game.
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Old July 12, 2012, 10:05 PM   #12
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i would be willing to get behind one of these new cartridges.. the 6.8SPC seems to be more suited as a general purpose role as an alternative to the 5.56.. grendel seems to be better suited as a long range target/sniper role.. its impressive to see either one putting out close to 2,000 ft/lbs of energy

what i can gather load wise is that both these cartridge have the same case capacity, grendel being a shorter, fatter case, spc being a but longer but skinner, which also restricts the length of the bullet

seems the max bullet lengths in an AR is about 140 grains in the grendel, about 130 in the spc.. can anyone confirm longer bullets can be used in either cartridge in the AR15?...

given both cartridges are fatter than the 5.56, im just curious how much ammo a standard 30-round size magazine would hold?.. i think teh grendel has to be single-stack?
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Old July 12, 2012, 10:14 PM   #13
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looking at load data for these two cartridges they put out the same amount of energy.. either one plenty for taking big game... so about these two cartridges itself, lets say you have one 6.8spc and one 6.5 grendel, equal amounts of kinetic energy, same type of bullet.. and for the sake of arguement, lets say the same bullet weight as well... how much of an energy difference would you guess there would be out to 1000 yards?
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Old July 13, 2012, 08:26 AM   #14
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I say 5.56, stick to 50gr barnes black hills TSX and 70gr TSX and trust me youll have no problems.

Nothing hitting a deer with a bullet that expands to .50 cal dimensions within 1" of tissue and twirls with 4 tearing petals of pure copper.

Another thing to note is 70gr TSX expands fully out to 300yrds out of a 14.5" M4
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Old July 13, 2012, 08:55 AM   #15
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Quote:
Originally Posted by jason41987
hmm, what size barrel length would the 6.5 grendel be best in?..
The local Grendel shooters I shoot with have everything from 16" up to 24". The short barrel guys have proven the 16" doesn't give up much at all. For a "hunting" Grendel 16-18" would be fine. Game is taken at much shorter ranges, 200-300yds max, the 6.8 or the 6.5 both do very well at these ranges. The Grendel shines past 600yds and well keep shining past 1200yds. In the AR15 platform the Grendel is the best for long range shooting. For hunting some of the larger .40cal+ rounds may do better.

If you think you may be hunting Elk then you should consider one of the 7.62 platform AR's. The 7.62/.308 allows much more flexibility for hunting big game.
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Old July 13, 2012, 01:10 PM   #16
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ive done some ballistics number crunching... finding the maximum length bullets for both 6.5 and 6.8 in the AR15 platform, and finding the average ballistics coefficiency for bullets offered in these sizes, increasing the velocity of each round to achieve the same amount of muzzle energy of 1900ft/lbs, both zeroed at 100, grendels using a 140 grain bullet with a BC of .520, grendel uses a 130 grain bullet with a BC of .460.. for the sake of eliminating variables, i used a hornady interlock SST boat tail bullet for each

what ive discovered is at 600 yards, grendel had 793ft/lbs energy and a drop of 118.5" - spc had 710 ft/lbs of energy and 115" drop

at 800 yards grendel had 584ft/lbs of energy and -249" of drop - spc had 503 ft/lbs of energy and 247" of drop

at 1000 yards grendel had 442 ft/lbs of energy and -455" of drop, spc had 374 ft/lbs of energy and and -458" of drop

so... to recap, i eliminated many unneccessary variables using the same bullets, the same kinetic energy at the muzzle, both cases have the same case capacity, and the only variables i left are those of the ballistic coefficiencies of the bullets, and the overall bullet weight (obviously, longer bullets give better coefficiencies in the same diameter and construction)

with all possible variables eliminated, only keeping the two variables that make these cartridges ballistically different, SPC has an edge out to 600, theyre about even at 800, and the grendel edges out at 1000, and none of these ranges are realistic for anything besides extreme-range target shooting, but even then i dont see enough of a different to base a decision on either of these on their individual ballistics, and i cant imagine the minute difference in kinetic energy

so i think im going to go for one which is going to have the largest support and backing by aftermarket and other shooters which at this point seems to strongly favor the 6.8SPC
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Old July 13, 2012, 01:19 PM   #17
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so i think this build will end up being a 20 or 22 inch heavy barrel, free float tube, bipod mounted to the tube, adjustable stock for comfort, larger grip for comfort (large hands) if anyone can confirm theres no accuracy loss with the short-stroke piston conversions, i would go that route, if not, it would remain direct impinged.. and i dont want to go with a hair trigger of 1 1/2 pounds, i think thats too light to remain practical for more than bench rest shooting, so im looking at a quality trigger with about a 3lb pull to it

could anyone recommend a good barrel, a trigger, and probably a good scope as well?... im thinking between a 6 and 8 times scope for hunting... something durable, rugged, and can take a bit of a beating, something thats can handle a little abuse?
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Old July 13, 2012, 04:37 PM   #18
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I don't understand your methodology...

You determine the maximum velocity (on average) you can push the bullet based on it's weight- and the energy is whatever it is...

You say you "increased the muzzle velocity" to obtain a certain level of energy? That's not how load development is done....

I'll bet a case of beer of your choice that, whatever bullet you're using for the 6.8 SPC, your velocity is unrealistic- or flat out unobtainable.

Please state the specific bullets you're using, the muzzle velocity of each and the load you're basing it on...

I suspect you'll see the 6.8 SPC cannot compare to the 6.5 Grendel at 1000 yards if you use realistic bullet weights and obtainable velocities.

The bullet of choice for most Grendel shooters is the 123 Amax, pushed at about 2350 fps.

What bullet, and what velocity are you estimating for the 6.8?

The 6.8 can hang with the 6.5 Grendel only to about 500 yards- then the higher BC, 6.5 bullets walk away.

I have never heard of anyone building a 6.8 SPC with 1000 yard shooting in mind.

Last edited by tobnpr; July 13, 2012 at 04:47 PM.
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Old July 13, 2012, 04:58 PM   #19
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both cartridges fire projectiles at similar weights, and have the same cartridge capacity, so muzzle energy isnt going to be very different, ive looked into some numbers from handloads fired from the AR15 platform and only fine-tuned the velocities to match the muzzle energy to eliminate just another variable that didnt need to be in there... also, since the loads used were on the upper end of the pressure limits i also tested a 120 grain 6.5 bullet against a 110 grain 6.8 bullet, and i was only testing bullets that i can find a manufacture that makes the bullet in both sizes at the bullet weights im testing

so.. for the 120 vs 110 grain test i used the ballistic coefficiencies in the barnes tipped triple-shock X spitzer boat tail bullets...

to answer the question above i used around 2,560fps for the 6.8 in both bullet sizes, so the more standard pressure tests put the 6.5 and 6.8 at 1600ft/lbs of energy, which is more common

the results of this test were roughly the same, though a tad more pronounced, the 6.8 had a SLIGHT edge at 600, about even at 800 and the grendel pulled ahead after that, but not by much
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Old July 13, 2012, 05:40 PM   #20
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The Barnes TSX, 6.8 mm, 110 grain has a BC of .323

The Hornady Amax, 6.5 mm, 123 grain has a BC of .510

At 2560 fps, the Barnes has a drop of 135 inches at 600 yards, and 627 inches at 1000...

At 2350 fps, the Hornady Amax has a drop of 128 inches at 600, and 508 at 1000.

So, despite the lower MV and heavier bullet, the 6.5 is moving away at 600.

The 6.8 SPC goes subsonic (1129 fps) beyond 700 yards- which makes it pretty much useless- with that bullet at least, beyond that range. At 1000, it has only 922 fps and 208 lbs. of energy.

The 6.5 Grendel is still humming at 1117 fps at 1000, with 341 ft. lbs.

I'm not going to argue the point further, your ballistic calcs. are incorrect.

There is no way on earth the 6.8 SPC can carry 374 lbs of energy at 1000 yards as you maintain.
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Old July 13, 2012, 05:51 PM   #21
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tobnpr, the barnes TSX boat tail hollow point has a BC of .323, the spitzer boat tail with the plastic tip has a BC of .377, both are 110 grains though.. and i didnt use the a-max in the comparison because i wanted to eliminate bullet type and construction as a variable, and couldnt find an a-max for the 6.8, which is what i was trying to find first before using a barnes, and none of these cartridges are ballistically fantastic after 800 yards, even if i was the type to take these extremely long range shots at a deer, which i dont, and usually hunt sub 200 yard ranges, i seriously doubt the 100ft/lbs difference at beyond 100 yards is going to do much with bullets made to expand at much higher velocities

i love the a-max bullets, ive been a user of hornady bullets for a while and the a-max are very efficient in long range ballistics, unfortunately without them making a 110 grain 6.8mm a-max bullet it just wouldnt have been a fair comparison
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Old July 13, 2012, 06:06 PM   #22
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You say your thinking of a 22" heavy barrel for a hunting rifle.... Yeah, your gonna enjoy carrying that in the woods all day.
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Old July 13, 2012, 06:51 PM   #23
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i was actually thinking more of a 20, and im used to carrying my 28" 12 gauge around all day
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Old July 13, 2012, 07:21 PM   #24
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Shotgun barrels have a lot less steel per inch of length than do centerfire rifle bull barrels.
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Old July 13, 2012, 08:03 PM   #25
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yeah, thats true, but the overall weight was still roughly the same as such an AR15 would be, and ive carried heavier things than either of them and it doesnt concern me much... when i hunt i have a few places i go to, and do more waiting than traveling on foot, so even if i had a 24 inch heavy barrel it still wont weigh as much as other rifles ive carried before
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