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Best long range ar15 caliber

fifdynutz

Pasture Poodle
Full Member
Minuteman
May 5, 2020
268
126
Iowa
Hey guys, im considering rebarreling a 20" 5.56 ar15 setup i have had for years and i want your opinion on what would be the most capable, accurate, long range caliber i could choose for this platform

it would eventually be suppressed (still waiting) and used occasionally to house one of my thermal scopes for night coyote hunting, but primarily will wear a day scope.

I currently use a 14.5" 6mm arc for night hunting that i love, so that round is certainly a consideration. interested to hear everyones thoughts. I would prefer to keep it around a 20" barrel but would go longer if needed.

My requirements listed by priority

1. long distance accuracy (400+)
2. flattest trajectory possible
3. ammo/reloading component availability (when things are "normal")

Thanks in advance
 
My thermal yote canon is a 6.5grendel, best caliber I have come across for relative flatness and "reach out and touch" from an AR15 lower.

Be aware that "ammo availability" makes everything new a difficult start. If you don't have ammo, this is mostly a hypothetical effort for you - unless you are ready to pay $100/20 rounds that usually go for $20.
 
6mmAR Turbo 40 Improved? Grendel based wildcat by Robert Whitley I believe.
Berger 108’s over 2850 FPS from a 20” according to his load data.
Reloading only, and barrel would probably have to come from him.
For off the shelf 6mm arc or 6.5 Grendel.
 
What is your max range? Under 500 or maybe a bit further, 204 ruger will be the flattest shooting and a great coyote round. After that, 6 Arc or 224 Valk would be the best picks. 6 Arc probably fits your needs better, but if you are worried about ammo weight 224 Valkyrie is very capable out to 1000. 6.5 Grendel will not be flat shooting, just not enough muzzle velocity. 20" should do fine on either, but if you can go to a 22" or 24" on either you will gain some muzzle velocity.
 
I'd like to play with it out to 750 or so if the opportunity arises
 
I'd consider a 204 and make it more of a hunting only rig also, any recommendations on a 204 barrel and bolt?
 
I'd consider a 204 and make it more of a hunting only rig also, any recommendations on a 204 barrel and bolt?
Shilen is what I have, heavy but shoots great. comes with a bolt pre-headspaced, just need a carrier. There are other options including white oak armament if you want something shorter. 39 blitzking vs 53 v-max from my 22-250 shoot the same trajectory after they leave the muzzle out to 400 so it is definitely flat, but it is a true varmint cartridge so the b.c. on 204 bullets is not great.
 
People recommending 6.5 Grendel as a flat shooter? It’s a great LR cartridge for the AR15, but that’s one of the areas it loses easily to the others. For the ranges I’m seeing from OP (400-750) I’d go 6 ARC or 224 Valk shooting something like 75 ELDs instead of the 90-95 SMKs. I’m really hoping a 22 ARC is in the works down the line.
 
Hey guys, im considering rebarreling a 20" 5.56 ar15 setup i have had for years and i want your opinion on what would be the most capable, accurate, long range caliber i could choose for this platform

it would eventually be suppressed (still waiting) and used occasionally to house one of my thermal scopes for night coyote hunting, but primarily will wear a day scope.

I currently use a 14.5" 6mm arc for night hunting that i love, so that round is certainly a consideration. interested to hear everyones thoughts. I would prefer to keep it around a 20" barrel but would go longer if needed.

My requirements listed by priority

1. long distance accuracy (400+)
2. flattest trajectory possible
3. ammo/reloading component availability (when things are "normal")

Thanks in advance
You already have the ARC, get a longer barrel and stick with it.
 
People recommending 6.5 Grendel as a flat shooter? It’s a great LR cartridge for the AR15, but that’s one of the areas it loses easily to the others.
I was gonna mention the same thing. If energy on target at longer ranges is the goal, then 6.5G ranks pretty high. But there are flatter things out there for sure.

If straight ballistic performance is the only factor then yes, 6ARC, 224V and even 22 Nosler are up there. Then you can get into wildcats. 22 Grendel, 6mm Turbo 40, 223AI etc.

But if you consider things like barrel life, component availability, part/magazine availability, factory ammo, reliability, versatility, I'll be the outlier here and say that 223 is a damn fine round for the AR platform, and it works past the effective range of most shooters.
 
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My 20" 223 seemed to run great with anywhere from 55g varmint bullets to 68g bthp...never tried anything heavier. It was a 1-7 so it could probably handle the 77s

I love my 14.5 arc setup, just wanna do something with this other rifle to make it more capable. I'm not against keeping it .223 at all either. That I also have plenty of ammo for
 
My 20" 223 seemed to run great with anywhere from 55g varmint bullets to 68g bthp...never tried anything heavier. It was a 1-7 so it could probably handle the 77s

I love my 14.5 arc setup, just wanna do something with this other rifle to make it more capable. I'm not against keeping it .223 at all either. That I also have plenty of ammo for
I was in your boat before I built my SPR. I wanted to go ARC, but ended up finding a nice 223 upper I really liked. With a 18” barrel, 8 twist proof barrel, a 77smk at 2750 FPS has no issues making hits at 500-600 yards. Little more sensitive to the wind than that 6 arc would be but I have not been disappointed at all.
 
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If I stayed .223, any barrel length/brands you would recommend that are quickly available?
 
What’s your budget for a barrel?

white oak, craddock, Proof, criterion (new core series looks interesting)

I wouldn’t cheap out on a barrel you are wanting accuracy out of especially with longer strings of fire
 
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id prefer to stay 400 and less, and i dont want to wait for a custom option
 
Any particular reason you don’t want to wait? I’d rather wait for a little while and get a nice barrel than to settle for something lesser and hate it the entire life of the barrel
 
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I just ordered one of the SPR barrels from PRI for $225 + shipping (FDE is on sale) as the final piece to my SPR build.
I've seen good things from Bergara's bolt action barrels, and have read very positive reviews of these SPR barrels online, so I figured at $225 it's a good bargain - and properly contoured for the AEM suppressor if you're lucky enough to live in a free state (unlike me).

If you're willing to wait, White Oak Armament, Compass Lake Engineering and Craddock Precision have great reputations for their barrels, but tend to have long lead times - because people know they do good work.
 
Any particular reason you don’t want to wait? I’d rather wait for a little while and get a nice barrel than to settle for something lesser and hate it the entire life of the barrel

Im marginally impatient when i get an idea in my head, and there should be plenty of quickly available options in my budget that will suit me fine.
 
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I just ordered one of the SPR barrels from PRI for $225 + shipping (FDE is on sale) as the final piece to my SPR build.
I've seen good things from Bergara's bolt action barrels, and have read very positive reviews of these SPR barrels online, so I figured at $225 it's a good bargain - and properly contoured for the AEM suppressor if you're lucky enough to live in a free state (unlike me).

If you're willing to wait, White Oak Armament, Compass Lake Engineering and Craddock Precision have great reputations for their barrels, but tend to have long lead times - because people know they do good work.
I'm new to all this and have started building my own AR platform rifles. I bought a 16" 300BO HBR barrel from Radical Firearms for one rifle and a 9" 300BO barrel from Ballistic Advantage for the other. Where do these barrels land in the good-bad barrel spectrum? Thanks in advance.
 
This thread has meandered a bit, but I keep coming back to stated purpose, at least in part, of it being a yote gun. Where/how I hunt yotes, speed on target is essential and a 20" pecker - longer with a can - ain't fast If super flat is "the" priority, there are definitely faster/flatter rounds than 6.5grendel.
If happy with the ARC and set up for it already, that is a solid option. I'm not sure what you are gonna get moving from 14.5 to 20 that is going to be super impressive. Yes, faster; more effective, maybe. Are we shooting for groups or popping targets or killing coyotes: a clarification on priorities would be helpful.

If it is an "I want it" conversation, rock on. If it is something else, this will be a listing of people's favorite caliber/setup for their specific task, and will have varying levels of overlap in actual utility for another objective.
 
currently leaning towards the criterion .223 match barrel and loading it with 80g SMK's seated to single feed...might be a fun little change of pace
 
Shooting steel/paper off a bench is going to be the guns purpose 80+% of the time. The rest of the time will likely be spent shooting sub 400yds off a tripod day or night. I have a couple rifles higher up on the selection list for my go-to varmint rigs
 
I just want this to essentially be the gun that I point at and go: "that's my most accurate ar15 setup, long or short range" when I want to sit down and smash some steel
 
currently leaning towards the criterion .223 match barrel and loading it with 80g SMK's seated to single feed...might be a fun little change of pace
If you're gonna single feed go with a modern bullet like a 75 or 80gr ELD.
Or modify mags so you can still pew pew with the long loads.
 
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my current thoughts:

20" faxon 5r 6ARC with regular type2 bolt
OR
20" criterion .223 match with matching headspaced bolt

i have ammo and reloading components for both of these calibers, and i have inferior versions of both setups. The 6arc would make for a harder hitting hunting round and have a little more distance/wind capability. The .223 setup would inherently be more accurate (better barrel) and a little flatter shooting at shorter distances. I at least feel like ive gained some ground today lol
 
we have seen people shooting 75 gr 223 to great effect at 1k not sure if that post is a good deal or not but franks video shooting the 224 at 1mile seems real do able probably lots of other rounds to choose from good luck picking yours .
 
my current thoughts:

20" faxon 5r 6ARC with regular type2 bolt
OR
20" criterion .223 match with matching headspaced bolt

i have ammo and reloading components for both of these calibers, and i have inferior versions of both setups. The 6arc would make for a harder hitting hunting round and have a little more distance/wind capability. The .223 setup would inherently be more accurate (better barrel) and a little flatter shooting at shorter distances. I at least feel like ive gained some ground today lol
The 223 isn’t really any flatter shooting at any distance (close or long) if you’re comparing apples to apples. Remember the 6mm can go down to 55gr or less if you want a short range varmint round, and in most apples to apples comparison it’ll achieve the same or faster speeds with a better b.c.

If it were me, I’d look into a 20”-24” 6mm ARC and make your 5.56 a 14.5”-16”. IMO that covers a lot more ground than the setups you have now.

with that said, the 6mm is good in all barrel lengths; even my 12.5” (earlier wildcat 6mm Grendel variant) is still easy to hit with at 600-700 yards and more, but the 24” does the same thing better.
FWIW, in my experience with 105gr loads in my 6mm arc variants, a 20” gains about 250 fps over a 12.5”, and a 24” about 100 fps more than that.

Also, if you’re loading for this - Leverevolution.
 
Any links on how to modify the mags for longer oal?
Just some simple cutting. Apparently my pics are too big to attach, some of them are floating around on this forum somewhere.
Notching out the front of a good stainless mag will get you 2.36" ish if I remember correctly. Filing a groove into the inside front of the magwell can get you to 2.42" or so.
I easily got 75gr ELD's going 2900fps from a 22" barrel. It's a whole different animal than old fashioned 77's going 2700fps.
 
224 Valkyrie. Shoots flat - 1300 yards- ammo is available and cheaper than 223 right now. Rainier Arms match barrel is awesome 1/2 to 3/4 moa 100 yards - but it was made for long range and coyotes
 
Hey guys, im considering rebarreling a 20" 5.56 ar15 setup i have had for years and i want your opinion on what would be the most capable, accurate, long range caliber i could choose for this platform

it would eventually be suppressed (still waiting) and used occasionally to house one of my thermal scopes for night coyote hunting, but primarily will wear a day scope.

I currently use a 14.5" 6mm arc for night hunting that i love, so that round is certainly a consideration. interested to hear everyones thoughts. I would prefer to keep it around a 20" barrel but would go longer if needed.

My requirements listed by priority

1. long distance accuracy (400+)
2. flattest trajectory possible
3. ammo/reloading component availability (when things are "normal")

Thanks in advance
You may want to check out 6.5 Grendel ballistics. .264" diasmeter is the sweet sp[ot for flat trajectory and wind resistance. The Grendel is touted as a 400 yd. cartridge; 400 yds on game may be a stretch. The cartridge is very efficient; you can get 50% more power than a .223/5.56 cartridge for just a few more grains of powder. If you want more long range power, you'll have to move up to the heavier AR10 in cartridges like the 6.5 Creedmor and larger. Staying with the AR15, I would recommend the Grendel.
 
The 223 isn’t really any flatter shooting at any distance (close or long) if you’re comparing apples to apples. Remember the 6mm can go down to 55gr or less if you want a short range varmint round, and in most apples to apples comparison it’ll achieve the same or faster speeds with a better b.c.

If it were me, I’d look into a 20”-24” 6mm ARC and make your 5.56 a 14.5”-16”. IMO that covers a lot more ground than the setups you have now.

with that said, the 6mm is good in all barrel lengths; even my 12.5” (earlier wildcat 6mm Grendel variant) is still easy to hit with at 600-700 yards and more, but the 24” does the same thing better.
FWIW, in my experience with 105gr loads in my 6mm arc variants, a 20” gains about 250 fps over a 12.5”, and a 24” about 100 fps more than that.

Also, if you’re loading for this - Leverevolution.
I agree with this for sure, but quality barrel availability is lacking right now for the arc. With a quick search the best option I can find is the 20" faxon