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Best ELR cartridge for an AR10 build

Matthew488

Matthew488

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Minuteman
Feb 21, 2017
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Gilbert AZ
I have an assortment of bolt action precision rifles from 204 Ruger to 375BAS. Recently got the itch to build a gas gun that can stretch its legs in the Arizona desert.
Purchased an Aero Precision M5 builders set, lower parts kit, trigger Etc. Now it's time to choose the chambering. I reload so not worried about factory ammo. Also not concerned about duplicating the performance of one of my bolt guns in a different style of rifle.
Looking for your suggestions on the best cartridge for a long range AR.
Thanks in advance
 
338 federal with a higher twist rate maybe. At least you'd be able to see splash and could shoot through transonic. Consistency at a mile is a lot to ask of a cartridge that size but you might be able to do ok.

-Alex
 
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Yeah, you're going to be limited to short action cartridges with that. I shoot a 16.5" .308WIN G28 but it really has a hard time past 1000m. I also shoot a 16" 6mm Creedmoor AR10 and it gets to 1200m. So my suggestion would be a longer barrel 6.5mm so you can get decent velocity and shoot heavier 140+ gr bullets. A barrel length in the rage of 24-26" would do the trick, but then at that point why not just shoot your bolt gun?
 
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However if you want to go down that road
Look up this guys. Accuracy Systems Inc, they can set you up with a short magnum based AR 10 that will get you there
Or go with a Falkor Defense Petra
 
wildcats said:
However if you want to go down that road
Look up this guys. Accuracy Systems Inc, they can set you up with a short magnum based AR 10 that will get you there
Or go with a Falkor Defense Petra
Click to expand...
A short Mag sounds good. I'll look these guys up.
 
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I wish I could have a 6.5 PRC AR. Good chance of getting that into the shorter end of ELR. Eventually, there will be a 300PRC AR, or something like that and it may perform fairly well. Not like a bolt gun in the hands of an expert, but one of you needs to tell me if it matters if I hit 1.5" from dead bullseye or 4" from a mile, I'm all ears. Just spitballing, trying to see where semi-autos are headed.
 
TripleBull said:
I wish I could have a 6.5 PRC AR. Good chance of getting that into the shorter end of ELR. Eventually, there will be a 300PRC AR, or something like that and it may perform fairly well. Not like a bolt gun in the hands of an expert, but one of you needs to tell me if it matters if I hit 1.5" from dead bullseye or 4" from a mile, I'm all ears. Just spitballing, trying to see where semi-autos are headed.
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I agree. I'd love to do 7 SAUM but think it's a bit to long.
 
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I am going on a limb here. Pretty sure you can load a new round manually from a bolt action before your first round hits when shooting 1500 plus. The advantages of semi auto very possibly are outrun by the disadvantages. Not to say its not a neat idea.
If you are dead set on semi auto. Stay in the ar 10 and use a 6.5 or 7mm bullet. It will not be a great ELR round, but be very useful in the 1k range.
If you are serious on the ELR, get a magnum bolt action. Make it viable to shoot large caliber bullets. You can make a 6.5 or 7 work, but is seems that bullet weight is your friend.
 
TripleBull said:
I wish I could have a 6.5 PRC AR. Good chance of getting that into the shorter end of ELR. Eventually, there will be a 300PRC AR, or something like that and it may perform fairly well. Not like a bolt gun in the hands of an expert, but one of you needs to tell me if it matters if I hit 1.5" from dead bullseye or 4" from a mile, I'm all ears. Just spitballing, trying to see where semi-autos are headed.
Click to expand...
This is overdue.

The dpms brought large frame ARs into the mainstream. We need another big manufacturer to do the same with an XL platform to open up the market.

I bet it would do well given the ARs popularity and the growing interest in LR shooting.
 
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Forward543 said:
I am going on a limb here. Pretty sure you can load a new round manually from a bolt action before your first round hits when shooting 1500 plus. The advantages of semi auto very possibly are outrun by the disadvantages. Not to say its not a neat idea.
If you are dead set on semi auto. Stay in the ar 10 and use a 6.5 or 7mm bullet. It will not be a great ELR round, but be very useful in the 1k range.
If you are serious on the ELR, get a magnum bolt action. Make it viable to shoot large caliber bullets. You can make a 6.5 or 7 work, but is seems that bullet weight is your friend.
Click to expand...
I appreciate your input but please re-read my opening post. I already have many precision bolt guns (204 ruger,6.5CM, 7mm Rem? 308Bear, 338LM and 375BAS) so I'm not looking to fill a void there. This AR build will likely have performance somewhere between the CM and Rem Mag.
Every cartridge has its own distance that would be considered ELR. Elr for my 204 would be short range for the 375BAS.
 
Matthew488 said:
I appreciate your input but please re-read my opening post. I already have many precision bolt guns (204 ruger,6.5CM, 7mm Rem? 308Bear, 338LM and 375BAS) so I'm not looking to fill a void there. This AR build will likely have performance somewhere between the CM and Rem Mag.
Every cartridge has its own distance that would be considered ELR. Elr for my 204 would be short range for the 375BAS.
Click to expand...
So while I agree in some regards that ELR ranges depend upon the cartridge, 1500 yards plus is usually the accepted definition for ELR.

I still think 338 federal and a fast twist rate is about the best choice. Going to be slow out the muzzle but you are going to end up with something much more predictable downrange and with higher retained energy than anything else that will fit in a 308 mag. Light and fast works up to a point a big part of elr is being able to see where you are missing and a big bullet makes a big splash.

-Alex
 
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Without a mag BF, 25 Creed w/ big Bergers or Blackjacks (if/when avail again) sounds good to me.
 
Matthew488 said:
I have an assortment of bolt action precision rifles from 204 Ruger to 375BAS. Recently got the itch to build a gas gun that can stretch its legs in the Arizona desert.
Purchased an Aero Precision M5 builders set, lower parts kit, trigger Etc. Now it's time to choose the chambering. I reload so not worried about factory ammo. Also not concerned about duplicating the performance of one of my bolt guns in a different style of rifle.
Looking for your suggestions on the best cartridge for a long range AR.
Thanks in advance
Click to expand...
I know you can build convert most ar10 style rifles into a 300
Wsm that would be my choice unless I went up to the next size rifle and got a semi auto 338 lapua or burnt 15k$ On the noreen BN408 semi auto cheytac
 
TripleBull said:
I wish I could have a 6.5 PRC AR. Good chance of getting that into the shorter end of ELR. Eventually, there will be a 300PRC AR, or something like that and it may perform fairly well. Not like a bolt gun in the hands of an expert, but one of you needs to tell me if it matters if I hit 1.5" from dead bullseye or 4" from a mile, I'm all ears. Just spitballing, trying to see where semi-autos are headed.
Click to expand...
You would think if they make 300 win mag ar platforms you could change the barrel for a 30 nosler or 300 prc right?
 
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338 Federal is an intriguing option. I would probably run a 26" barrel with a 9 twist and try pushing a predictable bullet like a 250 Sierra to 2500-2550 fps. Going to be way under supersonic at anything past 1300 yards but it's a forgiving bullet and seeing impacts/splash will be easier than lighter calibers.

Would be interesting to run it along side something like a 6.5 Creed with a 153 Berger LRHT for comparison.
 
I ran the numbers for you because I'm twiddling my thumbs right now:

1659563993248.png


250s may be a bit too much. Here's a 230gr ELD-X going just under 2400fps out of a 26" barrel. Ballistics look like this:

1659564125544.png

1659564142596.png


Not great.
 
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JBM... glossing over that, the loads are a bit conservative compared to published loads. With a drive band solid (assuming you could fit one to mag length) you would likely be able to go faster than most published loads.

In either case, look at the energy differential between 338 Federal and 260 or 308 at range.

-Alex
 
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@Dogtown

Maybe someone who loads for 338 Federal can chime in just for the sake of verifying factory published data. The above numbers look light to me but I've never loaded for it so I don't know.
 
To me ELR isn't defined by a specific number but as another poster mentioned, 1500 yards is probably a good starting point. Where it ends is left to many variables.

Suggesting a 6.5 Grendel is awesome at 1500 yards and beyond doesn't even make sense.
 
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On the AR10/LR308 platform, I’d stick with the 308/6.5 CM case size cartridges…
10 rounds in a 10 round mag…20 rounds in a 20 round mag…

Trying to fit WSM cases in a LR308 P-Mag successfully ends at 4-5 rounds…tops

Just some food for thought
 
Earnhardt said:
On the AR10/LR308 platform, I’d stick with the 308/6.5 CM case size cartridges…
10 rounds in a 10 round mag…20 rounds in a 20 round mag…

Trying to fit WSM cases in a LR308 P-Mag successfully ends at 4-5 rounds…tops

Just some food for thought
Click to expand...
I would agree for function but if your goal for the rifle is range mag compacity isn’t really important.. most elr rifles don’t have much for capacity
 
BTap said:
I would agree for function but if your goal for the rifle is range mag compacity isn’t really important.. most elr rifles don’t have much for capacity
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Mag capacity may not matter as much cause a 20 round ar10 mag is a pain in the ass to shoot with a bipod, but mag length loads do matter. There is a real world niche for semi-auto capability at long ranges. As terrible (and if you haven't shot one I mean really fucking awful) as the Dragunov is, it has been used to good effect for decades. This is an oddball project but not one without merit.

Hongdon data says that 225gr bullets at a bit over 2500 fps is doable in 338 Federal. With a ELR appropriate bullet, that may be hard to manage with mag length loads since the limits are going to be case capacity rather than pressure for most powders. Would be nice to hear someone with some experience in 338 Federal chime in. I'm aware of it but have never actually seen one and a paper solution is only so useful.

-Alex
 
After looking into some load development, 2350-2400 fps is prolly a lot more realistic for anything in a 250 range with 26" barrel, considering its a gas gun and longer bullets eating case capacity to work in a mag.

If staying supersonic is the goal either the 25 Creed with 135 Berger or 6.5 Creed with 144 or 153 Berger should be supersonic to between 1500-1600 yards depending on loads.
 
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.358 winchester.

Heavy leveled tripod mount it and just dump the entire magazine each time with a quadrant sight. Be kinda like a Mk19.
 
In my 24” 358 win I can only get 2720 FPS with 180 grain bullets
They have a ballistic coefficient of a rock
 
Ledzep said:
.358 winchester.

Heavy leveled tripod mount it and just dump the entire magazine each time with a quadrant sight. Be kinda like a Mk19.
Click to expand...

Nothing wrong with a Hail Mary!
 
I think everyone should be more concerned about ballistic coefficient, when talking about a 1500 yard shot
 
Form factor actually goes a step beyond just the BC itself. It allows you to pick a bullet relative to the speeds you want to push and compare how efficient the bullet actually is without looking at just a high BC number. Basically it's the bullet weight relative to BC and the lower the form factor the higher the efficiency.

Divide the sectional density by the G7 BC and you have the form factor. Lower is better.
 
potaytoe… potahtoe….
A 6.5 is going to be better than a 338 in an AR at 1500 yards
 
I’ll even go as far to say this…
A 6.5 CM or 260 REM would be better than a 338 WSM, in an AR10/LR308, at 1500 yards
 
Sandow the Heretic said:
Mag capacity may not matter as much cause a 20 round ar10 mag is a pain in the ass to shoot with a bipod, but mag length loads do matter. There is a real world niche for semi-auto capability at long ranges. As terrible (and if you haven't shot one I mean really fucking awful) as the Dragunov is, it has been used to good effect for decades. This is an oddball project but not one without merit.

Hongdon data says that 225gr bullets at a bit over 2500 fps is doable in 338 Federal. With a ELR appropriate bullet, that may be hard to manage with mag length loads since the limits are going to be case capacity rather than pressure for most powders. Would be nice to hear someone with some experience in 338 Federal chime in. I'm aware of it but have never actually seen one and a paper solution is only so useful.

-Alex
Click to expand...
A 1-1.5 MOA semi-auto isn’t really “awful” especially considering the doctrinal intent. I’d wager that the vast majority of opinion on Dragunovs come from folks shooting beat to shit guns obtained through BFR, while being fed some shit ball ammo.

But that’s neither here nor there, so to the OPs inquiry, you’re going to be in a tight spot limiting your self to a SA cartridge. You need velocity and BC to get out there and enough mass to kick up some sizeable splash. 6.5mm has the first two but unless you have super ideal conditions, it’s going to be hard to spot. 7mm ish is probably the best combination but you’ll have to come up with something more DIY in terms of putting it all together. I think .308/.338 are just going to be very finicky at those distances, your load development has to be spot on and conditions perfect.
 
Well if you're talking WSM sized cases, just step up to a 65 PRC and add another 200 fps.
 
IF you want to be in an AR-10 platform and have something that realistically works well and not some crazy custom one off thing that may or may not go boom (like the .338LM AR type guns tended to do), a long barrel 6.5CM AR10 with a fast twist barrel shooting solids is going to be probably about as good as it gets for long range shooting. However the splash would be hard to see for misses, so you may want to go with conventional bullets instead.

Realistically after that, you are in the bolt gun territory or the specialized custom semi-auto platform category, and not something easily done in an AR-10
 
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If we agree on the max COAL and the Boltface, I bet we'd also agree (or get pretty darned close) on the best cartridge for his stated purpose.
 
Rudy Gonsior said:
A 1-1.5 MOA semi-auto isn’t really “awful” especially considering the doctrinal intent. I’d wager that the vast majority of opinion on Dragunovs come from folks shooting beat to shit guns obtained through BFR, while being fed some shit ball ammo.

But that’s neither here nor there, so to the OPs inquiry, you’re going to be in a tight spot limiting your self to a SA cartridge. You need velocity and BC to get out there and enough mass to kick up some sizeable splash. 6.5mm has the first two but unless you have super ideal conditions, it’s going to be hard to spot. 7mm ish is probably the best combination but you’ll have to come up with something more DIY in terms of putting it all together. I think .308/.338 are just going to be very finicky at those distances, your load development has to be spot on and conditions perfect.
Click to expand...
Best I've seen was one that could manage 3 MOA with handholds but maybe I've only seen "bad" ones. Mediocre accuracy met expectations of soviet era crap but It was the ergonomics, recoil management, optics and even the way it sounded that I hated.

-Alex
 
Chickentoast said:
If we agree on the max COAL and the Boltface, I bet we'd also agree (or get pretty darned close) on the best cartridge for his stated purpose.
Click to expand...
Length 2.800”

Bolt face: Magnum (.532”), or .308 (.473)

You pick the bolt face…it doesn’t matter…Magnum or .308
In the LR308 platform, .308 caliber cartridges and below, is going to win at 1500 yards
And I’ll put my money on the 6.5’s to 7’s, whatever you choose
(Ok..more money on the 6.5’s)
 
Earnhardt said:
Length 2.800”

Bolt face: Magnum (.532”), or .308 (.473)

You pick the bolt face…it doesn’t matter…Magnum or .308
In the LR308 platform, .308 caliber cartridges and below, is going to win at 1500 yards
And I’ll put my money on the 6.5’s to 7’s, whatever you choose
(Ok..more money on the 6.5’s)
Click to expand...

With that COAL and mag face I'd say 6.5 SAUM 135 Badlands or 153.5 Berger.
 
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Chickentoast said:
If we agree on the max COAL and the Boltface, I bet we'd also agree (or get pretty darned close) on the best cartridge for his stated purpose.
Click to expand...
AR10 platform dictates 2.800" for length. Mag bolt face cartridges would likely offer better ballistics than a .473 would. Will not purchase the BCG until chamber is decided on. Less than 6.5mm would make seeing splash difficult at distance.
 
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