16-18" AR10, would you go 308 or 6.5 creedmoor?

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Having a tough time trying to decide between a 16 or 18" barrel for a large frame upper. i am going for a DMR rifle. from what i have read the 6.5 creed does best out of 20"+ barrels. i know that 16" and 18" 308 barrels are common for a DMR. i just am trying to figure out, if it were you and you did not have 308 or 6.5 currently, which would you get into if you were not going to reload. I already have 8mm mauser for reloading and don't feel like adding a second caliber.
 
Shooting .308 if you're not handloading gets expensive. For example, I shoot 3-gun with a FAL. I'm getting started in handloading specifically to load .308 for matches. Matches require the use of non-bimetal bullets and FALs experience kabooms from steel cased ammo.

Now, you could shoot steel .308/7.62 out of an AR10, but its still not cheap. If you're really trying to use this as a DMR, you're going to need a lot of ammo to git gud at distance. By "distance", I mean beyond 200 yards.

My vote is for the 6.5CM because of the modularity of the AR10, well, SR-25 really, platform. 6.5 may likely supplant 7.62 NATO within the next few years, maybe decade. Meaning, 6.5 will get cheaper, especially once military surplus and production overrun hits the market. Also, .308 is not a mild cartridge. A 6.5 is going to be milder and more pleasant to shoot, especially for someone in Mass who can't own a suppressor legally. So, while you'll pay more for ammo today with 6.5, it should decrease in the future and you'll already be ahead of the curve.
 
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6.5 for sure. I have both uppers for my AR10 and the 6.5 is far more pleasant to shoot and quite accurate with factory ammo. One caveat, be sure you use a high pressure bolt in it and NOT a standard .308 bolt. The firing pin hole (and pin) are smaller in a high pressure bolt which keeps you from getting pierced primers. These cause all kinds of weird issues when fragments get through the firing pin hole and inside the bolt. I can tell you from experience.
 
Having a tough time trying to decide between a 16 or 18" barrel for a large frame upper. i am going for a DMR rifle. from what i have read the 6.5 creed does best out of 20"+ barrels. i know that 16" and 18" 308 barrels are common for a DMR. i just am trying to figure out, if it were you and you did not have 308 or 6.5 currently, which would you get into if you were not going to reload. I already have 8mm mauser for reloading and don't feel like adding a second caliber.
Well that paired with what you've read about 6.5 doing best in 20+" barrels?
.308win hands down, especially given how much 7.62x51 in the world there is.
 
Well that paired with what you've read about 6.5 doing best in 20+" barrels?
.308win hands down, especially given how much 7.62x51 in the world there is.

No, it doesn't. Few factors:

(1) .308 for some reason took an extremely hard hit in recent buying frenzy. Here's some context: about a week before shit hit the fan with the 'rona, I bought a bunch of PPU M80 at exactly fifty cents per round. Now, the cheapest source for that same ammo is sixty cents per round.

(2) Surplus 7.62 NATO is out there but not in massive quantities. There's Lake City, 1980s Hirtenberger, Malay L2A2, PMC 1980s surplus, GGG, and whatever else you can find kicking around for sale by private sellers:

1588471251878.png

(3) In its mil-spec loading, like M80, 7.62 NATO is unnecessary as a rifle cartridge. Too much power for not enough benefit, arguably, with substantial detriments such as flinch-inducing recoil for the unaccustomed and barely any control in full-auto. The advantage of .308 is barrier penetration and long range for machine guns. As an infantry weapon, which a DMR is, the .308 is too much gun for most applications. The .308 exists because of US Ordnance's path dependency with .30-caliber cartridges.

For someone getting into these calibers as a newb, I don't see that much benefit to .308. Though either way, I advise handloading.

308 18"
6.5 20 or 22"

16" is pointless

The advantage of a 16" .308 is that its the shortest legal length of a rifle before SBR territory. This matters when running around stages, or in the woods, or jumping out of airplanes. For example, one of the FAL Para variants had a 17.something inch barrel, which makes sense if you're jumping out of a Dakota into the jungle or brush with a FAL. For a DMR-style gun, though, where you're shooting from a bench at paper targets, a 16" barrel .308 generates excessive muzzle blast unless you're shooting with a suppressor. Which, again, is illegal in Mass.
 
.308 / 7.62x51 is a time tested cartridge. It tends to be less expensive to shoot than 6.5cm and is undeniably more readily available (in both volume and variety) - outside of plagues and gun grabs I'd say every shop in the US has a good variety available. Military surplus exists from virtually every NATO country including our own. It's got a bit better knockdown power compared to 6.5cm. There are an exceptional amount of accessories available for the AR platform, and tons of load data... it's almost a no-brainer.

Sure, you can do less math with 6.5 when shooting paper or steel out around a thousand yards, and save a small amount of recoil. In the mean time if you're shooting enough for that to matter you're gonna burn through your barrel comparatively quickly. Maybe in the future it'll be a good choice, but right now it's barely out of the "novelty cartridge / flavor of the week" phase in my opinion. I've been holding out of 6.5cm as a serious investment because I've found .308win and .300WM to be superior choices when it comes to cost/effectiveness/availability/sustainability. If the military gets serious about adopting it my mind will be changed.
 
barrel life in 308 is significantly better

If you can afford to shoot either one on the reg this is almost irrelevant.

That said I'd still pick .308 because of the fact that this ammo is still likely better availability wise and will continue in the
future. The installed user base of 308/7.62 NATO is f***ing gigantic.

6.5 Kardashian, not so much.

-Mike

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308 18"
6.5 20 or 22"

16" is pointless
i prefer an adjustable gas block, something nice like the SLR
the choice of cartridge is fairly obvious
past ~600 yards or if user prefers less felt recoil, the 6.5 shines

barrel life in 308 is significantly better

came here to post this, thanks for saving me the time
 
@drgrant
regarding barrel life in 6.5 CM, it's roughly 1/4 the length of life as a 308. lots of variables play in especially heat. however not unusual for groups to start opening up at 2-3k rounds and for the barrel to be significantly less accurate by 5k. if I were building an autoloader in 6.5CM (e.g LR-308), I would probably minimize the rate of fire. the upside with such platform is the barrel can be replaced fairly easily, so one could argue it doesn't matter. in fact by this "barrel change argument" one could say the LR-308 is the perfect 6.5 CM platform because you're going to shoot the barrel out anyway, so might as well have it on an easily replace-able upper rather than something more complex like a bolt gun or other autoloader.

---
personally if i were going 6.5 it would a bolt action both to allow me to have more weight in the barrel (rather than the action) and because recoil of 6.5 CM is so minimal it doesn't benefit as much as 308 from a DI gas system. on the contrary I would prefer 308 in an autoloader since the barrel will be less sensitive to heat and recoil of the 308 is minimized by the DI gas system.

folks get very excited about an LR-308/AR-10 but they are clunky compared to a well balanced bolt action. while they look and function like an AR-15, I find them nowhere near as "useable". An optimized LR-308 in 6.5 CM should have at least a 20" barrel. between gas block, barrel, handguard, etc the rifle will be heavy and large. the upside is it will recoil like a 22LR and would easily be able to spot your hits.

The advantage of a 16" .308 is that its the shortest legal length of a rifle before SBR territory. This matters when running around stages, or in the woods, or jumping out of airplanes. For example, one of the FAL Para variants had a 17.something inch barrel, which makes sense if you're jumping out of a Dakota into the jungle or brush with a FAL. For a DMR-style gun, though, where you're shooting from a bench at paper targets, a 16" barrel .308 generates excessive muzzle blast unless you're shooting with a suppressor. Which, again, is illegal in Mass.

thank you for reminding me that 16" is the cutoff for SBR because i wasn't sure

if one is an operator "jumping out of dakota into jungle or brush", why would SBR laws matter?
is the OP "running around stages, or in the woods, or jumping out of airplanes"?
by this absurd argument all rifle barrels should be 16" to facilitate de-planing or defenestration

friendly reminder: this is earth and most of us are civilians.
 
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thank you for reminding me that 16" is the cutoff for SBR because i wasn't sure

if one is an operator "jumping out of dakota into jungle or brush", why would SBR laws matter?
is the OP "running around stages, or in the woods, or jumping out of airplanes"?
by this absurd argument all rifle barrels should be 16" to facilitate de-planing or defenestration

friendly reminder: this is earth and most of us are civilians.

People bandy the term "DMR" around a lot and we don't know exactly what OP's going to be doing with the gun. I stated the caveat that OP's likely not going to need such a short barrel if shooting from a bench. But some people are going to use such a gun for competitions that may involve cramped spaces, or may use such a gun for hunting, or might just want such a gun as a go-to for bugging out with.

The point I'm making is that a 16" .308 has certain applications. Whether or not those applications apply to the OP is for the OP to decide. 16" isn't even the shortest effective barrel length of .308 - some guys in suppressor-friendly states love 11" or 13.5" .308s for running suppressed.

Instead, you ignored my caveat and decided to pitch a fit like a child. You chose to think of my point as an "all or nothing" proposition, when I never said that. The world isn't an all-or-nothing situation. We're talking about a 16" .308 versus an 18" one. Know what the difference is? Two inches and maybe 100-200fps. You also don't know what "defenestration" means. Defenestration only applies to windows.

Definition of DEFENESTRATION

1588516458076.png

A door is not a window. One is also not thrown from an aircraft, but rather exercises autonomous volition to jump. Save your pseudo-intellectual attempts for someone else.
 
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Well plenty of posters are right, this gun's role is mostly range use, and if i ever get to texas, hog hunting. Most hunting will be done with my mauser k98 with LSR scope. I am not looking for an exclusive bench rifle. Going to rattlecan paint it a greenish color for hunting. Bug out, sure but i might tell my brother he has to carry that one. I already have my AR15 for that role. I am basing this build from an M110 and the M110A

I had a scar 17, it was super fun, sold it because i can build an AR10 for a grand less and then use the funds to put more glass on other rifles.

A 6.5 bolt action is on my short list to buy one day. So a 6.5 gas gun could save me from having to pick up another caliber. Both of these would be rarely get shot compared to cheap 5.56 or my reloaded 8mm.
 
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Well plenty of posters are right, this gun's role is mostly range use, and if i ever get to texas, hog hunting. Most hunting will be done with my mauser k98 with LSR scope. I am not looking for an exclusive bench rifle. Going to rattlecan paint it a greenish color for hunting. Bug out, sure but i might tell my brother he has to carry that one.

I had a scar 17, it was super fun, sold it because i can build an AR10 for a grand less and then use the funds to put more glass on other rifles.

A 6.5 bolt action is on my short list to buy one day. So a 6.5 gas gun could save me from having to pick up another caliber. Both of these would be rarely get shot compared to cheap 5.56 or my reloaded 8mm.

Let me ask a few questions:

(1) Do you own any .30 caliber guns?
(2) What, exactly, are you going to do with this gun? What competitions, what kind of shooting?
(3) How far are you conceivably going to shoot? 100 yards, 200, 600, 1000? Are you attempting to reach 1000?
(4) Have you been hog hunting before? How much do you intend to go?
(5) When you say that this isn't exactly going to be a bench gun, what does that mean?
(6) What manner or quality of glass are you putting on this gun?
 
1. Nope not anymore
2. Stage shooting from one awkward position to the next, i would like to do some rifle courses with it.
3. As far as i can try. Not staying in MA forever and there are a few long distance ranges outside of MA.
4. Would like to go at least once if i can, but most hunting will be done with the mauser.
5. I do not want to make a 12-15lb bench rifle. Shooting for 10lbs or less.
6. Either 4-12 , or my athlon 6-24
 
1. Nope not anymore

Ok, so you don't have .30cal bore snakes, cleaning rods, raw bullets, etc.? If you do, different story. But if you want 6.5 anyways, you'll need that in the future.

2. Stage shooting from one awkward position to the next, i would like to do some rifle courses with it.

If you're shooting with movement, you'll want a barrel between 16" and 20", which nothing much longer than that.

3. As far as i can try. Not staying in MA forever and there are a few long distance ranges outside of MA.

Followup question: how far can you actually shoot? As in, what's the furthest you've actually shot? How advanced are you as a shooter? Have you ever calculated bullet drop and where your impact is going to be?

4. Would like to go at least once if i can, but most hunting will be done with the mauser.

So, then, hunting isn't really a top priority.

5. I do not want to make a 12-15lb bench rifle. Shooting for 10lbs or less.

For a DMR rifle, you're going to need to add in the weight of glass and likely a bipod. Not to mention the loaded mag. I've never compared the weight of a loaded 6.5CM mag versus the weight of a loaded .308 mag, but barrel length adds a lot of weight to a gun and 6.5CM really starts at 20".

6. Either 4-12 , or my athlon 6-24

That's a ton of magnification when most DMR situations involve much lower magnification, like between 2x and 4x. You want to keep the field of view and eye box in mind. Eye box is very important if you're running during stages because a small eye box is going to be hard to find if you run, then jump down prone or onto a VTAC barrier. Field of view is important for identifying targets. Scopes that big also have huge objective lenses that add a lot of weight and just bulk to the gun. The bigger the scope, the more the gun's going to weigh.

Have you handled a gun like this before? How's the balance, especially with a scope and a loaded mag?
 
I would be fine with adding a second 1-8 lvpo to this build. The athlon 6-24 will end up on the 6.5 bolt gun at some point. I have never calculated bullet drop, because well MA. When i leave this state next year. I will finally get to :)
 
I would be fine with adding a second 1-8 lvpo to this build. The athlong 6-24 will end up on the 6.5 bolt gun at some point

That's a good idea and would be more practical if you're trying to use this for shooting with movement or in the field. You might want to get some trigger time behind guns of this type before making up your mind. I'm sure if you asked around to try out AR10 DMRs, some guys would step up. I don't have one or else I would.
 
1. Nope not anymore
2. Stage shooting from one awkward position to the next, i would like to do some rifle courses with it.
3. As far as i can try. Not staying in MA forever and there are a few long distance ranges outside of MA.
4. Would like to go at least once if i can, but most hunting will be done with the mauser.
5. I do not want to make a 12-15lb bench rifle. Shooting for 10lbs or less.
6. Either 4-12 , or my athlon 6-24

I'd say a 18" .308 would be pretty damn good for this role, put a nice brake one it and it'll shoot very soft. .308 CAN be ok for up to 1000yards, however we all know a 6.5CM would be better. I lean heavily on my .30 Cal rifles(.308, .300wm, .300RUM) They're great and very easy to load for different objectives.
 
I know 16 and 18" are pretty norm for 308, but it does look like 18" could be used for 6.5
20" sure is the norm, but that is a lot of barrel plus a brake on it

I do not reload for either.
 
If you are planning of doing PRS style shooting. Then I would go with 6.5.
Shooting off the bench at distance 6.5
Shooting into a berm at close range. 308...cheaper ammo
 
308 was never cheap to shoot. But neither is 6.5
When i want to shoot cheap i shoot 5.56

6.5 really sounds like it has a great advantage.
Hmm to go 18" or 20" fluted ballistic advantage barrel....
 
no brake needed on 6.5, a brake on 308 is harsh. I put one on mine and took it off again.
 
I went .308 because I'm more familiar with the caliber and would like to reload that round. That said, I'm actively searching for a 6.5CM upper to have the best of both worlds.
 
308 was never cheap to shoot. But neither is 6.5
When i want to shoot cheap i shoot 5.56

6.5 really sounds like it has a great advantage.
Hmm to go 18" or 20" fluted ballistic advantage barrel....
I shoot production ammo for .50/Rd and reload for .28/rd. .30 Cal stuff pops up all the time and at good deals.
 
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