2nd upper for dmr

[Clickjack]

[sigstroker]

If you're going to use it for precision shooting get a 20" or 24".

[hunterb]

Whatever you get, don’t cheap out on the barrel.

Best AR barrels IMO:
Bartlein
Krieger
Lilja
Douglas
White Oak Armory
Criterion
JP precision engineering
Ballistic Advantage
Noveske
Larue
Rainer Ultra Match

Best bolt:
JP high pressure

18” is fine, 20” is a bit better.

[smoothy8500]

Can't go wrong with any of White Oak's offerings:

https://www.whiteoakarmament.com/shop/barrels/high-power-match-competition-rifle-barrels.html

[Ki6vsm]

I agree with the others. If thinking of 18", may as well go 20".

[sfvshooter]

I have a FN DMR which is 18". I shoot MK 262. About 0.75-1 MOA. It's the only AR I have that's greater than 16" (all others are either 10.5", 14.5" or 16")

Personally, unless it's for plinking, I don't see why you'd want an AR over 18". If you need to reach out to 400+ yards, get an AR 10 in 308/6.5CM or better yet, a bolt action in 6.5.

[alpha_romeo_XV]

You can get a nice WOA 20" barrel with a crowned muzzle and equal the same length as a 18" with a brake. Hbar and freefloat for best rapid fire accuracy - don't want your shot group to walk off the point of impact as the barrel heats up.

[Paperchasin]

I would personally get an 18" barrel with a nice 2-10x scope.

[DrewTheBrave]

A longer barrel will give you more velocity, not necessarily accuracy. The quality & consistency of the barrel manufacturing process will affect accuracy, and the barrels recommended above are all great options. For the most part, you get what you pay for, with Kreiger, Bartlein and Lilja being among the best and most costly. In the next tier down, White Oak is probably the best value, but all options listed are worth your money.

If you're looking to extend performance beyond your 14.5", an 18" or 20" barrel would give you a little more capability at range. With that said, it might be worth considering another caliber like 6.5 Grendel or the new 6mm ARC to gain significant performance at ranges of 600-1000 yards. It really depends what your goals are, and if a new caliber is something you'd consider.

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[alpha_romeo_XV]

Do you reload? A huge factor for long range accuracy is shooting match grade ammo - either make it or pay a lot for it.

[Clickjack]

With that said, it might be worth considering another caliber like 6.5 Grendel or the new 6mm ARC to gain significant performance at ranges of 600-1000 yards. It really depends what your goals are, and if a new caliber is something you'd consider.

Do you reload? A huge factor for long range accuracy is shooting match grade ammo - either make it or pay a lot for it.

[DrewTheBrave]

Quality match grade ammo for 5.56 costs similar to match grade ammo for other calibers, so the difference in ammo costs will be minimal between most AR15 calibers.

I have an 11.5", 16" and 18" 5.56, but for long range fun I almost exclusively grab my 6.5 Grendel. Just last week I was smacking steel plates at 400, 500 and 600 yards in gusty conditions with 6.5G Hornady American Gunner ($0.75 per round). With that type of wind, it would have been a challenge for my 5.56 rifles.
My point being: if you're serious about long range shooting with an AR15, define what your goals are, and your decision will become much easier.

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[Clickjack]

Quality match grade ammo for 5.56 costs similar to match grade ammo for other calibers, so the difference in ammo costs will be minimal between most AR15 calibers.

I have an 11.5", 16" and 18" 5.56, but for long range fun I almost exclusively grab my 6.5 Grendel. Just last week I was smacking steel plates at 400, 500 and 600 yards in gusty conditions with 6.5G Hornady American Gunner ($0.75 per round). With that type of wind, it would have been a challenge for my 5.56 rifles.
My point being: if you're serious about long range shooting with an AR15, define what your goals are, and your decision will become much easier.

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What are you using the different length barrels for? I have an 11.5 & the 14.5

[sfvshooter]

And people don't really use 5.56 for "precision long range shooting." 77 gr match ammo will get you better results than M193 for typical 1:7 barrels, but otherwise, if you want to get into "precision long range shooting" try other calibers such as 308, 6.5CM, etc.

And if you're limited to getting an upper for an existing AR 15 lower, your options are 6.5 grendel, 224 valkyrie (though I might be the only one still shooting it), and 6mm ARC (brand new so who knows if it'll stick). These will allow you to shoot out to 1,000 yards.

[smoothy8500]

Then again, what is "longer range precision" to most calgunners? Anything past 100yds at the range? A decent barrel 18/20" with good 77gr projectiles will let you brag about "banging steel" all day at 600yds.

Bump it up to 80gr reloads and you'll do 800yds no problem.