18 or 20 barrel

[Aries144]

I'm trying to decide between an 18 or 20 inch barrel. I'm wanting to hunt with it and shoot distance. I have the range to shoot as far as I want. My hunting shots would be within 500 on coyote and with 200 on deer. Is there that much difference in these scenarios with 2 inches of barrel?

[VASCAR2]

The main difference will be velocity is a little higher with the 20" barrel compared to 18" barrels. The higher velocity gives you a little more distance before the bullet drops below expansion threshold. A friend and I chronographed four 6.5 Grendel AR-15's with a Magnettospeed chronograph a couple years ago. The barrels were a 16", 18", 20" and 24".

Here was the difference in average velocity difference 18" and 20" barrels.

Difference between 20” and 18” barrel 6.5 Grendel

120 grain PPU HP BT

25 FPS difference

110 grain PPU FMJ

44 FPS

123 grain A-Max

41 FPS difference

123 grain SST

18 FPS

Hand load 123 grain Nosler CC

55 FPS difference

Wolf 100 grain FMJ Steel Cased

44 FPS difference

[Aries144]

So in your research what effective hunting ranges am I looking at with each barrel?

[VASCAR2]

Really depends on the bullet in my opinion. For example if your using Barnes 100 or 120 grain TTSX/TSX minimum expansion velocity is 2000 FPS. The 123 grain SST, 120 grain Gold Dot, Nosler Ballistic Tip or Sierra Pro Hunter should impact at 1800 FPS or above. The Nosler Long Range Accubond (ABLR) expand down to 1300 FPS. Your elevation above sea level makes a significant difference on velocity and at higher elevation the thinner air puts less drag on the bullets.


Most any of these bullets will have enough velocity out of an 18" or 20" 6.5 Grendel to be effective from 300-350+ yards depending on your elevation and particular bullet.


I went to the Federal Ballistic calculator using factory load info for the 120 grain Fusion at sea level with a velocity of 2475 FPS which would be close using an 18" barrel.


290 yards -15.6 drop -5.1 MOA 10.6 drift @ 10 MPH 1799 FPS and 863 foot # energy.


One disadvantage of the Fusion is the low BC (.340 G-1) compared to the 123 grain SST (.450 G-1).

[Labrat198]

The 20 inch should in theory give you a little more reach, but YMMV. The other difference is the gas system length. 18 inch barrels can be Mid or Rifle length depending on manufacturer, 20 inch barrels are generally Rifle.

I am almost done putting together an upper for the deer and stretching my abilities at the range. I was going back and forth between an 18 or 20 inch and finally landed on the group buy 18 inch barrel. I spend a fair bit of time walking through heavy brush and most deer have been shot at less than 100 yards, so the lighter weight and mobility of a shorter barrel made sense for me.

[SightedIn]

I built my hunting rig a few years ago on an 18” and i wish i had chosen a 20”.
On an AR i think a 20” is ideal just my opinion

[Labrat198]

I built my hunting rig a few years ago on an 18” and i wish i had chosen a 20”.

Just out of curiosity, what has let you down with the 18" that make you wish you had a 20"?

[Deerfreak13]

Does nobody rock the 24" barrel anymore??? I've currently got a 20" and was considering replacing with a 24" to squeeze out the most velocity. I never carry this gun far so no issues there...

[SightedIn]

Just out of curiosity, what has let you down with the 18" that make you wish you had a 20"?

When i choose the 18" i felt that was better for ease of handling and was willing to sacrifice some velocity and therefore effective range. I learned though that an 18" is beyond easy to carry in the field and so wish i had chosen the 20" for the gained velocity/range. The hunts in all the states i hunt( Utah/Colorado/Nevada/Arizona) are all typically fairly long range( up to 400-500 yards) and so the 20" would have been slightly better.
Years ago I was coming from the mindset of a typical AR carrier, 16", so an 18" seemed long to me. But after lugging some 24" and 26" hunting rifles around a few times i realized that 20" is not bad at all.

[bj139]

You can always go muzzledeviceless and get nearly the same OAL as a shorter barrel.

[LRRPF52]

I'm trying to decide between an 18 or 20 inch barrel. I'm wanting to hunt with it and shoot distance. I have the range to shoot as far as I want. My hunting shots would be within 500 on coyote and with 200 on deer. Is there that much difference in these scenarios with 2 inches of barrel?

Since you'll be doing predator duty on coyotes, who are pretty skittish, you might consider the 20 over an 18, but practical differences will be limited.

More importantly, getting trigger time with the rifle for the beyond 250yd shots will really make more of a difference in your success than the 2" of barrel, and I would focus on fitting the rifle to you more than marginal muzzle velocity benefits.

If you're large in stature with medium build or more, consider the 20". If you're 5'7" or less with a slender build, consider the 18" with a medium or light contour.

I've been increasingly focused on the practical effects of matching the rifle weight/length/balance to the shooter height/weight over the past few years as opposed to raw cartridge and muzzle velocity performance.

The biggest practical difference I've seen between 18" MLGS and 20" RLGS is whether or not the shooter will eventually suppress or not. If so, I would go with a RLGS in either of the 2 lengths, as opposed to the MLGS, with the flow-through cans as exceptions.

18" RLGS suppressed is better than 18" MLGS suppressed due to cyclic rate and plug dwell time, much easier on the bolt and extractor, even with 5.56 NATO.

[SightedIn]

52 is right on with the gas lengths. Though I chose an 18” i did get one at RL gas for “future-proofing”

[Swampfox]

I love my 20in group buy barrel

[1Shot]

Like has been said it all depends on your hunting situation. I have both 18 and 20 and as far as handling there is not that much difference. My 20" is heaver but most of it is the steel handguard BCA uses on their uppers. I used a STNGR aluminum handguard on the 18" Oden Works barrel rifle I built from scratch. If you will be doing long range shooting I would go with a 24" and If you feel that for handling purposes it is too long when hunting I would go muzzle device less. Take off the muzzle device and it will handle like a 20" with the device. On average there is only give or take 40 fps difference between 18 and 20" barrel but put on a 24" and it would be well worth it for velocity increase.