View Full Version : 18" or 20" AR?
I know this might cause a bit of debate but I wanted to get some insight before I build AR #2. I already have a mid-length 16" AR, but wanted to build an AR with some optics for some longer distance shooting.
Should I go with an 18" or 20" upper? Does it make a difference?
Thanks.
Barrel quality and optics are going to make a MUCH bigger difference than 2 inches of barrel. There have been confirmed kills in the Middle East out to around 800 yards with the 18 inch barrelled Mk12. Trident82 on this forum has videos of himslef shooting out to 1000 yards with his 18 inch rifle.
Can you elaborate more? Your 16" with a good optic is every bit as capable as an 18" or 20" barrel.
Can you elaborate more? Your 16" with a good optic is every bit as capable as an 18" or 20" barrel.
I'm okay with a 16" with good optics. I just want to make sure that it would be an effective platform. Suggestions on optics? I don't want to kill the bank.
The rule of thumb is that a good scope/optic is going to cost as much as the rifle. I use an ACOG on my SBR at the moment.
On my 16" Recce rifle I was using a Leupold MR/T. Optics are something that you don't want to buy cheap.
I'm okay with a 16" with good optics. I just want to make sure that it would be an effective platform. Suggestions on optics? I don't want to kill the bank.
Barrel length in itself is not a determining factor for long range shooting. You have to consider other things along with it: thickness of barrel, quality of manufacture, acceptable weight, etc.
A longer barrel of the same quality will give more velocity, so a slightly flatter trajectory. Not more accurate but flatter. A shorter barrel of the same diameter will be stiffer and probably more accurate, likewise a thicker barrel for a given length. A thicker barrel of the same design will weigh more.
Also, the type of rifling, finishing and tolerances of the bore and rifling affect accuracy and velocity.
I don;t think 2 inches is very material compared to the other factors of diameter, quality of materials and manufacture, etc. If you are shooting long range then a 20" barrel is no less convenient than an 18" one. I suspect you would find a much greater selection of quality barrels in the 20" length.
silentmark
03-07-12, 22:29
I'm getting ready to rebuild my 20" AR into an 18" SPR. With the same quality barrel, the 18" will perform just as well as the 20".
I don't have a ton of experience with long range shooting, but it seems to me the 18" barrel would keep your AR easier to maneuver with keeping it handy.
mkmckinley
03-07-12, 23:48
If your 16" has a decent barrel then invest in really good glass for it and some high quality ammo. If you're 16" isn't very accurate I'd go with a 16" medium weight Noveske barrel and something with a Horus reticle, but that's just me.
I'd grab a Centurion or Noveske 18" for a precision rifle. That's just me.
16" does pretty good too as stated.
18 is just as good as 20, both use rifle length gas
16 is good too, midlength or intermediate gas length
figure out what what you need to do with it, the only way you would see me running around with a 18 or 20 is if it was some sort of dedicated 3-gun rifle
Actually there's a few gas system lengths for 18" out there. Just a data point...
yeah i know, theres carbine for 16 too, i was just giving a general overview
Cool cool. I'm just adding to the data I guess. :D
I just went through the same process with my new rifle. I ended up with an 18in barrel and for optics a vortex viper pst.
I found no good reason to add the two inches on to the length of the barrel for a few ft per sec difference in velocity.
Here's my take, and what I discovered, so take it for what it's worth, I chronographed bot my 18" SPR with a rifle length gas system, and my 20" DMR, both are Douglas SS barrels, after shooting a number of different rounds, I discovered the average feet per second between the two was about 9-10 feet per second off the top of my head. I would have to look it up to be sure, but I do remember I was shocked at how little difference there was, and that number has always stuck in my mind for that reason.
Mauser KAR98K
03-08-12, 13:44
I'm thinking of going the same route, unless I decide to to SBR my recent new stripped lower (Double Star-yes, I know, but it is a lower). If I go the 18" route, what buffer/buffer tube can I use: Carbine or Rifle/A5?
lifebreath
03-08-12, 13:59
I would go 18". I am looking currently for an upper to fulfill a similar desire and to mate with an A2 lower I have that has a Geiselle National Match trigger installed. 18" allows use of a rifle length gas system, which means smoother and more controllable recoil and followup. 20" offers no appreciable gain in distance or accuracy, just added weight and less maneuverability. There are good reasons why the MK12 SPR uses an 18" barrel and rifle gas system. Just need a quality match-grade barrel and nice low-profile glass.
I'm thinking of going the same route, unless I decide to to SBR my recent new stripped lower (Double Star-yes, I know, but it is a lower). If I go the 18" route, what buffer/buffer tube can I use: Carbine or Rifle/A5?
You can use either just depends on your stock.
So I am by no means an expert in ballistics or barrel design, but I would guess a rifle length barrel length and then loads of training will get you what you want.
I'm guessing your 16" is chrome lined and the 18-20" will be stainless/precision? My 18" Noveske (stainless barrel) does shoot most anything more accurately than my 16" Noveske CL (groups run about 50% better).
The 18" barrel also pushes the same 77 gr SMK load a good 100 fps faster. Ergo between these two specific barrels, one CL and one stainless, the 18" SS is better for both distance and accuracy. Some of this could be related to the difference in weight - heavy guns are just easier to hold steady. As to going 18" or 20" for a precision barrel, I don't really have an opinion - but assuming both were built for accuracy (over hard use longevity), I doubt it will make much of difference.
If you're looking at long range you should look into actual velocities of the ammo you're planning to use.
I found 40-60fps difference with 77gr ammo between 16" and 18".
After chatting with Noveske on my build, I went with a 16" midlength as it offered the correct dwell, weight, and velocity I wanted.
Aside note, Noveske and KAC do not use rifle length 18", they intermediate. I know rifle works, I just don't think it's actually "ideal". Just like I know 12.5" and 13.7", midlength WORK, I know 14.5"-16" is ideal.
TangoSauce
03-09-12, 11:43
I lean towards the 18'' myself here. There's a balance between velocity, bbl harmonics, and portability. If it were a 338 I'd suggest a 20, but for a nice precision 556 18'' has the best compromise between these factors.
Get a quality SS barrel. I opted for the Noveske SPR, and I'm very impressed. Get some quality 77 grain ammo, that also makes a big difference. I shoot 75 grain PRVI at the range due its price and accuracy.
Then invest in some glass that cost as much as your rifle, lol.
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