Barrel length

[grubbylabs]

I am looking at building a AR- 10 in 308

I want to build it mostly for target shooting. My question: am I going to see a big difference in a 18" barrel vs a 20" barrel as far as down range capabilities go? I know accuracy is not dependent on length but speed, and range are.

 

[urbaneruralite]

What is a "big difference" to you? Target .308s are usually around 21, 22" Also there was a thread recently where this topic got beat to death.

 

[grubbylabs]

Well from my limited knowledge it seems that keeping the speed up is going to reduce drop, and keep the bullet stable longer making it easier to hit targets farther out.

I know people do a 1000 yards with a 16" gun, but with a 180 grain bullet, at 2000 FPS I am dropping 725.5" at a 1000 yards and fps is estimated to drop to 993.

In my mind and very limited knowledge, I won't see a big improvement with an additional 2" of barrel, but 4" might be getting close.

 

[jmr40]

You'll lose 25-50 fps if you cut a 20" barrel down to 18". You could see 50-100 fps difference between barrels of equal length. It is entirely possible an 18" barrel on one gun could be 50 fps faster than another gun with a 20" barrel, or it could be 100-120 fps slower.

The individual differences between different barrels will make more of a difference than 2" of barrel. To guarantee more speed you'll need to be talking about 4"-6" or more barrel length.

High quality target barrels with close tolerances tend to not only be more accurate, but faster.

 

[redbullitt]

Go for the shorter barrel. Rifle will handle better and I seriously doubt anything you shoot will know that difference!

I shoot a 16 inch 308 bolt to 1k fairly regularly (out to 600 VERY regularly), as well as a 20 incher. Both rifles hammer the steel the same, but I will say that 16 is much easier to carry around.

My 16 inch bolt gets 2450 with 43.0g Varget and 175 SMK. The same load in the 20 inches is in the mid 2500s. Both loads are loaded long in the case and are quite mild.

A bench only gun maybe? Long barrel all day. If that is the case I would put a 30 inch tube on it lol. If it is going anywhere but bench my 308 and other short barrel friendly calibers get shorter barrels.

 

[grubbylabs]

So I won't likely see much of a difference between the 18" and 20" barrel. What about between the 16" and the 18"?



This will not be a hunting rifle, I have to many others for that.

 

[js8588]

For downrange performance, go with 24. Good news is, it's cheap http://www.dpmsinc.com/LR-308_ep_124-1.html

 

[grubbylabs]

After urging some numbers in to Ballistic AE I think I am going to go for the 18" barrel and go from 180 grain bullets to 168 grain bullets. Might try 175 grain bullets but I will likely stick with the 168.

 

[Robert101]

I don't see the justification for short barrels on 308s. If for CBQ then ok but choose an appropriate cartridge. So what is your application? For me in this caliber I want good velocity for down range optimalization of the caliber. Don't neuter the 308 down to a lesser performaning cartridge. My threshold is no less than 20" in the 308. I know many others have a different opinion. Thank goodness for women that come in various shapes and sizes too!!!!!

 

[Slamfire]

Cutting barrel length down to 18" will really reduce velocities. I would not go below 22", I would prefer a 24" if it balanced well.


M1A 22”1/10" 6 groove Douglas

150 gr Australian Ball MF83 headstamp (actually 147 grain)
T = 78 °F 2-May-05

Ave Vel = 2806
Std Dev = 91
ES = 344
Low = 2612
High = 2956
N = 10

PTR91 18" barrel

150 gr Australian Ball MF83 headstamp (actually 147 grain)

30 April 2008 T = 75 °F

Ave Vel = 2599
Std Dev = 23
ES = 63
High = 2630
Low = 2567
N = 10

poor accuracy

 

[urbaneruralite]

If it's a range rifle, get all the barrel you can stand. Try it for a while and if you don't like it for some reason you can chop it off.

 

[Surculus]

My question: am I going to see a big difference in a 18" barrel vs a 20" barrel as far as down range capabilities go?

There is less difference between 20" & 18" than there is btw 18" & 16"; the .308 normally burns up all its powder in the 18"-19" range, iirc. So if you prefer the quicker handling of the shorter barrel, go for it. You won't be sacrificing much.

 

[BigBore45]

i just tested a DPMS Lr-308B with 18" barrel in a thread and compared some rounds out of a rem 700 sps with a 26" barrel.
here is the thread:http://www.thehighroad.org/showthread.php?t=770828

 

[nastynatesfish]

I agree. If it's going to be a target gun Id go 24". I have a 16"recon and a 30" savage ftr. Also if look at 155 gr bullets. The increase In velocity will make up for the lower BC inside of 700yds. I can push a 175 in my savage almost 3k. I'm getting 2500~ in my 16". While world of difference.