Hello, my fellow ARFcommers,

I am preparing to build myself a .308 SR25-style rifle.  I am having a hard time deciding what barrel length I want to go with, though.

16" / 18" / 20" - All things being equal (i.e. rail type, ammo), what differences will I see when it comes to weight, velocity, and accuracy?

For the purpose of this query, assume that I would be using Federal Lake City M80 FMJ / 149 grain.

I figure my max range would be around 800 yards, though I would do most of my shooting at around 100-200 yards.

I'm leaning towards an 18" upper for the balance of weight and overall accuracy.

All I know that's worth sharing is that after 18" there is literally almost no increase in MV. So if you want to reduce weight, but maintain peak MV, 18" is the way to go. The only advantage to a 20" might be less muzzle flash and report.

I wish I would've gone with an 18" instead of 21". It gets old real fast carrying that thing around. 18 is just fine for a 308.

http://www.thetruthaboutguns.com/2013/10/daniel-zimmerman/the-truth-about-barrel-length-muzzle-velocity-and-accuracy/

Here is a good article about 308 barrel length.

For target shooting any of those lengths will serve you well.  For hunting I like the longer versions.  Here were my results for the factory hunting loads fired from my 20" DPMS G2 Hunter and my 16" SCAR 17.


Barnes 150g TSX:

20".... 2725 FPS

16".... 2585 FPS


Federal Fusion 150g MSR:

20.... 2830 FPS

16.... 2670 FPS


Not a huge difference, in my experience a 20" barrel gets you about 95% of what a 308 can do.

.308 AR's are pigs, there huge and heavy. Unless you're going to build one for longer range accuracy I would skip Lake City M80, it's junk. An 18" or 20" stainless steel match barrel and 168/175 grain Sierra Match Kings will shoot very well.

Even my 16" Noveske .308 is too heavy IMO. If you ever want to compete in NRA tournaments in the "service rifle" division the barrel has to be 20" in length, no longer and no shorter. That's something to consider if you want to develop your basic marksmanship skills.

Barrel length has very little to do with accuracy. A quality barrel and premium bullets are the key to small groups and that costs money. The older I get the heavier my guns become, something to consider for future reference.

No pig here. If you're going to carry it, do a 16" and pick your components wisely.

7lbs 9oz, no Optic or Mag

A little over 7lbs is awesome! That is what I am talking about! My next build will take weight into account this time!

Thread relevant to my interests. I'm thinking a high low mix. a 20" rifle and a 16" carbine.   I have a Aero Precision M5 upper/lower set and was originally looking to build a SR-25 MK11 clone(ish) with a 20" barrel.  Very hard to get parts and I've yet to confirm compatibility with what KAC vs. Non-KAC parts will work together, not to mention the price, so I might use the stripped receiver set to build a carbine first.

14.x" 308 and 22" 6.5 CM for me

Thanks for the replies.  The older I get, the lighter I like my toys to be.

Something else I was considering too - muzzle blast and flash.  I have a Springfield Armory SAR-8, which has about an 18" barrel, if I recall correctly.  It does not have a flash hider (stupid mock flash hider attachment to be import compliant).  It produces a hellacious muzzle flash about the size of a frieakin' beach ball.  If I add a brake to it, I'm sure anyone to my left or right at the range will not be happy.

So - shorter barrel 308's, be they 16 or 18 inches - how is the muzzle blast and flash?  With / without a brake or flash hider?

Wow!  Some really interesting stuff in that article.