16 inch barrel vs 18 inch.

[Bullseyeshooter]

I know this subject must have been asked but I am in the middle of a 308 build and am not sure which way to go.  I like the idea of a 308 carbine.  Better penetration power and can make the long shot out to 300 yrds when needed.  The Brits went with this idea in their purchase of the LMT LM308 MWSE.  Does anyone have the 16 inch barrel and how are your results?  I read the article on line about shorter barrels of 18 to 20 inch barrels.  I am looking for MOA shooting from 100 to 300 yrds.  Is there that much difference between 16 and 18 inch barrels?  Thanks.  <munch>

[Robocop1051]

...Is there that much difference between 16 and 18 inch barrels?

About 60-80 fps... Depending on the bullet, that's it.

A Sierra 168gr BTHP .308 only requires 15.5 inches of barrel for a complete burn of the powder contained in the cartridge. The bullet gains the most speed before the initial burn is completed. After the burn, the bullet only relys on the expansion of the already burnt gas to propel it. The increase becomes quite minimal very fast afterwards.

I say if 16" is too short, then you might as well go for a 24". The 16" barrel should hold most match grade ammo at supersonic velocity up to 500-600 yards. Supersonic speeds can be guesstimated at about 100 yards per inch of barrel after. Keeping your bullet supersonic beyond 1,000 yards with a 24" barrel

The first five inches are the most important, as the bullet quickly jumps to about 1550 fps. From that point the bullet gains another 140 fps per inch till it reaches about 2200 fps at about the 10 inch mark . At 15.5" (or 16")you should be shooting around 2500 fps , meaning an average of 100 fps per inch from the 12" mark. After that point you will generally only gain about 40-30 fps per inch tapering off gradually as the barrel gets longer. At 20" you should be flying at approx 2600 fps. With a high estimated 2700 fps at 24"

You have really maxed the bullet out at 24". I have seen nearly the exact same numbers from 24" and 26" barrels using the same bullet.

[edgecrusher]

Hey bullseye, welcome,  I have a Pws mk214, with a 14.5"bbl w/ a permanent muzzle break attached, and I get moa out of it @ 100yds.

[survivalshop]

Robocop gave a very detailed account on what goes on in the barrel.

The 16 will have no problem out to 500 yrds & beyond , it is a .30 bullet & weight helps down range .

Check this thread out if you already haven't , I give some chornograph comparisons between my 16 & 20 , the 18 will of course, come out some where in between .

http://308ar.com/forum/accurizing-the-308ar/why-shorter-barrels-may-often-be-better-article/