I know....Not this shit again.

Guys, I was really set on a 20" flat top.  I already have an A2 20" Hbar.  I want this next rifle to be....... more.......specifict to my needs/wants.

I was all settled on a 20" flat top.  I want to put optics on this rifle.  I want it to be effective out to 300-400yds.  I will be putting a Magpul M93A on this rifle also.

I am now revisiting the barrel length.  I beleive that 14" just takes away too much velocity for me.  I live in open country.  I want a rifle that will be effective out to 300yds.  I believe that is beyond the limits of a 14"+ flash supressor's capabilities.  

Is 2 more going to make any real difference?  Is a 16" barrel still going to be lacking in the effectiveness department?  I realize the accuracy will not be a problem.  I shoot surplus, as well as hand load 69gr ers, and soon 77's.  

What say you?

For the ranges you are quoting you should look at  the DPMS 308's or the Bushmaster AR10's.  The 308 will give you the stopping power you want at the ranges you are quoting ( that is asssuming you are shooting anything larger than a rabbit at the long ranges).

The 20" flat top is a great configuration, hence the Marines adoption of the M16A4.  Here's my A4gery:



You can get hits out to 3-400 yds with a 14.5, but personally I'd go with something longer.  The 18" SPR's were reportedly getting hits out to 600 yds and beyond.  

Quoted: For the ranges you are quoting you should look at  the DPMS 308's or the Bushmaster AR10's.  The 308 will give you the stopping power you want at the ranges you are quoting ( that is asssuming you are shooting anything larger than a rabbit at the long ranges).

I have considered the 6.8.  I'm still considering that, infact, but I believe I will probably stay with the 5.56.  

I probably overstated the ranges somewhat.  300yds would probably be the max I would expect the 5.56 to be effective on targets bigger than a rockdog.  I also think that with an Aimpoint, past 300yds, it will be difficult to make accurate shots on targets less than 6-8" in size.  Can some one tell me what kind of velocity differences there are between the 14.5", the 16", and the 20" barrels?  

I believe I have read here that in a 14.5" barrel, the 55gr and 62gr bullets fail to tumble/fragment after hitting a target after 100yrs?  Or something close to that?  

What is the range for a 16" barrel, that these rounds fail to fragment/tumble?  150? 200yds?
Thanks for your help, and opinion.
guns762

Quoted: The 20" flat top is a great configuration, hence the Marines adoption of the M16A4.  Here's my A4gery:

bsbg,
Very nice looking rifle.  Other than a Magpul stock, I think that is close to what I want on this set up.   I'm just reconsidering the barrel length again.  

Quoted:  Can some one tell me what kind of velocity differences there are between the 14.5", the 16", and the 20" barrels?   I believe I have read here that in a 14.5" barrel, the 55gr and 62gr bullets fail to tumble after hitting a target after 100yrs?  Or something close to that?   What is the range for a 16" barrel, that these rounds fail to tumble?  150? 200yds? Thanks for your help, and opinion. guns762

Check out this post from the Ammunition section:

www.ar15.com/forums/topic.html?b=3&f=16&t=189353

A 20" barrel will fail to fragment and perform at the ranges you specified (300 yards) with ANY ammunition in 5.56... you need a larger caliber.  The rounds "tumble" at any range but fail to fragment.  At 300 yards the 14.5" barrel is failing to fragment and so is the 20" barrel so why add all that weight and length?  Your decision is based off bad assumptions.  You want a 6.8 or 7.62 if you want 300 yard+ performance.  Even with 75 grain Hornady TAP and a 20" barrel you are limited to 200 yrds of fragmenting range and the difference for your 55 grain M193 clone is only about 35m for 20" and 14.5" barrel.

If you use the best commercially avaiable ammo your distance of optimal terminal performance will be like

110 yards 14.5"
150 yards 16.0"
200 yards 20.0"

6.8mm ammo will perform over 200 yards from a 14.5" barrel and I beleieve around 300 yards from a 16" barrel.  A 5.56 is really a 150m caliber and 6.8 is your 300m caliber.