Cutting 16" barrel to 14.5" on AR-15

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Laubage

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hmmm... ok well maybe I'll just sell my upper then? I will still need someone to pin my muzzle device if I do manage to sell it, because I want to put a free floating quad rail on my upper, but with a pinned flash hider, I won't be able to remove the front sight post. I have to do it all correctly from the begining
 

Beercules

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You might consider a CMMG 14.7" upper or barrel if you're going for an 'M4gery' on a Title I lower. The added .2" allows for the use of a standard A2 flash suppressor to be pinned and welded for the required 16" OAL. Two friends have them and love them, and they are virtually indistinguishable from a 14.5" gun until you place the uppers side by side.

Any idea which FF rail you'll install?
 

ez bake

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hmmm... ok well maybe I'll just sell my upper then? I will still need someone to pin my muzzle device if I do manage to sell it, because I want to put a free floating quad rail on my upper, but with a pinned flash hider, I won't be able to remove the front sight post. I have to do it all correctly from the begining

Are you planning on replacing the FSB as it is (in front of the FF Quad) or getting a low-profile gas block and running the FF Quad over the top of the gas block?

Depending on the Quad-rail and the size of the gas-block, you might be able to install it without removing the new gas-block (or if you cut the factory FSB down - same thing).

Who makes your upper/barrel? Yanking a barrel and replacing isn't that hard with just a few tools that lots of folks on this board own.
 

Garand

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Well, I just like how it would be more consistent with an M4 that the military uses. I bought an ACOG TA31RCO-M4 (if you remember my delivery fiasco) which is calibrated for a 14.5" barrel...

There are other things you could do to remedy this issue..

Ammo for instance, .223 specific ammo is typically a bit slower than true 5.56 ammo because of the pressure difference in the specs..

Take the Hornady TAP ammo as an example. Hornady produces this round in both 223 Rem, and 5.56mm

So if you were shooting this "223" ammo out of a 14.5" barrel you'd be nearly 200fps off what the 5.56(which the ACOG was likely configured with) is throwing.

Long story short, when you're dealing with BDC reticles you need to be shooting a round at the same velocity as the BDC was calculated to use irregardless of the rifle barrel length.

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Here's where all this data comes in to play..

"The Hornady 75 grain bullets are considered to have a fragmentation threshold of 2200 fps +/- 50 fps. Based on the conservative figure of 2250 fps the table below shows the range (in yards) at which fragmentation can be expected to occur for the two loads being tested. It also shows the gain (in yards) before reaching the fragmentation threshold for the 5.56 TAP load. "

Thats quite a bit of difference in range that you get the full potential of the projectile.
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Beercules

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I think I mis-interpreted the M4 part of your previous post....

To Garand's point, your ammo selection will make a bigger difference in how 'well' your BDC works than the difference in a 14.5 or 16" barrel if that is your primary concern. The ballistics table I have floating around here shows the difference in trajectory between a 16" and 14.5" gun firing M855 to be within 1 MOA out to 500yds. Keep in mind that M855 is generally 2 or 3 MOA ammo at best, too!

I run a TA31F on a 20" gun, and M855 is basically dead on the BDC, M193 is almost as good, and everything else differs. As a result, I shoot those two loads 99.9% of the time. Wolf and other lower velocity stuff is no where near the BDC ranging by the way, so keep that in mind when you select ammo and start shooting.

With that being said, the fixed BDC does provide convenient reference points for holdover even if you aren't shooting the load it was designed for or the barrel length it was designed for. I have plopped my ACOG on a 11.5" SBR, with no change in zero, and within a few rounds been hitting steel at 500m.

All that to say...don't be too quick to chop your barrel or replace the upper for the sake of the ACOG...you will very, very likely never see the difference.
 

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