Originally Posted by bushmaster74
I'm changing the barrel cause I want to. I don't like the stock barrel with fixed front sight. I'm real sorry if I'm an inconvenience to you all. I didn't know it was a big deal to ask questions. I see on other thread about 24 barrel do funny things to reciever but never explained any further. So I asked the question on this thread to see if I got response. I'm still figure in out what length I want. I know 20 is more than enough. Was just goin for look. Real sorry I posted anything at all. In future I will not
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Its hard for me to keep track of conversations if they stretch over several.threads.
Anyway what i meant by it doimg funky stuff. Is the weight of the barrel can be a problem when you go super long in a ar15. It can cause bad harmonics to show up since the barrel only sits in a smooth hole in the receiver held in by pressure of a nut only. You start to get some warp going on.
The other thing is extending the barrel too far out (21+ inches) tends to have a negative effect on accuracy. The longer the barrel the more it can whip around as the bullet travels down the tube. Shorter thick barrels are more rigid and a bit better at giving repeatable shots as they heat up and cool down.
You see 24+ barrels in varmint guns not because of the long range accuracy but because a longer barrel has more mass so it heats up a bit slower allowing a few more shots before the prairie dogger has to let it cool.
Ive got about a half dozen ar15 of different types. The most accurate are 20" barrels followed very closely by 18" ones.
The 556/223 is a 600 yard cartridge. Adding 4 more inches is not going to get you to 700... it really does nothing except in my add negatives. More weight and more vibration.
You can build how you want i just think its a huge mistake hanging a long barrel on a ar15.
Way back military arms makers used long barrels to get the front sight as far out as they could to increase sight radius of iron sights. Today we dont need to do that and using a good optic means we do not have to hamstring our rifles with over long barrels in order to line up on a distant target.
Using iron sights length means accuracy because the margin of error of iron sights is far greater than the negative effects of a long barrel. In other words the barrel can outshoot the user with iron sights.
When you use a modern optical system you start to run into a situation where its possible for the user to outshoot the mechanicalmaccuracy of the barrel and thats where shorter barrels show their benefit
So this brings us back to the ar15. Sights are limited by the either the length of the handguard or length of the gas system. So you get no benefit from extending an ar15 barrel since your not going much past a max of a 18" sight radius.