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whats best barrel length on a sbr? ar-15

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bkoenig:
Ok, that is sexy.

Burnsy87:
I prefer the 12.5" on a 5.56 SBR

mike_p:
I went with a 10.5" barrel for my SBR.

I do get A LOT of back pressure when shooting suppressed. I put in a gas vent and did not help much. If I did it over again I'd do 12.5".

skydve76:
I am building a 7" version.  I'll let you know how it goes.  Been looking at pigtail tubes, and adjustable blocks.

I think the best bet for me is to load the ammo differently since I do my own reloads.  There seem to be some pistol powder loads but I think I will experiment with 1/2 ar comp loads to start.  Since most of the powder is wasted I figured less powder is a good idea to reducing pressure. 

I'm reading timing is also an issue, the brass still expanded when it tried to get extracted...hmm would steel case be better in a rifle his short? 

What have you guys tried?

MHicks:
I've got a 7" that I haven't had a chance to run through any ammo with.  I have a variety of loads that worked well in other firearms of the same 5.56 caliber I plan on testing in it.  I know I won't get the same muzzle velocity but the paper won't know the difference.

To my understanding the manufacturers change the gas port size to accommodate where the post is in relation to the gas key.  I can't remember off the top of my head but I believe the farther down the barrel it is the smaller it gets.

Pulled from another site;

For 5.56mm
Colt's gas port sizes are:
* 10.5" - .093
* 11.5" - .081
* 14.5" - .063
* 16" - .063

The concept would make sense given the dwell time after the round passes the port prior to leaving the barrel.  In a shorter barrel there will be less dwell time before the bullet leaves the barrel therefore the port will need to be larger to cycle the action.  When you have  six or seven inches of barrel after the gas port a smaller hole will suffice to get enough pressure to cycle the action.

...I think....

All that mumbo jumbo said, I plan on working up some loads using magnum handgun/shotgun powders to see what I type of ballistics I can get using less powder.

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