Velocity decrease 20" barrel to 16" barrel: 223

[ronas]

I do not have a chronograph.

I have a new AR15 type rifle with 16" barrel. All my reloading data show veolocity but a 20" barrel was used. I know there is some reduction in velocity but do not know how much.

Is there a rule of thumb to use to figure approx. decreased velocity?

 

[jet_lagged]

Re: Velocity decrease 20" barrel to 16" barrel: 223

Don't know about a rule of thumb. Chrono results for average vel for 10 shot groups from 20" AR, 18" AR, and 14.5" AR barrels:

Privi M193 55gn: 3246, 3155, 2933

Federal Frangible 50gn: 3265, 3131, 2830

Hornady TAP 75gn: 2597, 2568, 2389

All chrono'd same day/conditions. Should give you some idea.

 

[Rovieairto]

Re: Velocity decrease 20" barrel to 16" barrel: 223

You'll see a top of around 1150 ft x lbs. with factory ammo in a 16" barreled 223.
Work backwards with bullet weight to solve for velocity.