.223: Velocity loss going from 20" to 18"

[Mylhouse]

I'm sure this has been discussed before, but my search skills are lacking.

I'm thinking of a 1 in 8" twist .223 AR bull barrel upper with a 18" tube for prairie doggin and target.

For those of you that have spent some time behind a chrono, what kind of velocity loss does the 18" AR15 barrel suffer when compared to a 20" tube with 55gr, 62gr, and 75gr loads?

Reason I ask is I can get an 18" upper NOW, or if I hold out for a few weeks, then I can get the 20" if the difference is significant.

Thanks

 

[John Ross]

75 FPS less with 55 grain bullets, 60 FPS less with the 75s, in an 18" .223 barrel compared to a 20" one.

Go to http://www.john-ross.net/suggestload.htm for a modeling program so you can answer these questions for yourself.

It is MUCH more accurate than saying, "Well, I heard you lose 75 FPS per inch, but maybe that was handguns..."

JR

 

[Mylhouse]

Wow, I didn't know you were that John Ross! Excellent website, and thanks much for answering my question!