Calling all muzzleloaders

[Smittyboy]

Hey all, I have a ballistics question for ya! not only external but internal as well! First off I'll present the question... What is the difference in muzzle velocity between a 26" and 28" barrel when using a black powder substitute? The load charge is 120-125 (for operator error) grains loose powder 777 ffg, and the projectile is a barnes TMZ copper slug in a sabot. All testing I've seen in regards to velocities and their corresponding charge/bullet combo's have been out of a 26" barrel... So here's the elemental question... What kinda muzzle velocity can I expect from the aforementioned charge and bullet out of a 28" barrel?
Thanks in advance for any answers...
not that it's relevant, but this has a b.c. of .210, which seems pretty high...correct me if I'm wrong.

 

[champion221elite]

No clue about the overall velocity of a blackpowder load since I don't have access to a chronograph.

With smokeless powder, an inch of barrel is typically good for a difference of 20 feet per second. This is effected by powder type and density, humidity, ambient temperature and overall case volume.

I would imagine that a black powder load (or substitute) would most likely take advantage of the added barrel length and increase your velocity. Depending on grain size (Fg, FFg, FFFg... and so on), black powder has different burn rates. A coarser powder granule size will burn over a longer period of time and give more velocity from a longer barrel. This is because the burning powder charge has a longer period of time to "push" the projectile. Burning a slower powder in a short barrel will result in a large fireball along with added smoke.

Regarding your specific question, a 28" barrel will probably shoot a given bullet with the same powder charge faster when compared to a 26" barrel. I just can't tell you how much faster.