FF -VS- FFF Burn Rates

[mtmeredith]

I found some interesting discussion below on barrel lengths and their relationship to % of powder burned during a discharge. Interesting reading. Is there a difference between FF and FFF in burn rates? Does FF require a longer barrel because it burns a little slower?

Thanks

 

[necchi]

Much of the burn rate issue is surrounded by the caliber, projectile, wadding(if used), patch thickness(if used) and the lubrication of the patch/projectile used in any given barrel.

Point is the resistance the projectile has in the barrel as well as it's weight have affects as well as barrel length.

So given just the one variable as questioned (Barrel length) it's hard to answer in a definitive way.

I'm sure some folks will answer Yes or No as it applies to the circumsatnces of their own experiance, but more things than barrel length apply when speaking of the efficiant burn of either 2F or 3F.

 

[Sinner]

fffg burns faster than ffg, and also builds pressure quicker. Whether or not a longer barrel is "required" or not is a whole nuther story! Most people find that calibers greater than .50 have better accuracy with ffg. I haven't seen a great difference in my .54, but I'm not as picky as some. Are you asking just for general knowledge or do you have something specific you are looking to solve?

 

[Matt85]

with my limited experiance id say 50 cal is the middle caliber. so under 50 cal you should use FFF and 50 cal or over you should use FF.

with 50 cal itself, you can use which ever seems to shoot the best for you. some people like 3F while others like 2F. im assuming it has to do with barrel length and rifling speed. im afraid i cant get any more scientific sense black powder ballistics is still new to me.

 

[Dphar]

I found some interesting discussion below on barrel lengths and their relationship to % of powder burned during a discharge. Interesting reading. Is there a difference between FF and FFF in burn rates? Does FF require a longer barrel because it burns a little slower?

Thanks

BP is a surface burning propellant. So the greater the surface area the faster the burn.
From what I have been told by an actual expert in BP FFFF is twice as fast as FFF is twice as fast as FF is twice as fast as F. But this is a GENERAL rule. Close but not absolute.
Burn rate can also vary between brands, between lots of the same brand and even in the same can of some powders. Though this last has been largely corrected in the last 5-10 years.

This does not mean FFF makes twice the pressure of FF so don't jump to conclusions.
There are other factors related to manufacturing and materials that effect burn rate. Milling time quality of the charcoal and other components and the amount of Potassium Nitrate used. "Sporting" grade powders of the past and I think Swiss today uses 76% saltpeter. A high polish on the grains (not graphite) as in Swiss, will actually somewhat retard the initial burn rate but its slight. But apparently enough to be measured by breech pressure.

I would not worry about burn rate related to barrel length. This would require a lot of testing and as was shown in Lyman's first BP loading manual, variations in powder from lot to lot (can to can) can offset any conclusion based on the grain size used.
I do not subscribe to the notion that its possible to calculate how much powder a barrel will burn based on the capacity of the bore.
If so the bench gun line at Friendship would likely erupt in a fast fire from all the ejected unburned powder some of these shooters use a LOT of powder for the bore size. Far more than will burn according to the formula I have seen.
Dan