VERY rough "rule of thumb"?

[cyclone]

Just wondering (not stating ! ) , but am I wrong in thinking that as a rough & general "rule of thumb" a measure of Bullseye is basically 80% of a similar measure of Unique for a given calibre and "weight of bullet" , and that a measure of (IMR/Hi-Skor) 700X is basically 80% of a similar measure of Bullseye is basically 80% of a similar measure of Unique for a given calibre and "weight of bullet" ? ...


Again, just a VERY rough example: my "back of the envelope" calculations for .44 Russian actually worked out like this:


4.2 grain of Unique = 3.6 grains of Bullseye = 2.8 grains of IMR 700-X


Questions/comments ?.......

 

[mooncoon]

I think you need to keep in mind that the burn rate of smokeless powders increases with pressure and pressures can increase exponentially once you get past 30 or 40,000 psi. What that means is that some relatively small increases in powder charge if you have estimated high on the basis of a rule of thumb ratio between two fast burning powders. In rifles you can probably work up slowly and watch for flattened primers and fins of metal into the firing pin hole but with handguns your maximum pressures are going to be much lower than those pressure indicators

cheers mooncoon

 

[cyclone]

Using 'Cartridges of the World' (11th Ed.) , I found the "listed" smokeless recipes to be pretty light.....

 

[10x]

I would not use bullseye powder in any antique firearm and I would not be extrapolating loads with any fast pistol powder for antique handguns. All it takes is one pressure spike to damage the gun
I suggest you read the current copy of Rifle (November 2012, #265) page 24 "Smokeless powder in Black Powder guns" by Gil Sengel that outlines the possible damage that can be done by high pressure loads.

Bullseye powder burns faster than Unique. That means a shorter pressure curve. It also may mean a higher pressure curve. Combine these two factors and a fast burning powder may simply generate too much pressure too fast for the old alloys used in an antique handgun. Unique is the fastest burning powder that I will use in an antique handgun that is in good shape. I prefer loads with a slower burning powder. I also prefer loads that get the ball to the target accurately with the smallest amount of powder. My choice of loads for antique handguns when using smokeless powder is the lightest bullet available with a load of the slowest burning powder listed.

All that being said, in the 1960s it was rumoured that there was an individual who reloaded ammo for a police service using bullseye powder in 38 special for S&W model 10 revolvers. A significant number of revolvers were damaged due to pressure. After a change was made to Unique powder there were no more reports of damage due to pressure. Maybe the "weaker guns" were weeded out by the bullseye loads and those left would have handled either powder with no problem, or maybe some batches of Bullseye powder (or something in the reloading sequence) allowed higher pressures. Bullseye powder can reach very high pressures very quickly. That pressure threshhold is lower than Unique. There are too many variables (bullet crimp and bullet alloy) that can cause that pressure threshold to change with a resulting pressure spike. And that is why I would never recommend any one use Bullseye powder in an antique.

Your calculations do not match the pressures shown for 700x, Unique, and Bullseye powders in the Lyman Cast bullet manual (4th ed) for the 45 ACP where the same weight of 700x and Bullseye give similar velocities and pressures for the same bullet. Burn rate charts are not reliable indicators of pressure either as Bullseye is listed as a much faster powder than 700x.

 

[cyclone]

The idea of using light smokeless-loads to "obturate" does tend to require faster-burning powders.......but your comments are well and duly-noted, and very much appreciated !...

 

[tacfoley]

Much of the problem with smaller loads of Bullseye and its predeliction for destroying revolvers seemed to stem from the so-called 'surface detonation' phenomenum. Instead of the flash from the primer passing into a column of powder as would happen in a large load that filled or nearly filled the case, the flame from the primer travelled across the entire exposed surface of the powder, igniting it all near instaneously, in physics terms. The resultant pressure spike - the propagation of the gas generation taking place much faster than usual - may well have been the cause for so many guns to have been destroyed by this happening.

Regardless of the wisdom of using smokeless propellant in an old gun designed to shoot BP, I would not consider doing it under any circumstance.

tac

 

[dingus]

Buyllseye is just to easy to throw a double charge as everyone knows im a big fan of light loads of smokeless in antiques but bullseye is just to dam hot and as the charges are so small in the bigger cases.
i can see a double loading geting thrown if your distracted by the dogs chaseing a cat thru the house or a phone call or whatever when your reloading.
i like unique and i like trail boss in my better guns trail boss is nice because it almost fills the case with any charge so you will over flow the case with a double charge and know you fuked up.
Tho it can spike fast if you over load it i like it at recomended levals.

Black powder can blow up guns to if you get a air space in the case when reloading.
smokeless can be safe if you follow the reload guidelines keeping the presures down

Member Win 3855 on CGN did some great work with the 44 russian and some smokless loads do a search on 44 russian and see the powders he used they have very close to the same presure curve as BP but no mess to clean up.

 

[Win 38-55]

Another thing to consider is the bullet diameter. For example, the 45 Schofield has 10% more base area than the 44 Russian. What this means it that for the same pressure and bullet weight, the 45 Schofield bullet will experience 10% more force pushing it down the barrel with translates to higher velocity for the same pressure. Or for the same velocity, the 45 Schofield requires less pressure.