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Has anyone out there got muzzle velocity figures for a .58 PRB with various powder charges? Barrel length and twist are not real important - I'm just looking for some "ball park" figures that someone gets for anything from 70 to 120 grains of Pyrodex or JSG.
 

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per Lyman, a 58 PRB, 28 inch Zouave barrel at 100 grains of FFG Goex gives muzzle velocity of 1215 ft per second. same set up with 120 grains of the same gives 1322 ft per sec. at 70 grains there is 998 ft/sec.

The point of diminishing returns is reached between 80 grains and 90 grains. By diminishing returns, I mean that for every ten grains increase in powder the muzzle velocity increase becomes less and less. ie for every ten grains from 50 grs to 80 grains, the velocity increases by approx 95 ft per second. But from 80 grains to 90 grains the increase is only 63 ft per sec. from 110 to 120 grs the increase is only 53 ft per sec. This occurs because for every ten grains of powder, the powder takes up more and more room in the bore, meaning the PRB has less barrel to travel to the muzzle. In addition, the additional powder is not fully burned before the ball exits the muzzle, resulting in increasing muzzle flash. So while the actual velocity continues to increase, the actual efficiency of the increased powder goes down. Even though the PRB velocity increases at a decreasing rate, the breech pressures continue to climb at a steady rate. The result is that risking dangerous breech pressures in higher powder charges actually results in little velocity benefit, and even less increase in energy retention at 100 yds.

Don't fall for the Popeye syndrome. More powder is not better.
 

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Interesting that Thompsons Data shows much higher velocities They don't state what powder was used.

With a 279 grain patched round ball:

80 grains................1302 fps 1050 ft lbs
90 grains................1373 fps 1168 ft lbs
100 grains..............1428 fps 1263 ft lbs
110 grains..............1519 fps 1430 ft lbs
120 grains..MAX......1595 fps 1576 ft lbs

http://www.tcarms.com/assets/manuals/current/Shooting_TC_Side_Lock_Black_Powder_Guns.pdf

Out of my Thompson Big Bore 58, I usually use 90 grains of American Pioneer FFG. It seems to group the best for me.
 

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length of the barrel, whether they used 3fg instead of 2fg, the tightness of the patch ball combo and a number of other things can affect the stats. (although I would never use 3fg in a 58 cal.) Some powders pack much more punch. Swiss is known for being "hotter'". Triple 7 is also hotter than standard GOEX.

TC's stats are a little strange. look at the jump in velocity for the ten grain loading increments. it goes up 71 ft per sec, then 55 ft per sec, then 89 ft per sec. and then 76 ft per sec. On the other hand the increases in muzzle energy have similarly wild variations. It goes up 118, then 95, then 167, then 146.

Why would an addition of ten grains from 90 to 100 add substantially less velocity than from 100 to 110? It doesn't make any sense.

Lyman used a .560 round ball which weighed out at 260 grains. Obviously TC used a larger heavier ball. probably .570.
 
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