Muleskinner(I like that name),
* * * * * * * * * * * * * * * * * * *Being classified an expert is probably debatable, but I would like to attempt to tackle your question and possibly educate you in the fine sport(art, science, obsession ?) of cast bullet shooting.
* * * * * * * * * * * * * * * * * * * With proper cast bullets, projectiles of the same weight and bullet style can be driven faster with less or equal pressure. HOWEVER, there are many variables to be considered, such as bullet hardness, quality of bullet lube used, bearing surface of bullet in question, checked or unchecked bullet design, bullet diameter, and condition of the bore in which the bullets are to be propelled from.
* * * * * * * * * * * * * * * * * * * *As to hardness, a bullet with a BHN(brinell hardness number) of 21 or greater is desired for driving a cast bullet as fast as its jacketed counter part for high velocity rifles(2600 fps or higher). Softer bullets can be used for lower velocity calibers, with superior results,(less than 2300 fps). The higher the BHN, or harder the bullet, makes for a lower co-efficient of friction(fancy way of saying drag). The lower the co-efficient of friction, the faster a bullet may be driven with less pressure to do so.
* * * * * * * * * * * * * * * * * * * * Bullet lube is also factored into the equation. Superior bullet lubes such as Marshall's or LBT are the best for driving bullets to maximum velocity. The less effective the lube, the higher the pressure involved. Same goes with gas checked bullet design. Gas checked bullets can be driven faster than non-checked bullets with better accuracy, and less pressure involved, as the hard copper cup protects the bullets base, which is the stearing mechanism of the bullet.
* * * * * * * * * * * * * * * * * * * * Bearing surface is the part of the bullet that actually touches the bore. The more bearing surface, the higher the pressure. This is why streamlined jacketed bullets can be pushed as fast as a round nose bullet with less powder, given an equal drag factor for the jacket. So there is a balance between the bearing surface of the cast bullet in question compared to its jacketed nemesis.
* * * * * * * * * * * * * * * * * * * * * Bullet diameter is an important aspect in regards to cast bullet accuracy and pressure. Usually best results with cast bullets are those that measure .001-.002" over groove diameter. Anything larger is generally for naught, while unnecessarily increasing pressure. Most jacketed bullets are undersized in this regard, and only ride the bore in most factory barrels. That's why you should always work up your loads with a custome gun with tighter tolerances.
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* * * * * * * * * * * * * * * * * * * * As to bore condition,(both lands and grooves), the smoother the bore, the better. A smooth bore promotes less drag for the bullet in question. Best accuracy with cast is obtained with a smooth bore with no constrictions, which is best obtained by fire-lapping.
* * * * * * * * * * * * * * * * * * * * So in answer to your question, cast can generally be driven as fast or faster than jacketed, WHEN all the factors are taken into account. When in doubt, start loading slowly and cautiously with your handloads. No sense blowing up yourself or your gun in the interest of science
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* * * * * * * * * * * * * * * * * * * * * Hope this helped you out.
* * * * * * * * * * * * *Jeff
P.S. The reason the reloading manuals are so conservative in their load data is because of all the variations involved for any particular cast bullet. There is a fine balance of all the above listed factors and more(some known, some unknown) that contributes to a load that is par excellence, to a mediocre or dude load. This is the challenge that casters and reloaders love so much ! But once that combination is found, there isn't a more satisfying feeling in the world.
There's an old saying that states reloaders never have too much time on their hands, too many loads to try out !
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