If you are hunting with the rifle you are better off, perhaps much better with a slow twist RB gun of larger bore. 54 to 62. Though most are well served with a 54 for most hunting. Game much larger than Mule Deer might be better shot with .62-.69 calibers. Though 54s have killed a lot of elk and buffalo both back in the day and in modern times.
The 18 twist will stabilize 45 caliber bullets to about 600 grains depending on shape, its a very popular twist for BPCRs shooting heavy bullets for long range target shooting. It was the twist generally used in the last original longrange BPCRs. These are of very limited usefulness in a ML that is not used for bench rest shooting. A 45 caliber ML for bullets need not have a twist faster than 30-40" if its to be used as a hunting rifle.
However, using elongated bullets, even bullets in the relatively light 250 grain range for a 45 is extremely erosive to the vent or nipple. The cure is a platinum lined nipple which I think are about 80 dollars each now. There are no flintlock vents that will stand the abuse for very long.
Basically in a BP hunting rifle used to 120-140 yards the the RB will generally perform better than the conical if both bullets are of equal weight. Shoots flatter, lower pressure.
Modern "wisdom" tells us that the conical is superior to the RB for hunting. But in practice this is not the case. A 45 caliber round ball will be outperformed by a 45 caliber bullet of 300 grains or so IF THE DESIGN IS GOOD and the alloy soft.
If we increase the RB weight to that of the conical the RBs effectiveness is greatly increased and it performs very well in relation to the bullet, usually better. The RB does not tend to move away from the powder as some conicals can. The conical hunting bullet of the past was the cloth patch picket and it was not a complete panacea needing more tools for loading than the RB.
A friend killed a deer at 120 yards with a 45 round ball last fall and got complete pass through on a broadside lung shot.
If you are planning a hunting rifle you should search Google Books for "The Sporting Rifle and Its Projectiles" By James Forsythe and download it. It will explain the details very well and may prevent your making a mistake.
Most of the modern hype about elongated bullets for hunting MLs is simply a way to sell the latest "new and improved" bullet or sabot etc.
Rifles using rbs over 54-58 caliber or bullets over 250 grains need to be carefully stocked to prevent undesirable recoil characteristics. Early American/Jeager or English buttstock design is best. Later styles like the Hawken tend to be abusive over 54-58 caliber.
Dan
