Sabot load Vs pressure

[rajb123]

I have been using the same load of Pyrodex in a 50 cal ML for many years.

The recoil from a round ball is much less than that of a 300 grain sabot load. Does this mean the pressure is much higher too?

Sabots seem more accurate but I assume my rifled bore was set up for round balls (White Mountian carbine)

 

[Loyalist Dave]

Well with Newton's third law, the lower mass of the patched round ball = less kick backward toward your shoulder. As for the mass of the sabot, it takes more energy to overcome its inertia, so the pressure within the barrel should be higher than when using the same load on the lighter, patched round ball.

The WMC was originally made to be a very short "traditional style" muzzleloader. (iirc) They could have anywhere from a 1:20 to 1:48 twist depending on the caliber and when made. If it has the 1:20 twist rate, which was available for the .50 caliber models, it was probably made for sabots.

LD

 

[rajb123]

thx... it is a 50 cal White Mountian.... how do you tell if it has a 1:20", or 1;48" twist or something else?

 

[mykeal]

Determining the twist rate on short barrel long guns (aka carbines like the WMC) is a bit tricky but it can be done if one is patient and uses care.

Attach a .50 cal cleaning jag to your rod (best choice: a stout range rod with a T handle), oil two cleaning patches and place them over the muzzle. Insert the cleaning jag, forcing the double patch load down the barrel; this should be a very tight fit, so it's important the patches are oiled. When the jag/patch combination bottoms out at the breech, place a piece of tape around the rod at the muzzle, essentially marking on the rod where the rod exits the bore. Make a vertical line (a line along the length of the rod) on the tape with a pencil or ink pen at the point next to the front sight blade. Slowly pull the rod from the barrel, allowing the rifling to turn it as it comes out. When the vertical mark indicates the rod has turned 180 degrees (exactly opposite the front sight blade) place another piece of tape on the rod where it exits the bore. Measure the distance along the rod between the two pieces of tape (using the lower edge of each piece). Multiply that distance by two to get the twist rate.

Thompson Center's web site lists only two twist rates for the WMC, depending on caliber. The 45 and 54 each had a rate of 1:48, while the 50 is listed as 1:38. There is no other listing for the .50. Thus for your 50 cal WMC the distance between the pieces of tape should be one half of 38, or 19 inches; since the WMC barrel is only 21" long the rod will have very nearly come completely out of the bore by the time it rotates 180 degrees. If the twist rate were to be 1:48 the rod will not make it to the 180 degree point before completely exiting the barrel. At a rate of 1:20 distance between the tapes will be 10", or essentially half way out of the barrel.