41 Long Colt: I'll let the experts ponder this...

[Harry O]

I did a test today. It was testing a "new" 41LC bullet against one I previously tested. The first one (which I have lots of data on since it was my first bullet mould for the 41LC) is a Rapine hollow-base 386185 mould that casts at 188gr with 40:1 lead/tin. The second one (which I fired today) is a modified Rapine 386185 mould. It has a shorter hollow-base-pin and it casts a 218gr bullet with 40:1. There are no other differences other than a very slight difference in length. It is difficult to tell the difference between the two unless you put them side-by-side.

I have loaded the 188gr bullet with 17gr of Swiss 3F BP and a small-pistol magnum primer. The accuracy was not bad, considering the OD of the bullet is 0.386" and the groove diameter of the barrel is 0.400". It was not quite as accurate as ONE of the heel-base bullets I tried, but close. It was equal or better in accuracy than any of the other heel-base bullets I tried.

I loaded the new 218gr bullet with 16gr of Swiss 3F BP and a small-pistol magnum primer. The 1gr less of BP was to keep the amount of compression with both bullets about the same. I shot 10 groups of 6 shots each from a benchrest at 15 yards (the same distance I tested my earlier bullets). Bore and chamber cleaning was done between groups. The groups from the heavier bullet are between 1/4 and 1/3 smaller than those of the lighter bullet. Overall average is almost exactly 30% smaller. In fact, the accuracy of the heavier hollow-base bullet is essentially equal to the most accurate heel-base bullet I have.

I would be interested on theories on why the heavier bullet is more accurate. I am not complaining. I am just trying to understand. Here is more information on the previous tests.

http://harryo.sixshootercommunity.org/

[runfiverun]

it has a longer bearing surface.

[Harry O]

it has a longer bearing surface.

True, but not by much. The bearing surface of the lighter bullet is 0.547" front-to-rear. The heavier one is 0.576", a difference of 0.029". That is only an increase of about 19%.

[Uncle R.]

Heavier & longer bearing surface means more resistance to moving means better "bumping up" means better fit to bore.
Only a guess, so that and five bucks gets you fancy yuppie coffee at Starstrucks.

[runfiverun]

more bearing surface can make or break a boolit at times it's not a hard fast rule just something i have seen before.
one more band and a bit less nose can change groups by half or more all else being equal.
sometimes there is really no change.
it's just the ability of the more bearing surface to grip the rifling better,be better at sealing the bore and leave the bbl more stabil it could be any of those or a bit better at all of them that adds up.
in a revolver it could be as simple as it keeps the cylinder in alignment better/longer as the boolit makes the cylinder gap jump.

[Mk42gunner]

Harry,

My SWAG is the shorter hollowbase moved the balance point of the projectile to the rear; thus allowing the bullet to stabilize better, similar to the hpbt Match bullets.

Of course I could be all wrong on this.

Robert

[Harry O]

When I first cut the hollow-base-pin, I miscalculated. The first boolits I cast with the modified mould were about 145gr. I melted them back down and modified the pin again to make it halfway between what I had and what it was originally. Maybe I should have tried them first?

[leftiye]

I think it is the better bumping up to make a better bore fit that has yielded the improved accuracy. You might try modifying a reamer to cut the lands of your mold open enough to cast a bullet that is at least bore diameter (if it isn't already - .386 in a .41?). Them hollow base boolits act as bore riders, and the skirts do the sealing.

Better still would be to go groove diameter (depending on your chamber mouth diameters - which could also be opened up). Revolters can make a nightmare out of "bumping up." And even with black powder, bumping up is not necessary in a revolver. IIRC in cartridge arms, bore diameter boolits were used at first because the boolits were paper patched.

[Mike Venturino]

leftiye: The .41LC was developed in the time of heelbase bullets. After the ammo factories switched to inside the case bullets the diameter had to be reduced to .386 and the base given a hollowbase to expand like a Minie ball. Chambers in a .41LC won't accept cartridges with larger bullets than .386 (or perhaps minutely over that.).

[HORNET]

leftiye, IIRC, the groove diameter on the barrels was .400/.401 as was the larger diameter of the heel boolit for the .41 LC. The hollow bases have to be .386 because they're inside the case (.386 boolit + 2 case wall thicknesses have to be smaller than a .401 chamber). Love that outside lubrication.