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For the GM .40 barrels, what do you think would be a good skirt thickness to try on a .40 hollow base?
GM / .40 Holow Base Skirt Thickness
- Thread starter nkbj
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There are a lot of variables here. What is the depth of your rifling? What is your intended powder charge? Do you already have a mold and if not what are your options for a skirt thickness? Can you make a custom base plug for a mold?
Deep rifling, as for a patched round ball, would require a thinner skirt so as to expand into the rifling and seal. A heavy load needs a thicker skirt to prevent it being blown out when leaving the muzzle.
Deep rifling, as for a patched round ball, would require a thinner skirt so as to expand into the rifling and seal. A heavy load needs a thicker skirt to prevent it being blown out when leaving the muzzle.
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The base ring on these fired hollow bases show the imprint of the Green Mountain rifling geometry.
The bore diameter is 0.403". Only have one of these GM .40's now, the 28" drop-in barrel like they used to make in the 90's. Those hollow based bullets grouped inside of 2" at fifty yards but that was the best I got them to shoot. Thinking about it, I maybe never did work up loads with FFg.
Any how, those in the picture were fired with 50 grains of Jacks Battle in a long 38" barrel and you can see the gas cutting on the base. The cavity diameter versus the skirt thickness, it didn't seal real well. But, you know, it wasn't real bad either.
I'm thinking maybe a little thinner skirt and a gentler charge would work out OK.
The bore diameter is 0.403". Only have one of these GM .40's now, the 28" drop-in barrel like they used to make in the 90's. Those hollow based bullets grouped inside of 2" at fifty yards but that was the best I got them to shoot. Thinking about it, I maybe never did work up loads with FFg.
Any how, those in the picture were fired with 50 grains of Jacks Battle in a long 38" barrel and you can see the gas cutting on the base. The cavity diameter versus the skirt thickness, it didn't seal real well. But, you know, it wasn't real bad either.
I'm thinking maybe a little thinner skirt and a gentler charge would work out OK.
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Maybe I could use a chamfering tool and give the base cavity a conical contour to thin the lip, recover some fired slugs and see how they did.
That is an incredibly thick skirt but I'm used to looking at minies. I can understand why it didn't seal well but 2" at 50 yards isn't awfully bad considering, certainly good enough for hunting. Seeing the depth of the bottom grease groove I can see that you can't make a new base plug for the mold. It would leave the wall so thin at the grease groove it might blow through there or the bullet may collapse longitudinally at the grove. To me the base plug would reduce the wall thickness by about a third, have mildly tapered sides and a blunt end and extend into the bullet at least a third of its length but it can't be done to that one.
