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View Full Version : Gas checked bullet design theory: Length of the shank.



nitro-express
08-24-2015, 09:19 AM
I am looking for a new mold for my 38-55 and in my search I’ve discovered that the length of the shank for the gas check is longer in some designs. Most bullet designs have a shank just long enough to accommodate the gas check, and in a few others the shank is almost twice as long as it needs to be. What began as a quick Google has become a quest, yet another cast bullet conundrum.

My foray into the land of cast has not been long, but it has not been without learning. I have a 38-55, a Winchester 94 Commemorative and it came with loaded ammunition and a small supply of cast bullets. The ammunition that came with the rifle is accurate, and I have used the supplied bullets and load data to reload more.

Unfortunately, the mold for those bullets is lost, having disappeared in the liquidation of an estate. I believe it is an early, 280 grain version of the discontinued Ideal 375296. My bullets are sized @ 379, and with gas check and lube weigh an average of 280 grains.

My tickle trunk has a Lyman 375248 mold of recent manufacture, that casts 378, which I size to 377. Cast hard or soft, this bullet has not showed any promise. Lyman does make a larger diameter version of this, 380681, and it is one of my choices for a new mold. Sized 379 it probably stands a better chance of being a performer.

My third bullet is one from a commercial caster, a ME 38 55-260 RNFP GC sized @ 379, and Magma makes and sells the mold. It shoots well in my 94. As supplied, checked and lubed, they weigh 265 grains.

The shank on the 375296 is long enough to leave room for a modest amount of lube, whereas the ME 38 55-260 RNFP GC does not. Most other bullets that I have looked at have a shank that doesn't leave room for lube.

Is having an extended gas check shank an advantage or not. What would the desired state be?

I also wonder about the whys behind the size of the band in front of the GC. Is a wider band better?

BTW; in the picture of the 3 cast bullets, from L>R they are; 375296, ME 38 55-260 RNFP GC and 375248.

Tatume
08-24-2015, 02:21 PM
The gas check shank should be somewhat longer than the gas check. The reason is not to carry lube (although that is a nice secondary benefit), but to ascertain that the gas check can be fully seated. If the check should hit on the edge, that will leave it unsupported in the interior. The check should be completely seated on the shank, with no air space inside. There should be space on the shank above the check.