Bullet design question: base band width

[PBSmith]

On a plain base rifle bullet, has experience shown that base band width is important?


What leads me to ask this question is study of several molds for .32 caliber bullets.

The one on the left is Rapine’s Pope style, 325175. Many of Rapine’s designs in .45-70 molds also had very narrow base bands like the one shown here.

The center mold is Ideal 321232. Note its relatively wide base band.

The mold on the right is Saeco 632. It’s base band width is intermediate between the narrow Rapine and the wide Ideal

All of these bullets are of about the same weight. The Rapine and Saeco are tapered. The Ideal is not.

(The height/width proportions on my screen are badly distorted but you should be able to see what I’m talking about.)

Seems like a wider base band might offer a better chance for stable launch at ignition. Looks to me like the least little flaw in the base perimeter of that Rapine would affect its launch.

Curious to learn what experts here have to say.

Thanks,
PBSmith

242394242395242396

[RED BEAR]

I an no expert by any stretch of the imagination. But i would have to agree with you i think i would like the larger base. But i also shoot gas check bullets without the gas check leaving no base at all and i can't tell the difference on those so who knows but if i were looking for a new mold i would still go with the bigger base band.

[Outpost75]

At black powder pressures not to exceed about 14,000 psi, using soft alloys of 8-10 BHN, a narrow base band about 1/10 of the bullet diameter presents no issue.

My experience has been that once you get into .38 Special +P, .45 ACP, and Winchester '92 levels in the .44-40 over about 20,000 psi, you then want a base band not less than 1/5 of bullet diameter, above 25,000 psi increase this to 1/4 of bullet diameter. A light bevel base of about 0.030." added to a base band 1/5 of bullet diameter, helps to reduce "finning" when a throat-diameter revolver bullet is extruded into a barrel groove diameter that is substantially smaller than the cylinder throats in Ruger .45 Colt loads and the .,45 ACP or .38 Special +P, as well as in medium velocity .44 Magnum and .44-40 revolver loads.

In loads which approach the strength limitations of plainbased bullets, about 1250-1300 fps in the .357 and .44 Magnum revolvers and 1400-1500 fps in those same calibers for rifle use, and black powder rifle calibers such as the .45-70, I like to see the base band 1/4 of bullet diameter and alloy hardness of 10-13 BHN, using a compressed case full of powder such as 4227, 4198 or RL7 in the .357, .44 Mag and .44-40, or even 3031 or Varget in the .45-70 and .444, as needed to achieve the desired velocity. A tuft of Dacron fiber, about 1 grain in .30-.357 calibers and 2 grains in .44-.45 calibers, over the powder to aid compression and a "grease cookie" such as a pea-sized dab of white lithium grease, will prevent leading in rifle bores up to 1600-1700 fps in the .30-30, .32-40, .357 Mag., .38-55, .44 Magnum, .444, and .45-70, using 1:20 or 1:25 tin-lead with powders such as IMR4198, RL7 or IMR3031.

Yes, 4198 or RL7, full case with 1/8" compression as if loading black powder will give good "full charge" results in .357, .44-40 and .,44 Magnum revolvers".

I have not done the finite element analysis or strength of materials calculations on this, but over 50 years I have found it to agree with experience. Your mileage may vary, but anyone trying this with good results, I would sincerely appreciate anyone who cares to post independent validation.
242412

[upnorthwis]

My experience with the Lyman 457125 that also has a narrow base band is that it slows up production. Have to wait longer for metal to cool or the base breaks.

[Outpost75]

My experience with the Lyman 457125 that also has a narrow base band is that it slows up production. Have to wait longer for metal to cool or the base breaks.

I use a wet sponge to cool the sprue before opening the mold, which addresses this issue pretty well.

[PBSmith]

Outposted responded: "At black powder pressures not to exceed about 14,000 psi, using soft alloys of 8-10 BHN, a narrow base band about 1/10 of the bullet diameter presents no issue."

That might well explain the narrow base band on the Rapine molds. Black powder shooters were among Ellsworth "Ray" Rapine's most loyal customers.

The base band on the Rapine mold pictured measures about 0.0450", which amounts to 14% of the bullets base diameter.

Next cast I'll be paying attention to the problem that upnorth mentions. I've wondered if the Rapine bullet might be better off with the bottom grease groove eliminated, which would make its bottom band about the same as that of the Ideal bullet.

Thanks for your responses.