Author Topic: Cup base verses a flat base bullet? (Read 944 times)

Donna · « **on:** July 08, 2003, 07:39:25 PM »

Hello all,

Some people like to put dish or cup bases on their pistol and even on rifle bullets. Have you found any advantage or disadvantage to a dish or cup base over a flat based bullet in your experience of swaging?

Donna

Rick Teal · « **Reply #1 on:** July 08, 2003, 08:45:13 PM »

I read somewhere (probably Corbin's books) that cup bases are OK for pistol bullets, but they're no good in rifles. Something to do with air flow at transonic velocities. However, minie balls seem to work OK in muzzle loaders - and they're moving faster than sound.

talon · « **Reply #2 on:** July 09, 2003, 04:27:06 AM »

Aren't they a convenient place to stuff the tails of paper patches? Too, I think the deep dish on Miniballs is to allow the bullet's skirt to expand into the groves when the rifle is fired. In combat a soldier would 'drop' his Mini bullet down the barrel, bounce the rifle butt down on the ground to 'seat' the bullet, and fire.... Not the best for accuracy, but firepower is multiplied by 2 or 3 times. I do know that dish bullets add to the cost of bullet molds. Without any scientific basis, or any real experience in using dish bullets, I think they are a holdover from earlier days when a lot of experimentation was going on without adequate resulting data. I have a .41 colt die set that has a dish. Never used a bullet from it myself. My .43 Mauser die has a dish base. Can't hit a barn door with that bullet, but that may be the rifle's or my fault. That's the only dish bullets I make.

Kragman71 · « **Reply #3 on:** July 11, 2003, 03:53:15 PM »

Donna,
My best guess is that a dished or hollow base on a slower-moving cast bullet will enhance the ability of the bullet to fill the grooves in the barrel. This prevents gas cutting and also allows slightly smaller diameter bullets to be fired.
This is not very practical on a high velocity bullet,because it is not really shaped s well as a flat base or boat tail bullet for accuracy.
Frank

Leftoverdj · « **Reply #4 on:** July 13, 2003, 03:53:13 PM »

For what it's worth, there have been commercial bullets made with cup bases, actually a slight dimple in the base maybe 1/3 of diameter deep. I had a batch of Norma steel jackets 6.5s years ago. I still have several hundred .318 bullets with conventional jackets with the cup base. These are repackaged bulk, but I think that I was told whan I bought them that they were made by Norma.

I have found no difference in accuracy between these and flat based bullets, but I have not shot them in anything that would show a small difference. I have no idea why they were made in that form.

If anyone wants one as a curio or to examine, email me an address and I will send you one.

Donna · « **Reply #5 on:** July 20, 2003, 09:10:12 PM »

Hello Leftoverdj,

Thank you for the two cup based rifle bullets. The one is a copper jacket while the other has mild steel for its jacket material. The mild steel jacketed bullet has impressed into the cup base a crest that looks like a badge with an “R” in it.

I have often done something similarly to mark my various LadyHawks and G-2 bullets for identification. From adding cup bases to using a base guard punch without the added base guard disc, this leaves a small dimple in the center of the bullet’s base and does not harm ballistics. I have even thought about having a base punch monogrammed, just thought it would be cute. :roll:

Donna :wink:

Leftoverdj · « **Reply #6 on:** July 21, 2003, 12:11:27 AM »

I thought the RWS emblem in the base was kinda cute myself. It would sure put an end to those arguments about whose bullet killed the deer.

For what it's worth, the cup based rifle bullets I have run into have all been European made, round nosed, and heavy for caliber. I still have no idea why they were made that way.