Why are moulds designed to have the sprue on the base?

[XXXXXXXXXX]

My understanding is that the base is the most important for accuracy yet we make our moulds such that the sprue is on the base. Wouldn't it be better if the sprue was at the bullet nose and we filled the base first?

There must be a reason?

[bhn22]

You can buy nose pour moulds, too. But, since you mention it, I don't remember hearing that they're any more accurate that base-pour.

[Bret4207]

In theory a perfect base is the most accurate. I have some nose pour moulds and they shoot good. Basically a nose pour requires a bit more machine work making the double ended sprue plate. More money, more chances it'll not be right.

[deltaenterprizes]

A lot of nose pour molds are single cavity lathe bored due to the cherry for nose pour molds being very thin and fragile where the nose of the boolit and the shank meet.
I have 3 cherries from a now deceased mold maker named Eagan that are nose pour and they are a piece of art work.
Another thing is that you can not vary the boolit weight by varying the cherry depth with a nose pour design.
If you want to test the theory that nose pour is more accurate get some cast double ended wadcutters and load some sprue up and some sprue down and then shoot sprues up, down and mixed and see which groups the best.

[fredj338]

I would agree, a nose pour is likely going to porduce a more perfect base, but then you have fewer nose options; HP, meplate size, etc.

[Maven]

Lotsa X's, The answer, as already mentioned, has to do with greater machining costs and thus, a much higher price to the purchaser.

[Buckrun]

I would think that the rim around the outside of the base of the bullet is the most important part of the bullet. When casting cut the sprue, the first thing to look at is the base of the bullet. If it is good I drop it in my water bucket. If bad it goes in with the sprues to go back in the pot.

I have never used a nose pour bullet mold but would think it would be harder to check the base of the bullet while casting.
Steve

[PAT303]

All the most accurate muzzleloaders use nose pour molds.I don't know of any of the old time makers that used base pour. Pat

[HollowPoint]

I recently built a nose pour three cavity cramer-style mold for my air gun projectiles.

Since most of the common problems and benefits have already been stated, I would also like to
include one more thing that I found with nose pour molds.

While trying to get a maximum streamlined profile on the nose of my bullets, this meant that the holes in my sprue plate had to be small but, not so small as to keep my alloy from flowing down into my cavities.

Even with the "not to small" sprue plate holes, the hot lead will flow but, that flow is slowed down enough that the alloy starts to cool. It looses some of its viscosity and therefore hinders the fill out of my bullet cavities. Out of necessity I ended up having to make bigger sprue plate holes and correspondingly ended up with a larger flat nose.

Originally what I wanted was an aerodynamic profile with a shallow and narrow hollow point. As fredj338 has mentioned, because it's a nose pour mold, a hollow point is now out of the question unless I create my hollow points in a second operation.

The mold I'm working on now will be a more refined version of the last one. I've been racking my brain to come up with a way to hollow point them at the time of casting. So far I've only come up with one way but, that would require a CNC mill. I'm working with manual machines.

As far as accuracy goes, I haven't done a whole lot of testing yet but preliminary shooting shows alot of promise. (I should mention that I'm casting rebated-boat-tail pistol bullets specifically designed for big bore air rifles)

I'm glad I stumbled onto this post. I had never heard about bullet bases being the "basis" for accuracy. I always assumed it was concentricity and good design.

HollowPoint

[Jeffrey]

If one side of a boolit clears the bore before the other side high pressure gas jets out of that side disrupting the path of the boolit (or so I've been told). Swagers that make .223 projectiles out of 22 rimfire shells that still have the notch in the rim could speak from more direct experience.
Jeffrey

I'm glad I stumbled onto this post. I had never heard about bullet bases being the "basis" for accuracy. I always assumed it was concentricity and good design.

HollowPoint[/QUOTE]

[ilcop22]

It's always been my understanding that the sprue plate's purpose is for ease of knocking off excess poor and getting a clean base. :coffeecom