This topic might be better under the Bullet Making, but there don't seem to be many folks that visit that site, so since I am asking this for a DR, I decided to post here.
I would like to try some lead bullets when my Classic Searcy arrives.
Since I am a novice machinist, I would like to try and make my own mold, but need some guidance.
The 470 NE uses jacketed bullets of 0.474 diameter.
I understand that when using lead that those bullets are often made a bit larger than jacketed ones. If that is correct, how much larger.
I also heard that a mold cavity would need to be slightly larger than the desired finished bullet diameter, since some shrinkage is expected after the lead cools.If that is correct, how much larger should the mold cavity be.
If I want a 450 grain bullet, what would be the total bullet length. The length of a 400 or 500 would also help.

One really cool thing about the .470 NE is that you can use the pistol bullets and moulds for the 475 Linebaugh and 480 Ruger. An easy load is the 400gr Hornady XTP softs and HP's with the same powder charge. Searcy told me my regulation load was a 500gr bullet and 106gr of IMR4831. Same load with the Hornady bullet is six inches high at fifty and dead on at one hundred,

Rich

Bob,

Visit the Cast Bullet forum and ask the question there. I bet you will get a good deal of feedback.
http://castboolits.gunloads.com/

Go to NEI hand tools; they make lots of molds for the .470. I have used their molds for many years and they are top quality.

I found that my Searcy 470 leaded up bad with cast bullets. I tried 500gr Meister Hard Cast, but saw bad leading of the bore. I chronographed 500gr Woodleigh Softs at 2207-2215 ft/sec with 106gr IMR4831. This seems about 30-35 ft/sec faster than most people are getting with their Searcy 470's. Mine is a 2006 PH model, and it regulates perfect with this load...Butch shot the test target with this load, when he re-regulated for me. It just seems a bit fast for cast bullets.
I love the Meister Hard Cast at BPE speeds...1700-1800ft/sec.
ND

Try teflon tape patching to eliminate leading. Have to expand the necks a bit more so as not to tear the tape on bullet seating, but it works. Paper patching works too but you use soft lead for that and smaller bullets; that is a whole nuther skill.

I could not tell you how much bigger to make the mold to allow for shrinkage but that information should be easily found as it would pertain to any size bullet. I do have some cast lead .470 bullets I purchased commercially that I could measure for you. As I recall they have two grooves filled with grease. I have only used them with reduced powder loads and would not recommend any unjacketed lead bullets at full pressure. I am at the beach till Monday. PM me if you want the measurements.

I did shoot a lot of cast bullets out of my 470 Merkel,I did not cast my own,I used Cast performance 425 gr and 500 gr from mt Baldy cast bullets,all my loads were full house loads,they were all gas checked,never had any leading problems,worked great on pigs,cheap on the wallet,let me shoot as much as I wanted.

You would probably want a bullet of around .476" and using wheelweights, your mould cavity should be on the order of .480". Make it for gas checks unless you plan on 1700fps or so and less. Water quenched wheel weights should be good to at least 2000fps.
No problem pushing 50cal cast bullets to 2600fps without leading, but accuracy so far, decreases after about 2200fps. I like LBT blue soft lube for many loads, but check out White Label lubes also.

Brain fa#%. Put down .470" on mould cavity diameters instead of the .480"