Cavities off center

[Humbo]

Hi,
I purchased a new RCBS mold, but the cavities are off center. Is it any cause for concern, do you think accuracy may suffer? I prefer the sprue to be cut centered on the base, but I'm not really certain if it affects accuracy. It's also a gas checked design.

[geargnasher]

Humbo,

Are the cavities actually off center in the blocks or is the sprue plate located such that the sprue holes are not centered on the base of the boolit?

If the cavities are off center then you would probably have difficulty in dropping the boolit from the blocks. If this is the case then I would return the mould and I'm certain that RCBS would replace the mould. If it is the sprue plate that is a bit off center it is not a problem if you are allowing the sprue to cool enough that you are not creating a divot in the base.

The last Lyman mould I purchased was a Lyman #358311. The cavities in this mould were cut so far off center that I only made one cast from it as the boolits had to be removed from the blocks by driving them out with a hammer and a punch.

PB

My thoughts too. Make sure the sprue plate is closing fully.

Gear

[MtGun44]

If significantly off center in the blocks you will never get the boolit out of the cavity. If the
sprue plate is misaligned it is no big deal.

Bill

[Lance Boyle]

OK, maybe I'm missing something here on how blocks and cherries actually meet.

I was almost a 100% sure that the cherries are stationary and the uncut virgin blocks are closed around it, otherwise you'd never get grease grooves. If the cherries were used in drill press fashion all you would have is a featureless straight boring. Therefore why wouldn't the bullet release in off center blocks, the clearance should have been cut on the deeper cut block. Granted you'll have an out of round bullet as the major diameter is deeper than the mating surface.

This is just a discussion on how mold blocks are cut and in no way am I saying to keep a poorly cut mold set. I have no compunction about sending molds back, in fact I'm waiting on my second set of returned lyman molds, a 314299 that casts . 312bands/.299nose. I figure in about another month I'll have a propper cut mold back.

[theperfessor]

Does RCBS use cherries or are they now lathe bored? I guarantee that an off center lathe bored mold will give you problems getting the bullets out of one block.

[TheBigBang]

Does RCBS use cherries or are they now lathe bored? I guarantee that an off center lathe bored mold will give you problems getting the bullets out of one block.

As far as I know RCBS is still cherry cutting their molds. You're right though, an off center lathe-bored mold would be a real mother to get bullets out of. You might have some fun with kids though - "Here boy, get this bullet out of this mold." or "Hey, what did you do to my mold, that was my best mold!"

[zuke]

Don't screw with them.
Box'em up and ship them back,it should be covered under warranty.

[MtGun44]

Even cherried molds with the cav off center are a PITA to work with, they just
don't like to drop easily. Lathe bored would be a thrill if off center.

Bill

[GP100man]

Sprue line up is not crucial as long as it`s not on the edge of the base ,but off center mold is .

For instance lets take a 429 Keith style boolit the mold is casting em .430 ,now with the off centered hole the opening of the offset half is closed to .426 or less porportioned to how off center it is. An undamaged boolit will never be produced from that cavity.

[Cap'n Morgan]

In case some of you were wondering how much offset is too much:

A .358 cavity bored .01 off center would have a "cavity gap" only .0006 smaller than boolit diameter. With a boolit shrinkage around .002 the boolit should drop easily from the mold. At .017 offset the shrunken boolit would just match the cavity gap and from there it would get progressively worse.

[Humbo]

Thanks for all the replies guys! I should've taken a picture to show what the mold looks like, but I'm out of town til Sunday. Anyway, bullets drop fairly easily so I think it's more of a case where the sprue plate is off center. But I was thinking all the RCBS sprue plates are the same, and therefore the cavities are cut differently from other RCBS molds. The sprue is cut closer to the edge of the base of the bullet, but it's not touching. I was thinking it might cause the bullet to be unbalanced and therefore be detrimental to accuracy, but they seem to shoot just fine. Maybe I'm just a bit anal about how I want my bullets to look.

[DeanWinchester]

I have an RCBS 45 caliber 255g Keith that is eccentric. It's not off center, at least not the base, but the nose is visibly off center to the base. I was seriously P'd off when I got it. This is an older mold and they probably wouldn't do anything about it. I cast a pile and loaded them up. They shoot great. I guess the larger mass, the added wumpum of Blackhawk pressure loads, and the fact that I'm shooting inside 25 yards helps a lot too. If it were a rifle boolit, I'd say they wouldn't fly for nothing.

[44man]

If significantly off center in the blocks you will never get the boolit out of the cavity. If the
sprue plate is misaligned it is no big deal.

Bill

This is the answer. Nice job my friend!

[44man]

I make my own molds and the very hardest job with my cheap equipment is making sure the cavities are centered. It takes me a long time.
I try with the sprue plate to be perfect but it is secondary.
We have many here that make exceptional molds and I admire them to no end.
You need to try your own to see just how hard it is.
Production molds have standard stamped plates while most custom makers make a plate just for the mold. Only CNC stuff can allow them to duplicate.

[MikeS]

OK, maybe I'm missing something here on how blocks and cherries actually meet.

I was almost a 100% sure that the cherries are stationary and the uncut virgin blocks are closed around it, otherwise you'd never get grease grooves. If the cherries were used in drill press fashion all you would have is a featureless straight boring. ...

Lance, the original method of cherry cutting moulds did in fact involve a stationary cherry, with the mould blocks mounted into a vice that allowed both blocks to move (there's a name for this type vice, but I forget what it is) in toward the cherry. There's another newer method of cherry cutting moulds that's come about due to CNC machining. The mould blocks are mounted in a vice firmly held together, then a hole is drilled into the blocks roughly the size of the lube grooves, then an undersized cherry is plunged into the hole, then using a circular motion programmed on the CNC it rotates in a small circle to cut the features of the mould before coming back to center to be removed from the mould. It's due to this method that several of the custom mould makers can offer different diameters of the same boolit in the same group buy. An example is how Mihec can offer his 45 cal moulds cut to drop either a .452 or .454 diameter boolit (they actually drop a slightly larger size, those are the target sized diameters). It's also due to making moulds this way that Mihec was able to offer his clone of the H&G #503 made as a 45 boolit. (.452)

[felix]

Walt Milander(?) used the terms to "lean on it a little" for making a bigger boolit. My assumption that was he leaned on the rotating cherrie. I guess if the stem of the cherrie was long enough he could get at least a couple of thousands growth without any future mold use failures. ... felix

[44man]

The old PA rifle makers would cut a mold for each rifle. They could not control bore diameters so each rifle needed it's own mold. They hand made RB cherries and cut with a brace and bit.
I have to hand it to the gents.
One fella even set up a water wheel in the creek to power a rifling machine that self indexed and advanced the cutter and you need to remember the cutters in those days were shimmed to take the next cut. He set it up and went to bed. In the morning he had a rifled barrel. Is it true? I don't know but you need to consider what they did with hand and water power, no electric.
They had to make their own files and cutting tools, not easy to strike cutting edges in a piece of steel with a chisel, then harden and temper it.
Now how hard would it be to file a plate stop to center a sprue hole?
I see it all over when a neighbor calls for help. I have to take my tools because most don't even have a wrench or screw driver. Even the knives in their kitchens are worse then butter knives. One hunter friend brings me 10 knives to sharpen before every season.
I hate to sound harsh but a few minutes work is cheaper then postage and a long wait.
Now I am not as good as I used to be. I would drill 1/16" holes down the center of 1-1/2" long 6-32 brass screws by hand, no drill press or lathe, for my lighted bow sights.
I rigged my radial saw to make spindles for a rocker that were broken, I had no wood lathe.
But I would love to see the tiny problems taken care of yourself so 3 pages of posts are not needed.
You can do it because it is like recoil, lose the fear, you can do more then you think you can. That is advice from an old fogy!

[44man]

Walt Milander(?) used the terms to "lean on it a little" for making a bigger boolit. My assumption that was he leaned on the rotating cherrie. I guess if the stem of the cherrie was long enough he could get at least a couple of thousands growth without any future mold use failures. ... felix

Yes, Felix. That would work.
I just heat the blocks and turn the cherry by hand with a wrench. You would be surprised how much more metal is removed and the boolit is more round.
Heat from the blocks will also expand the cherry.
A warped cherry when hardening it is a problem too so I turn it in my drill press while heating. Once hot enough I shut the press off and open the chuck so the cherry drops straight into oil. Any angle as it hits oil will warp it.
Making your own cherries is an experience. Since they cost as much as $275 for a custom, it is worth it.

[Lance Boyle]

Lance, the original method of cherry cutting moulds did in fact involve a stationary cherry, with the mould blocks mounted into a vice that allowed both blocks to move (there's a name for this type vice, but I forget what it is) in toward the cherry. There's another newer method of cherry cutting moulds that's come about due to CNC machining. The mould blocks are mounted in a vice firmly held together, then a hole is drilled into the blocks roughly the size of the lube grooves, then an undersized cherry is plunged into the hole, then using a circular motion programmed on the CNC it rotates in a small circle to cut the features of the mould before coming back to center to be removed from the mould. It's due to this method that several of the custom mould makers can offer different diameters of the same boolit in the same group buy. An example is how Mihec can offer his 45 cal moulds cut to drop either a .452 or .454 diameter boolit (they actually drop a slightly larger size, those are the target sized diameters). It's also due to making moulds this way that Mihec was able to offer his clone of the H&G #503 made as a 45 boolit. (.452)

Ah, regarding the variable diameter, that makes some sense, an eccentric setup that cuts a true circle thanks to computer precision. I've got a fairly decent mechanical mind for visualizing how things must be made but some stuff like that just catches me by suprise. neat stuff!

[MtGun44]

I'm almost certain that MP just turns out mold halves on the CNC and the are just the
same until the sprue pin and screw are tapped. One side gets female alignment sockets
and the other gets male alignment pins. This shows the amazing precision of modern
CNC machines, when the tooling and fixturing is good enough. Cut two halves and then
assemble them and the boolit is perfectly round and aligned. . . . . NEAT!

As said, this makes it easy to cut diff mold diams. Note the pix of Miha's cherries - they
are way too skinny to really be a cherry, they are profile cutters more like, just
drive them in a little circle to cut the half cavity. You can use the same one for .41, .44
or .45 if you really wanted, I would assume.

Bill