Sorting Bullets From a Two Cavity Mold For Accuracy

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fc60 posted this 3 weeks ago

Greetings,

The only documentation I have is that each cavity is slightly different in shape and weight.

I have a SAECO RG4 that the previous owner placed a small prick punch mark in the grease groove of one cavity. It was also marked on the opposite block to, in theory, maintain the balance as it spins.

I can now sort my bullets by cavity.

Weighing each bullet makes more sense when you are measuring the same cavity.

Cheers,

Dave

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Wm Cook posted this 3 weeks ago

I’ve heard of a prick punch on the driving band but not in the groove. Theory being that sizing the bullet will wipe off the prick mark. I have a 225438 that drops about .3g / .4g different front to back but for practical use with a Hornet or a K Hornet the 45 grain 225438 would never ever show any difference.

But if I were casting for high end accuracy, competition, the difference in the two cavities might make me think a bit.

A lot of folks that shoot competition use single cavity molds for just this reason. But I’m certain that some are using double cavity molds. Specifically those shooting Lyman’s silhouette bullets like the 311299, 314299.

I was just wondering if anyone ever ran a trial to see if it was worth it, and if so, where did they mark the mold. Probably a stupid question. Thanks, Bill.

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RicinYakima posted this 3 weeks ago

Actually, a very good question.

Severall of us solved the problem but simply making them the same. We cast linotype bullets and polished out the cavities. Cast from F was used to polish B and vis-versa. This was repeated back and forth until we couldn't measure any difference in size or run out. Using 600 grit valve compound and doing it by hand only took a couple of hours.

FWIW, Ric

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Millelacs posted this 3 weeks ago

I have some molds with marks in them. One punch near the nose for the front cavity and two marks for the rear cavity. Then it’s easy to segregate the bullets by cavity. I load by cavity.

With the marks near the nose, the sizing and seating process’ flatten out the marks to where they are almost not able to be seen.

I found that a center punch works better than an awl.

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Wm Cook posted this 3 weeks ago

“……. doing it by hand only took a couple of hours. ”

Ric, how do you turn the bullet when it’s (assumed) clamped in a vice to hold the mold together?

Would a barrel lapping tool be too harsh? Bill.

I’d imagine that would be hard to do on an iron mold. Or wouldn’t it?

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RicinYakima posted this 3 weeks ago

Not hard to do. Leave the blocks on well fitting handles, no Lees. Bottom of the blocks are flat on a drill press table or some other flat surface. The cast bullet is chucked in the lathe, or some where, and drilled to allow you to turn in a small sheet metal screw.

Dope the bullet and place it in the opened cavity. I use a small tap wrench to turn the bullet as I GENTLY squeeze on the handle. You will not be able to fully close the blocks at the begining. Work on the other cavity.

Clean the blocks and cast new linotype bullets and do it again. Slow and easy. Aluminum actually cuts very quickly so you have to be careful not to increase the diameter more than you want. Iron is easier to work with, just slower.

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Wm Cook posted this 3 weeks ago

Thanks. I had understood that iron was a no go. It should be easy to use on brass as well. We’re talking about bore riders right? Thanks, Bill.

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RicinYakima posted this 3 weeks ago

Anything! Just be careful to keep things square and go slow. Useing power tools will screw things up really quickly.

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Aaron posted this 3 weeks ago

Useing power tools will screw things up really quickly.

Rules me and my Dremel tool out!

With rifle in hand, I confidently go forth into the darkness.

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Tom Acheson posted this 3 weeks ago

Not sure how John Alexander would react to this subject. Until YOU do an exhaustive test program with your mold to convince yourself that there is a discernible accuracy difference between cavities. Do that before convincing yourself you need to undertake the above efforts.

He might caution us that some of our assumptions are unproven but often repeated theories. Just like cleaning the primer pocket is not proven to be a significant accuracy influencer.

Two reasons to use a single cavity mold…it’s usually a large (heavy) bullet and casting cadence can vary as the time to ladle-fill the cavities is different. And the makers of large bullet molds don’t always offer multi-cavity molds.

Tom

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Wm Cook posted this 3 weeks ago

Ric, if you’re still following this, you said

“…. until we couldn't measure any difference in size or run out.”

1) Could you guess how much you’d expect the + diameter of the nose to change. I know you have to go until the cavities are equal but in a round about way I’m asking how much material was removed. .0005, .0010? .0015?

2) And the second question was, what effect did this have on the nose being out of round.

I’ve had 6 single cavity molds (brass & iron / #2 alloy, Linotype / ladle cast, bottom pour) in the past 3 years and every one drops greater in the cross mold seam direction than the “in line” direction. Typically the best bullet fit I expect now is seeing 4 lands.

Thanks, Bill.

Side note: This seems to be one for one with lapping the mold for a better bullet to bore fit. The option being Beagling.

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Wm Cook posted this 3 weeks ago

“ He might caution us that some of our assumptions are unproven but often repeated theories. Just like cleaning the primer pocket is not proven to be a significant accuracy influencer.”

Absolutely agree with both you & John. This is driven more out of curiosity than practicality.

The theory I’m pecking at is based on bullet to bore fit and that accuracy is defined by the first inch that the bullet travels into the bore.

To believe that makes a difference requires the use of match grade casting, reloading and bench equipment, and match grade casting, hand-loading and bench practices. Meeting those requirements leaves 99% of us in the dust.

But when you’ve reached the point that the load, mold, rifle, shooter will not get any better…..

As for the accuracy John’s getting out of a rifle with + 23000 rounds through it with virtually no lands touching? (I hear rumors he’s using match book covers to beagle his mold ). Give some of the credit to the guy pulling the trigger. He’s good. And after pulling the same trigger 23000 times I’d imagine there’s a kinship between rifle & shooter that few of us will ever realize. I’m hearing of a 10 shot group or two he shot at this year’s Nationals that’s being looked at.

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RicinYakima posted this 3 weeks ago

Bill,

If you only want the nose to be larger, only put the compound on the nose and leave the rest of the bullet bare. A little bit will do you.

First one I tried was a Lee single cavity with an electric drill, and 10 seconds made a 0.006" increase and crooked. Why I like to do it by hand. It is harder for me to make an iron mould cavity much more than 0.0015" and still be straight. This can be a three handed operation with the third hand holding the block down on a flat surface.

This is time consuming because of the need to clean the blocks, warm them and cast new bullets.

Moulds cut with cherries are almost never round because they are being flooded with lube/coolent while the double acting vice is closed. Always fluid between the blocks unless cleaned for the final cut.

Ric

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John Alexander posted this 3 weeks ago

It looks like I can stop writing comments that sound like a broken record by harping on the "If it ain't broke, don't fix it" refrain. Both Tom and Bill seem to have my script down almost word for word.

As for annoying people for the last 40 years by wondering aloud, and in articles,if several, time honored, cast bullet "Must do practices" really have to be done to win matches, I don't think I have changed many minds. That is fine. This is a hobby after all and if you like to weigh powder charges to 0.01 grain, or other unproven techniques it is nobody's business but yours. My worry is that by claiming that several usless refinements for shooting cast bullets are necessary to new or potential cast bullet shooters we reduce the chance of keeping a critical mass of cast bullet shooters so that we can have the CBA supporting a match program and publlshing a journal for exchanging information and reporting match results.

John

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RicinYakima posted this 3 weeks ago

John,

As you once told me, it is about the confidence in the load. Is it as perfect as I can make it? If I miss it because of lazyness, that is the same as jerking the trigger.

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John Alexander posted this 3 weeks ago

Ric,

You are right, confidence in your loads is important. I try to build confidence in my loads by focusing on the things that I can prove shrink group size, and not doing some other things, usually considered necessary, but making that decision only after determining to my satisfaction, by shooting tests, that they don't help. If something that takes time to do can't be verified as helpful by shooting competiting groups, I don't do it. You are also right this amounts to lazyness.

Others gain confidence by eliminating all the possible things that might expand groups, whether they have proof that ] they enlarge groups, or not.

The first approach works for me, at least to the extent that I can avoid doing a bunch of "required procedures" and still remain competitive in the CBA class I like to shoot in.

The second approach obviously worked for you by winning national matches when you were a competitor. And it works for a lot of other shooters.

As I said above, it's a hobby, we should do it the way we enjoy most.

John

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Hornet posted this 3 weeks ago

I have had a few molds where the cavities produce bullets that consistently weigh differently. Sometimes this is a venting issue, sometimes there has been a fill issue, sometimes I never did figure out what was going on. I do have a few 2 cavity molds that I only run as single cavity to avoid the issue. This also helps when the blocks overheat when running both cavities ( I've got an old Ideal 375248 2 cavity on small blocks that only has about a 3/32" gap between the 2 cavities- it overheats FAST).

I usually run a new mold until it's up to running temp, save a few sets marked by cavity with small marks on the base, then weight and measure to see if there's a clear difference. 4 cavity molds sometimes get strange on what they want for a fill sequence too.

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BJung posted this 2 weeks ago

Sorting bullets from a 2 cavity mold is better than sorting from a 4 and 6 cavity mold. I get less variation.

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TRKakaCatWhisperer posted this 2 weeks ago

I have had a few molds where the cavities produce bullets that consistently weigh differently.

...

... marked by cavity with small marks on the base, then weight and measure ....

THE BIGGEST Improvement in MY casting was done by weighing EACH bulled while the mould cooled. That way I could ID the reason for the variation which I caused.

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John Alexander posted this 2 weeks ago

Does anybody know of an instance where a shooter any where or anytime has ever claimed to have proved that bullets from one cavity of a two cavity mold shot better groups, or shot to a different point of aim by shooting enough groups of bullets from each cavity (say maybe 6 five shot groups, or three ten shot groups from each cavity) to be resonably sure that the difference was real?

Surely there have been such bad molds but has anybody ever proved it. Not that there was a difference in weight or dimensions of the bullets, but an actuall difference in group size.

John

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Sorting Bullets From a Two Cavity Mold For Accuracy

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