bullets coming out undersized, any idea why?

[Lefty bullseye shooter]

On a bullseye pistol shooting forum a guy new to casting is having an issue with bullets coming out of the sizer undersized. He is using a Star sizer labeled .452 and bullets are coming out .450-.451. He is casting with a Lee 6 cavity hg68 clone mold and bullets are dropping at 208-210gr. He doesnt know the alloy but judging by weight it sounds soft. He cast the bullets and sized some the same day. I don't size the same day and wait at least a week usually months before i get around to sizing and have never had undersized bullets. The only thing I can think of is the sizing die isn't actually the size it says it is. I don't see how a bullet could come out smaller than the die. Any ideas on whats going on?

Scott

[Dusty Bannister]

What are the bullets measured with a mic after casting? It might be helpful to look at some raw cast bullets and carefully measure them to see if perhaps they are not well filled out due to cold mold, cold alloy, or just needs a little tin to get a good fill out. Perhaps it is the casting method, and not the sizer at all?

[Lefty bullseye shooter]

He said they are .453 before sizing measured with a caliper and .450 after. Havent seen what they look like.

[owejia]

Either the boolits are hot when he measures them or his sizing die is undersize.

[upnorthwis]

I wouldn't trust a caliper. Get a 0-1" micrometer instead.

[Dusty Bannister]

Take a really good look at some of the sized bullets to see if the bands are consistent in width around the bullet. If there is a difference, then the blocks have shifted a little and he might be measuring the fat side before and the skinny side after sizing.

The caliper is usually not the correct tool for this level of accuracy. Lee molds are not really noted for their concentrically or their accuracy in maintaining the cavity diameters. I have a 6 cav mold in 45 caliber that is proven to drop from .451 to .453 through the range of cavities. I have isolated the small cavity and use it as a 5 cavity mold to make life simple.

The Star dies, perhaps depending upon who makes them, are marked to size a projectile slightly undersized so that the alloy spring back will then expand back up to about the correct diameter. It is made with pin gauges, and not by testing with a known alloy hardness bullet. Fresh cast will not have as much "spring back" as bullets with some age on them.

Before you suggest that he modify his die, or spend money on another one, verify the measurements since you say he is new to casting and is using a caliper and not a mic. Also keep in mind that a soft alloy will not have as much "spring back" either. Walk him through this slowly so he understands what is happening to his alloy as it age hardens. Dusty

[Lefty bullseye shooter]

I was wondering about the spring back as well. I told him to let the rest of the bullets age at least a week and see what they come out size wise. How long do most let their bullets sit before sizing?

[reddog81]

Has he used this die before with different result? I've never heard of spring back accounting for anything close to .002 discrepancies- more like .0002. It's possible the sizing die is off, it's also possible the measuring device is off.

The only way to verify anything will be to find a pin guage set and use that.

I regularly size within a day or 2 of casting or right after the bullets cool off from the powder coat oven.

[mdi]

If one isn't familiar with measuring tools, color a bullet and run it through the sizer. Is the color (marker) evenly rubbed/swaged off? This will tell the user if the sizer is doing anything to the bullet. If so and the bullet measures undersize, the die is undersize...

I don't know of any metal the will "spring back" smaller...

[sutherpride59]

There could always be something stuck in the sizing die, wouldn’t be the first time something like that happened.

[243winxb]

Soft alloy does not spring back, like antimony rich alloy.

Antimony makes the alloy harder, more spring back.

Time does not change diameter of a sized bullet.

[JonB_in_Glencoe]

I'd bet money that the 'bullseye pistol shooting forum guy' that's new to casting doesn't know the proper procedure to measure a boolit. He needs a 0-1" Micrometer.

I doubt a .452 star die will be off, but on the rare chance it is, it shouldn't be "coming out .450-.451"
But that variation is understandable since you mentioned he is using a caliper.

If using a Mic correctly, he wouldn't see any noticeable variation in measuring sized boolits..that's why we size them, so they are uniform.

[fredj338]

With good calipers, most of us can measure within 0.001"+/-. Something is wrong if the bullet measures 0.453" before sizing & same calipers measures 0.450" after? My bet is the die is marked wrong.

[GregLaROCHE]

My guess is the die is marked wrong. Good calibers. How many of us have really good calibers? I don’t, but I do have a good micrometer. Calipers work great for case length, but if boolit dia. is in question, I always mic it and quite a few of them.

This person could also consider power coating if he doesn’t want to return the sizing die.

[Bird]

If he is using a soft alloy, then after going through a .452 sizer, they will end up at .450 to .451''.
A decent quality clip on wheel weight will put it closer to the .452.
Lyman no2 mix will should end up at .452 after sizing.
Some good reading, http://www.lasc.us/castbulletnotes.htm

[RangerDan]

A harder alloy might also bring his sized bullet up a little.

[RED BEAR]

ether the bullet is small to start with or the die is wrong size. i have to disagree about calipers not accurate enough. used calipers all the time at work for tolerances that close first you need a good one i always preferred brown and sharpe but starret makes a really good one. i am sorry but you can't expect a cheap Chinese one to be but so accurate. you must also learn to use one you must develop a feel for them it is not just putting something between the jaws and mashing down on it. just like a micrometer you need a feel for it.knew many starting out had trouble reading a caliper or microm told them to set down with a set of gauge blocks and practice should be able to read calipers to .001 and micrometer to .0001.

[David2011]

^^ Agreed. When in doubt of my calipers I go to a good mic. They always measure the same. I use my cheap Chinese calipers whether digital or dial to measure COAL and to build model airplanes. I use the good dial calipers to measure boolit diameter and for machining. I have more trust in the good dial caliper than any of my digitals. Even then, if it's critical I use good mics when machining. Digitals are great for COAL and anything where quick readings where a .001"- .0015" tolerance is good enough.

[mattw]

I use a good set of Mitotoyo calipers... No they are not a mic and I do pull out a good mic from time to time. But, with practice .001 +/- .0005 should be doable. It would be interesting to slide a telescoping gauge thru it to see if any steps can be felt in the diameter end to end. Again, not super accurate, but might be interesting.