Talk to me about springback

[Paul D. Heppner]

I as of late have been having some trouble with some spring back. I am using a size die that I know gives me .433 with straight coww. I have started to play around with different alloys, mixing coww and lino. With that change I am seeing .4341 coming out of said .433, and .4335 from a .431 die. The .431 die is a new one to me so I can't verify a dia with straight coww. Is springback dependent on size, alloy, or hardness?

[geargnasher]

Yes. Probably better described as size, alloy, and state of anneal (WW-type ternary lead alloys can be quench hardened or annealed like many other alloys) which can also change with age (weeks/months), even after sizing.

Gear

[runfiverun]

definitely alloy and age are factors.
even after being sized some boolits will gain diameter [aiirc some of the copper alloy's gain diameter for about 2 weeks]
anyway the closer to soft lead you have the closer to it's initial cast size it will stay and it will stay sized too.

many target rifle shooters will size just before they load and shoot for this reason.

[243winxb]

Alloy

[MtGun44]

Alloys can expand as they age, over weeks to months.

Bill

[leftiye]

As has been said here alloy boolits can expand as the crystalline structure adjusts over time. Otherwise, it's not the alloy spinging back from sizing (lead don't). It's the dies being stretch/bulged by a hard/tough alloy.

[243winxb]

From Lyman FAQ
H & I SIZING DIES Q: I have run my bullets through the sizing die, however they do not come out at the expected diameter. These were cast in wheelweights, would that make a difference?
A: Yes, bullets cast in pure lead or wheelweights will come out smaller, bullets cast in linotype will come out larger. This is due to the spring-back of the bullets being sized. The sizing dies are made to produce the diameters using #2 alloy.
My test bullets made with Lawrence magnum shot, have not grown or changed diameter more that .0003" in many years.
(American Standard) with Equivalent Hardness Factor of:
4-6% Antimonial Lead Alloy
Made this hard by water dropping, is my guess, as shot falling from the towerl drops into water. My test bullets were are cooled.

[badgeredd]

I as of late have been having some trouble with some spring back. I am using a size die that I know gives me .433 with straight coww. I have started to play around with different alloys, mixing coww and lino. With that change I am seeing .4341 coming out of said .433, and .4335 from a .431 die. The .431 die is a new one to me so I can't verify a dia with straight coww. Is springback dependent on size, alloy, or hardness?

Pure lead will size smaller than COWW which will size smaller than high antimony alloys. As mentioned above, copper added to an alloy will cause it size even a little bigger yet,,,all with the same sizing die. The larger the diameter of the finished bullet the more pronounced the effect of spring back will be noticed.

Edd