Bullet Springback?

[MasterBlaster]

I have a 41 LBT mold for a 250 WFN-GC and using straight linotype they weigh 238 with gascheck and LBT blue lube. The mold size is .412 and I have run bullets thru my Redding Saeco lubsizer using sizing dies in .411, .410 and .409. I find the bullets consistently measure .001 to .0015 over the sizer die measurement. I doubt the sizers are all off so I was wondering if there is such a thing as bullet springback or some other explanation that would account for the size difference. As you probably know linotype is composed of the following...lead 85%, antimony 13% and tin 2%.Not sure if that would make a difference and my apologies if this has been discussed but I didn't find anything. Thank you

[felix]

Yes, you can count on boolit springback when using boolit designs with small, shallow and reinforced (round) lube grooves. The boolit would have to be on the tough side, however. Pure lead, for example, will have no significant springback. Alloys. or anything without some antimony percentage, will not springback and stretch lengthwise instead, and that includes material bleeding into the lube grooves. ... felix

[Bret4207]

I think you assumption that the dies aren't all off is flawed to start with. Actually, "off" isn't the right term, it's a matter of your measuring instrument and the guy honing the dies instrument varying a bit. Add in the variety of alloys and the different amount of spring back and you can easily have a thou. If the guy honing the dies was a having and off day or if they were farmed out to a low bid contractor then a little oversize is even more possible. And if you use a scrunch more pressure on the mic than he did then you can add another thou.

I don't use Redding dies but have found RCBS and Lyman over and under more than .002 from marked size, one was well over .003 UNDER marked size. It happens. That's why measuring YOUR boolits as sized with YOUR dies with the same instrument YOU measured YOUR barrel slugs with is advised. Measuring against a standard to start with is a help, but you never know if he did!

[Doc Highwall]

Bret4207, said it all.

[1Shirt]

The over and under comments are right on. The days of exacting percision on stuff we can afford to buy has long gone by the way side in this country, right along with ethe economy.
1Shirt!:coffee:

[RobS]

Whether a die is off specification or people making the dies have different tools for measurement or a manufacturer is running their machines with poor quality control, whatever, the fact is springback will happen with harder antimony alloys. Case in point the same die will size a bullet cast from air cooled WW alloy smaller than ones that are water quenched or heat treated. I have different dies to size the same diameter for air cooled WW boolits vs water quenched boolits.

[MasterBlaster]

I appreciate the responses. I agree its a matter of putting all the variables together to make sure it all works. It is frustrating and expensive to run thru 2 or 3 sizers to find what works but I guess its the nature of the beast. And once you got um you got um.

[MasterBlaster]

I asked Veral Smith at LBT this question and this was his response. thought you might find it of interest;

"The springback you are getting is real. Part of it is the bullet and part is from the dies expanding as the bullet is pushed in and brought back out. In other words. If you had the die out where you could measure it, pushed one of your hard bullets in, and measured the die, you'd find the dies outside diameter would be approximately the same amount larger as your bullets are oversize.

Ever hear of Newtons law? For every action there is an equal and opposite reaction. -- If a fly lights on a railroad track, the track will bend down where he is setting, an amount relitive to his weight vs the rail road tracks strength. When you drive your rig down a super expressway, the road sags under your rig then comes back up behind you. Ditto when you walk across a concrete floor of any thickness, or a wood floor. The amount of sag in any of those cases is easily measured with high precision instruments. Few machinest have a clue of how important this fact is to their livehood and skill, but it counted high to me during the 25 years which I rebuilt high precision metal working machinery. When I was working to real close tolerances, I had to wait for up to a half hour after handling metal for the hand temperature to stabalize so any warp would come out of the part before taking measurements.

Newtons law applies to your bullets and dies, your reolading press frame, and your firearms, which stretch and bulge every time you drop the hammer. The cylinders in your auto engine bulge and shrink back with every ignition of the gas, even if you are punching it up to 100 MPH.

Lino comes to full hardness quite a bit quicker than quenched WW alloy, with both reaching about the same hardness in their appropriate times. With either though, when you have this problem, cast for only about an hour at a time. If you are quenching to improve hardness, pull your bullets from the water immediately, dry them well and size while they are soft. While soft, bullet diameter will be very close to ACTUAL sizer diameter, which certainly isn't as stamped on many dies..

I have have measured this spirng back thing going well over .002 thousandsth of an inch. It will be worse with large diameter bullets, whcih mean the sizer die walls are thinner and weaker, and less with smaller diameter bullets which leave a thicker sizer die wall. The most severe springback I've had is with heat treated high speed babbit metal which reached a hardness of close to 40 bhn, and would CLEANLY penetrate 1/2 inch steel out at 100 yards when shot from a 30-06 at full power, by the way."

[lwknight]

The amount of pressure required to expand a sizer die any measureable amount would be impossible to obtain with a hand powered press. It could take 30-40 pounds pressure on the handle just to expand a brass case by 1 or 2 thousandths. I doubt that even the Hulk could expand a sizer die.

Try this if you believe that you could strech your sizer die. Get a steel plug that is just 2 ten thousandths larger than your die and try to force it through. You can use any lube that your imagination can dream up.

It aint going!!

[onondaga]

Bret Got it right. I start with Lee boolit sizer dies undersize and hone them and test size measuring with my Starrett micrometer that I measure my bore slugs with.

Gary

[303Guy]

If you had the die out where you could measure it, pushed one of your hard bullets in, and measured the die, you'd find the dies outside diameter would be approximately the same amount larger as your bullets are oversize.That's almost but not quite correct. There would be a proportional amount of expansion on the outside of the die (about 80% - splitting hairs I know ;-)). However, the expansion of the die itself, while real will be quite small and very hard to actually measure. It might even be lost in the expansion due to temperature changes. (Not sure about that one).

Get a steel plug that is just 2 ten thousandths larger than your die and try to force it through.That would be an interferance fit on such a small diameter but your point is taken. Hard to measure.

[lwknight]

Yes we can make force press fits but it is totally beyond the capacity of a bullet sizing machine.

[Char-Gar]

Over the counter dies are famous for not sizing how they are marked. I bought two .313 dies that didn't size .313 until I had Buckshot make one and it is dead nuts on .313.

It would be interesting to see what Buckshot says about this issue, because if anybody would know he does. When he makes a sizing die it sizes what it says.

I quite paying much attention to Veral Smith years ago.