Do cast bullets "rebound" after sizing.

CWLONGSHOT

Well-Known Member
The reason for concern in this instance is that I am trying to develop a maximum accurate load in 375 Magnum for my Win 92.
I want a powder coated bullet of .3575” max. My pc’d bullets are .359“-.360”. This would be fine for most of my shooting, plinking etc at low pressure. But I don’t want the pressure buildup that would be caused by the resizing of the bullet at the throat, so I would like the bullet to be groove diameter or half a thousandth larger, only for these max loads.
I do not want bullets of less than groove diameter because I think this could cause leading and accuracy problems. My .357 Lee sizer is sizing .356”. I am attempting to enlarge it with sandpaper on a hardwood dowel.

Jeff H, I understand your concern for a tapered hole. Are you using abrasive paste directly on the metal rod? How do you get a rod of the proper diameter?
Why again do you feel the need for that diameter bullet??

Do you know or are you assuming a issue with a larger bullet?

I have shot and prefer to hoot, fat cast bullets for many decades and never seen issue with choosing it.

Cast are not jacketed and do not see the pressure spikes when larger or seated into rifling.

Ian and I have gone round with these .001 pc thickness numbts before. I don't believe it. Thats .0005 per side!!! MAYBE ya might see some areas @ .00175/.002 but .003 + is more likely. What & how we do PC simply is not that precise! But that is neither here nor there the PC is what it is and nice thin PC hasn't been a issue. Thick gloppy applications are a different story.

CW
 

Rockydoc

Well-Known Member
Why again do you feel the need for that diameter bullet??

Do you know or are you assuming a issue with a larger bullet?

I have shot and prefer to hoot, fat cast bullets for many decades and never seen issue with choosing it.

Cast are not jacketed and do not see the pressure spikes when larger or seated into rifling.

Ian and I have gone round with these .001 pc thickness numbts before. I don't believe it. Thats .0005 per side!!! MAYBE ya might see some areas @ .00175/.002 but .003 + is more likely. What & how we do PC simply is not that precise! But that is neither here nor there the PC is what it is and nice thin PC hasn't been a issue. Thick gloppy applications are a different story.

CW
CW, please see my post #12 above. It explains why I don’t to use the chamber throat as a sizing die. Maximum loads only.
 
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Walks

Well-Known Member
Back in the 1950's - 1960's, My Dad used to shoot the old Bullseye 3 caliber Matches. He used a Pre-War Colt Officer's Model match as 1 gun. He had a pair of Lyman #358395 HB molds that were a Special order. They would drop at .359 with 20-1 or 30-1 (can't remember which) then pan lubed. No sizing wanted. I seem to remember that one mold dropped on the right side of the pot, the other on the left side. Bullets were weighed and inspected. No one was allowed to speak to him when he was casting match bullets. Wish I had molds or revolver. Had a framed target in his office. Six shots you could COMPLETELY cover with a quarter, signed/dated by His 6 man team. Don't remember 50ft or 75ft.

Reduce as many variables as possible.
 
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Bret4207

At the casting bench in the sky. RIP Bret.
FWIW on enlarging sizer dies. I prefer to use as stiff a steel rod as possible with good quality abrasive paper applied so that there's no overlap. Then I roll the die back and forth on my thigh. I've had good success with Lee dies using this method. You want to keep the rod, or where you grip it anyway, as close to the die as you can to minimize tapering.
 

Snakeoil

Well-Known Member
Ian, your point about grooves is well made. I must admit that the mental picture (fuzzy at it may be) I formed did not include lube grooves which was just a simple brain phardt. Yes, I agree and take back that statement that they will grow longer. The grooves will just get filled in a bit.

I enjoy discussions like this because it makes one think deeper into what is going on tham one would normally in the normal process of casting and reloading.
 

462

California's Central Coast Amid The Insanity
Not unless the bullet has no grooves or other features to interrupt the flow of metal.

Swerve alert, but this is good stuff which pertains also to sizing bullets.... bear with. There is some difference of opinion among powder coaters regarding slicks versus grooves and if grooves what style is best. One thing is for sure, all bullet styles seem to work. Some who shoot at high velocity and pressure (rifles) have experienced very challenging barrel fouling in similar fashion to Barnes' early copper monolith bullets. Relief or "displacement grooves" as I'll call them reduce pressure on the bullet against the barrel steel and reduce friction abrasion and galling. Why? Well, the grooves supply a path of least (lesser) resistance for the alloy as it is swaged into the bore than if the entire bearing length has to be compressed and drawn. Same thing for cast bullets. Now, you say "but copper jacketed bullets draw in length when engraved and don't foul excessively!" Ahhh, but they generally have very soft, ductile cores (on the order of 2% antimony and little to no tin) and are contained in a thick copper bag which is a sort of dynamic extrusion die that controls how the drawing action of being engraved happens, i.e. keeps the nose and boat tail form concentric with the bore and prevents irregular bulges or bends from occuring to the base (maintains squareness) or ogive. PC doesn't do this for us because it isn't strong enough to contain alloy flow, nor is our monolithic core as soft and ductile as copper jax cores. So I treat pc cast as a monolith and insist on displacement grooves to PREVENT gross form extrusion of the bearing length and contain the metal displaced by the rifling to the driving bands themselves and only 10-15 thousandths deep into the 'skin' of the bullet
This tidbit of education is why I read all the threads and their posts, even the ones that don't pertain to anything I do (even the ones about 9 mm ;)). I don't paint bullets . . . yet . . . but if I were to ever do so I'm now that much smarter.
 

Brad

Benevolent Overlord and site owner
Staff member
Try different alloys. Measure before and after pushing thru same sizer. Bet they don’t all size the same after a trip thru.
Heat treat some wheel weights and compare post sizing diameter On as cast, just heat treated, and heat treated after 14 days.
 

Jeff H

NW Ohio
...

Jeff H, I understand your concern for a tapered hole. Are you using abrasive paste directly on the metal rod? How do you get a rod of the proper diameter?
I use abrasive PAPERS mostly, lubricated with a spritz of cheap WM "Spray Lube," which is probably just kerosene that doesn't smell. It's not worth much as a general lube, but is a cheap and convenient oil to use on oil stones and wet/dry abrasive papers.

I keep stuff. If I can't find a piece of something that fits inside the hole with some abrasive paper wrapped around it, I sometimes resort the the end of a twist drill that goes into the chuck. Having an assortment of letter, number and fractional drills has come in handy. If the size, manufacturer, etc. is stamped onto the shank of the drill, I file or hone that smooth first.
 

fiver

Well-Known Member
Doc your only gonna see about 3-400 psi in pressure rise from the throat.
your actual pressure jump is gonna be from the soft lead bullet plugging up the barrel to maximum efficiency.

that is why you see cast bullets having higher pressures than jacketed ones.

so .0005 or .002 neither is gonna matter as far as pressure is concerned.[and especially with a slickery coated projectile]
your only real concern at that [throat] point is what Ian is saying about alloy flow/displacement over the bullets contact sections.
 

Jeff H

NW Ohio
Doc your only gonna see about 3-400 psi in pressure rise from the throat.
your actual pressure jump is gonna be from the soft lead bullet plugging up the barrel to maximum efficiency.

that is why you see cast bullets having higher pressures than jacketed ones.

so .0005 or .002 neither is gonna matter as far as pressure is concerned.[and especially with a slickery coated projectile]
your only real concern at that [throat] point is what Ian is saying about alloy flow/displacement over the bullets contact sections.

I don't have pressure-testing equipment, but my Rossi 92 had a .355" groove diameter, and I shot .358" and .359" bullets (not PC'd) through it from 450 fps (four hundred fifty) to 1800 fps, 125 through 190 grains and my brass stood up admirably. I have abused some 357 Mag brass in my time, back when I got two or three firings before primers almost fell into the primer pocket. That was long before the Rossi. I took the brass not wearing out in the Rossi to mean that I wasn't hitting pressures like I'd seen in my younger days, even with fat cast bullets.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Add to the equation the time the pressure is at max. IMO a cast bullet, even if it seals at 100% efficiency, is going to displace whatever metal has to displace faster/easier than a jacketed bullet of the same size/length/profile/etc. I would think the closer you are to pure lead, the faster this happens. Pressure curve is the term I'm grasping for I think.
 

RBHarter

West Central AR
Adding pressure curves drags dwell times along kicking and screaming .
25 kpsi applied between 1&3" from the case mouth with acceleration from zero to 800 fps in 2" and on to 1000 fps in the remaining 2" is going to be different than the same 25kpsi that doesn't peak until 2.5-3" where it's still at 800 fps but still gets it's 1000 fps in that last inch . It doesn't stay in the barrel longer because of the slower start but it's moving faster and subject to the peak pressure for a shorter time so there's less dwell time for the pressure to deform the base ..........somehow that sounded better before I tried to write it down .......

When I was trying to figure stuff out and what was really happening when I hit the point where groups fell apart I did a bunch of work with one bullet , alloy , rifle ,case , primer lot , and 2 powders . Red Dot and Unique . The Red Dot loads fell apart just a little bit above where the Unique really started to come together over the Chrono and on paper . My possibly flawed conclusion was that the pressure in the velocity overlap had to be pretty close but was happening more slowly resulting in a more gentle acceleration even though the over lap speeds were the same .

It's hard to focus on when it happens in .0007 seconds after the mechanical stops and the chemical takes over .
 

shuz

Active Member
I don't know if you'd call it rebounding, but many times in my experience with hard alloys, the boolit diameter that comes outta the sizing die is a thou or two greater than the number marked on the die.
 

fiver

Well-Known Member
that's how it works...

yeah RB that's why i try to explain it in terms of when the bullet is rather than where it is.
the whole procedure is gonna happen, your only choice is the time which the events take place.
it helps to envision things better if you use where the bullet is as it happens, versus just trying to see what the powder is doing and looking at things from only the back end of the bullet.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Der-zackly! Took me a loooong time to get a mental picture that moved, so to speak. Still a pretty dim picture in my case, but it helps.
 

RBHarter

West Central AR
Some times you give the bullet a hard solid sledge hammer kick and sometimes you give it a nudge like a sticky wind up car in a stiff breeze .
 

Ian

Notorious member
You have to be able to imagine this stuff in 3D, in slow motion, with all the fluid dynamic and pressure calculations scrolling down below the image.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Ian, it's all I can do to bring up a mental picture done in Crayolas and moving in jerks like a 1915 movie. Please don't make me feel any more inadequate!!! ;)