Do cast bullets "rebound" after sizing.
- Thread starter Rockydoc
- Start date
CWLONGSHOT
Well-Known Member
I read this a few times but have not experienced it. I size within hours of casting, normally.
Im of the opinion its alloy specific.
CW
Im of the opinion its alloy specific.
CW
Rockydoc
Well-Known Member
I sized after casting. Then powder coated. That was a month or so ago. Lyman #2/roof sheathing(almost pure lead). 50/50. I suppose the number on the side of a Lee push through sizer doesn't always match the diameter of the hole down the middle of it?
Snakeoil
Well-Known Member
Cannot speak for Lee sizers, by my Lyman sizing dies are exactly what is etched on the die. And I just happened to measure some bullets the other day and they are exactly the same OD as the sizer size.
I guess I could envision a really hard alloy springing back a few tenths. But I cannot see a full thousandth. How are you measuring your bullets. My guess if you are using a dial caliper, it is off and the die and the bullet are just fine. Always clean your caliper jaws with a piece of paper and check the zero. Adjust accordingly. Calipers are prone to distortion by nature of their design. They can be very accurate if treated well and used properly. But in the machine shop when I was a young apprentice, they were called "guess sticks".
I guess I could envision a really hard alloy springing back a few tenths. But I cannot see a full thousandth. How are you measuring your bullets. My guess if you are using a dial caliper, it is off and the die and the bullet are just fine. Always clean your caliper jaws with a piece of paper and check the zero. Adjust accordingly. Calipers are prone to distortion by nature of their design. They can be very accurate if treated well and used properly. But in the machine shop when I was a young apprentice, they were called "guess sticks".
Man, this is a not so simple question.
Does a bullet rebound when sized? U less pure lead, yes they do. How much depends on alloy composition AND BHn. A wheel weight bullet just cast as opposed to heat treated and aged will react differently to the sizer. May be just .0005 but it does matter sometimes.
Think of it this way as well, the higher the Sb, as a rule, the larger they will measure after being run thru the same sizer. Same thing with as cast size, more Sb often gives a larger bullet with pure lead being the smallest.
Next we need to consider age hardening and growth. Some alloys do age harden over time then stabilize. Some alloys will grow a little with age. Again, May only be .001 but that can cause some issues with tight fitting loads.
My suggestion is to measure a few bullets then set them aside. Measure again in 15, 30, and 45 days. See what YOUR alloy does.
Does a bullet rebound when sized? U less pure lead, yes they do. How much depends on alloy composition AND BHn. A wheel weight bullet just cast as opposed to heat treated and aged will react differently to the sizer. May be just .0005 but it does matter sometimes.
Think of it this way as well, the higher the Sb, as a rule, the larger they will measure after being run thru the same sizer. Same thing with as cast size, more Sb often gives a larger bullet with pure lead being the smallest.
Next we need to consider age hardening and growth. Some alloys do age harden over time then stabilize. Some alloys will grow a little with age. Again, May only be .001 but that can cause some issues with tight fitting loads.
My suggestion is to measure a few bullets then set them aside. Measure again in 15, 30, and 45 days. See what YOUR alloy does.
CWLONGSHOT
Well-Known Member
Lee sizers are different. They use a very thin band to size and rarely are as marked. (Have seen Big or small)
Id venture this has something to it.
I size LAST! The PC alone upped your diameter.
CW
Id venture this has something to it.
I size LAST! The PC alone upped your diameter.
CW
Bret4207
At the casting bench in the sky. RIP Bret.
Spring back with lead alloys is a pretty "iffy" thing. If it does, you probably won't be able to measure it accurately with a standard thousandths reading mic, with a tenths or smaller reading mic, yes, much easier. All that depends on us properly using the mic. Consistency is super important when you're trying to measure a thou or under, as is cleanliness of the anvil faces. The other question is are you measuring them around the whole circumference? Not all sizers are truly round, and they can wear over time. So it's not unusual to have a sized bullet that's a little oblong instead of perfectly round, but that can screw with your measurement. No, sizing dies aren't always exactly as marked, but sometimes that's because they actually aren't the marked diameter and other times it's because our measuring equipment isn't set properly to a standard.
FWIW- I know one machinist that prefers to use a vernier because, as he puts it, "It can't easily go out of adjustment." He's kinda old school in more ways than just that!
FWIW- I know one machinist that prefers to use a vernier because, as he puts it, "It can't easily go out of adjustment." He's kinda old school in more ways than just that!
Petrol & Powder
Well-Known Member
1. I agree that you must know what you are measuring. If you take more than one measurement of a bullet that is not truly round, you'll get more than one value because you're measuring an oval, not a true circle. So that's the first issue.
2. Even if the bullet is perfectly round, your measuring technique needs to be consistent, or you will still get more than one value with multiple measurements. (That's the old saying that a man with one watch knows what time it is - A man with two watches is never quite sure).
3. If there really is some "Spring Back", meaning after the bullet exits the sizing die, it re-expands a bit to assume a diameter slightly larger than the diameter it was forced to inside the die - how much and when does that "Spring Back" occur? Does it immediately expand back a little? (like a brass casing exiting a sizing die?) OR, does that expansion (if it occurs) take place more slowly?
I agree with Bret - it is an "iffy" thing.
A malleable metal, such as a lead alloy, can easily be deformed. When you push a bullet through a die, the diameter is reduced but the length may increase (that metal has to go somewhere). Does it tend it return to its original diameter? That would appear to be a function of how soft the metal was to start with. I think it is safe to say there may be some "spring back" but it will be minimal with a soft alloy.
One test would be to push a bullet through a die and then push it through a second time and note the force needed on the second pass.
2. Even if the bullet is perfectly round, your measuring technique needs to be consistent, or you will still get more than one value with multiple measurements. (That's the old saying that a man with one watch knows what time it is - A man with two watches is never quite sure).
3. If there really is some "Spring Back", meaning after the bullet exits the sizing die, it re-expands a bit to assume a diameter slightly larger than the diameter it was forced to inside the die - how much and when does that "Spring Back" occur? Does it immediately expand back a little? (like a brass casing exiting a sizing die?) OR, does that expansion (if it occurs) take place more slowly?
I agree with Bret - it is an "iffy" thing.
A malleable metal, such as a lead alloy, can easily be deformed. When you push a bullet through a die, the diameter is reduced but the length may increase (that metal has to go somewhere). Does it tend it return to its original diameter? That would appear to be a function of how soft the metal was to start with. I think it is safe to say there may be some "spring back" but it will be minimal with a soft alloy.
One test would be to push a bullet through a die and then push it through a second time and note the force needed on the second pass.
I have a hypothesis, based on a single incident, and difference in alloy, as mentioned, seemed to make a difference, BUT it seemed to mostly be the die.
I opened a Lee .430" die to .4325", which seemed to work just fine on softer alloys, like WW/Pb. When sizing straight WW or harder, they came out .433" - .0005" larger than when using the softer alloy. Since I took it for granted that the bullets were coming out .4325", I did not measure as I sized. LATER, I wondered if they had "rebounded." Double/triple checked mics and zeroes, wasn't the measuring tools.
What I THINK happened, is that when I opened the die with abrasive paper and a wooden dowel, I created a shorter, rounded minimum diameter in the die, instead of a longer, straight section, like in a Lyman die. What I believe happens is that the shorter section of minimum ID displaces metal ahead of and behind the portion being squeezed, such that the OD of the bullet is not "springing back," rather it is displaced forward of the minimum ID as the bullet passes through that choke-point. This happens with the harder stuff, not the softer stuff. I have been careful since to use a metal rod, as large as possible, to hone or lap dies to larger IDs in an attempt to maintain a longer section fo minimum ID.
Basically a somewhat informed conjecture on my part. Not sure it exactly addresses the actual question, but may contain a clue for someone who possibly has another puzzle piece it fits into.
I opened a Lee .430" die to .4325", which seemed to work just fine on softer alloys, like WW/Pb. When sizing straight WW or harder, they came out .433" - .0005" larger than when using the softer alloy. Since I took it for granted that the bullets were coming out .4325", I did not measure as I sized. LATER, I wondered if they had "rebounded." Double/triple checked mics and zeroes, wasn't the measuring tools.
What I THINK happened, is that when I opened the die with abrasive paper and a wooden dowel, I created a shorter, rounded minimum diameter in the die, instead of a longer, straight section, like in a Lyman die. What I believe happens is that the shorter section of minimum ID displaces metal ahead of and behind the portion being squeezed, such that the OD of the bullet is not "springing back," rather it is displaced forward of the minimum ID as the bullet passes through that choke-point. This happens with the harder stuff, not the softer stuff. I have been careful since to use a metal rod, as large as possible, to hone or lap dies to larger IDs in an attempt to maintain a longer section fo minimum ID.
Basically a somewhat informed conjecture on my part. Not sure it exactly addresses the actual question, but may contain a clue for someone who possibly has another puzzle piece it fits into.
Snakeoil
Well-Known Member
I would suspect that any time a bullet goes thru a sizer that one of two things happen, maybe both.
1. the alloy is compressed such that any tiny voids and such are collapsed. Yeah, I know, we all cast perfect bullets.
2. the bullet gets slightly longer.
So, I suspect that the ease at which it can be extruded into a longer bullet plays a significant roll in if there will be any springback after exiting the die.
Brad's comments that the higher the Sb content, the more springback experienced, supports this theory as I would expect a harder bullet to resist deformation/extrusion.
But Rockydoc has also added another variable, PC. I have no idea how much PC can be compressed and stay compressed. So, when it runs thru the sizer, do both the alloy and PC compress, just the alloy, or just the PC? PC is basically a plastic, and by virtue of that, I assume it compressed easily. Does it spring back? My guess is yes.
You could machine a steel rod that is a few thousandths smaller than a sizing die and PC it. Measure before and after and then measure again after 24 hours. My guess is the PC will have sprung back a bit. Plastic likes to find it's original shape. It's call creep.
1. the alloy is compressed such that any tiny voids and such are collapsed. Yeah, I know, we all cast perfect bullets.
2. the bullet gets slightly longer.
So, I suspect that the ease at which it can be extruded into a longer bullet plays a significant roll in if there will be any springback after exiting the die.
Brad's comments that the higher the Sb content, the more springback experienced, supports this theory as I would expect a harder bullet to resist deformation/extrusion.
But Rockydoc has also added another variable, PC. I have no idea how much PC can be compressed and stay compressed. So, when it runs thru the sizer, do both the alloy and PC compress, just the alloy, or just the PC? PC is basically a plastic, and by virtue of that, I assume it compressed easily. Does it spring back? My guess is yes.
You could machine a steel rod that is a few thousandths smaller than a sizing die and PC it. Measure before and after and then measure again after 24 hours. My guess is the PC will have sprung back a bit. Plastic likes to find it's original shape. It's call creep.
Rockydoc
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?
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?
Rockydoc
Well-Known Member
Powder coating is only .001“ to .003” in thickness. The bullets in this instance the PC is .001”. I don’t think pc is part of the problem when the sizer is reducing the bullet from .360” to .356”, eg: .004”.
Incidentally, after polishing with 800 grit sandpaper trying to open the diameter, the “roughness “ created has removed some of the PC.
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JonB
Halcyon member
As Brad pointed out, rebounding (right after sizing) and age growth are two different events.
If you end up loading some and they sit on the shelf for over a year, you could encounter some age growth that could cause pressure increase problems. I had some loaded 45acp (with PC'd cast bullets) that did have enough age growth on the nose, to make them not chamber in a gun, that chambered ammo from that same batch of ammo, a couple years earlier. Best I could tell with my measuring skills, they grew nearly 0.001"
I have a related question.
How would the heat treatment of the PC (you are also heat treating the bullet), effect age growth of a alloy (that would be an alloy that is susceptible to age growth)?
If you end up loading some and they sit on the shelf for over a year, you could encounter some age growth that could cause pressure increase problems. I had some loaded 45acp (with PC'd cast bullets) that did have enough age growth on the nose, to make them not chamber in a gun, that chambered ammo from that same batch of ammo, a couple years earlier. Best I could tell with my measuring skills, they grew nearly 0.001"
I have a related question.
How would the heat treatment of the PC (you are also heat treating the bullet), effect age growth of a alloy (that would be an alloy that is susceptible to age growth)?
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JonB
Halcyon member
Polish that die !!!
Flitz and some sort of tight fitting cotton covered thingy.
I use a battery drill mounted cotton Bore Mop (they are typically used in the BP front stuffers).
Rockydoc
Well-Known Member
Yes, Jon, I intended to do that when I get it to the size I want. I discovered this PC removal when running a bullet through to test progress of my enlargement efforts. I think I will use pin gauges to check progress now instead of continuing to de-PCing bullets
.
Snakeoil
Well-Known Member
Not sure what you have available to you, Doc, but I would suggest you taking a bullet, drilling a hole in it and use that as a lap in your drill. Running a wooden dowel up and down pretty much guarantees you will have a belly in the middle because the ends each get one pass and the middle gets two. You could drill a piece of hardwood and pour a cylindrical lap that you would then run thru your sizer. Drill it, mount it and put it in your drill, preferably a drill press to eliminate side loading from cocking a hand drill. Run is and just go up and down enough to distribute the lapping compound and avoid low spots due to compound concentration. Will take you longer, but will give you a straight, cylindrical hole.
If you have access to a lathe and a Dremel. Put the die in the lathe (preferably a collet) and then mount the Dremel to the compound. Turn the die slowly and run the Dremel all the way thru and then back. This should give you a nice straight and round hole as well. I have a handpiece for my Dremel which make mounting it to the compound pretty easy.
If you have access to a lathe and a Dremel. Put the die in the lathe (preferably a collet) and then mount the Dremel to the compound. Turn the die slowly and run the Dremel all the way thru and then back. This should give you a nice straight and round hole as well. I have a handpiece for my Dremel which make mounting it to the compound pretty easy.
Ian
Notorious member
Brad and others saved me a lot of typing.
For the problem at hand, lubricate the first bullet through your enlarged die and it won't shed any significant coating. Once the micro-scratches are embedded with plastic, the die becomes self-lubricating nut needs help initially. Sizing within hours of curing the coating will be easiest due to bullet softness but age growth may occur down the road. Best policy with mixed antimony scrap alloy is bake, size, wait a couple months, check, and THEN load your bullets.
I would enlarge the die until it is producing bullets NEARLY as large as you want right after curing the coating, and let the bullets rest a while (at least 2 weeks) and see if they grow. Harder (aged) bullets will spring back more than soft just cast or just oven cured bullets, so if you have to re-size them later you want to be sure your sizer is small enough to still meet your target diameter with an age-hardened bullet. You can't just anneal them again because that resets the precipitation-hardening and growth process. I think a lot of us in the powder coating game end up with an array of bullet sizers representing fine increments for each caliber, not to make bullets different sizes but to make ONE final size in light of many variables.
I find PC cast bullets as a "rule" need minimum of a half-thousandth more diameter than groove diameter or they gas-cut, lead, and fly sideways. For revolvers, my method that seems to work well is size the usual way of making them push through the cylinder with resistance but not enough to break the shaft of a wooden pencil. This assumes the cylinder throats equal or exceed groove diameter.
For the problem at hand, lubricate the first bullet through your enlarged die and it won't shed any significant coating. Once the micro-scratches are embedded with plastic, the die becomes self-lubricating nut needs help initially. Sizing within hours of curing the coating will be easiest due to bullet softness but age growth may occur down the road. Best policy with mixed antimony scrap alloy is bake, size, wait a couple months, check, and THEN load your bullets.
I would enlarge the die until it is producing bullets NEARLY as large as you want right after curing the coating, and let the bullets rest a while (at least 2 weeks) and see if they grow. Harder (aged) bullets will spring back more than soft just cast or just oven cured bullets, so if you have to re-size them later you want to be sure your sizer is small enough to still meet your target diameter with an age-hardened bullet. You can't just anneal them again because that resets the precipitation-hardening and growth process. I think a lot of us in the powder coating game end up with an array of bullet sizers representing fine increments for each caliber, not to make bullets different sizes but to make ONE final size in light of many variables.
I find PC cast bullets as a "rule" need minimum of a half-thousandth more diameter than groove diameter or they gas-cut, lead, and fly sideways. For revolvers, my method that seems to work well is size the usual way of making them push through the cylinder with resistance but not enough to break the shaft of a wooden pencil. This assumes the cylinder throats equal or exceed groove diameter.
Ian
Notorious member
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
Rockydoc
Well-Known Member
Voilá (French for success?). With sandpaper on a hardwood dowel I went successively from 80 to 180 to 400, 600, 800 and then to JB Paste on a bore mop and then cleaned the die up and sized .360" bullets to .3575" bullets with NO LOSS of PC.
Thank you all for your suggestions.
This has developed into a very useful and interesting discussion.
Thank you all for your suggestions.
This has developed into a very useful and interesting discussion.