Resizing slugs
- Thread starter bigHUN
- Start date
I see couple LEE presses in my local classifieds for very affordable, but I would like to go more into heavier casting just to make it future proof?
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While there seems to be a few highly experienced engineers/gunsmiths present… when finding the optimal projectile diameter (with pneumatic power plants/bore pressure <5000psi), are you attempting to have the width be as close to the lands as possible or do you want to have it be the groove diameter? Or are you going for something in between? Presumably the number has to be less than or equal to the groove diameter and greater than the land diameter but is there a target/formula?
Projectile diameter = x
Land bore diameter = y
Groove bore diameter = z
(Presumed) Mandatory range z >= x > y
(Not real but example to illustrate what I’m wondering) Ideal formula to solve for x:
(y + z)/2?
Should you be going for the average between the 2 values or is it more like, as close to the groove diameter as humanly possible without actually have it touched the bottom of the groove once seated?
Also I know in real life it’s probably more complex like
m = malleability
i = (something to do with projectile shape)
f = friction rating
{(y + z)/m * (i/80)} + 0.0012f
But just trying to get the general concept.
Or if anyone has recommendations for reading so I can help myself answer this question, that’d also be appreciated! I know Google works wonders but if there’s a book you read that covers this type of stuff, please point me in that direction!
Thank you!
Projectile diameter = x
Land bore diameter = y
Groove bore diameter = z
(Presumed) Mandatory range z >= x > y
(Not real but example to illustrate what I’m wondering) Ideal formula to solve for x:
(y + z)/2?
Should you be going for the average between the 2 values or is it more like, as close to the groove diameter as humanly possible without actually have it touched the bottom of the groove once seated?
Also I know in real life it’s probably more complex like
m = malleability
i = (something to do with projectile shape)
f = friction rating
{(y + z)/m * (i/80)} + 0.0012f
But just trying to get the general concept.
Or if anyone has recommendations for reading so I can help myself answer this question, that’d also be appreciated! I know Google works wonders but if there’s a book you read that covers this type of stuff, please point me in that direction!
Thank you!
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Sizing to groove diameter. Experiment from there and the rifle/barrel will tell you what it likes with better groups.
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I have a NOE sizing die setup that you can easily change the sizing die insert and have a variety of sizes say for the 45 from 458 down to 452 going down a 1000th at a time so I can size my NOE 460-315 all the way down to 452 if I want, that way I can use this bullet in my Texan, Bushbuck or XP Ranger.. It's a great concept and works great I use a little swage lube I bought years ago from Corbin.
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I was watching those NOE sizing dies for a while, but never bought any. The jump between sizes in 1 thausands (like 0.217 to 0.218) is 25 microns. I could accept a jump 1/3 rd or 1/4 of that but not more. For next season I will outsource couple dies to a CNC shop.
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@bigHUN and @DesertSilver half of .001 can make a huge difference. In my 357, bullets sized to .3572 have blow by, not as good of accuracy, and much slower than a properly sized to my barrel bullet, I size to .3575. at .358 which my original slugs I was trying measured out of the box, I lose 30+ FPS over what I eventually ended up at and accuracy is poorish, small differences can be huge. First sizing with die as received was something like .3563 and those shot so slow from blow by it wasn't funny. I had something like 3 steps getting to .3575, each step velocity climbed as I opened the die, after .3575 velocity dropped. I took the unmolested die and lapped it to .3575.
I use Lee bullet sizing dies which I adjust to what I need, they are cheap. Kind of slow and tedious to adjust, but I buy two in the same size, which will be much smaller than I need. I put one aside and work with the other. I use firelapping compound, which I have a bunch, but it is not expensive to buy. Get extremely hard cast lead bullets that are too big and take a clean slug and size it, measure it accurately after sizing. Now coat a couple slugs per directions with course firelapping compound, and push both through die. You can use the same bullets with compoiund 2 or three times in a row before between it sizing down, and compound originally put on is used up and it does nothing any longer. Clean the die completely and size a new uncoated bullet and measure, you need good accurate calipers because you likely did not even get .00015 off the original size. This is just to get an idea of how much you take off the die. I try to go .0002-.0003, then switch to a few medium grit lapping compound, followed by the fine grit compound, cleaning the die before going to finer size lapping compound each time. Take a few new clean lubed slugs and size them measure them accurately, test in pcp, mostly interested in velocity so each shot should be with the same pressure every time...bit of a pain. Repeat, process until velocity drops from previous test, you now know exactly what size slug is best for your bore from a velocity standpoint. Take the sizing die you put aside and lap it up until the previous size to have a perfect fit sizing die for your bore. The lee dies are cheap, and any single stage cheap press works just fine.
I use Lee bullet sizing dies which I adjust to what I need, they are cheap. Kind of slow and tedious to adjust, but I buy two in the same size, which will be much smaller than I need. I put one aside and work with the other. I use firelapping compound, which I have a bunch, but it is not expensive to buy. Get extremely hard cast lead bullets that are too big and take a clean slug and size it, measure it accurately after sizing. Now coat a couple slugs per directions with course firelapping compound, and push both through die. You can use the same bullets with compoiund 2 or three times in a row before between it sizing down, and compound originally put on is used up and it does nothing any longer. Clean the die completely and size a new uncoated bullet and measure, you need good accurate calipers because you likely did not even get .00015 off the original size. This is just to get an idea of how much you take off the die. I try to go .0002-.0003, then switch to a few medium grit lapping compound, followed by the fine grit compound, cleaning the die before going to finer size lapping compound each time. Take a few new clean lubed slugs and size them measure them accurately, test in pcp, mostly interested in velocity so each shot should be with the same pressure every time...bit of a pain. Repeat, process until velocity drops from previous test, you now know exactly what size slug is best for your bore from a velocity standpoint. Take the sizing die you put aside and lap it up until the previous size to have a perfect fit sizing die for your bore. The lee dies are cheap, and any single stage cheap press works just fine.
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I know, I grew up with german engineering in mm I can't talk inches.
0.001" = 25 microns
For sliding shaft in a bushing 12 microns is plenty clearance between diameters, but if you wanna make it right lets talk 6 microns - total gap... and not - overlap (oversize).
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I'm a 35 year veteran machinist and mechanical engineer,I totally agree with tight tolerance and precision but at the same time tolerances in microns on something that is mass produced will never happen .the reason being is tolerance that tight will only hold in a controlled environment ( mainly temp) .out CNC mills have dedicated cooling for the ball screws and bearings to maintain micron type tolerances and has to be in a constant controlled temp one of the first demonstrations shown to me when I first started out was the lead machinist took a piece of 1.5" round stock/rod micd it and then held a bic lighter under it for maybe 20-30 seconds and the material grew .020" with that in mind think about how trying to maintain micron tolerances would work especially on our airguns ..thermal expansion/contraction is something compan ies and engineers have factored in as best as possible.You guys talking inches and thousands just to confuse me?
The difference between .217 and .218 is huge... it's like a schoolbus.
25 microns.
(A side note only, When I started my engineering careers in a high precision company we were making a shaft slide freely in a hole with 5 micron gap. That was called DIN standard.)
OK, joke aside.
I will make some drawings for my local cnc shop and order couple bushings. I think I still have a 6-7 mm honing tool somewhere in my toolbox, but I will also check on ali.
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Me about a same, only difference I grew up with mm. Below 1 micron tolerance on .25 cal I can do by hand lapping, of course this is a single piece for myself only, definitely not for mass production.
At this moment I am convinced the pellet/slug OD shall be less then the rifling groove, not sure how much less 1 or 2 microns, the burr from resize will expand from the airblast enough, and btw a 1 micron gap is not a blow-by.... I know from hydraulic manifolds won't leak the oil...
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Not sure about slugs but pellets actually flare out or swell when the pressure hits the skirt ànd I would think the same effect on some of the hollow base and dish base slugs . something else you need to consider is some of that friction/resistance is actually necessary for velocity.
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But if you really wanted the most concentric perfect slug the way to do it would be precision grinding.
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All my liners are choked, some more and some less, but still a choke. Interestingly one that was advertised for slugs that is a heavies choke.
Yes, friction resistance will get from lands only, and just ran into the choke before taking of....
Up to 100 meters I am not really a fan of shooting slugs anyway. Not at all. This resizing project will be for next season 200 meters range, will see how it goes. Always easy to make the hole larger.
I just lost my last chance for this latest exotic $ contract bid, looks like I will be a real full time retire until summer
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I know I was wondering what all I need to get started to size my own slugs and some helpful members pointed me in the right direction. As a result, I got my press and sizing bushings piecemeal. Like @karl_h I purchased some affordable Lee sizing dies. Then I recently found a link to this sizing kit that NOE sells while perusing some of their other products.
https://noebulletmolds.com/site/shop/bullet-casting-reloading/sizing-tools/complete-sizing-kit/
I thought it might help someone to gain a better idea of what to purchase or what’s needed.
https://noebulletmolds.com/site/shop/bullet-casting-reloading/sizing-tools/complete-sizing-kit/
I thought it might help someone to gain a better idea of what to purchase or what’s needed.
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I already got their. 215 through .218. There are a little ruff, but polish up pretty easy. Made a .217 out of my .216
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