Copper or Aluminum

[TD1886]

Why do you think there are different gas check thicknesses from 10 thous thick up to 20 thous thick?

I do not think that. What I meant to say is on the smaller caliber like .224 and .243 I use the aluminum flashing as it's thick enough for the gas check shanks that are on bullet which is determined by the mould. On the larger calibers the flashing is too thin and after you applied it, it's not the full diameter you size too. I don't believe in doubling up on the flashing. So I obtain thicker aluminum material for those larger calibers. I hope that I have explained it. Look at all the brands of moulds that are out there. I don't think there is a standard for what thickness gas check they use.

[gloob]

If a 0.010" copper check works for 223, do you think it would work for all calibers, if the shank were sized correctly?

If it was just about the "hardness" as a gasket material, then why are there at least 4 different thickness of copper checks for different caliber bullets? 0.010", 0.014", 0.017", 0.020".

[TD1886]

If a 0.010" copper check works for 223, do you think it would work for all calibers, if the shank were sized correctly?

If it was just about the "hardness" as a gasket material, then why are there at least 4 different thickness of copper checks for different caliber bullets? 0.010", 0.014", 0.017", 0.020".

I can't answer your question I'm not the engineer/engineers that designed them. As I said though as caliber goes up, to a certain degree, I use the thicker aluminum. You realize that a larger caliber doesn't necessarily have more pressure. It may be the larger calibers have more base area then the smaller ones. One thing I never do it anneal my gas check either copper or aluminum. Would you think that them being softer would let the pressure distort the base of the bullet more?

[megasupermagnum]

The various thickness options have nothing to do with their performance. They offer those thicknesses completely for fit options. A good example is 30 caliber rifle, and 32 caliber handguns. Both use a .284" shank, but one is typically sized about .310" or .311", and the other is sized .313" or .314". You can definitely use .017" thick checks on both, but you are deforming the 30 calibers more since you are squeezing that shank down an extra .004" verses if you were using .015" checks. You can sometimes get away with .015" checks on 32 handguns, but sometimes you get a loose fit, thus it's recommended to use .017" thick checks. I've never seen .020" thick checks, but I suspect they would be good for oddball sizes and calibers. An example might be the 9.3mm calibers, which I assume use the same shank as a 35/38 caliber. The thin checks are almost exclusively for plain base bullets, which you want the thinnest possible since you are going to be deforming that bullet a ton no matter what. I'm assuming much under .010" aluminum and they probably don't form very well.

[gloob]

Sage's or Gator offer different nonstandard thicknesses, and these can come in handy if and when your bullet mold is off.

But bullets have a standard thickness of gas check and shank. There's a sticky at the top of the forum, if you want to check it out.

The thickness of the check affects how much heat can be redistributed and absorbed. Barrels aren't perfect. If and when a leak forms on the bullet that allows gas to jet by, that spot will get real hot, real fast. A gas check will absorb and spread that heat around the entire base of the bullet. There needs to be enough material in the check to do that. Aluminum is less than half the density of copper, so for any given thickness of check, it has much less ability to redistribute and absorb heat!

If all you needed was a check thick enough to not get cut through by the rifling, then all checks could be made 6 thousandths thick.

Paper patching and PC work a little differently from checks. PC and paper are both insulators that cover the entire bearing surface. If you put PC or a paper patch only on the base of a bullet and 1/8" up the side, I bet that wouldn't work very well. Any gas jet that formed, the paper/PC would not absorb/redistribute any heat. The bullet would get ruined.

[megasupermagnum]

Sage's or Gator offer different nonstandard thicknesses, and these can come in handy if and when your bullet mold is off.

But bullets have a standard thickness of gas check and shank. There's a sticky at the top of the forum, if you want to check it out.

The thickness of the check affects how much heat can be redistributed and absorbed. Barrels aren't perfect. If and when a leak forms on the bullet that allows gas to jet by, that spot will get real hot, real fast. A gas check will absorb and spread that heat around the entire base of the bullet. There needs to be enough material in the check to do that. Aluminum is less than half the density of copper, so for any given thickness of check, it has much less ability to redistribute and absorb heat!

If all you needed was a check thick enough to not get cut through by the rifling, then all checks could be made 6 thousandths thick.

Paper patching and PC work a little differently from checks. PC and paper are both insulators that cover the entire bearing surface. If you put PC or a paper patch only on the base of a bullet and 1/8" up the side, I bet that wouldn't work very well. Any gas jet that formed, the paper/PC would not absorb/redistribute any heat. The bullet would get ruined.

That's the first time I've ever heard that theory. I'm not necessarily doubting it, I also don't think that's the reason we use the thicknesses we do. To use your example of a .006" thick gas check, someone would likely have to make a custom die to form that, and even then I'm not sure how well it would work. Copper that thin is more like paper than metal. In my research on gas checks, there are multiple theories on what exact functions they provide, but none of the more well known ones involve heat. I'm sure there's a point where a check would be cut or destroyed by rifling, but beyond that the main purposes revolve around providing a better seal against pressure, providing a more positive engagement of the rifling, and maintaining that grip right at the muzzle where it matters.

[gloob]

That's the first time I've ever heard that theory. I'm not necessarily doubting it, I also don't think that's the reason we use the thicknesses we do. To use your example of a .006" thick gas check, someone would likely have to make a custom die to form that, and even then I'm not sure how well it would work. Copper that thin is more like paper than metal.

Lots of casters make plain base gas checks out of soda cans that are less than 4 thousandths thick aluminum. That's all it takes for that particular boolit to no longer foul and tumble in that particular load and gun. Yes, they're pretty flimsy and maybe not great for a commercial product. So let's forget the "paper thin stuff" and go on to factory checks. In 223, a factory check is only 10 thousandths thick.

the main purposes revolve around providing a better seal against pressure, providing a more positive engagement of the rifling, and maintaining that grip right at the muzzle where it matters.

If 10 thousandths copper check works in 223 to do these things, why do they make 30 caliber checks 17 thousandths thick? Why wouldn't they just make all checks 10 thousandths thick, if it made no difference? 10 thousandth thick checks are plenty thick enough to survive shipping and handling and applying, even up to 45 caliber.

Some people think that plain base checks could make regular checks and gas check-shanked bullet molds obsolete. Just put a 4 thousandths thick aluminum check on a 308 boolit, and sky's the limit. I think if they try it, first, they might be disappointed.

[gloob]

We can make boolits really, really hard. Hard enough to grip the rifling. We can alloy small amounts of copper in them to make them stupid hard.

The problem is that the boolit has a pretty low melting point. The other problem is the boolit alloy is really bad at conducting heat. That means the bullet not only melts at a low temperature, it is also easy to melt the surface of the bullet before the center even gets warm.

I don't think it's a coincidence that copper, aluminum, and zinc (zinc washers were a thing, in the past) all have very high thermal conductivity and higher melting temp than lead.

[TD1886]

Lots of casters make plain base gas checks out of soda cans that are less than 4 thousandths thick aluminum. That's all it takes for that particular boolit to no longer foul and tumble in that particular load and gun. Yes, they're pretty flimsy and maybe not great for a commercial product. So let's forget the "paper thin stuff" and go on to factory checks. In 223, a factory check is only 10 thousandths thick.



If 10 thousandths copper check works in 223 to do these things, why do they make 30 caliber checks 17 thousandths thick? Why wouldn't they just make all checks 10 thousandths thick, if it made no difference? 10 thousandth thick checks are plenty thick enough to survive shipping and handling and applying, even up to 45 caliber.

Some people think that plain base checks could make regular checks and gas check-shanked bullet molds obsolete. Just put a 4 thousandths thick aluminum check on a 308 boolit, and sky's the limit. I think if they try it, first, they might be disappointed.

I believe I mentioned this before. I think they make checks from thinner material for the smaller calibers such as .224 because they don't have as a thick recenss where the check goes on the base shank as larger calibers. Let's say your cast bullet is .224 for an example. If they used the thicker 17 thousandsths check for them the shank would have to be 14 thousandths smaller in diameter and that will leave too small of a shank. I would like to believe that the mould designers are the ones that determine what thickness of a gas check will fit the bullet. Am I making any sense?

BTW "free checked bullets" are good up to the very low 2000 fps bracket. I don't free check plain base cast rifle bullets, but do a lot of pistol revolver ones. Not too much of an inconvienance as you apply them when lubing/sizing. That is if you use that lubing/sizing method.

[Willie T]

The smaller the circle, the greater the strength, and ability to withstand more pressure. As an example: If you load your own shot shells, as the bore gets smaller with the sub gauges, SAAMI pressure specs are higher. That is due to the incremental gains in strength as the diameter of the barrel decreases. The .223 diameter is less than 1/2 the diameter of a .45. That smaller diameter makes the cylindrical portion of the check structurally stronger. Thus able to withstand more pressure and hold its shape in the grooves. That increased structural strength at smaller diameter with the same thickness also does not bend as readily to seal the corners in the grooves as easily. Hence a thinner check works better in small calibers.
As for aluminum and copper checks. I have made aluminum and I buy Hornady copper. I don’t load super fast. A little over 2,300 fps in 30-30 and a 357 carbine are the fastest I load cast for. Both homemade aluminum and copper Hornady have worked equally well for me to eliminate leading. I have not been able to match the accuracy I achieve with the copper Hornady checks using my homemade aluminum checks. In the event I can’t get Hornady checks, I can make aluminum. As long as I can buy the Hornady checks for a reasonable price, they are what I use. Learning to make my own checks that match the accuracy I get in my firearms with the copper Hornady checks would reverse that. Self sufficiency is a big part of the reason I cast but I’m addicted to accuracy. I can’t comment with any reasonable insight regarding whether or not the aluminum checks are abrasive to the bore. With that in mind I will refrain from publicly speculating either way.
Willie

[gloob]

Interesting finding regarding accuracy. I suppose accuracy could be affected due to being lighter, which affected the balance of the bullet. Or maybe because the aluminum checks were less symmetrical than factory Hornady checks?

2300 is plenty fast though, I have to say. I think pressure (and time spent at high pressures and potential gas cutting) is the more direct reason for boolit failure than velocity, but you can't get to 2300 fps without high pressures!

I'm not convinced about the smaller diameter strength thing, though. The boolit should provide plenty of strength. Even 4 thous aluminum checks can make the difference in 40+ caliber boolits! (I personally use 10 thous aluminum checks in 10mm, and they not only leave no fouling, they clean out the fouling of previous boolits!) There is also a difference in gas check thickenss between 452 caliber (thinner checks; typically lower pressure pistol cartridges) and 458 caliber (thicker checks; typically higher pressure rifle cartridges).

Surely someone has tried soda can checks in a caliber that should reach 2300 fps with boolits! I would try it if I could. I don't have plain base molds in any caliber that can do that. And my dies won't make soda can checks!

[gloob]

Regarding the "structural strength" thing, I have also recovered checks that fell off the boolit, because they were not seated correctly. The mouth of these checks was barely hanging onto the shank of the boolit. These 10 thous aluminum checks that fell off didn't have any rifling marks on them. Without the bullet shank to provide the strength, I don't think the check has much structural strength to contain pressure.

[Willie T]

As much as I wanted to make my own checks that were the equal of the copper store bought Hornady checks, it was a bitter pill to swallow that I never quite got there.
Willie

[Willie T]

Regarding the "structural strength" thing, I have also recovered checks that fell off the boolit, because they were not seated correctly. The mouth of these checks was barely hanging onto the shank of the boolit. These 10 thous aluminum checks that fell off didn't have any rifling marks on them. Without the bullet shank to provide the strength, I don't think the check has much structural strength to contain pressure.

Agreed. When you get up around 40,000psi, which is in the neighborhood I’m loading to, neither the cast bullet or the gas check is anywhere close to enough to seal and hold by itself.

[Larry Gibson]

Agreed. When you get up around 40,000psi, which is in the neighborhood I’m loading to, neither the cast bullet or the gas check is anywhere close to enough to seal and hold by itself.

I'm loading the 30 XCB bullet to 2900 fps with Hornady GCs to 50,000+ psi w/o any problems of "sealing and holding". However, above 3,000 fps it appears the GCs get hot enough in the 31" barrel that the shanks melt with the GC coming off on muzzle exit.

[gloob]

^Thanks. I had considered requesting specifics from you, in my last post. But I didn't want to impose.

This seems to go along with my thoughts that copper > aluminum for the same reason thicker > thinner. Ability to absorb/redistribute more heat.

By the time Larry's check is hot enough to melt off the shank, copper is such a good conductor of heat, the ENTIRE check has reached the melting temp of the boolit alloy. That's what gives the boolit just enough time to make it out the barrel intact. If it weren't for that check, a spot on the side and bearing surface of the boolit would have been cut and melted long ago. A thinner copper check should have reached the melting point earlier. And if thin enough, one spot on the rim (the worst of the spots that develop a leak) would have gotten way hotter even more prematurely, before that heat could be distributed to the rest of the check. Now that jet of exploding gas (and that point on the base of the boolit) isn't being cooled enough to stop the meltdown. The gas jet will melt the boolit like a torch on wax, the surface melting away, first.

Aluminum isn't as good a thermal conductor as copper, and it's way lighter so there's less of it. It's like using a thinner copper check.

[TD1886]

^Thanks. I had considered requesting specifics from you, in my last post. But I didn't want to impose.

This seems to go along with my thoughts that copper > aluminum for the same reason thicker > thinner. Ability to absorb/redistribute more heat.

By the time Larry's check is hot enough to melt off the shank, copper is such a good conductor of heat, the ENTIRE check has reached the melting temp of the boolit alloy. That's what gives the boolit just enough time to make it out the barrel intact. If it weren't for that check, a spot on the side and bearing surface of the boolit would have been cut and melted long ago. A thinner copper check should have reached the melting point earlier. And if thin enough, one spot on the rim (the worst of the spots that develop a leak) would have gotten way hotter even more prematurely, before that heat could be distributed to the rest of the check. Now that jet of exploding gas (and that point on the base of the boolit) isn't being cooled enough to stop the meltdown. The gas jet will melt the boolit like a torch on wax, the surface melting away, first.

Aluminum isn't as good a thermal conductor as copper, and it's way lighter so there's less of it. It's like using a thinner copper check.

Then why doesn't the paper patch on paper patched bullets just burn up? You know the highest percentage of heat on the bullet is from friction. Sometime look up friction welding on the internet. Want more proof? Have a contest to see who can bolt, pump, lever a fired case out of a rifle the fastest. I bet that case isn't even luke warm. Next take any semi auto and fire the same load and try picking the empty up...even 22 rimfires are real hot. Ever had one go down your shirt? Need more proof....make bow fire starter. There's no flame heat there, it's all 100 percent friction heat.

The bullet along with it check are only in the barrel in the nano seconds. This was talked about when some people say firing a harden lead alloy bullet totally anneals it. Not enough time and there is no evidence of the recovered bullet being as soft as if it were annealed when it hits the target, that is in the dirt, wood, etc.

[gloob]

I'm not sure why paper doesn't burn or at least scorch in a spots along the rifling marks (The rifling lines are where I suspect gas leaks to occur). Either it takes longer for that to happen to paper? Or maybe paper is a better gasket material than copper or aluminum, able to maintain a perfect seal the entire length of the barrel?

The reason that the case isn't as hot coming out of a lever rifle is easy. That's because it's in the relatively cooler chamber for a lot longer than the cases flying out of a semiauto. The heat from the case gets transferred to the chamber for as long as it takes for you to work the lever after firing it, versus the few milliseconds the case stays in the chamber in a semiauto.

I have made the observation that the cases fired out of my Glock come out hotter (read are more painful when they go in my shirt) than the ones out of my FN, and that the FN slide gets noticeably hotter than my Glock after firing a couple mags. And if you examine the point where the case gets extracted, the Glock spits them out after about half the slide travel as the FN. So the case is presumably in the chamber for significantly longer, in the FN. I have also noticed that a batch of hot S&B ammo that caused sticky extraction in my Glock was no problem in the FN, presumably for that reason. You really think the cases get heated up from the friction of extraction after the powder just went off at 2000 degrees and 30k+ psi? One of the problems the military has faced with caseless ammo is that the barrel/chambers overheat much faster, without the case to carry away much of that heat.

Regarding boolits getting annealed, I didn't make that claim, and I agree with you. It doesn't sound very realistic to me. Unless maybe you're trying to shoot boolits in a Whisper at 4000 fps. I read that the bullet manufacturers had to develop a jacketed bullet that didn't explode in a spray of molten lead, immediately after exiting the barrel. But in typical boolits at typical pressures and speeds, the boolit isn't in danger of entirely melting. It has too much mass. The surface of the boolit is a different story, due to the poor thermal conductivity of lead.

[Willie T]

I'm loading the 30 XCB bullet to 2900 fps with Hornady GCs to 50,000+ psi w/o any problems of "sealing and holding". However, above 3,000 fps it appears the GCs get hot enough in the 31" barrel that the shanks melt with the GC coming off on muzzle exit.

Interesting hypothesis on why the jackets shed. Those speeds with cast are uncharted water for me.

[TD1886]

I'm not sure why paper doesn't burn or at least scorch in a spots along the rifling marks (The rifling lines are where I suspect gas leaks to occur). Either it takes longer for that to happen to paper? Or maybe paper is a better gasket material than copper or aluminum, able to maintain a perfect seal the entire length of the barrel?

The reason that the case isn't as hot coming out of a lever rifle is easy. That's because it's in the relatively cooler chamber for a lot longer than the cases flying out of a semiauto. The heat from the case gets transferred to the chamber for as long as it takes for you to work the lever after firing it, versus the few milliseconds the case stays in the chamber in a semiauto.

I have made the observation that the cases fired out of my Glock come out hotter (read are more painful when they go in my shirt) than the ones out of my FN, and that the FN slide gets noticeably hotter than my Glock after firing a couple mags. And if you examine the point where the case gets extracted, the Glock spits them out after about half the slide travel as the FN. So the case is presumably in the chamber for significantly longer, in the FN. I have also noticed that a batch of hot S&B ammo that caused sticky extraction in my Glock was no problem in the FN, presumably for that reason. You really think the cases get heated up from the friction of extraction after the powder just went off at 2000 degrees and 30k+ psi? One of the problems the military has faced with caseless ammo is that the barrel/chambers overheat much faster, without the case to carry away much of that heat.

Regarding boolits getting annealed, I didn't make that claim, and I agree with you. It doesn't sound very realistic to me. Unless maybe you're trying to shoot boolits in a Whisper at 4000 fps. I read that the bullet manufacturers had to develop a jacketed bullet that didn't explode in a spray of molten lead, immediately after exiting the barrel. But in typical boolits at typical pressures and speeds, the boolit isn't in danger of entirely melting. It has too much mass. The surface of the boolit is a different story, due to the poor thermal conductivity of lead.

Do you know how a diesel engine works? Do you know why an air compressor gets hot? You never did mention anything about why a bow/drill can start a fire. To answer your question do I really think an ejected cartridge case main heat source is friction, no, I know it is. Thing is you haven't a clue about any of this and are grasping at straws.

Gloob I'm editing to say I'm finished with this area of discussion, but you may have the last word.