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Thread: The real story on Gas Checks

  1. #81
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    Quote Originally Posted by ddeaton View Post
    Has anyone done any post shoot detective work? Recovered boolits from a backstop or shot into gel? It would be cool to see what happens. I am gaining info here to start casting for my 308.
    Yep. I have a perfect .357 w/ GC intact back home. I recovered it from a backstop. I'll post pictures when I get home to CO.

  2. #82
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    Hi geargnasher;

    Are you any relation to my cousin Toothgnasher? (BG)

    >Wow, there's so much I've missed in the old publications. No lube at all, just achieving 100% obturation is all that's needed to stop leading?

    It's not exactly easy to do, but that seems to be all it takes. It's a little easier to follow when you understand that leading is caused by the very hot propellent gas etching micro-droplets of lead from the surface of the bullet. These droplets are of course hotter than blazes, and don't have much trouble wetting out the steel of the bore, especially when slammed against the steel with 40 or 50 thousand PSI. They actually solder to the bore - which explains a lot of how bullet lubes work: Greasy metal is a LOT harder to solder to than clean metal. (But lubes do have other functions: Paraffin wax can prevent leading quite well, but gives very poor accuracy.)

    >I've certainly noticed cleaner targets when using Dacron, and I can increase the velocity of the 311041 unchecked in my 30-30 by at least 200 fps over the "lead point" simply by adding the filler, so I'm convinced the Dacron alone aids obturation significantly, it just never occurred to me to use it with another, compacting filler. I have also noticed that with Dacron, I can go all the way down to just lubing the space above the check and have no leading at very high velocities, and that if I don't I get a shiny-wet bore full of lube that causes flyers every three or four shots and worries me about barrel ringing.

    Most anything that retards the flow of gas around the bullet should help. But granular fillers are the only things I've found to completely prevent the problem. I don't think the pinch of cotton or dacron does a whole lot except to keep the Cream of Wheat from mixing with the gunpowder charge and losing its effect.

    >I was just discussing this a day or two ago with another member who was wondering why bore-riders don't lead the lands since there is no lube on the noses.

    Actually, I've done a lot of formal research in this area. I've tried everything I could think of that might influence the adhesion of lead to steel. Speed of contact (up to several thousand fps) has no effect, nor does pressure of contact (up to ~ 40,000 psi) nor cleanliness (or otherwise) of the steel. I have never been able to obtain any adhesion of lead to steel under any condition that does not involve some melting of the lead. This was my first clue to the true causes of leading, and the real functions of bullet lubes.

    >I'm very much in the camp that argues that lube itself functions at least as much as a stop leak as it does a film lubricant, if not more.

    Frankly, I've wondered about this myself, but the waxes that we use for lubes melt into a water-like consistency at such low temperatures that it doesn't seem likely they could serve as a plug - and efforts to add high temperature fibers or particles are consistent disasters to date - although one test I've wanted to try for years is to melt some Alox / Beeswax lube and stir in some Cream of Wheat. This probably wouldn't feed well through a luber-sizer, but a few bullets lubed by hand could be very informative.

    >I'm also wondering if just a little smidgen of lube on your plain boolits with the dual fillers would improve accuracy?

    One might think so, to judge from a lot of past history and experience with cast bullets. However, my experience has been that while sizing the bullet to reduce the neck diameter and allowing the round to chamber easily causes no problem, any lube added to the bullet invariably results in larger groups and fliers. I have no idea why this is so, but there is no question in my own mind.
    Last edited by Molly; 12-29-2010 at 09:31 PM.
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  3. #83
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    Quote Originally Posted by Calamity Jake View Post
    "2. That it prevents the super-hot sand-blasting effect of the powder gasses from melting the lead base of the bullet, which in turn leaves lead in the bore..."

    The hot gasses are not in contact with the base long enough to melt it.

    I did an experiment not long ago with a cutting torch(1800+°), I applied this heat to the base of a 30 cal WW boolet with someone using a stop watch, it took aprox. 2 seconds to show signs of melting on the base.
    One thing that needs to be considered is sublimation. I know sublimation is not something most people think about on a daily bases, but one common occurrence that most can personally related to is the dark tint that can form on incandescent lightbulbs as they age. That dark tint is caused from sublimation of the tungsten filament, and it's "reverse" sublimation (sometimes referred to as deposition) onto the cooler glass bulb. No melting is involved.

    Is sublimation an issue with leaden bullets and a way barrel leading can form? No clue. But it's certainly a possibility, particularly for undersized non-jacketeds that have hot gas flowing past them.

  4. #84
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    Sublimation is a good word that explains what we have stated here many times before. That is why boolits need to fit to a T. ... felix
    felix

  5. #85
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    Quote Originally Posted by felix View Post
    Sublimation is a good word that explains what we have stated here many times before. That is why boolits need to fit to a T. ... felix
    Sublimation is also a good word for an exceedingly slow process. It is the word used to describe the gradual evaporation of solid ice and snow from your steps over a period of weeks in sub-zero temperatures.

    Does anyone really beleive that lead (which is far less volatile than ice and snow) really sublimates at a rate significant enough to be detected during the firing of a cartridge?

    To repeat my earlier post above: Leading is caused by microscopic droplets etched from the surface (especialy edges) of a cast bullet, and blasted against the steel bore of the gun. Anyone who believes otherwise is invited to try to get lead to stick to steel under ANY circumstances or conditions that do not involve melting of the lead. I have done some serious research into the matter. Contact speed (up to several thousand feet per second) will not result in lead adhesion to steel. Contact pressure (up to ~ 40,000psi) will not result in lead adhesion to steel. Nothing I have found will result in lead adhesion to steel except melting of the lead, which then solders itself to the steel if it is sufficiently clean. If the steel is dirty or greasy, temperatures must be considerably higher before lead adhesion will occur. (Does this give anyone any hints about how bullet lubes prevent leading?)
    Last edited by Molly; 12-30-2010 at 08:58 PM.
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  6. #86
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    Molly, your theory also explains why lead adheres to the sprue plate of a mould that has not been lubed with bull plate or some other type of lubricant.

  7. #87
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    Quote Originally Posted by Molly View Post
    Sublimation is also a good word for an exceedingly slow process. It is the word used to describe the gradual evaporation of solid ice and snow from your steps over a period of weeks in sub-zero temperatures.
    I'm not at all attempting to contradict your take on what causes barrel leading, but let me just say your understanding of sublimation is woefully inadequate. I'll stop here, but if it was as you describe, it would make general aviation much easier.

    Sorry to ruffle any feathers. I happened to come across this thread, and thought I'd add an additional consideration.

  8. #88
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    Yeah, Molly, it's amazing that sublimation can occur at very cold temperatures. Where does the energy come from to do so? Who says it has to be heat? Cannot it be wave energy? Then, what about 4000F heat? Enough energy there to do a number on a lead compound/alloy? Think about what is going on, please. Research it. You are a smart guy, and a good communicator as well. Let's try and not get hung up on word meanings, but by all means pay attention to concepts. Granted, sublimation might be a word with a very specific meaning which is being misused here. 'Bout like the meaning of the dictionary meaning of SEE versus the way we have been using it. ... felix
    Last edited by felix; 12-31-2010 at 10:49 AM.
    felix

  9. #89
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    Quote Originally Posted by felix View Post
    Yeah, Molly, it's amazing that sublimation can occur at very cold temperatures. Where does the energy come from to do so? Who says it has to be heat? Cannot it be wave energy? Then, what about 4000F heat? Enough energy there to do a number on a lead compound/alloy? Think about what is going on, please. Research it. You are a smart guy, and a good communicator as well. Let's try and not get hung up on word meanings, but by all means pay attention to concepts. Granted, sublimation might be a word with a very specific meaning which is being misused here. 'Bout like the meaning of the dictionary meaning of SEE versus the way we have been using it. ... felix
    You know Felix, I was sincere when I made my post above, but I find I have been mistaken. Sublimation is defined as the transition of a solid to a gas without an intermediate liquid state. The example I was given in school (many MANY years ago) was the sublimation of ice into vapor at sub-freezing temperatures, with the necessary energy coming from wind and winter sunshine. But that's only an example. There is nothing in the definition I was given that requires the transition to occur at low temperatures.

    I HATE being ignorant. So I did a web search on lead sublimation, and received a real education. Lead not only sublimates, the process can be sufficiently rapid that it is used for the commmercial production of lead pigments. (Or was used: Lead based paint pigments aren't real popular now.)

    I still do not believe that sublimation is at all likely to play a role in barrel leading, but I need to retract my earlier comments, and apologize for them. I also need to render thanks for being corrected. I have no better friend than someone who teaches me. Thank you sir, for the lesson. I am in your debt.
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  10. #90
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    Molly, absolutely zero debt about anything, and definitely no apologies needed for learning from others via any kind of media. Effort expended for learning is the minimum payment paid. Learning is a never ending quest one way or another, consciously or otherwise. We ALL are ignorant of facts, and that's saying the least because we are not the Author of any fact. We can only observe a phenomenon and use an evolving language (i.e., math, symbols) to visualize that phenomenon. ... felix
    felix

  11. #91
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    Too deep for me. I just hate having to remove lead from a gun after the Boolit has left.
    It ought to take it's trash with it.

  12. #92
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    If I had to go into debt for every time I learned something here, even just from felix, I'd be a broke man.

    Sublimation is really a neat phenomenon. If you want to spend a little more time in this realm, you may find triple-points interesting, or look up carburetor icing. (more than one new pilot has had a really bad day from carburetor icing, which is a potential threat even at up to 70F).

    Quote Originally Posted by mold maker View Post
    It ought to take it's trash with it.
    Maybe we could get some legislation passed that will whip those Pb atoms into shape.

  13. #93
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    Quote Originally Posted by mold maker View Post
    Too deep for me. I just hate having to remove lead from a gun after the Boolit has left. It ought to take it's trash with it.
    Moldmaker, that particular problem was solved quite a while back. All it takes is a pinch of cereal under the bullet ... and a pinch of cotton to hold the cereal in place and keep it from mixing with the powder. My experience has been with dry Cream of Wheat granules, but others have reported success with Grex, the polyethylene granules used in shotgun shell loads.

    There are extensive write-ups elsewhere on the forum if you want more details, but the short version is that it will not only prevent leading, it will also remove every trace of leading you might already have in the bore, and it only takes a few shots to do it. Feel free to PM me if you want.
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  14. #94
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    Quote Originally Posted by felix View Post
    Molly, absolutely zero debt about anything, and definitely no apologies needed for learning from others via any kind of media. Effort expended for learning is the minimum payment paid. Learning is a never ending quest one way or another, consciously or otherwise. We ALL are ignorant of facts, and that's saying the least because we are not the Author of any fact. We can only observe a phenomenon and use an evolving language (i.e., math, symbols) to visualize that phenomenon. ... felix
    WOW! What a statement. This should be required reading [and understanding] by everyone.

    Larry

  15. #95
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    Quote Originally Posted by largom View Post
    WOW! What a statement. This should be required reading [and understanding] by everyone.

    Larry
    Yeah, he's pretty good!

    Guys -- I'm getting a real education as well, and I thank you. Had no idea I'd start something with so rich of wealth of information over such a simplistic question over the little copper cups that go on SOME of our boolit designs!


    At the risk of hi-jacking my own thread (which I think is perfectly legal, actually ), I'm curious how the old trick of wrapping bullets with teflon plumber's tape fits in with this theory of escaping leading, especially as explained by Molly? (I'm theorizing that it would be an alternative to fillers in the application Molly has described, as the teflon tape would protect the lead from the hot gasses??)

    (Yet another twist to the quest...)

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  16. #96
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    I don't know about the theory of using teflon tape, but I know a couple of people who tried it and soon abandoned it. For whatever reason, they got much worse leading than with untreated bullets.

    Hope this helps.

    Fred

  17. #97
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    Quote Originally Posted by MakeMineA10mm View Post
    At the risk of hi-jacking my own thread (which I think is perfectly legal, actually ), I'm curious how the old trick of wrapping bullets with teflon plumber's tape fits in with this theory of escaping leading, especially as explained by Molly? (I'm theorizing that it would be an alternative to fillers in the application Molly has described, as the teflon tape would protect the lead from the hot gasses??)
    (Yet another twist to the quest...)
    FWIW, I tried the teflon tape idea a very long time ago, but never had any success with it. I'm not sure why, but PERHAPS it was because the tape is so fragile, and would be blown away by early gas. BTW, don't bother to try patching with aluminum foil either. That stuff is THIN, and it takes a lot of wraps to build bullet diameter. And when you've done all that, it doesn't shoot worth a darn anyhow.

    In the context of eleminating leading, it is noteworthy that PAPER patched bullets don't require a gas check, even when loaded to magnum velocities. Properly applied and loaded, they will shoot very well in rounds like the 300 magnums without producing a trace of leading. The explanation (it seems to me) is that paper does not melt, nor does the flame penetrate it to reach the bullet. It is rather surprising at first examination that the paper isn't instantly consumed by the propellent gas, but it isn't. So the gas never gets a chance to etch the bullet, and leading simply doesn't occur.

    HTH
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  18. #98
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    Yes, that helps reference the teflon tape. Sounds like more research might be useful. I recall the article I read about (maybe 20 years ago), said something like having to wrap it according to the direction of twist of the rifling, just as with paper-patched boolits.

    As far as paper-patched goes, I had a friend who was an engineer at a paper-label manufacturing plant, and he told me that paper is a very good metal polisher, as all the drums on the machines that ran the paper through became polished like chrome after they ran for a couple months. Made us conjecture whether you'd ever have to clean a barrel fired with paper-patched bullets!

    One last curiosity to set your minds to: It is interesting that the paper-patch is so successful, but when half-jacket bullets (which are really just extra-long gas-checks) are pushed too hard, they lead. I've seen this blamed on the extremely soft, pure-lead core, which just barely sets against the barrel at the joint of core and "jacket" with the writer saying that the nose slumped under too hot a load and put even more lead in contact with the bore, which resulted in leading. BUT you all have very accurately explained how it's gas-action, not lead "rubbing" (for lack of a better word... So, what's going on with those half-jackets??
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  19. #99
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    Quote Originally Posted by MakeMineA10mm View Post
    ... One last curiosity to set your minds to: It is interesting that the paper-patch is so successful, but when half-jacket bullets (which are really just extra-long gas-checks) are pushed too hard, they lead. I've seen this blamed on the extremely soft, pure-lead core, which just barely sets against the barrel at the joint of core and "jacket" with the writer saying that the nose slumped under too hot a load and put even more lead in contact with the bore, which resulted in leading. BUT you all have very accurately explained how it's gas-action, not lead "rubbing" (for lack of a better word... So, what's going on with those half-jackets??
    Well, I'll take a crack at it. Without examining the exact loads and results, I can speculate that the slumping with hot loads (which DOES occur) brings lead out to the surface of the bore. The half jacket is indeed a 'super gas check', but gas leaks around gas checks all the time. I can detail the process for you, but not at this time. The pertinent fact is that they DO leak gas past the base of the bullet. As pressures go up, so does the leakage. Not only that, but hotter loads actually wear away the side of the land engraving, producing an engraving that is wider than the lands that made them. The extra width is simply a sort of drainage tube that channels propellant gas along the side of the bullet, up to the front. If the lead has slumped, it simply becomes feed for a molten metallic spray of lead onto the bore, with substantial leading occurring.

    Paper patching, on the other hand, generally involves bullets considerably harder than pure lead, and much less succeptable to slumping. Also, the paper does not wear like hard lead and even copper will do, and the gas leakage is thus much reduced.

    Some folks have argued with me about this engraving enlargement, but all you have to do is recover a few high-power bullets from the backstop and compare the width of their rifling to the rifling of a bullet you used to slug the bore. It's easy to do, and the different groove widths will leave no doubt in your mind.
    Last edited by Molly; 01-02-2011 at 02:10 AM.
    Regards,

    Molly

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  20. #100
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    Great answer, well explained. Understand it the way you described it, perfectly. Thanks!!
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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check