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Thread: The real story on Gas Checks

  1. #21
    Boolit Grand Master
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    My opinion is that's it's a combination of boolit base protection and a scraping action. I did an experiment a while back with some "non conventional" boolit lube that heavily leaded the revolver barrel to the point where 25 yard groups were 8". I then fired a cylinder full of gas checked boolits, and not only was the leading removed, the groups shrank to 1.5".
    You cannot discover new oceans unless you have the courage to lose sight of the shore

  2. #22
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    i agree with the scraping action theroy. A gas checked bullet will clean out leading as well as a jacketed bullet will. I personaly think its a combination of that and when the base bumps up (I hate that terminology) it creates a much better seal then any lead alloy can to resist gasses from leaking by. I also think it gives a perfect base for gases to press against in a consistant manner and aids in accuracy because of this.

  3. #23
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    I dont know bout the boolit and check not being in sink. If that were so the land cuts in the boolit would show wider than in the check You see that on revolver boolits on the forward band where the boolit didnt begin to turn until more of its bearing surface was engauged. You never see it at the base. On the base band the land cuts will be the same as on the check.
    Once that boolit is in the rifling the check is crimped and is geared to the boolit. Dont matter what it does after it leaves the barrel only when its in there. It can fall away because it already did its job.
    Same thing with PP, it falls away once out the barrel but it surnuf was driving the boolit.
    You will find land cuts on the boolit for the length of the papar bearing surface.
    If that check is not geared to the boolit when under pressure then what is it that holds a soft boolit that is fired beyond its pressure limit without a check. If you fire a pure lead boolit with a check way beyond a pressure that pure lead can handle, kinda like the first factory 44 mag ammo it shoots OK because why? Its not because the check is cleaning the barrel its because its holding the boolit in the rifling. Yea yea yea it does other things too like protect the base and yata yata yata but it has to offer machanicle advantage to holding on the rifling. It has to do more than just check gas. I am gonna stick with the drive gear idea.
    BIC/BS

  4. #24
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    So all of this being said what is advantage of annealing (sp) gas checks. I have read hear of putting them in a pipe nipple and putting in you a wood stove for a while. are many of you using annealed checks. Does making the check softer give it a better hold on the bullet or a better bite in the rifling.

    Kirb

  5. #25
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    It eliminates spring back.
    sometimes, when the check is sized on, it can open up. Annealing allows the check to be sized on, and stay there.

  6. #26
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    I'm pretty much in agreement with most of what's been said. I'll add that I've recovered a fair number of boolits with the check still on the base, 6.5x55 , .357 and .44 mag, both from berms and animals. However, not all of them in any given session retained the checks.

    I'll also add that checks can limit the lead build up on the face of revolver cylinders significantly. Especially true in revolters like the Redhawks with oversize chamber throats, (.432). I've had Redhawks in which the cylinder would bind after less than 100 rounds of naked cast, but could spit out thousands of checked bullets without binding. So some base protection occurs, at least in revolters.

    IMO this is another one of those areas in which individual firearms can be a law unto themselves, so many varibles are in play that it's tough to make any kind of blanket judgement as to what is occurring in any individual situation.

    My preference in something like a full house .44 mag load is a tight check on a stout rear drive band with a lube groove just forward of the crimped on check. It just seems like that arrangement can pass down the barrel thousands of times with consistent accuracy, no barrel leading and no cylinder binding.

    BD

  7. #27
    Cast Boolits Founder/B.O.B.

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    IMO this is another one of those areas in which individual firearms can be a law unto themselves, so many varibles are in play that it's tough to make any kind of blanket judgement as to what is occurring in any individual situation.
    I submit ALL firearms are individuals and respond accordingly to the individual cartridges fired.
    Manufacturing tolerances are such that it cannot be otherwise.
    Boolits= as God laid it into the soil,,grand old Galena,the Silver Stream graciously hand poured into molds for our consumption.

    Bullets= Machine made utilizing Full Length Gas Checks as to provide projectiles for the masses.

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  8. #28
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    I don't believe Gas checks are needed for MOST handgun loads. even the 44 mag CAN get by with out one. It's in the hi pressure loads that gas checks come into their own. Hi pressure and NOT hi velocity is the key. I've shot 1000's of them in lots of guns trying for ultra hi speeds. I have found checks on the base of most bullets when crimp ons were used. Even some lyman non clip on checks stayed on when shooting into some wet pack media. I had a chance to shoot some sick goats with cast bullets and studied the remains for evidence of the effects of shooting them. I can't say there was any thing UN expected in the remains.

  9. #29
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    I love this place! You guys are great.

    TONS of great information here. I'll be re-reading it in the future for sure!

  10. #30
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    Quote Originally Posted by Bullshop View Post
    I dont know bout the boolit and check not being in sink. If that were so the land cuts in the boolit would show wider than in the check You see that on revolver boolits on the forward band where the boolit didnt begin to turn until more of its bearing surface was engauged. You never see it at the base. On the base band the land cuts will be the same as on the check.
    Once that boolit is in the rifling the check is crimped and is geared to the boolit. Dont matter what it does after it leaves the barrel only when its in there. It can fall away because it already did its job.
    Same thing with PP, it falls away once out the barrel but it surnuf was driving the boolit.
    You will find land cuts on the boolit for the length of the papar bearing surface.
    If that check is not geared to the boolit when under pressure then what is it that holds a soft boolit that is fired beyond its pressure limit without a check. If you fire a pure lead boolit with a check way beyond a pressure that pure lead can handle, kinda like the first factory 44 mag ammo it shoots OK because why? Its not because the check is cleaning the barrel its because its holding the boolit in the rifling. Yea yea yea it does other things too like protect the base and yata yata yata but it has to offer machanicle advantage to holding on the rifling. It has to do more than just check gas. I am gonna stick with the drive gear idea.
    BIC/BS
    Have you been reading all of my posts again?
    I have NEVER seen a melted boolit base and I shoot hard cast PB at high pressures where the land marks on the base are land width. Shoot a soft boolit so it doesn't grip the rifling at the base and you need a check.
    The thing was not named right, it should have been called a hard drive band! Of course it will scrape out lead from skidding boolits. When it gears to the lands and grooves, it has no gaps.
    Guess what? Fit a hard cast that doesn't skid and it will ALSO clean out leading.
    I know a lot of you have had poor fitting gas checked boolits that leaded the crap out of your barrels. Also gas cut boolits when gas got past the under size checks and boolits.
    Bullshop, the ONLY thing I disagree with is when a check drops off some boolits and not others. I want it to stay on until the target is hit. If EVERY one dropped into the same pile in front of the muzzle, it would be OK, but they won't. Keep them on the boolit.

  11. #31
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    Maybe I didnt say what I ment. I didnt mean to say it was good if the checks fell off after the boolit leaves the barrel what I ment was that even if they do fall off they were still driving the boolit when they were under pressure in the barrel. If it springs back and is blown off like a paper patch when it exits it has still done its job in the barrel.
    As to accuracy since you cant get them to all fall in the same place like a PP it is best if they stay on.
    BIC/BS

  12. #32
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    All else being equal, it’s a rare firearm indeed that shoots a PB bullet more accurately than a gas checked one. With proper pressures, good barrels etc...equally well yes...but rarely better.

    Gas checked bullets allow increased velocity performance in nearly all rifles and some magnum class handguns... exceptions largely being those designed for black powder where pressures must be held low... well within the strength of a non-checked bullet.

    Largely repeating what others have already said...but since the question was asked, I believe gas checks yield those positive results primarily in 4 ways. Gas checks:

    1. Provide a scraping action to remove lead. This allows some leading to occur as each bullet is fired...the gas check restores the barrel to its pre-fired unleaded condition and prepares the barrel for the next shot.

    2. Eliminate or greatly reduce gas cutting...important in higher pressure loads and in firearms with somewhat undersized cast bullets, large throats, wide spots in the barrel etc. This is accomplished by the greater yield strength and melting temperature of the gas check. Note some gas cutting or leading could still occur as long as it is not enough to overwhelm the scraping action of point 1 or the riflings abillity to grip the bullet.

    3. Provides increased bullet yield or shear strength for the rifling by replacing what would otherwise be lead with a copper alloy. In many cases, this also results in more bearing surface providing additional strength.

    4. Provides a uniform base to the bullet...important as the bullet exits the barrel. Non-uniform bases adversely affect accuracy...always a possibility with PB bullets unless care is used in casting and seating.

    (A contributor to both effects 1 and 2 above may be the “spring back” quality of the check and likely expansion of the check itself that takes place when pressure forces out any air remaining between the check and the shank and obturates the shank itself.) This would enhance the scraping and sealing qualities of the check.

    Gas checks do not accomplish their mission by preventing the melting of the base...far too little time exposure to accomplish this by temperature alone. Exposed lead bases in jacketed bullets fired under high pressure have long ago refuted this theory. It is high velocity gas cutting along the sides of the bullet which erode and destroy the bearing surface. This lead is then condensed in the barrel ahead of the bullet as the pressure and temperature drops.

    What effect(s) comes into play is dependent on the bullet, load (read pressure), firearm, lube, etc.. Low enough pressure in a smooth barrel with a proper fitted boolit with good lube and nothing is to be gained by the check. None of the 4 points above are necessary. However, as pressure goes up, barrel quality goes down, bullet quality and lube deteriorates (to include loss of bullet bearing surface and size), etc. and some or all of the above become important.

    In short, a gas check allows many things to be less than perfect while maintaining acceptable accuracy and higher performance and velocities than we could otherwise achieve without it. In many cases it makes life much easier for the casting novice as it reduces the need for the more extensive testing with bullets, lubes, and loads that would otherwise be required...to say nothing of bore lapping.

  13. #33
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    Gas checks are scrapers and heat shields that extend the useful range of pressure a bullet alloy can work within by strengthening the bullet's base to reduce skidding/stripping and control of lead deposits (scraping). The gas check also controls fusion caused by large amounts of fast burning pistol powder.

    When pressures are high and bullets soft, bullets skid or strip in the rifling.

    When pressures are low and bullets hard there's no obturation to keep gasses from from blowing by the bullets base even if gas checks are used. Lube is lost and friction leaves lead deposits too great for the scraper to control.

    For good loads, pressure and alloy hardness should be coordinated. Using the formula 1422 x BHN will provide the minimum pressure yield point for your alloy. Lyman #2 and WW air cooled alloy are typically BHN 14-15 so starting loads should be selected that develop at least 20K psi to provide a gas seal... obturation. When pressure is increased to the point that the gas check can no longer control the amount of lead being stripped from the bullet maximum velocity for your load combination has been reached.

    To find the bullet hardness desired, divide the working pressure by 1422... 35K psi / 1422 = BHN 24.6 or less.

    Boomer
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  14. #34
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    I never considered a check as a scraper, I have cleaned highly leaded barrels (revolver) with a hard PB boolit.
    I have also leaded barrels with an ill-fitting hard boolit, I use checks to reduce gas cutting at higher pressures.

    There's some good thoughts here guys, keepem coming.
    grit yer teeth an pull the trigger

  15. #35
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    Quote Originally Posted by MTWeatherman View Post
    All else being equal, it’s a rare firearm indeed that shoots a PB bullet more accurately than a gas checked one. With proper pressures, good barrels etc...equally well yes...but rarely better.

    Gas checked bullets allow increased velocity performance in nearly all rifles and some magnum class handguns... exceptions largely being those designed for black powder where pressures must be held low... well within the strength of a non-checked bullet.

    Largely repeating what others have already said...but since the question was asked, I believe gas checks yield those positive results primarily in 4 ways. Gas checks:

    1. Provide a scraping action to remove lead. This allows some leading to occur as each bullet is fired...the gas check restores the barrel to its pre-fired unleaded condition and prepares the barrel for the next shot.

    2. Eliminate or greatly reduce gas cutting...important in higher pressure loads and in firearms with somewhat undersized cast bullets, large throats, wide spots in the barrel etc. This is accomplished by the greater yield strength and melting temperature of the gas check. Note some gas cutting or leading could still occur as long as it is not enough to overwhelm the scraping action of point 1 or the riflings abillity to grip the bullet.

    3. Provides increased bullet yield or shear strength for the rifling by replacing what would otherwise be lead with a copper alloy. In many cases, this also results in more bearing surface providing additional strength.

    4. Provides a uniform base to the bullet...important as the bullet exits the barrel. Non-uniform bases adversely affect accuracy...always a possibility with PB bullets unless care is used in casting and seating.

    (A contributor to both effects 1 and 2 above may be the “spring back” quality of the check and likely expansion of the check itself that takes place when pressure forces out any air remaining between the check and the shank and obturates the shank itself.) This would enhance the scraping and sealing qualities of the check.

    Gas checks do not accomplish their mission by preventing the melting of the base...far too little time exposure to accomplish this by temperature alone. Exposed lead bases in jacketed bullets fired under high pressure have long ago refuted this theory. It is high velocity gas cutting along the sides of the bullet which erode and destroy the bearing surface. This lead is then condensed in the barrel ahead of the bullet as the pressure and temperature drops.

    What effect(s) comes into play is dependent on the bullet, load (read pressure), firearm, lube, etc.. Low enough pressure in a smooth barrel with a proper fitted boolit with good lube and nothing is to be gained by the check. None of the 4 points above are necessary. However, as pressure goes up, barrel quality goes down, bullet quality and lube deteriorates (to include loss of bullet bearing surface and size), etc. and some or all of the above become important.

    In short, a gas check allows many things to be less than perfect while maintaining acceptable accuracy and higher performance and velocities than we could otherwise achieve without it. In many cases it makes life much easier for the casting novice as it reduces the need for the more extensive testing with bullets, lubes, and loads that would otherwise be required...to say nothing of bore lapping.
    You covered every point I would have made. The only thing I would add is it takes a proper fitting GC to get the benefits of a GC. Put one on lopsided or use one that is too small for the bore and all you did is waste your money. There'll be no scraping action with an undersized GC or one where the edge of the GC isn't meeting the lands at least. Instead you'll get a burnishing action that will sort of iron the leading into the barrel. Took me a while to figure that one out on an oversized/worn 8mm barrel.

  16. #36
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    with good bbls i use the g/c to protect the base of the boolit and fill the area in front of it with lube, as the lube will act as a hydraulic seal and should stop the scraping action.
    in other guns i leave the area open so that the check has an area to scrape lead into.
    now is it actually spraping lead into this area, i hope not.
    i would hope i have fit the boolit to the gun well enough. but a lot of the g/c designs move the lube grooves forward and the pressure doesn't seem to hydraulic the lube as well.
    this i think is why your velocities are kept lower with a g/c design not fired with the g/c.
    then it would be with a p/b design.

  17. #37
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    I'm saying it makes for a flat base so as to have even forces pushing on the base of the boolit as it leaves the muzzle. Without it, at too high of pressure, would be just about like shooting out of a barrel with a bad crown.

    Just a guestimation..

    Now that someone mentioned the paper patched boolits...I have never done up any of those but from looking at them, the base of that paper isn't exactly flat looking with that little twist on it. Now I don't have any idea!
    I also have fired many rounds thru my carbine. You get a little lead on the gas piston after a few hundred rounds maybe but no big deal. I also have shot the Ruger Deerfield with numerous cast boolits and haven't seen any buildup of lead after almost 200 rounds. I get more crud from the lube than anything. The carbine is a snap to clean and the Ruger requires a bit of patience.
    Last edited by Newtire; 12-15-2008 at 09:30 PM. Reason: Another thought

  18. #38
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    Just an estimation was about the best statement yet. Its one of those questions like what does bullet lube do? Nobody has the right or wrong answer because nobody really knows the total story. All i know is gas checked bullets are usually easier to get to shoot accurately and i guess thats good enough for me.
    Quote Originally Posted by Newtire View Post
    I'm saying it makes for a flat base so as to have even forces pushing on the base of the boolit as it leaves the muzzle. Without it, at too high of pressure, would be just about like shooting out of a barrel with a bad crown.

    Just a guestimation..

    I also have fired many rounds thru my carbine. You get a little lead on the gas piston after a few hundred rounds maybe but no big deal. I also have shot the Ruger Deerfield with numerous cast boolits and haven't seen any buildup of lead after almost 200 rounds. I get more crud from the lube than anything. The carbine is a snap to clean and the Ruger requires a bit of patience.

  19. #39
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    Quote Originally Posted by Bret4207 View Post
    The only thing I would add is it takes a proper fitting GC to get the benefits of a GC. Put one on lopsided or use one that is too small for the bore and all you did is waste your money. There'll be no scraping action with an undersized GC or one where the edge of the GC isn't meeting the lands at least. Instead you'll get a burnishing action that will sort of iron the leading into the barrel. Took me a while to figure that one out on an oversized/worn 8mm barrel.

    Good point.

    You also indirectly pointed out the two major disadvantages of gas checks...the required investment of time and money.

    Care must be exercised in seating each check squarely on the base...not done correctly and there goes your uniform base and accuracy along with it. Slows production time to much below what a simple resizing and lubrication of a PB would be...and eliminates the simple method of using an unsized bullet with tumble lube..

    Checks require an investment of money in a resizing die to seat and size those checks and those checks are no longer of small cost themselves. They've gone up significantly in price over the past couple of years...now 2 1/2 to 5 cents apiece for most calibers. Though the cost of copper has now fallen to near the levels of 5 years ago, I have yet to see this passed on in the reduction of gas check prices. Cynic that I am...I don't expect to see much reduction either. With Hornady essentially having a monopoly on them (they make Lyman as well and except for the GB Gators, there is no competition), there is no reason to drop prices...no real competition to force them back down.

    So...all is not positive with checks. If a PB boolet fits your needs, makes sense not to use a GC design.

  20. #40
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    I’m on board with most of what has been said already. I just thought that I would submit a few pictures to show what I’ve seen. The first one shows the basses of some 150-grain PB semi-wadcutters. The ones on the right in that first picture were pushed to 1250fps by a warm charge of H-110. The heavy cratering on the bases makes me think that this charge should be used with a GC. The ones on the left show what I get when I push the same boolit with Bullseye or Unique.

    The next two pictures show some recovered .223 slugs. Even at 2600fps, I still find some boolits with the GC still attached, although about 85% of them do come off. The ones that come off almost invariably are found in the target near the spot where the boolit stops. This is true if I am shooting at crumb rubber or game animals. I am pretty sure that my GCs are still attached when they hit the target. Other people with looser fitting checks may have different experiences, but this is what I see with mine.
    Attached Thumbnails Attached Thumbnails BoolitBases.jpg   GCattached2600.jpg   GCoff2100.jpg  
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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