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Thread: The real story on Gas Checks

  1. #1
    Boolit Master


    MakeMineA10mm's Avatar
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    The real story on Gas Checks

    OK, we've had some good discussions about esoteric casting topics, so here's another...

    How is it that a Gas Check really works?

    I've heard -

    1. That it scrapes the lead away that is laid down in the barrel by the front portion of the bullet's passing. (A second similar argument is that it scrapes away lead left in the bore from previous shots...)

    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...

    And, while this isn't a theory - I've also heard that it is permissable to use lead bullets with gas checks in firearms that otherwise aren't supposed to see bare lead, such as the M-1 Carbine or Old-Model Ruger 44 Carbine. Any input on that?
    (And, if you do, and say that it does allow this, please explain why/how?)

  2. #2
    Boolit Master
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    The gas check increases the shear strength of the alloy so can allow higher pressure than the alloy alone. It acts as a drive gear, geared to the land/groove of the barrel and geared to the boolit in reverse, inside the check.
    I think it has little to do with sealing the gas, pressure takes care of that. In fact I think a gas check at pressure below or just barely adaquit of what is needed for obturation may prevent a good seal. Depending on how high the pressure is the base is what will obturate to make a seal. The higher the pressure the more length of the bullet will obturate. If pressure is not high enough to obturate past the check you may loose the seal. Most leading problems in revolvers is not from too soft a boolit as many think but just the opposite they are too hard for the pressure used. Read Dave Scovilles book loading the peacmaker for some good info on that. What the gas check is doing is making a harder boolit from a softer one.
    With a given hardness of alloy a PB boolit can shoot quite well up to a limit in pressure after that limit it needs a gas check and after that limit it need a harder alloy and after that limit it needs a FLGC.
    About your last question I remember when the desert eagle gas operated 44 mag semi auto came out. In their operator manual they said it could be used with cast boolits but only with gas check. I think now they say no cast, why? I have used them and Garrands, and carbines with nothing but cast with no problems with lead build up in the gas systam. Lotsa folks here doing that.
    BIC/BS
    Last edited by Bullshop; 12-08-2008 at 02:57 AM.

  3. #3
    Banned 45 2.1's Avatar
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    The gas check increases the shear strength of the alloy so can allow higher pressure than the alloy alone. It acts as a drive gear, geared to the land/groove of the barrel and geared to the boolit in reverse, inside the check.
    I think it has little to do with sealing the gas, pressure takes care of that. In fact I think a gas check at pressure below or just barely adaquit of what is needed for obturation may prevent a good seal. Depending on how high the pressure is the base is what will obturate to make a seal. The higher the pressure the more length of the bullet will obturate. If pressure is not high enough to obturate past the check you may loose the seal. Most leading problems in revolvers is not from too soft a boolit as many think but just the opposite they are too hard for the pressure used. What the gas check is doing is making a harder boolit from a softer one. In addition to the above, it keeps most of the heat/flame off of the boolit. Filler can do the same thing.

    With a given hardness of alloy a PB boolit can shoot quite well up to a limit in pressure after that limit it needs a gas check and after that limit it need a harder alloy and after that limit it needs a FLGC.
    Maybe so, maybe not. Filler and freechecs can do the same thing to velocities much higher than you think are possible.

  4. #4
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    I'll keep my opinion to myself for now and see what theories are aired. Thia might make a sticky!

  5. #5
    Boolit Master


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    Now, here is my theory and it pretty much is in line with everything posted so far, but I am going to add that with my home grown gas checks, they are formed out of very soft, 16 thou thick aluminum which allows them to obturate slightly as well as the alloy, providing somewhat of a seal. I am in total agreement with Bullshop, a factory gas check will not seal much.

    Best wishes from the Boer Ranch,

    Joe
    WWG1WGA


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  6. #6
    Boolit Master

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    "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.
    Calamity Jake

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    Shoot straight, keepem in the ten ring.

  7. #7
    Boolit Master ddeaton's Avatar
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    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.

  8. #8
    Boolit Master

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    I have shot thousands of gas check boolits through a 30 carbine with no ill effects---dale

  9. #9
    Boolit Master on Heavens Range
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    Powder should be shot at 3600-F for at least a micro-micro second. Low pressure loads prolly will get to 1800-F like was suggested, unless the powder formulation promotes a faster heat rise to make more heat. Powders needs a pre-determined heat or pressure (which is converted into heat) to burn itself properly. Yes, powder granules will be pushed into the boolit base with ease on a naked boolit, and the base will be forced into a concave pattern once the boolit/bullet is moving. ... felix
    Last edited by felix; 12-08-2008 at 11:28 AM.
    felix

  10. #10
    Boolit Master
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    Well I always felt the name says it all- gas CHECK. It checks, i.e. regulates, the flow of gas to the bullet. (Plasma I suppose, not gas). It's a harder metal than the bullet itself. While I would not have the audacity to disagree with some of the guys here smarter than I, I would question anyone saying that it is to protect the base of the bullet. I've shot many thousands of USGI M2 jacketed bullets with exposed lead core bases of pure lead. That didn't melt even with a full power rifle load. Rather, I think the check is arresting blow by gas. Even if the bullet obdurates properly to the bore, it is still a soft material and that high pressure gas can and does etch its way by the base of the bullet and spalls/etches/cuts/blasts lead off whatever you call it on its way by, causing leading. The gas check, being harder, isn't as prone to the gas blasting by. Same thing for fillers; a large quantity, relatively speaking, of a substance between the bullet and plasma keeps etching/blow by down.

    Just my take.

  11. #11
    Boolit Master on Heavens Range
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    Absolutely correct. ... felix
    felix

  12. #12
    Boolit Grand Master

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    I agree that the heat is applied for too short a time melt a bare lead base as has already been stated. A boolit is only in the barrel for approximately 0.001 of a second for 20" barrel at 1500 FPS.

    Hot gases leaking by the sharp edge of the base erode small bits of lead which can be melted/vapourized then redeposited as leading.

    Some of my first small bore (.30 cal) cast boolit shooting was with the Lyman 311041 in a .308. I lived in a remote area and didn't have gas checks so loaded without them not ever having had problems with PB boolits in .45-70 Marlin and Siamese Mauser with "J" bullet loads under PB cast boolits.

    Well, to my surprise I had .30 cal boolits going sideways through the paper at 50 yards. I dug some out of snow and found that there were literally no lube grooves left and the sides of the boolits were smooth and rounded. This was with a load of IMR 3031 to Lyman load data. I tried lower powder charge but no real improvement. Turns out a neighbour had a box of .30 cal gas checks and gave them to me. Problem solved. Same boolits ACWW with and without gas checks.

    In the end I went to IMR 4227 and somewhat lower pressures and velocities with very good results.

    In my .44 mag if I push the pressure envelope with PB boolits I find I get gas cutting. Worse with groove size or slightly under groove size boolits but even happens with oversize boolits, just right at the edge of the base and a little ways along the shank.

    There is a large pressure drop as the gas leaks around an edge and especially if there is room to expand after the edge. I believe one of the functions of a gas check is to provide that initial pressure drop and a surface that is more erosion resistant to the gas. What I am saying is that it doesn't seal perfectly, it just helps to reduce leakage enough to get the boolit out of the barrel.

    Gas checks may also help to rotate the boolit too as some claim but I suspect if true only to a minor degree as the contact area is extremely small. Also, some people claim they have gas checks fall off boolits after the leave the muzzle. If so they can't possibly help rotate the boolit.

    Just a couple of thoughts.

    Longbow

  13. #13
    Boolit Master
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    When should a gas check be used then, if ever? What material should it be made of? Should it be sized the same as the bullet, or bigger, or smaller?

  14. #14
    Boolit Master

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    I will make a comment I dont rememberof digging out any boolits with the gas check attached. do any of you? rick

  15. #15
    Boolit Grand Master


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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.
    Your experiment is valid in a none presurized situation... You need to duplicate the HEAT plus PRESSURE that occurs inside a barrel.
    Last edited by missionary5155; 12-09-2008 at 06:05 AM. Reason: Spelling

  16. #16
    Boolit Grand Master


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    Recovered Gaschecks... I have recovered gas checks still attached to Lee 155 .314 fired from my Chicom SKS fired into a soft sand burn at no more than 50 yards I had on my property yearas ago in West Indiana. All that I learned from them was I could reuse them after opening the mouth a bit.

  17. #17
    Boolit Master
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    Couple of thoughts. First, it seems to me that a GC needs to be sized to the same size as the boolit. Larger, and it presents issues with stretching the neck larger than t he boolit thus inducing a problem with neck tension. Of course there is some spring back depending on the condition of the neck. Smaller and, well,... why would you want to?

    My other thought is that it is possible for the boolit and check to rotate at different speeds. Even though a check is 'crimped' on, the crimp is radial, not length wise. Push a boolit hard enough and it will strip, not so I think for the hard GC. Nowhere is it written that they have to turn as one.

  18. #18
    Boolit Master Morgan Astorbilt's Avatar
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    I'm sure gas checks "upset" to conform to the bore. I remember seeing somewhere, maybe an old Lyman reloading manual, a photo of a jacketed bullet shot out of a barrel with only a chamber, and the base mushroomed out. A fired bullet, is subject to two inertial forces. When being fired, the base starts to move before the nose, and when if hitting an object, (steel plate), the nose starts to stop before the base.
    Morgan

  19. #19
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    In "The Bullets Flight", I think, it was quoted in Precision Shooting, Dr. Mann wrote of a 30-06 that had blown up due to an excessive charge. The cartridge shot in it was a 270. In order for the action to blow, the pressure had to expand the jacket bullet to groove diameter not just vent past the .031" of gap that existed. I am in the checks expand under pressure camp. I did smear some LY black moly under a check and fire 3 in a 44 once. Recover showed some lube left on them though not as much as I put. I do not consider that scientific by any means but it did teach me the bullet was not in the bore for very long. Gianni
    [The Montana Gianni] Front sight and squeeze

  20. #20
    Boolit Master
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    I'm going to suggest that the gas check does two things, scrapes the bore and adds a bit of help to alloys that may not be up to the presures they are being fired at!

    I have seen unburned powder stuck to the base of boolits and think that, because powder burns progressively and does not explode like BP, many time it is it's own filler.

    This will be with rifle cartridges of course. Most pistol rounds will use smaller amounts of much faster powders and may see these issues come to light much faster than in a rifle.

    How often have we seen the the leading question posted and seen these three suggestions made:
    Check hardness, check boolit diameter, and switch to a slower powder?

    This is a good thread and I think we'll see some great ideas posted, mine are simply "food for thought"!

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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