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Thread: What and why is a gas checked bullet?

  1. #1
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    What and why is a gas checked bullet?

    I keep hearing that if you want to run a lead bullet really fast you need it to be gas checked because this makes it more accurate or prevents leading or something. Is that a thing?

    I'm interested in loading up some stout .357s for my Ruger Security Six.

    Do you need to seat the gas check yourself? Do you buy bullets that have a GC pre attached? Is it strictly a revolver thing or would it be a good idea for a high pressure semi auto like a 10mm? Should you gas check a coated bullet?

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  2. #2
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    First, you have to quantify "really fast". If you're going to be pushing ~158-grain bullets from your Security Six with a 4"-6" barrel, and you're using bullets that fit the throats, you can probably live without them. My Old Model Super Blackhawk shoots standard commercial cast bullets at >1300 fps with little-to-no leading.

    Gas checks are small copper cups that fit on the base of a cast bullet that has been designed to use them. They're attached to the base of the bullet as you size that bullet. They look like these. They're not something that you can add to the base of a bullet that you buy. It's been over 30 years since I cast my own bullets, so something may well have been developed in the meantime.

    You can buy cast bullets with gas checks attached, but the ones I've seen cost as much as or more than JHPs because they're hand-cast rather than mass-produced.

  3. #3
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    Quote Originally Posted by revchuck38 View Post
    First, you have to quantify "really fast". If you're going to be pushing ~158-grain bullets from your Security Six with a 4"-6" barrel, and you're using bullets that fit the throats, you can probably live without them. My Old Model Super Blackhawk shoots standard commercial cast bullets at >1300 fps with little-to-no leading.

    Gas checks are small copper cups that fit on the base of a cast bullet that has been designed to use them. They're attached to the base of the bullet as you size that bullet. They look like these. They're not something that you can add to the base of a bullet that you buy. It's been over 30 years since I cast my own bullets, so something may well have been developed in the meantime.

    You can buy cast bullets with gas checks attached, but the ones I've seen cost as much as or more than JHPs because they're hand-cast rather than mass-produced.
    What does it mean for the bullets to fit the throats? Does that have to do with the part that is immediately past the barrel/cylinder gap or is it some part of the cylinder?

    Again, apologies but this is really not my lane at the moment. I don't expect to be running a 158grainer much past 1300fps (I don't think I have the correct powder to do that right now anyways)

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  4. #4
    Site Supporter gringop's Avatar
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    I am not an expert at loading high velocity lead bullets but here is my take.

    The big issue with driving lead bullets at high speeds is that the higher gas pressures and temps erode the rear of the lead bullets and also can escape around the sides of the bullet as it travels down the bore. This can disrupt the bullet affecting accuracy and increasing leading of the bore.

    The copper gas check adds a barrier to the gases eroding the rear and and sides of the lead bullet allowing higher velocities without the issues that come with using only lead bullets. Note that soft lead bullets show the same issues at lower velocities, ie. increased bore leading and deformed bullets compared to hard cast bullets.

    In the past, there was considerable cost savings using gas checked hardcast bullets vs fully jacketed bullets, not sure if it still is.

    These days, powder coated lead bullets allow higher pressure loads than plain hardcast, this probably has cut into the market that used to use gas checks.

    Gringop
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  5. #5
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    Quote Originally Posted by 45dotACP View Post
    What does it mean for the bullets to fit the throats? Does that have to do with the part that is immediately past the barrel/cylinder gap or is it some part of the cylinder?

    Again, apologies but this is really not my lane at the moment. I don't expect to be running a 158grainer much past 1300fps (I don't think I have the correct powder to do that right now anyways)

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    The throat is the part of the cylinder right in front of the chamber, where the bullet passes through before it hits the forcing cone. The way you check for bullet fit is to drop the bullet into the chamber. Ideally, it'll stick in the throat and be able to be pushed through with moderate pressure using something like a pencil. If it's tough to push through, it's not ideal but it's okay. If it falls right through, it's too small and will lead. The standard size for .38/.357 is .358", and it usually works.

    If you haven't worked with lead bullets before, I'd recommend going with coated bullets rather than lubed. Coating provides a layer between you and the lead, smokes less on firing, and is less messy when loading and also when cleaning brass and the revolver itself. I haven't noticed any difference in terms of leading or accuracy.

  6. #6
    I think gas checks might make more sense if you are casting your own.

    My father and I had a casting business. It was a business because we sold them, but I was just hand casting most of the bullets, and I hope I have saved enough money that I will never need to cast my own bullets. Anyway, I gas checked a buttload of bullets, and in today's labor market I would think paying someone to gas check bullets you are buying probably doesn't math, because a machine can make a JHP with less labor $ content.

    OTOH if you are casting bullets for fun and want to crank em up, gas checks can help. Though I have little experience shooting them, because if I went through the trouble to gas check a bullet it better have been for a customer order.

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    Last edited by mmc45414; 12-24-2022 at 06:32 PM.

  7. #7
    Site Supporter Trooper224's Avatar
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    Powder/Polymer coating is a better mousetrap compared to gas checks. As already stated, they aren't as messy or smokey compared to plain lead bullets, gas checked or otherwise. Most of the smoke and grunge comes from the bullet lube, something that's unnecessary with coated bullets. Properly sizing the bullet to the barrel is really the key with either one.
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  8. #8
    Abducted by Aliens Borderland's Avatar
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    Quote Originally Posted by revchuck38 View Post
    The throat is the part of the cylinder right in front of the chamber, where the bullet passes through before it hits the forcing cone. The way you check for bullet fit is to drop the bullet into the chamber. Ideally, it'll stick in the throat and be able to be pushed through with moderate pressure using something like a pencil. If it's tough to push through, it's not ideal but it's okay. If it falls right through, it's too small and will lead. The standard size for .38/.357 is .358", and it usually works.

    If you haven't worked with lead bullets before, I'd recommend going with coated bullets rather than lubed. Coating provides a layer between you and the lead, smokes less on firing, and is less messy when loading and also when cleaning brass and the revolver itself. I haven't noticed any difference in terms of leading or accuracy.
    That's my take on it. I hear old timers talk about using lead bullets for 30-30. They use gas checks under those because the velocity is above 1500 fps or in that neighbor hood. Most pistol and revolver loads don't require those as the velocity is below 1500 fps. Rifle bullets usually start around 2000 fps. I've never used them opting for jacketed bullets when the velocity creeps up beyond that cut-off. i had two P-220's that leaded barrels because the barrel was oversized by .001". Gas was creeping past the the .452 lead bullets. I sold them both because of that. Big mistake.
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  9. #9
    Hillbilly Elitist Malamute's Avatar
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    Im not up to speed on how coating bullets works for cast rifle bullets, but gas checks are pretty common for most rifle cast loads. Looking in the Lyman cast bullet manual, many rifle bullets seem to fall in the 1800-2300 fps top velocity bracket as to best accuracy, some may do better. If I were building moderate to full power cast bullet loads for use in a 357 pistol and carbine id use a gas check design bullet.

    Sizing the bullet to your individual gun is part of the formula for success with cast. In revolvers, the chamber throats matter, in most other stuff, the groove diameter does. Theres no guarantee what any individual gun will measure for groove diameter in the case of auto pistols or rifles, the only way to know for certain is slug the bore and measure the slug. Forums are full of people asking "whats the groove diameter of my XYZ gun?" Nobody knows until that individual gun is checked. 100 or 1000 other guns may measure the ideal spec, but any other single gun may or may not. Add in that rifles in pistol caliber are often showing larger allowable groove diameter specs in the SAAMI drawings for the same chambering as a pistol.
    Last edited by Malamute; 12-24-2022 at 07:54 PM.
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  10. #10
    The Nostomaniac 03RN's Avatar
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    I only get a tiny bit of leading with .357 handguns shooting hard cast bullets under 1300fps. I get zero leading in my m92 pushing hard cast bullets up to 1800fps.

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