Gas checks?
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Old 09-21-2012, 01:29 AM   #1
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Default Gas checks?

What exactly do they do, I'm new to casting bullets. People have told me they help accuracy while others have said they keep the barrel from leading.one person even told me they keep the back of the bullet from melting while being fired.NO CLUE

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Old 09-21-2012, 01:53 AM   #2
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There are two schools of thought on this;
1. The gas check scrapes the barrel clean after the lead passes through.
2. The gas check prevents the high pressure, hot gasses from contacting the lead and vaporizing small amounts that then stick to the barrel.

Personally, I tend to go with #2. I have seen the small craters left in cast bullet bases that are apparently from the hot gasses.

I use gas checks on VERY high velocity bullets only. Magnum pistols pushed to the limits (1400 fps or higher) and rifles in excess of 2100 fps. I use a plain base 340 gr bullet for my .45-70 that leaves the Guide Gun at 2100 fps. I use a VERY hard alloy of 50% wheel weight and 50% linotype and have ZERO leading problems.

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Old 09-21-2012, 01:59 AM   #3
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Quote:
Originally Posted by reloader97 View Post
What exactly do they do, I'm new to casting bullets. People have told me they help accuracy while others have said they keep the barrel from leading.one person even told me they keep the back of the bullet from melting while being fired.NO CLUE
Hi Reloader. Gas check are only required for higher velocities. I cast with straight wheel weights and keep my velocities to under 1000 FPS, so I don't need gas checks. I do use them on my high velocity stuff, and use much harder lead (lino-type). For more info on gas checks go to youtube and do a search on "gas checks". You'll get a ton of videos about them.

Don <><
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Old 09-21-2012, 07:53 PM   #4
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i kinda buy into both of the thoughts raised by robocop.

my alloy is a little softer than wheelweights, but lubed with liquid alox and sized correctly, i'm good with plain-base bullets to 1300-1400 fps; for rifle, bullets are checked with velocities around 1800 fps. no leading in either case.

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Old 09-21-2012, 08:12 PM   #5
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Eeeek! I've been shooting pure lead without gas checks out of my .308 time for a good cleaning.

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Old 09-21-2012, 09:29 PM   #6
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I shoot linotype in a .22 Jet up to 1,540 average FPS. The LT is 24 BHN I do not use GC and there is no leading. As in all cast bullets they must be the proper size to bore.

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Old 09-21-2012, 10:02 PM   #7
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Yup, i got it.

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Old 09-22-2012, 12:41 PM   #8
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Eeeek! I've been shooting pure lead without gas checks out of my .308 time for a good cleaning.
Shooting PB or pure lead bullet at high velocity is not always an issue when it come to leading,it's when you mix high velocity generally anything over 1400 fps. and high pressure 35 to 40K PSI together that a gas check becomes useful. It's perfectly normal to shoot a PB bullet at 1700 fps. but in a low pressure load like the 45-70 with no leading issues at all.

Leading is a complex issues and can have many causes it can be caused by one thing or several things combine. Bullet fit is the key if the dia. is to small to begin with your going to get leading. Once you have the bullet dia. correct you can build your load based on bullet BHN and how it relates to velocity and pressure your load generates.

Gas check basically have two purposes. One is they allow you to shoot a much softer alloy bullet ie HP or soft flat nose bullets for expansion purposes at a much higher velocity and pressure than the lower BHN bullet could normally withstands. Gas checks also help seal the bore and keep any high pressure gases from taking advantage of any rifling induced defects to the bullets base that can cause gas cutting and then leading.

Aside from all the above gas checks also help with new revolvers with misaligned cylinders or with forcing cones and bores than may have rough factory tooling marks that haven't been polish out from shooting lots of jacketed bullets. They also provide better grip for cast bullets shot in micro-groove barrels that have shallow lands and grooves.

Gas check bullets don't make cast bullets inherently more accurate if that were the case the 38 Spec. wadcutter would have a gas check. There just another option that allows you to shoot cast lead bullet in certain situations that the normal plain base bullet might not preform as well of be the best option for a piratical load or firearm.

I shoot gas check bullets in both handguns and rifles in all action types,different BHN combination and velocity/pressure loads.
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Old 09-22-2012, 11:38 PM   #9
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Originally Posted by res45 View Post
Shooting PB or pure lead bullet at high velocity is not always an issue when it come to leading,it's when you mix high velocity generally anything over 1400 fps. and high pressure 35 to 40K PSI together that a gas check becomes useful. It's perfectly normal to shoot a PB bullet at 1700 fps. but in a low pressure load like the 45-70 with no leading issues at all.

Leading is a complex issues and can have many causes it can be caused by one thing or several things combine. Bullet fit is the key if the dia. is to small to begin with your going to get leading. Once you have the bullet dia. correct you can build your load based on bullet BHN and how it relates to velocity and pressure your load generates.

Gas check basically have two purposes. One is they allow you to shoot a much softer alloy bullet ie HP or soft flat nose bullets for expansion purposes at a much higher velocity and pressure than the lower BHN bullet could normally withstands. Gas checks also help seal the bore and keep any high pressure gases from taking advantage of any rifling induced defects to the bullets base that can cause gas cutting and then leading.

Aside from all the above gas checks also help with new revolvers with misaligned cylinders or with forcing cones and bores than may have rough factory tooling marks that haven't been polish out from shooting lots of jacketed bullets. They also provide better grip for cast bullets shot in micro-groove barrels that have shallow lands and grooves.

Gas check bullets don't make cast bullets inherently more accurate if that were the case the 38 Spec. wadcutter would have a gas check. There just another option that allows you to shoot cast lead bullet in certain situations that the normal plain base bullet might not preform as well of be the best option for a piratical load or firearm.

I shoot gas check bullets in both handguns and rifles in all action types,different BHN combination and velocity/pressure loads.

Excellent explanation. I've been using gas checks in selected loads for almost 50 years.
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Old 09-23-2012, 02:40 PM   #10
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As the others have said, Gas checks are primarily used to prevent "gas cutting", when hot gasses melt the back of the lead bullet, sometimes even cutting channels around the bullet, it they forces past the bullet through the rifling grooves. Google "gas cutting". This minute amount of melted Lead keeps adding inside the barrel, being hard to remove and slowly constructing the barrel, ruining accuracy and leading ultimately to higher pressures and a very dangerous situation in extreme cases.

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