Help me understand gas checks

[HoCoMDHunter]

I am trying to understand gas checks.  I understand that this is something that enables one to shoot lead bullets at higher velocities.   I have seen them a Midway and they look like copper disks.  Do I need to cast my own to use these or can they be added to a commercially made bullet purchased w/o gas check?  I am pushing these bullets through a 454.

[hubbard]

gas checks can only be added to gas check style bullets which have a recessed base. the gas check is then crimped into place, when the bullet , with the gas check installed, is run through a sizing die. a gas check cannot be added to just any bullet , but only the ones specially designed for them. a gas check helps seal the bullet base against the expanding hot gasses and prevents melting of the lead at the base area of the bullet and keeps it from splattering on the bore.

[Aladin]

gas checks can only be added to gas check style bullets which have a recessed base. the gas check is then crimped into place, when the bullet , with the gas check installed, is run through a sizing die. a gas check cannot be added to just any bullet , but only the ones specially designed for them. a gas check helps seal the bullet base against the expanding hot gasses and prevents melting of the lead at the base area of the bullet and keeps it from splattering on the bore.

Not quite technically correct.. The bullet base does NOT melt per se-- what happens is the high pressure gases blow by the bullet base to bore fit and work up the side of the bullet. This is breech leading, a failure to seal those gases. The check material of course is much stronger and resists this gas seeping forward-- hence the term 'gas check'.

Gas can also travel up the land to bullet fit as the bullet starts this trip-- and if the barrel is significantly otta spec [terms of runout] those gas leaks can cause bullet metal erosion that is deposited on the bore walls. The Lube plays a major part in sealing gases--- that is it's MAJOR job.

[mugs]

Gas checks can also make for a more accurate cast bullet. The gas check creates a near perfect base to the bullet. The bullet base is as important as the muzzle crown for accuracy.
Mugs

[Aladin]

Gas checks can also make for a more accurate cast bullet. The gas check creates a near perfect base to the bullet. The bullet base is as important as the muzzle crown for accuracy.
Mugs

Again not quite technically correct. Look at the accuracy level of the Schutzen competition-- which uses PB bullets. Yes the best BR cast competition surpases that accuracy level now-- but due primarily to gun design and capability more than the check addition. If anything-- the PB mold slugs well made would surpass the base uniformity of most casters shooting checks.

There's some runout in check squareness using the common mounting system the luber/sizer [which actually are only lubers for accuracy shooters].  Easy to prove this-- bump some check bases flat and compare those groups to non bumped checks. You will see the difference.  Thing is-- the check while a great addition to the slug, is also an accuracy variable.

[Flash]

Sorry Aladin, your lamp just blew out! A gas check absolutely does improve the accuracy of a bottom pour, cast bullet. When the bullet exits the barrel, the base has to be perfectly perpendicular to the muzzle crown, otherwise the gas exits on either side of the bullet first and throws the projectile to the opposite side. This happens in milliseconds and is what contributes to a group size at a short distance. The next time you hand load for your favorite handgun, cant the bottom of a lead bullet and load it. Mark the case to correspond with the shorter or longer side and chamber this mark to set at 12 o'clock. I guarantee you that the bullet's impact point will directly correspond to the placement of that loaded round in your chamber. I hate to bust your bubble again but the Schutzen competition is dominated by nose pour, cast bullets that have a perfect 90 degree base. Whew.......let's talk about something else. :lol:

[Aladin]

Sorry Aladin, your lamp just blew out! A gas check absolutely does improve the accuracy of a bottom pour, cast bullet. When the bullet exits the barrel, the base has to be perfectly perpendicular to the muzzle crown, otherwise the gas exits on either side of the bullet first and throws the projectile to the opposite side. This happens in milliseconds and is what contributes to a group size at a short distance. The next time you hand load for your favorite handgun, cant the bottom of a lead bullet and load it. Mark the case to correspond with the shorter or longer side and chamber this mark to set at 12 o'clock. I guarantee you that the bullet's impact point will directly correspond to the placement of that loaded round in your chamber. I hate to bust your bubble again but the Schutzen competition is dominated by nose pour, cast bullets that have a perfect 90 degree base. Whew.......let's talk about something else. :lol:

Flash you have alot to learn-- I dunno quite where to start.  Many of the best Schuetzen molds are base pour-- this feature doesn't eliminate first rate quality by any means.  You might spend the time actually firing thousands of checked slugs than post on it-- you'll see what I'm talking about. Sure the checked slug makes it easier for the average loader to get the gun to shoot-- but not really from the standpt of the recycled rationale ya use.

Your first sentence defines you-- sez 'I flash am a zit faced kid who opens my mouth w/o thinking".  It defined you...

[Flash]

  Sorry, I couldn't resist. I cast my first muzzle loader bullet for my Parker Hale Zouave back in 1971. Started casting for centerfire around 1975, using a gas check mould. Thanks for the compliment on my youth........I only wish it were true.

[Cat Whisperer]

A gas check absolutely does improve the accuracy of a bottom pour, cast bullet.

A lot of variables here to say 'absolutely'.  Any time one assembles components there are more places for variation to occur, such as dimensional thickness, concentricity etc.  Of course when sized the assembly is sized much the same as a single component.

[Flash]

You are correct in that the dimensional thickness plays a part but only before sizing. Which will swage the gas check to a uniform dimension allong with the bullet, regardless of the thickness. As for the concentericity, the axis of the projectile and the gas check become one after installation so there is no way they will become concentric. I use "absolute" loosely, only because the benefits from a gas check on a bottom pour mould are tremendous. It prevents "gas cutting" to make a good seal inside the grooves, which spin the bullet faster and it also protect the bands from deformation. Give me some good bore cleaner, some time to work up a good load and I'll ABSOLUTELY get Howard County, Maryland's 454 to shoot like it should.

[sundog]

Interesting conversation.  I'll submit another variable to you, and that is that the check can also spin on the boolit.  It is not integral to the boolit, nor is permanently attached.  It is conceiveable that a checked boolit can strip the rifling under some conditions and therefore NOT provide the additional purchase one would ordinarily assume that it would while the harder check turns with the rifling.  Now, if you think that can't happen, try some Lyman checks that can be shucked off after departing the muzzle (I can replicate this with one of my 25 cal boolits and Lyman checks).  The boolit rotates at one speed (slower as it is being stripped) and the check at another (same as the rifling).  Just thinking out loud.

I will agree with one thing though.  The projectile must leave the barrel squarely, and that includes a round ball.  The boolit base is not necessarily flat, but it must be concentric (include bevel base and boattails) and geometrically even.  Still thinking out loud.  sundog

[Cat Whisperer]

Good comeback, Sundog, glad to see you made it over here.

Your comments lead to an interesting point - that of IDENTIFYING ALL the variables.  That leads to much research - the enumeration of the significance of varying each variable.  That leads to which ones can be controlled by varying temperatures, alloy, cavities, sizing and swaging as well as design and fit to the bore.

At work I'm getting into vibration analysis for the next month or so to be able to identify potentially bad bearings on newly assembled motors.  It's going to have some offshoots into bullet making/launching I can tell right now.

Thanks,