Domed gas checks

[beagle]

What with a cold winter, rainy weather and a knee replacement this winter, I've had too much time to think and that can be dangerous and expensive.

I'm about to sit down and write Pat Marlin and run this idea by him on making a custom set of PB check dies for me, His extra effort would be minimal.

I want to make a gas check with a domed, convex bottom to it. Understanding I'd have to modify my sizing die plunger to the same profile or it would end up flat. The dome would be about 1/16" deep.

Here's my thinking. Install check and load cartridge. When fired, the pressure would collapse the dome and apply pressure sideways to give a tighter bullet to bore fit. Should give better fit.

Lee bottom punches could be easily modified as well as those for he Lyman and RCBS. Stars should be no problem as is.

What do you guys think? Comments solicited./beagle

[Winger Ed.]

At best-- it'll work just fine, with less chance for blow by, and further reduce any potential leading.
At worst-- it's a solution for a problem you don't have.

It does sound interesting, and I'd be curious to see how they work compared to conventional checks.

Something to investigate:
With the natural strength of an arch or dome--
And the chamber pressure being even all the way around and under the boolit's base,
Would the domed check compress, or crush out flat at all?

[dtknowles]

Wouldn't you get the same outcome if you used a regular gas check with a concave sizing punch.

This would be best with a nose pour mold with a convex base.

Tim

[tomme boy]

Size them base first in a Lee die. That always makes the round bottom for me. You will do better just making sure the checks are seated then size them nose first.

[dimaprok]

Size them base first in a Lee die. That always makes the round bottom for me. You will do better just making sure the checks are seated then size them nose first.

What he said. That's what I try to avoid! There is no way of knowing how its going to collapse, you might end up with ridges, frankly I don't think it's a good idea.

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[maxreloader]

http://castboolits.gunloads.com/show...-Checks-before

[Soundguy]

Sounds like a hollow based bullet concept..excetp at gas check pressure/speed?

[Soundguy]

Sounds like a back to back check soldered together ...hmm..

[beagle]

From shooting HB bullets, and seeing the sometimes oval shaped HB cavities blow out to a perfect circle, it will flatten to assume the contour of the bullet base which is flat. This leaves no alternative for the metal to spread horizontally which should guarantee and enhanced bullet to bore seal../beagle

At best-- it'll work just fine, with less chance for blow by, and further reduce any potential leading.
At worst-- it's a solution for a problem you don't have.

It does sound interesting, and I'd be curious to see how they work compared to conventional checks.

Something to investigate:
With the natural strength of an arch or dome--
And the chamber pressure being even all the way around and under the boolit's base,
Would the domed check compress, or crush out flat at all?

[beagle]

That picture is what made me start thinking,/beagle

http://castboolits.gunloads.com/show...-Checks-before

[Soundguy]

I'd have a weird fear of an in crimped gas check coming off in the barrel somehow. Not likely..i realize..like a wad or shot cup following I guess.

[jrmartin1964]

That's precisely how John Barlow's 1907 patent describes his gas check... and why Ideal handooks stated a special pin (slightly concave) was needed for seating gas checks with the Ideal lubricator/sizer.

Jim

[Bazoo]

I say it won't work. I think the pressure won't pancake a gas check. Reason I say this, is pressure don't fully seat gas checks that are applied crooked.

[Land Owner]

Check with Pat Marlin. My neighbor has been trying to get Rock Docks from him for more than 8 months. Covid had Pat shut down for some time. IDK if Pat is working at present and was having difficulty getting materials, especially plate aluminum. Whether the dwindling supply of materials affected his gas check making side business I have no idea.

[GregLaROCHE]

Do you have problems with leading with regular gas checks? Do you think you’re not getting a good enough seal? Why fix something that’s not broken?

[dimaprok]

With 1 step GC maker the gas checks already come out slightly dome. Making a forming pin a dome shape is a 5 minute task on a lathe but making a concave pin is more complicated but I don't think it needs to be matching, as long as you got a ring of support pushing on the edge the cavity doesn't need to be exact dome shape. Also as Tommy mentioned you can size it with a push through die with a gas check head first. What caliber you're trying to make that for?

P.S. I just realized that I have a round end mills, this should be easy.

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[Bazoo]

Don't take my comment the wrong way. While i don't think it will work, I am all for the idea of bettering GCs or figuring out new ways.

[beagle]

With a mill, it's easy enough. Just don't want to modify the set of Pat's dies I have now.

Was thinking about .30s for a trial. Recovered dozens of checks from shooting steel plates with .30s. They flatten out about the size of a nickel. The most stressed point on the recovered check seems to be the base/bore junction and that's where we get our leading trouble.
Now, I'm talking aluminum PB checks here and I know the pressure would be ample to flatten a domed check. I've recovered enough PB .30 Carbine bullets driven by 2400 and you can see the impact marks of the 2400 granules on the base. For darn sure enough to "iron out" a slightly domed aluminum check./beagle

With 1 step GC maker the gas checks already come out slightly dome. Making a forming pin a dome shape is a 5 minute task on a lathe but making a concave pin is more complicated but I don't think it needs to be matching, as long as you got a ring of support pushing on the edge the cavity doesn't need to be exact dome shape. Also as Tommy mentioned you can size it with a push through die with a gas check head first. What caliber you're trying to make that for?

P.S. I just realized that I have a round end mills, this should be easy.

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[GregLaROCHE]

With a mill, it's easy enough. Just don't want to modify the set of Pat's dies I have now.

Was thinking about .30s for a trial. Recovered dozens of checks from shooting steel plates with .30s. They flatten out about the size of a nickel. The most stressed point on the recovered check seems to be the base/bore junction and that's where we get our leading trouble.
Now, I'm talking aluminum PB checks here and I know the pressure would be ample to flatten a domed check. I've recovered enough PB .30 Carbine bullets driven by 2400 and you can see the impact marks of the 2400 granules on the base. For darn sure enough to "iron out" a slightly domed aluminum check./beagle

So you are getting leading. Looks like you’re using aluminum checks. Have you tried copper checks to see if you have the same leading? Is the aluminum you are using the same thickness as copper checks. If it’s not, that could be suspect of causing the leading. If your checks are thinner, maybe you need a larger diameter on the heel of the boolit where the GC sets.

[dimaprok]

So you want to make a domed FB GC for 30 cal? That's an odd choice, why not just go with something like RCBS 115gr that takes regular gas checks?

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