Gas Checks Becoming Concave

[ghh3rd]

I wonder what might be causing my gas checks to become somewhat concave after they are installed. They sort of curve inward toward the middle, although the boolit base is flat. I first noticed it when I was rubbing the bases on a rag to remove excess lube. There was a small amount of lube in the middle, where the dip is.

I would imagine that having that base of a boolit be as flat as possible, whether with gas check or not, would be desirable, and wonder how much effect this has on accuracy.

Anyone else notice this on their boolits?

Randy

[Philngruvy]

I wonder what might be causing my gas checks to become somewhat concave after they are installed. They sort of curve inward toward the middle, although the boolit base is flat. I first noticed it when I was rubbing the bases on a rag to remove excess lube. There was a small amount of lube in the middle, where the dip is.

I would imagine that having that base of a boolit be as flat as possible, whether with gas check or not, would be desirable, and wonder how much effect this has on accuracy.

Anyone else notice this on their boolits?

Randy

My guess would be that the Gas check is too small for the boolit (or vice versa) and it is not seating directly onto the base of the boolit leaving a small space between the boolit base and the inside base of the check. Then when you seat the check, the punch is pushing the base of the check inward into the base of the boolit.

[357maximum]

Are you using a lee push through die that is a fairly loose fit to the boolit by chance?

[Marlin Hunter]

When the boolit and check are sized the material for the copper needs to go somewhere. since it is thin, it just buckles instead of compresses.

[Marlin Junky]

What kind of equipment are you using? Is there lube building up on the top of the sizing die punch? Are you seating the check before crimping it in place?

MJ

[Tazman1602]

I've noticed that on *some* of my molds. Most of my big bore stuff, 44 45 etc the GC's just snap on and we go. I've got ONE .30 cal mold (Lyman 173gr GC for my 30-30) that will NOT seat right.

Wife solved it for me. I've got this itty bitty teeny weeny ball peen hammer and the ball end fits perfectly in a .30 cal GC. On small slap with a rawhide mallet and they snap right on and no more concaving.........

More than one way to skin a cat

[Doc Highwall]

I wonder if annealing the gas checks would help.

[mrbill2]

"I first noticed it when I was rubbing the bases on a rag to remove excess lube. There was a small amount of lube in the middle, where the dip is."
Lube under the gas check when sizing.

[Rusty W]

I use the Lee system and have noticed the dip too. I wonder if they were pushed through with the base first if it would do the same thing. I have a RCBS 325gr FP 45/70 boolit I may try it the next time I cast some.

[Wayne Smith]

I use a Lyman die to seat and have some just the opposite, concave. I figgure that, when the big lightbulb goes off, they flatten right out!

[AZ-Stew]

If you have divots in your boolit bases where the sprue tore rather than cutting off smoothly, and you have some boolit lube on the sizing die center pin, the hydraulic pressure you create when forcing the boolit into the bottom of the die will cause the check to deform and try to fill the depression in the boolit base where the sprue tore out.

Regards,

Stew

[fourarmed]

I have seen that on some SAECO bullets that have very short shanks.

[high standard 40]

What kind of equipment are you using? Is there lube building up on the top of the sizing die punch? Are you seating the check before crimping it in place?

MJ

I agree. If you are using a lubrisizer this is most likely the issue. The same thing was happening to me. My sollution was to use the gascheck seater with my Lyman 450 to first seat all my gaschecks before I size and lube them. Takes an additional step but the results are much better. I only saw this issue on bullets that had a very tight fit of the check on the bullet base.

[randyrat]

I've ran into a similar problem and i found out i had a mis matched sizer punch...The thingy that pushes the cast bullet through the die. It messed up a bunch of cast bullets untill i caught it.

[XWrench3]

use the Lee system and have noticed the dip too. I wonder if they were pushed through with the base first if it would do the same thing. I have a RCBS 325gr FP 45/70 boolit I may try it the next time I cast some.

from experience, and experimentation, i can tell you that running them through the lee sizer backwards (or more correctly, up side down) is what i do now. gives a much flatter base (mine dimpled as well), plus i think it crimps the check on better.

[beagle]

Think it's a quirk that comes with nose first sizers. Some of mine do it as well but the accuracy seems to not be affected./beagle