how to crimp gas checks on lube sizer and get a flat gas check? mine are cupped.

[Whiterabbit]

So I've got things setup now that I can seat all my gas checks in a separate operation so they are PERFECTLY bottomed and flat. I have my lube sizer die set perfect so it takes very little pressure to seat and crimp. The gas checks come out tight and the lube is perfect.

But the plungers on the lube sizers arent flat, they are bowl shaped:



So the bullets don't wind up flat. The bottom is shaped like a bowel, follows the contour of the plunger. Is there any way to get it flat? I assume it's cupped for a reason? I assume it would be a bad idea to face the end flat?

For the people here who crimp their gas checks via lube sizer, do they come out flat? how to fix?

Thanks!

[waksupi]

Once the powder puts the pressure to it, it will be flat!
The concave surface helps the GC to curve, and crimp.

[Gunslinger1911]

I'll second waksupi's answer, I haven't had any issues with bulges, bowls, etc on the bottom of gas checks.

[Whiterabbit]

I'm going for 44man accuracy in pistol, and so far on a good day with the stars aligned I've done 2.86" at 100 yards from my revolver, looking to reach <2". I'm onboard with the idea that the GC WILL flatten with 40ksi of pressure, but can I count on it being uniform enough to not affect point of impact at 100 yards?

[mrbill2]

If you want to see if it makes any difference with the cuped end or flat end up, remove the pin and turn it upside down. Provided it ain't beveled on the flat end.

[Mike Hughes]

If you want to see if it makes any difference with the cuped end or flat end up, remove the pin and turn it upside down. Provided it ain't beveled on the flat end.

That is how I do mine, I turn it over. If they have a bevel, I file it flat. Puts the checks on nice and tight

[williamwaco]

So I've got things setup now that I can seat all my gas checks in a separate operation so they are PERFECTLY bottomed and flat. I have my lube sizer die set perfect so it takes very little pressure to seat and crimp. The gas checks come out tight and the lube is perfect.

But the plungers on the lube sizers arent flat, they are bowl shaped:



So the bullets don't wind up flat. The bottom is shaped like a bowel, follows the contour of the plunger. Is there any way to get it flat? I assume it's cupped for a reason? I assume it would be a bad idea to face the end flat?

For the people here who crimp their gas checks via lube sizer, do they come out flat? how to fix?

Thanks!

I assume you have tried the gas check seater that comes with the 4500?
I use it and like it but I don't think you will be happy with it.

Take a small thin, flat steel tool. I use the wrench that is used to turn the nut that holds the die in the lubri sizer.

Pick up your bullet.
Seat the check straight and as far on the base as you can manually.
Place the die nut wrench across the top of the die nut and the die.
This will completely block access to the die.
Place the bullet, base down on the flat tool directly under the top punch.
Slowly align the top punch with the nose of the bullet so the bullet is straight up and down setting on the flat tool and with the nose in the top punch.

Now use the 4500 as a press to force the bullet down into the gas check.
The result will be a seated but not crimped check.
It will have a perfectly flat base ( if the bullet doesn't have a lumpy sprue )
( Yes occasionally one will mess up and seat crooked. )
Now set the wrench aside and size the bullet normally. This step will crimp the die in place.

[reloader28]

I keep a quarter next to my 450 and use that seat certain checks as I dont have the factory wrench.
The quarter works good too.

[arkypete]

When I buy a fresh box of gas checks, the first thing I do is anneal them.
The gas checks are work hardened and need to be softened.
I dump the checks in an old skillet and turn up the heat. When the checks start turning black and other colors take the skillet off the stove to cool.
The checks will conform to the bullets and get a tight grip.

Jim

[Smokin7mm]

The internal plunger of the die is cupped to allow the check to be seated flush/square around the circumference of the bullet as that is the most important part to have a uniform base around the bullet. Verel Smith of LBT even suggests more of a counterbore to leave just a ring around the base. This allows the check to seat square even if the base/sprue is not completely flat.
Just my 2¢
Bret

[HiVelocity]

FWIW; I've taken a small hammer and hammered .30 caliber checks on a cast bullet after sizing to make them lay flat. It does no harm and I've had no problems occurring with them in fired cases. Mine were flat nosed cast bullets for 30-30 and similar calibers.

HV