Problems with Gator gas checks on Lee 158 grain SWC bullet

I am having problems with seating gas checks on my Lee 158 grain lead SWC bullets. It is a gas check mold design. I am using the Lee .358 push through sizing die with Sage's Gator gas checks. I can attach the gas check flush and use the push through sizing die, but my gas checks are not being crimped tight on the shank of the bullet. I could pull every gas check off but one by hand. I am not blaming the gas checks because I possibly could be doing something incorrectly. If you have any ideas to help, please let me know. Thanks for any Sage advice. No pun intended.

I was having a similar problem with a 6.5mm mold. I tried powder coating the boolits before seating the gas checks and it cured the problem.

It seems like magic when you get a boolit to have the perfect size GC shank for a particular GC. When that doesn't happen, there are a couple things you can do...which amounts to something like putting "English" on a pool ball.

Here are a couple tricks to rectify a loose crimp on a GC.

1. Increase the size of the shank...that can be done by casting cooler, so the boolits aren't frosty. A shiney boolit, depending on alloy, will be a tiny bit larger. A more aggressive (advanced) tactic would be to polish the area of the mold that forms the GC shank.

2. Run the boolit through the sizer twice. First without the GC, then install the GC, then run it through again. What happens is, the GC area is likely to expand slightly during the first sizing, depending on how soft/hard the alloy is and how much friction is created during that first time through the sizing die.

I had never considered that JonB, I'll have to keep that in the memory bank.

Some other tricks I've used before.

#1 anneal your checks. Sometimes they just have too much spring back to work well. You stick the checks in a metal can, then put them in the grill for a while. You can find more detail instructions online. I actually prefer to anneal regardless, it just makes things go easier.

#2 use a thicker check. This isn't always an option. Sages sometimes offers checks of both .015" and .017" thick material. The thicker material will crimp down harder on the bullet shank. Also, if you bought aluminum, try copper.

What does the shank measure??
If it is under .340, its too small.
what is your alloy??

Shiloh

What happens when you size and seat the gas check by pushing the SWC bullet through base first?

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Originally Posted by Dusty Bannister

What happens when you size and seat the gas check by pushing the SWC bullet through base first?

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I always do base first and it works for me. I use generic Hornady .35's on Lee sizing die .357 on 158gr LWC base first. I'll get one every now and again that needs a second trip.

used Hornaday and gator checks with my rcbs 158and 180 g gc molds never had a problem.yes i use lee 358 push through sizer after ive used lee tumble lube .

The easiest solution to this issue is to stop pulling off your GCs.
If any effort at all is required to remove them, then there is no problem.

When fired, the GC is pressed into the shape of a gear, with half of it's circumference now at .350 diameter due to the rifling lands. This happens while being pressed against the bullet base with tremendous force.

Nothing can crimp it on tighter than that.