Two questions...

Are gas checks needed for building low velocity practice rounds for a .404 Jeffery?

Where can I find them?

Thanks

AT

My 404 won't shoot plain based cast for love nor money, low or high velocity, but slap a 44 cal gas check on the same bullets bum and it shoots lights out.
I use Hornady crimp on copper checks but homemade aluminium ones work fine too.

Thank you for your advice. Much appreciated.