In the Riflemans Guide To Rimfire Ammunition, the author mentions a gas check on the lead bullet.  This is the narrow band just in front of the case mouth with a very narrow deep groove just in front of band.   I have noticed this on the bullet before, but this is the first time I have seen it identified as a gas check.  Observing fired slugs, this groove is completly closed.  Just wondering how the narrow band/groove would check the gas?  The heel on these bullets is shaped nearly like a sphere with hollow in center...even with very soft lead it is amazing how they swage up to full bore dia. with the tiny powder charge.

I’ll take a look in this book.  It has about 75 pages on 22’s alone, more if you include Magnum and special military cartridges. 

It’s a good book for the shelf. It was advertised in the journal.