In another post, I had a "What is it???" on this.
It's a Neil Jones 22RF head space gauge.
Took it to the range today to play and see if it really makes a difference.
Rifle I used was a Polish WZ48 .22RF training rifle.
Probably not the ideal rifle to try this out on, but it's what I've been practising with.
Rifle shoot good dispite the bad sights.
Gauging a half box of Blazers, I found most were about the same. #1 to #2
A few were way off. #4 to #5
But after shooting, it didn't make any difference.
I'm thinking the head space of the rifle is so large, it just didn't matter.
I don't have any high dollar tight head space/chamber rifles.
Mostly military trainers, old pumps, bolts and semis.
I'll try and sort more and try a different rifle.