Measured Headspace - Now What?

[gravityfan]

British Military head space
If you reload and fire form your cases using the rubber o-ring method of an o-ring slipped around the rim of the case the word head space becomes meaningless.

As An example I lapped a zero bolt head to a head space of .084 and fired factory loaded Prvi Partizan ammunition without any ill effects using the rubber o-ring to control headspace. Actually it is zero headspace even at .084 because the o-ring is holding the case against the bolt face.

I am intrigued. I have been reloading .303 for a while, but I've not heard of this O-ring thing. Please tell me/us more; size, type, source, etc. Or would anyone like me to make a separate thread of this?