while reading about all the ideas and work on BP's lately on the forums and the wonder of o-rihgs,wounld't making various thicknesses of metal shims to custom fit a breechplug to a particular gun be a cheap alternitive or have you folks already walked down that path...karl
Walked?
I can promise you it wasn't a "Walk", more like a slow crawl.
The biggest problem with shims is they are not very forgiving, they are usually very thin, and unless they are very hard they will expand into permanent. Lots of pressure in some of these loads. There are also other options, but the o-ring is cheap, and easily replaced.
I have custom fitted breech plugs that were intentionally made longer than needed. It is a lot easier to remove metal than put it back on. Problem is, the rifle manufacturers need to have a tolerance window to mass produce barrrels, receivers, and breech plugs. Some get lucky and end up with tight fits, some (most) somewhere in the middle, and some unfortunately with everything on the loose side. It is just something we have to deal with.
Then after all of that you can throw in the 209 primer tolerances, they can be as much as .005" to .012" different in just length alone from one brand to another, and as much as .005" from the same package/lot.
You can easily change your lock-up/headspace just by changing brands of primers.