I know he catches a lot of flack but the easy button is to call Dave at PTG. They make a big percentage of the reamers used by most of the die makers, like redding, rcbs, hornady etc. The value in this is he knows the reamer dimensions for the dies from most if not every major die maker. HUGE resource right there!
I started spec'ing my chamber reamers around readily available, usually Redding type s bushing dies, a long time ago, maybe 15 years or so IIRC. Now we can debate the value of custom dies later but a sizing die has a very basic job to do and the issue of most importance and the subject of this thread is essentially the dimensions of whatever sizer die and how it works with your chamber's dimensions.
I found that a die that is .003 smaller than the chamber reamer works great. We can split hairs but a .003 under die will typically yield ppc/br/grendel etc brass that is about .0005-.0006 smaller at the .200 line and about .0015 or so smaller at the shoulder, with brass that has a few moderate to pretty ghot loads on them. The reason that a .003 under die yields different number top and bottom as well as not .003, is simply springback of the brass. The brass at the .200 is thicker and harder than the shoulder area, of course.
Again, we can split hairs all day but this is a number that just works and the whole principle of spec'ing chamber reamer to work with off the shelf dies is just golden, IMHO. And it just makes a ton of sense to me. The only downside is IF the die maker changes their dimensions at some point, by some small amount. But if ya think about it, it's not a big deal, you're just back to a custom die, but we're talking a pretty extreme change as well as it being pretty rare too. I have had it happen with grendel dies. Some engineer decided they needed to be .0005 small, likely due to gas guns, but in the end, I think it added a whopping .0001 smaller at the .200 line, which was not a bad thing and far from what I'd deem as over working the brass.
I go a tad tighter on dies for bigger cartridges, hunting rifles and gas guns but not much at all.
I personally see no value in spec'ing chamber reamers around virgin brass dimensions. That was a trend several years back and the custom die makers loved it because you pretty much had to go custom then and that whole idea just caused problems and IME did not cure of help anything at all.
I'm reasonably sure this info is available from most reamer makers if you ask but I've either used Kiff or extrapolated my own numbers when using a different reamer maker that I go this route on. The beauty is how simple it is and negates the biggest reason for spending the money on the often long wait time for a custom...but you can still go custom, now or later if ya choose to, for whatever reason.
I'm just sharing this because it has worked so well for me and the simplicity of doing it this way. Sure, you can fudge the numbers to your own satisfaction or idea of what they should be but these numbers just work, and as Tooley would say, they don't make the phone ring. Lol! It's up to you what you do with this info but it's good info imho and it didn't cost you a thing either way. I do encourage this method be tried but like so many other things in this game, if it's different than what some do, it can't possibly work, right? Lol!
