WOW! The rim does nothing for headspace in your barrel, but, as I understand it, thats not the way it's supposed to be. It sounds as if the rim cut was made WAY too deep when they chambered that! Ideally it would headspace correctly at the rim and shoulder, per SAAMI spec.
IMHO, on a rimmed case it should headspace primarily at the rim thus giving you some latitude on re-sizing die adjustment for the shoulder position.
As long as you treat it as a rimless case in reloading you are OK, but this just doesnt seem right to me.
There is no way on a T/C that you can get your head space off two different points of a cartridge, you should always try to use the shoulder for head space. Here's why you shouldn't use the rim for head space on a T/C anyway; If you have one you will understand that on a brake open, the barrel pivots on a pin in the receiver. Lets say T/c makes you ten receivers, there is going to be a tolerence of + or - ? on where that hole is drilled, now you buy 10 barrels for each of these receivers (100 barrels) and some of them are aftermarket barrels. These barrels have the hole in the mounting lug that lines up with the hole in the receiver that you put a pin through. If the mounting lug is welded .002" forward or backward of the Ideal spot on the barrel, then when the barrel locks up with the receiver there will be a gap bigger or smaller than the optimum .002 -.003" gap between the barrel and receiver. Now lets say on your hundred barrels that one manufacturer makes the rim cut .002" deeper or shallower than another but still within SAAMI specs, now between the two manufacturers you just added a tolerence of up to .004". This is called Tolerence stacking and as you can see, it can add up to alot of head spacing issues, it only takes .001 - 002" on each item to make a huge difference, now how are you going to cut the chamber of this barrel and have it head space off both the shoulder and the rim, you can't! Even if your chamber is cut perfect, the rim recess is perfect, the lug would have to be welded perfect and hole drilled in it perfect and then T/C would have to have the holes in the receiver in a perfect spot. Now you can head space off the rim and have a perfect .002 - .003" head space. With all these area's having a tolerence of + or - you can see why my barrel has a head space of .010" when the rim is resting on the rim cut. I could email you a link to the sensored persons article if you like, it's a very good read on head spacing.
I have two barrels from this manufacturer, both with a rim, both will allow exactly .010" headspace with the rim resting in the rim cut. Now the barrel with a bottleneck cartrdige is no problem, I resolve this by adjusting my sizing dies, but the barrel that is for the straight walled .444 I let have it's .010" head space. If you read the head space article on a certain sensored persons web site, you will see that this is not that uncommon of a problem. He does suggest that with a straight wall cartridge, you can adjust head space by messing with the rim, but it shoots clover leafs at 50 yrds and not much bigger at 100 yrds and for a hunting barrel, I am ok with the accuracy. If I can eliminate an accuracy problem with the bottle neck by letting the cartridge head space off the shoulder as it should, I will do this and the rim is used mainly as an extraction feature for the break opens.
Gary
