Use your Bellm Headspace Indicator to measure case heads for squareness to the breechface and also compensate for out of square case heads by proper size die adjustment to get correct headspace
One of the characteristics of all the TC break open guns is the fact that both the barrel and chamber are not square to the breechface.
Typically, the only time a chamber would be square to the breech face would be if its misalignment with the bore resulted in it accidentally being square to the breechface.
You can readily observe this fact. In fact, you have seen it, but probably had no clue what it meant.
You have no doubt seen a rub mark in the finish on the end of the barrel just above the chamber on barrels with virtually no barrel-to-frame gap. The fact that the barrel only hits the firing pin bushing in the breechface at the top of the bushing indicates the barrel is dropping into the frame to a point below square to the bushing/breechface.
When the pressure is sufficient to push the case head back hard against the breech face, the head will be bent out of square to the rest of the case.
This means that if you have a batch of fired cases with heads out of square with the breechface, the high spot will rub hard on the breech face closing the barrel in a random manner depending on how the case is rotated when chambered compared to where it was when it was fired.
This points up one more reason to full length resize cases and leave about .001" actual space (headspace) between the case head and breech face.
Getting away from this is impossible unless a barrel is made with the vertical location of the hinge pin hole exactly correct to cause the barrel to drop into the frame's barrel seat exactly parallel to it.
As it is with most barrels, the hinge pin hole is lower on the lug than it should be for this to happen. The result is it holds the barrel up in the frame at the hinge pin area and lets the barrel teter over the seat at the rear. This is the reason why the actual contact point marks on the barrel are normally only at the extreme rear of the seat even though the seat is much, much longer than the marks left on the barrel.
Again, the best you can do is to resize your cases so that the case head is not being pushed on by the firing pin bushing in a random direction depending on where the high spot on the case head happens to land.
This is just a fact of life.
The location of the hinge pin hole is necessary to allow for the wide range of fit on the thousands of frames they might be used on. It is there by design and is pretty consistent on all TC Contender/G2 and Encore barrels, including most all custom after market barrels.
Back in the 70s & 80s, one shop used to clamp the barrel into a frame at the barrel seat, then use a taper reamer to ream both the frame and barrel hinge pin holes at the same time, thus creating a perfect height of the hinge, BUT ONLY FOR THAT ONE BARREL DEDICATED TO THAT ONE FRAME. A tapered hinge pin was also used.
Reaming a barrel like this also then ruined the barrel for use on any other frame unless another frame could be successfully reamed larger in the same manner and fitted with a tapered hinge pin.
While it produced some outstanding guns that showed up mostly on the silhouette ranges, it was not done very commonly. Once in awhile one still crops up, but they are relatively rare, and I do not recommend going to this extent. One can do it, and under some circumstances, I might consider doing it, but normally no. Like I said, it is pretty much a one way deal, and it defeats the attractive interchangeable barrel feature of the TC guns.
If you care to do so, marking your cases for orientation in the chamber or only loading and shooting all cases with, say, the caliber on the headstamp positioned at the top of the chamber then shooting reloaded cases with the headstamp turned 90 degrees, 180 degrees, 270 degrees, etc. may demonstrate the effect the out of square case heads rubbing on the breech face is having on accuracy.
Again, correct resizing for proper headspace, leaving some space, may well be a real key to accuracy in any given barrel chambered for a bottle neck case.
Give it some thought and better yet, rotating your Bellm Headspace Indicator over cases in the chamber will show if one edge of the head is higher than the rest of the head.
Paying attention to this characteristic of the TC break open barrels may turn out to be a means to improving accuracy or solving more severe accuracy problems.