Sorry, I made another post not long ago about getting a new-to-me Chaparral 1876 rifle.
Yes, the Jamison case rim is larger than the Winchester brass 45-70 cases I cut down to the 45-60 length. The Winchester 45-70 case rim is .600 and the Jamison 45-60 case rim is around .680. They are Ten X rounds made for the 45-60 WCF. I would think they should chamber if they are made specifically for the 1876 rifle in 45-60 caliber.
I have trimmed the case rims on the Jamison rounds I shot to the same size as the Winchester 45-70 cases but have not yet loaded them or tried to chamber one.
Buckaroo Lou,
First off, I have a Chaparral 45-60 and use 45-70 trimmed cases. I have never encounter Ten X or Jamison brass. The rim diameter that the Chaparral pamphlet lists is the same as the original Winchester -- 0.629". That Jamison rim diameter is totally off or out of spec, if the 0.680" diameter is correct. If it is correct, then I can understand why your bolt and guide tab is making those dents.
You stated that you reduced the Jamison to the 45-70 diameter. I hope you did not do all of them. It would be nice to see if a piece cut to the proper 0.629 or slightly smaller, would function and eject better, than the extremely small diameter of the 45-70 brass.
My biggest issue with the Chaparral rifle, I bought/received was excessive extractor to bolt face gap. I corrected that by installing a WinchesterBob 1876 extractor that resulted in a correct 0.060" gap. But the ejection of brass was still weak because the tab was not pushing of the bottom on the rim. As an experiment, I was able to extrude the rim diameter to 0.620" before the rim thickness of Winchester/Remington 45-70 brass got too thin. These attempts still resulted in weak ejection from the rifle. As I stated above, it would be nice to see if a piece cut to the proper 0.629 would function better.
While I was typing this reply it came to me -- Could your 'bolt guide tab' have been 'welded up' to give better contact, for use with the standard 45-70 rim diameter? This would cause the dents in the Jamison brass even if the rim diameter was close to the original 0.629". (EDITTED --- Sorry missed DJ posting comments before typing this line.)
Good luck with your rifle. It sounds like it is a good shooter so far.