Pleasure!

Your 6.5 had a wierd chamber for sure, Afro408.
Sounds as if the .257's original chamber was a bit 'off'.

I chambered up a barrel for my daughter, using a .260 Rem reamer, but ran the reamer in .145" further than normal.

It had the normal .260Rem. shoulder diameter and angle of .454" and 20 degrees, along with the short .260 neck, however the case the rifle was chambered for, was a slightly shortened 7mm mauser(or necked up 6mm Rem, or shortened 8mm mauser or shortened .270, .280 .30/06 or .35 Whelen - blown out to .260's dimensions.
It had the same capacity as the 6.5x.284 Norma round - 60gr. It drove the 120gr. "Barnes "XCL" at 3,308fps, only 50fps slower than my .264Win Mag did with it's 85gr. capacity.

I love wildcats, but one must have an idea what he's playing with. Sometimes working up loads for rounds that have no known data can casue grey and/or white hair to appear, overnight.