So, which one was it, the re-grind, the chip breaker, or supporting with the tailstock?
All three

So, which one was it, the re-grind, the chip breaker, or supporting with the tailstock?
It's been awhile since I had a Broughton barrel blank, but as i remember, there was a sticker on each and every one that said; "do not shorten this barrel with a parting tool,, use a saw". That's probably not an exact quote, but it's close. The thought being, a cut-off tool not set-up properly might harm the barrel blank. You might have a wreck (like discribed in previous posts) or whatever. Just stick to the basic machining principals, make sure the tool is centered, work as close to the chuck/collet as feasible, make sure the tool is sharp , use proper feeds and speeds IF YOU HAVE A FLOOD COOLANT SYSTEM TO CARRY THE HEAT AWAY. I don't remember ever grinding a chip breaker into a "P" style cut-off blade. When 'parting off' we always use an angle across the cutting edge. That way there is no 'ring' left behind on the part (in the case of a part that has a hole all the way through it) or there's no 'tit' left on a solid part.
Parting tool too far out of holder. Not enough rpm. All other comments also
A Heavy 10 shore ain't heavy. I always cut my barrels with a bandsaw and then indicate and machine. Lots of good info here. Don't hang your part out any further than necessary. In this case, according to the photo if could be cut right at the jaws. I have a lot less trouble if my cutting tool is hanging out only enough to do your depth of cut. I have had a lot less trouble parting if I use the power feed. Yea, I flood cool it also.I would like to think mine is rugged, I mean it's no H10 but, she is heavy!
I've cut-off tens of thousands of parts on turrent lathes, hundres of thousands of parts on multiple spinde automatics, never have supported with a live center. Seems like that would 'trap' the cut-off blade as the part was cut off. Another 'wreck' just waiting to happen.......+1 on using live center in the tailstock to support work piece, I run mine at 360 rpm and a light drip of dark threading oil with no problems..
Eddie in Texas
I've cut-off tens of thousands of parts on turrent lathes, hundres of thousands of parts on multiple spinde automatics, never have supported with a live center. Seems like that would 'trap' the cut-off blade as the part was cut off. Another 'wreck' just waiting to happen.......