Re: 6.5x55 loading issue
First off, you are loading well below max with that bullet and powder combination. Nosler data shows a max of 47.5 g of RL-19 with a 130g bullet in a 6.5x55 at a COAL of 3.025. Given that you are most likely loading much longer than that and have a long throated chamber, I would not be surprised to find that your real world max is a couple of grains above what Nosler is showing. The low pressures your loads are producing are the reason for the blowback. I would also venture to say that you are getting poor accuracy because you have not yet reached the optimum pressure range for your powder. If the seating die you are using can be adjusted to provide a light crimp, it may help to do that.
I recommend working up in .5 grain increments to find your max, using virgin or once fired brass and watching carefully for pressure signs. When your fired loads stop smoking the case necks, that is a sign that you are developing enough pressure to expand the case neck and seal the chamber. At that point, you are starting to enter the working pressure range of the powder you are using. Keep working up carefully to find your max. Stop when you see pressure signs (such as shiny spots on the case head, ejector marks, or sticky bolt lift).
Treat the lowest powder charge at which you stop smoking the case neck as your starting charge. Treat the last powder charge BEFORE you start seeing pressure signs as your max. Using your starting charge, seat your bullet one caliber deep in the case neck. Treat that as your max overall length and work back from there following the Berger seating depth test instructions. Once you find your best seating depth, do your powder charge workup.