Breechplug
I just now think that the T7 Primers that Im using are too loose and let too much blowback out because of there looseness.
That seems a bit odd to me. As you know I am in the middle of this Remington project and just completed measuring various primers. The longest primers I have are the Win T7 and W209's. They both measure right at .300. You would think with that length when you close your barrel the primer would be pushed up tight against the rear block. If you go to other primers they will get shorter and allow a less tight fit.
I have never handled an Accura, but I have a Triumph, which is as clean as you get; but it uses the Speed Breech. I just put a T7 primer in it and closed the barrel. I thought it might touch the rear block as I closed it - it did not - so I would say it might be somewhat loose also. In the Omega which has the older style breech plug which I assume is what is in an Accura - it also gets very dirty because of primer blow back - not blow back from the bore. I solved that problem when I switched to the 25 acp. All the rest of my inlines have the regular type old style breech plug and they all get dirty.
Busta has done a lot of work with the NEF and the use of 'O' rings to stop the problem by forcing the primer up against the 'O' ring to create a tight seal.
Grouse is struggling with the same problem with the Knight DISC series guns trying to clean them up.
It is my assesment that you need a long breech plug with a larger flash channel under the nipple to really provide enough space to stop the primer blow back. Knight did this somewhat with the new BP for the Vision - it is really not longer but the flash channel has been bored larger giving more room for expanding gases.
I would also tell that the T7 primer is one of the dirtier primers, which really has never bothered me to much because I like the way it works with T7.