Good morning.
If you were shooting PRB , the first thing I would suggest is that you were having patch issues . In other words you would need to go out and take a look at your patches and see what was going on
But you say your using conical so that leads me to think your having an issue with the conical expanding to the rifling .
That could be caused by a lot of things , distortion when loading , overly pitted rifling . Even powder .
Myself I have never been a fan of elephant powder . I have read some say that its gotten better . My experience however was that it was inconsistent and fouled badly do to the poor choice in charcoal used .
As to your ignition issue . Magnum caps are probably just a Band-Aid . . But as long as they work for you , 2 thumbs up . However if you start having inconsistent ignition with those . My bet is you will find that you flash channel is fouled to the point its restricting the fire from the caps from reaching the main charge . that�s very common in the CVA rifles do to the longer necked bolster . Since you said the PO didn�t keep it well maintained . The channel is probably plugged so tightly with carbonized fouling that the flash channel is down to about the size of a needle , all the way from the base of the nipple and through the neck .

So here is what I would do .
Clean the rifle very well . Make sure that the flash channel is completely clear . That means removing the clean out screw on the bolster and cleaning out the flash channel of the bolster . The hole going from the base of the cap , though the neck of the bolster will be 1/8 to 3/16 . Make sure when you put the clean out back in , you use anti seize so that it doesn�t corrode to the point it wont come out . Once its cleaned out , if the hole is properly maintained , you shouldn�t have to remove it very often . If you can get the cleanout removed , then you will have to use repeated soaks with solvent and repeated picking with a wire to clean it out .
If your wanting to use PRB , start by shooting off a bench rest . Start working a load . In other words shoot 4 or 5 shots for group . Go out and collect the patches from those shots and see whats happening . If your load is tearing holes or burning up the patchs , there is one of your issues that you will need to work on . Work on changing your powder charge tell you come up with a load that reduces the group to its smallest .
Once you have that small group , then move your sights tell the group is where your aiming

[Linked Image]