I don't believe it's a Ballard stock Frank. Ballard put some straight grip stocks on pistol gripped receivers like the #6 Schuetzen, and the early #6 1/2 Rigby rifles. But they did not put pistol gripped stocks on straight grip receivers. The stock is well made, and nicely checkered, so done by a skilled craftsman, but not by Marlin.
Marlin stocks and buttplates are all serial numbered to their guns. On a Ballard the buttstock has the serial number stamped on the mating edge to the receiver, so removing the stock and looking ta that end will show a serial number. If it came off a pistol grip Ballard, and was refitted to your Ballard, it will have a mismatched serial number there. Buttplates have the serial number on the inside, so removing the plate will reveal if it's Ballard, or if it matches the stock's serial number.
Marlin made some rare Pacific models with pistol grip frames. I have a friend who has two of them, and one is marked "Browning Bros. Ogden, Utah" on the barrel. Both of his are plain, uncheckered wood. Both of his also have a loop lever, as usually used on PG receivers/stocks.
This is the standard Marlin Ballard buttplate. And my Rigby is also in .40-63! I load a 350 grain bullet to around 1350 fps, and it's not abusive at all shooting offhand.
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