jeff, knowing that we are comparing apples and oranges, my 38-55 shoots just fine with Federal Large Pistol Magnum primers, no misfires. Problem is that I have given up a bit of accuracy as compared to the same loads with Large Rifle primers. I would think that the flame of the Mag Pistol primer would be similar to the Large Rifle, may have more to do with the cup hardness itself. I too have difficulty getting even ignition from 1680, Haywire once suggested to me CCI Small Rifle Magnum. Said that the switch to these in his 357 Max improved accuracy.
Part of the problem here is pressure. 1680 was meant to burn at 50,000 psi or so in the 7.62X39. All other applications are afterthoughts. I'd suggest moving up to Large Rifle Magnum, develop the loads from start as you know and see what you get. Once I get my 38-55 igniting Large Rifle primers properly again, that's where I'm headed, but like you I ain't changing nothing now, deer season here is two weeks away. Time to zero up with the current loads and fill the freezer