Thank you, CaptCurl. That is interesting information. I am mulling it over.
The 1880s Lancaster .450 BPEs all shot paper patched 350-grain bullets with "about" 100 grains of powder. The catalogues all say this, and my reading of the original Lancaster ledgers revealed nothing new, unfortunately.
The instructions for this particular individual gun say two wraps of paper and 100 grains of powder with millboard and greased cloth. Nothing said about the bullet style, although the 1889 Lancaster catalogue says different bullet styles can be accommodated. A picture of the bullets they used, or of a contemporaneous Lancaster mold, would help settle this.
My understanding is most if not nearly all BPE rifles were tapered, as is this one (it has gain twist, too). What is different here is the smooth bore. It is cavernous. Filling it correctly is a challenge. Tomorrow I am shooting three NFB loads with a .452 diameter soft lead grooved bullet patched up to .463.
Some of the larger diameter bullets patched with 9# paper left lead at the muzzles, with NFB. Black powder did not leave leading, interestingly. Makes me wonder if the bullet heel did bump up. If so, it did not improve accuracy...
The Olde Eynsford 1.5 did not perform well in this rifle, neither at 100 grains nor as a duplex of 85 grains OE over 5 grains 4198 as a priming charge. The duplex load did shoot cleaner and with about half of the wonderful flame. Going to try WLMR primers with Olde Eynsford, probably closer to the large Berdan primers they had back then.
I may try a smooth sided bullet so long as it is .008 or so smaller than the bore average, and can be patched up with 16# paper to .462. That way I have confidence it won't stress the bore too much.
Again, thank you for the advice.
PA