The rapine has PLENTY of lube cavity for a 30in barrel.
It is very similar to the PRS bullets for 45lc and Mav Dutch bullets for 44-40 and snake-bite bullets for 357/38s.
I have fire the mav dutch bullets along side Lee .429 bullets from my pan lube method and neither one has gummed up after a 6 stage match.
You are only talking about 40-45gr of powder anyhow, which should not pose a problem.
I have experienced NO hard fouling in my 20" carbine with modiefied Lee bullets. And they only have 2 puny little lube groves.
The softer the lube, the less you will need.
The slower the bullet, the softer the lube.
The more the powder, the more the lube.
The heavier the bullet, the softer the lube.
So, you can roll your own, or, just use SPG. (SPG works pretty darn well...just don't care to pay the price for it)
Here is another lube that acts just like SPG, but, is not as temperature sensitive.
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=689293I have spoken to 2 shooters who use this in 45-70 and a 50-90 shooter and they both swear by it.
(even though they pan lube)
I am now mixing 1lb bees wax, 6oz bol-wax, 6oz crisco, 6oz canola oil and getting REALLY good results. Pan lubes REALLY nicely. (I have to heat it to 375 F for it all to melt together, then, I can pan lube at 300 F from then on)