Seriously folks....!?
"Big" lube grooves really are not a lot of help for BP purposes. (now the fight starts)
If you think about it; consider the total amount of 'lube' that can even possibly squeeze out between the barrel bore and the bullet lands in the time and distance during a firing shot.
Really, the secret to all the lubes is content. The bullet needs absolutely no "lube" to slick down the bore it will go nicely with none at all. The consequence of no "lube" is leading and bore ejecta. Proper elements in the lube will inhibit leading, additional elements will soften the powder/lead ejecta so as not to wear on the bore. The good/better/best anti-leading element is Beeswax, simple pure beeswax used with at least a 30% mixture with anything else it will all but eliminate leading in a proper bore. The rest of the formula can consist of any heat/cold non-sensitive, easily attained and properly mixable element. One of the better is lanoline then Crisco, STP, lithium grease, or any smooth catalyst to get a batch. Some folks even add a 'cutter' to serve as a de-grease element Murphy's soap, Dawn detergent, or hydrogen peroxide. The combinations are limitless depending on your chemistry background and material available.
In serious long range BP circumstances, where consistency and clean counts heavily, the more , but thinner groves work better, or did when I was involved. The lube had to do, and did, the same job of anti-leading and ejecta softening. The more lube on the bullet that wasn't used in the bore then came off intermittently going down range was both a waste and a major contributor to poor groups and definite loss of accuracy. Same with Big Lube bullets, it mostly comes off on the way down range or all over the target.
That's my story and I hope it provides some chance for thought on your part.
Good shooting and good luck.
Ol' #4