THE IMPROVED BRISTOL KNOT
How Many Wraps?
When I tied the "improved bristol" knot, I intuited that five to seven wraps with the leader up the braid loop and the same number of wraps back down ought to be a good number for that braid (30-pound) and that leader (50pound). Turns out it was: A few trials suggested that even three turns up/back held up respectably but not quite as strongly, whereas many more turns up and back became much more difficult to tie/cinch.
However, I believe the number of wraps that make for the best bristol changes according to several variables that affect the knot. These include (1) the absolute thickness (diameter) of both braided line (or mono if that's your main line) and leader; (2) the relative thickness - i.e., the heavier the leader is compared to the braid, the more difficult it is to tie a good bristol (e.g., 30pound braid with 50pound leader should be no problem, but tying 8pound to 50 with this knot is likely to drive you nuts); (3) the type/material of braid (and to a much lesser extent, the leader). Braided lines vary greatly in their feel: Some are slick and tend to slip; with others (typically the fused polyethylene lines versus the true braids), you can feel their "stickier" surface. Slicker braids may cinch down better, permitting more wraps, and that's good because they typically need more wraps to hold.
If you try to add many wraps similarly with a thicker, fused braid, you might have a devil of a time trying to cinch the wraps closely together - and are probably tying more wraps than you really need. In other words, as best I've been able to determine, there is no formula to guide an angler as to the number of wraps to lay down when tying a bristol. I've found that whenever I tie this knot, my two best buddies are trial and error. After a few attempts, you should be able to get a pretty good idea of how many wraps are optimal for a given braid size/type to a particular leader size/type. A simple rule of thumb that seems to work well: Use as many wraps as will ultimately cinch down reasonably well.
Finally, this caveat: As great a little knot as the bristol can be (and usually is) - durable, with a tiny footprint and reliable - it can on occasion (at least for this angler) be a bear to tie. On occasion, I've tried to cinch it tightly only to have the braid pull through, repeatedly and maddeningly; I think a few braided lines may just be too slick to "grab" some heavy leader materials with enough purchase to hold.
Cinching the Knot
Most of the time, lots of saliva and a pair of gloves will be requisite to really cinch down a bristol. Without gloves, the braid will lacerate your hands and you still may not get tight coils on your knot. With gloves, you can pull hard enough (and you'll be surprised at how much pressure it takes) to pull the coils into a neat, seamless knot. That said, from my experience, if you cannot cinch a lot of wraps into a close package, even though the knot won't look as nice, it may not be a problem. In testing, I watched many bristols with rather loose coils gradually, under great force, pull together, and only well after that did the knot eventually fail. More wraps are of course harder to cinch down but will make a stronger knot. Note that Andersen Berry, who submitted the second-strongest bristol in this challenge, acknowledged that his 10 to 13 wraps didn't cinch down completely, yet his knots broke at an impressive average of 49.2 pounds.