It's all in the crown - sharp crowns as delivered on rifles will cut patches and resist allowing the ball to seat. Get some 320 Emery, or wet or dry paper, use your thumb, rotating round and round, turn the barrel, keep doing this until the crown is nicely radiused.
I load a .400" ball in a .398" bore with .0215" denim patch and spit or LHV lube- no problem. The short stud on the starter's knob is placed on top of the ball, and one easy whack with the palm puts it down into the muzzle 1/4" to 3/8". The long shaft is then put on the ball and one easy whack with the palm and the ball is down 6" or so. The 3/8" rod puts it the rest of the way down.
Sonny, like you, if I try to skimp on patch thickness with .395" balls, ie: .018", they'll blow - burn spots to shreds if the temp is above about 60F. The above noted barrel will allow a patch as thin as .015" with a .400" ball but the accuracy suffers.
In the .45 barrel, I use a .445" ball and the .0215" denim patch(10 pound denim). I can use a slightly thinner .019" to .020"(10 pound different mfg) but accuracy isn't as good and in hot weather, the patches will blow. With a ball .010" smaller than bore, I can use the same .0215' denim patch, but accuracy isn't as good as the larger ball provides. Loading is easy. Starting involves one light whack with the palm on the starter's knob over the ball and patch, then a punch down using the long shaft.
A couple weeks ago, one of the guys took a short movie of me loading. We'd already shot finished the trail so we'd all shot around 50 to 55 shots, no one had to wipe the bore at any time. If I can get Taylor to send it to me, I'll post it under a new thread. It shows just how easy it is to load a tight combination if the muzzle is shaped to allow this. That day, the guys were all using .005" under balls and .020" to .025" denim patches - LHV or windshield-washer fluid and oil for lube. Taylor's Jaeger uses a .535" ball and a .025" denim patch. Loading is easy. Taylor doesn't use a short stud on the starter's knob, but holds the shaft in his palm and brings the end of the knob down on top of the ball with a blow to seat the ball flush with the muzzle, then the shaft punches the patched ball down into the bore 5 or 6 inches with another blow of the palm. Punch - punch then down it goes with the rod. - that fast. There is no work involved - it's easy and fast. In punching the ball down into the muzzle, the sprue on top of the ball is flattened slightly. Enough force is used to seat the ball flush with one blow. If less force is used, multiple blows might be necessary - this will deform the ball - one punch does it without deforming the ball. We load all our rifles this way - even my wife with her .45. She is using a .440" ball in a .450" bore, with .020" denim patch and LHV but with only 50gr. 3F. This load shoots just fine in her short 32" barrel and is easy loading for her. Our starters have a section of Moose antler taken form just above the base as the knob - it is heavy and dense helping with starting. Another starter of mine has a section of Hockory Axe handle and it works just about as well. Note the shrot stud on the starter knob's end. This is a .30 M1 carbine case cupped on the end with a drill, then glued into one end of the horn. The side of the horn has a hole that fits over the rod's end when seating the ball down onto the power, the last inch or so. At no time is the starter used as a hammer or mallet - no hammering or pounding with a mallet is needed - even when Taylor tried a .508" ball in his .50 'Ginny' with a .020" denim patch. The crown's radius allowed that tight combination to swage into the bore. It was quite snug so he choked up on the rod and put it down in 6 to 10" stages.
The crown's shape and smoothness is of utmost importance. If there is a sharp angle where the angle of the crown meets the bore and groove depth, that sharp edge will resist swaging the tight combination into the bore. The thumb and emery will smooth this sharp edge allowing the ball and patch to swage together into the bore.