Just another thought on how much powder. Is it possible to over charge to the point that you would just be pushing unburned powder out the end of the barrel? Thought I remembered reading years back about shooting over a sheet or snow and see if there is unused powder laying in front of the shooter after the shot. Meaning there was more powder than the rifle could burn and thus "overcharged". Not sure about my memory but thought I would put it out there and see if we could get some opinions.
Bob
You gun will always increase speed with more powder, but as DP says, the increase per grain will diminish after a point. That point seems to be in the 1,800fps range - as he says - in his rifle, 80gr. 3F gives only a little less speed than 90gr. With BP and a .45 or .50, every increase of 10gr. seems to increase the speed about 100fps. After a point, this might drop to 60 to 75fps. Depending on the range one shoots, increasing speed further becomes an accuracy situation more than a power situation. One should load his rifle for accuracy within an effective velocity range.
With all my rifles, I develop an accuracy load that produces a flat trajectory. In effect, they are accuracy/hunting loads that get used for all shooting no matter the range. I know people who add powder as the range increases. The have a powder charger or powder charge they use for 25 yards, 50 yards and 100 yards. I find the "One" load produces the flattest trajectory and the best accuracy at all ranges, where on merely drops int he charge, loads the patched ball and out to 75 yards, takes a 'flat' sighting for a centre hit, or a hit within 1" of where the sights are aimed. For 100 yard shooting one merely raises the front sight about 1/8" and 'takes' that shot for a centre hit. Every year at Rendezvous BC, I hear, "Oh Rats"(or words to that effect) I've got my 25 yard charge and that looks like 60. They don't know where to hold. Having a single charge eliminates all problems such as this and makes it easier to 'learn' where the gun shoots.
Most rifles, if placed dead on at 25 yards, will be about 1/2"high at 50yds. on again at 70 yards and about 3.5" to 4" low at 100. Pretty simple with one charge for all ranges, isn't it.
The larger calibres- ie; "bore" rifles generally kick too much to use one charge for all ranges when 'plinking' but the normal run of guns to .54, do well with a 'standard' hunting/accuracy load.
If the gun looses accuracy with an increase in powder to a hunting charge, the culprit is usually to thin a patch for the pressure generated. For a given speed, 3F produces more pressure than 2F, although one must use more 2F. Therefore, 3f usually demands a tighter combination than 2F.