T.O.- I have the same barrel on my longrifle. I spend a lot of time finding out what the gun wants and through comprehensive testing, end up with a rifle that prints 5 into 1/2" at 50 yards, or the work isn't done.
The GM .45 shoots identically to my especially made MATCH barrel in .40 cal - ie: 1/2" off the bags at 50 yards. 25 yards will only tell you the gun is going off and give you a range to zero at, which will also give you a 50yard zero.
As to balls and patches, I wouldn't even try .440's. I did and cut my groups by 25% by going to a .445" ball. I use 10oz denim for patching - which will measure between .018" and .0225" depending on how you measure it and with what tool.
As I like to have an accurate load with both 3F and 2F, I test both. My GM barrel gives up 1/2" gorups at 50 yards using the following 3F load - 75.0gr. + 10 oz. (.0185-.0225") denim patch and an oil-type lube, ie: LHV. Hoppe's #9 Plus shoots exactly the same load. For a 2F load, the gun demands the same ball and patch, along with 85gr. 2F. both these laods are over 2,000fps and with a zero at 25,. are 0'd at 50 and only 2 1/2" to 3" low at 100.
Note that I do not wipe or clean the barrel until the day's shooting is over, be it 20 shots or 100 shots. The accuracy does not change during shooting at all - it always stacks them off the bags. It never fouls with this load, as it will with a thinner patch. Also, a thinner patch will not give you the accuracy I am getting.
If using a water based lube, like spit, or WWW fluid (Winter Windshield-Washer) fluid & cooking oil (25:1) the powder requirements will be approximately 10gr. under what I've listed. The more slippery the lube, the more powder it seems to take to maintain accuracy. Any of the lubes listed will allow unlimited shots without having to wipe.
If this load is too difficult to load, your muzzle's crown needs attention. if you haven't polished your crown, it's now time to do it. There are several threads here that should surface with a 'search'. We ALL shoot this combination ratio up here - .005" under ball and 10 oz. denim or same thickness ticking patches, ie: around .020" thick. None of us has to wipe at any time, not even the beginners, and loading is easy- not two fingers, but perhaps three.