I remember once reading about problems reducing smokeless powders too low. I want to load some 45-70 down to as low as 18 gr H4198 to test the strength of an old gun and to plink with a different very light weight gun. I enjoy plinking my bigger guns with light recoil yet I hunt with full loads as I don't notice recoil in the  the heat of the moment. The older I get - the less I like heavy recoil. Thanks for any response.

I don't think that's too light, or so light it could cause safety issues. But light loads can cause other issues. Such as velocity spreads getting pretty bad from inconsistent ignition. I've played with as low as 18.0 grs. of 4198 in my .40-65 and found the accuracy and deviation in velocity was unacceptable. I also noticed unburnt powder in the barrel after firing, so I moved back up to 20.0 grs. or more to get better, cleaner burn rates, and consistent velocities.
The load of Unique that CBAshooter mentioned would be a much better low level load than 4198. Some powders do reduced loads much better than others.

I'll second Unique for light loads in large cases.
I've shot lots of 13.5 gr / 405 gr. cast bullet 45-70 loads,
also some 9 gr. / 250 gr cast bullets in 38-55. No fillers.
Just need to be vigilant about no double charges because it is quite possible to do given the case volume.
I also put rounds primer down in the box and try to not tip them nose down when loading.

I think that situation was with super slow powders.

I've use 14 or 13 grains of Unique with pistol primers in my 45-70's for years. With light loads of Unique I've gotten the best accuracy in a variety of cartridges with the pistol primers. Velocity of the 45-70 load at 13 grains duplicated the velocity of Remington factory loads, 1100+.

JS

Couple tips.

Little flare left on the case helps seal. It’s true light loads are powder position sensitive. Load the cartridge rifle muzzle down bring it to level same way every shot . Don’t use fillers. Which way the powder lays not important . Same way every shot very important.

Good way to look for unburned powder run a lightly oiled patch through the bore. Light it with a match (outside) watch it burn . Fizzes its unburned powder no fizz soot. Bump the load up half a grain until it burns properly. 

Boats

desert-dude wrote on Sep 12^th, 2020 at 10:46pm:


Can't say I agree with that 100%  because some of the best reduce load powders are single base 4759 4198 come to the mind.

Go from what I know to what I think.

Couple classes of reduced loads. Very light using pistol powders like Unique. Mid level like we use in SS Rifles. “Right” powder different, Depending  on Bullet weight case volume and velocity. I think it’s about pressure and burn rate, no different than internal combustion engine. Some Gas some Diesel some Heavy fuel. Wrong fuel causes problems.

Best authoritative work on reduced loads is Sharpes “Complete guide to Handloading. Book worth having.

Personal experience never tried to push pistol powder loads with heavy bullets or higher velocity. Have tried to slow down loads with 4759 & 4227, inconsistent burn poor results. It’s likely slower the powder more likely to have problems with reduced.

That’s all I think & know about it.

Boats