Hey there BajaBill. The brass (and plastic) powder measures you refer to are used as volume measures for black powder, as well as for black powder substitutes like Triple 7, Pyrodex, Blackhorn 209, etc. There's no real danger with overcharging any of these powders +/- 10 grains. Consistency in how much powder you throw with each charge is more important for accuracy than for safety. Most modern guns handle up to 150 grains safely, but most accurate loads usually fall in the 80 to 110 grain range with black powder or any of the subs.
I always use pre-charged powder tubes in a hunting situation, and often at the range - though I sometimes use a powder measure at the range instead of pre-charged tubes. When I use powder tubes, I sometimes I fill them using a volume measure, and sometimes weigh the charges I put them in them.
IMPORTANT: If you're going to weigh charges you must understand that, except for FFG real black powder, a 100 grain volume measure of powder does not actually weigh 100 grains, and the weight of different substitue powders will be different. For example, 100 grains of Pyrodex RS in my TC U-View powder measure actually weighs a little less than 80 grains, and 100 grains volume of T7 FFFG actually weighs a little less than 90 grains. So you must first establish the actual weight of the volume charge you want and use that actual weight to fill your powder tubes. For example, if you want to shoot a 90 grain load of Pyrodex, fill your volume measure to the 90 grain level, then weigh the charge. Do that five times or so then average the five weights. That will give you the actual weight of the charge you want.
There are lots of powder tubes available. Many of us favor the ones available from Lane Nebraska on the forum. Check here. http://huntingnet.com/forum/hunting-gear/262982-wts-black-powder-storage-tubes.html
