What are you putting the shavings into?

I'll spend several minutes with mine, getting it into the finest tinder I can. It is usually stuff that the spark alone would work with if it was perfectly dry, and the magnesium gets the temp up so you can puff it into flames. *shrugs* I've had good luck with mine, but I'm not using it to light a sheet of birch bark. Instead, I'll sliver the birch bark, then put then under and around somethign like part of a fluffed cat tail head, and add the shavings into that nest. Then the sparks. If I had pistol cartridge around, I'd use the powder the same way. Neither powder nor magnesium shavings is really tinder to me, but it is better than a match. I find that putting magnesium into 0000 steel wool, even when it is wet and a little rusty, works really, really well.

As for the weight, magnesium is almost as light as aluminum. Not sure the equivelent weight is all that much, but the equivelent volume might be a good substitution if you have some difficulty with these.