Mike, morning.... This cure #1 mix calculated below, is how to calculate for 100 Ppm, based on weight, in a liquid....
1 gal = 8.3 #'s
1 # = 454 grams
cure #1 = 6.25 % nitrite
3768 grams in 1gallon water X 0.000100 Ppm = 0.3768 grams nitrite / 0.0625 = 6 grams cure #1 in 8.3 #'s water.... = 100 Ppm Nitrite mix cure #1
If you do not have a grams scale, or powder scale in your reloading room, I highly recommend getting one... They can be had for about $20.... The safety considerations, when curing meat, make the $20, a very worthwhile investment.... Volume measurements are not always the same between tsp. or Tbs. or even salt manufacturers.... When talking food safety, err on the side of caution... Dave