If you are using archery alone as the means of progressivley building up poundage, you are missing the mark. Yes, it will build up your ability draw a heavier bow, but you will become more susceptible to injuries as a result. A bow is far from an ideal strength training device.
Why?
Archery is a bilaterally imblanced activity, that is, unless you shoot an equal # number of times (with the same weight bow) with both your left and right arm as a bowarm (which no one I know of does). In other words the musculoskeletal demands placed on your bowarm are distinctly different and from those your draw arm. If you shoot ambidextrously with the same number of shots (with the same weight of bow) with both your left and right arm as the bowarm, there wouldn't be a problem. However, if you use your bow as your strength training device, and shoot with the same bow arm all the time (as almost all archers do) you will likely create significant bilateral imbalances (scoliosis is a particular concern) that will predispose you to injury.
If you wish to increase your strength so you can pull heavier bows comfortably, the safest way to get their is to develop your base strength with a well designed weight training program (preferably with an emphasis on dumbell work rather than barbell). While using the weight training regimen to build your base strength, progress with gradually increasing bow weights that are comfortable to draw & shoot repeatedly that well under your absolute maximum ability. The weight training should require the effort, the bow drawing & shooting should be effortless.
Mark Reisdorf MSc. (Exercise Science/Anatomical Biomechanics)