What steroids do not shut down natural test production?
I don't think there is such a thing.
they reason that steroids shut down test production is because, well, steroids IS testosterone. just different variations.
when you use steroids to any significant degree, you will no doubt have a test level that will be deemed by the HPT mechanism as being excessive. The HPT mechanism (axis) is responsible for controlling the testicles natural level of test production and when it detects excess levels for a significant period of time (roughly 12 weeks), it will, in turn, shut the testicles down.
I have never heard of any method to prevent that natural process, unless some of the AAS's that are a product of test conversion (such as DHT), where testosterone serves as a prohormone, can be used without affecting the HPT process. But I don't think this is the case since masteron is a DHT derivative and I know for a fact that it will affect the a HPT.
Besides, DHT is useless as far as mass gain goes.