Testosterone propionate was introduced in 1937 by Schering AG in Germany under the brand name Testoviron .  It was the first ester of testosterone to be introduced,  and was the major form of testosterone used medically before 1960.  In the 1950s, longer-acting testosterone esters like testosterone enanthate and testosterone cypionate were introduced and superseded testosterone propionate.  Although rarely used nowadays due to its short duration,  testosterone propionate remains medically available and is still marketed in the United States .  
Keep in mind that using enanthate this way will cause a significant build up of testosterone in the bloodstream that will not cease to increase until four or five weeks of injections. This is due to the fact that taking a four hundred milligram injection, and another four days later, still has at least 200mg working from the previous dose. The third injection then adds another four hundred and the first is still not entirely used up. You may realistically have over a gram or so in the bloodstream before you know it. Just be careful, and keep this in mind when figuring out your dosages.