Is Gordian Ist?

I think so. Looks nearly exactly the same as this one:

Weren't coins usually clipped to make them equal in weight/value to another denomination? My guess is it was clipped to equal the weight of a Dupondius or As

I'll bet it is not a Gordian I. Sestertii were not clipped (which was a process to remove valuable precious metal), but they were sometimes made with flans that were not fully round, especially in the time of Decius and later. Try to match it up with a Trajan Decius sestertius.

While it looks similar I concur that it is probably not 'Gordo'. The squared flan does not come into 'style' until the 250's. The books say this is because the blanks were being cut with a chisel from long strips of bronze. The Sestertii of the later period were no longer orichalcum ie brass but had been degraded by the evaporation of the zinc during the remelting of earlier issues. The legend (CAES M?) looks like Gordian I . But I can't make out anymore. If it could be shown to be orichalcum then the argument for Gordian I is much stronger. But the shape indicates otherwise. Knowing the weight would help quite a bit. Based on the shape I tend to think it would fit in with the 250's ...... About 15 or 16 grams