Where is the 100yd group centered? Right in the middle? Did you try firing more than 3 shots?
4" group at 100yd doesn't sound good, but it is good enough for military rifles, barely though. Saiga is not military rifle. I would expect it to do better. I have an AR in A3 configuration, cheaply put together for no more than $550. It can do 1.5" without even trying hard.
-TL
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