Seeing as you are new I have a few suggestions.
1" at 100 is more than accurate enough for most hunting. I would still suggest more time on the rifle first though. Fire a couple more packets through with 4 or 5 shot groups and see if the first group was a good representation of you and your rifles performance. If using it on goats etc a 2 inch group at 100 is about a 4 inch group at 200 so you are well within accuracy to hunt humanely. If you find the group opens up with more rounds then it may mean the combination of you and the rifle is not quite as accurate as that. For a guide find a 5 inch circle and practise hitting it at 200m. If you can hit a 5" circle at that range consistently then your accuracy will be well within the kill zone on a goat.
It wont hurt to try different brands and more importantly a few different bullet weights. I cannot remember the twist rate of the Zastava, but if it is 1:7 or near then you may find heavier projectiles like 62 or 69 gr will perform better, but if it is 1:10 or 1:12 then it will prefer lighter bullet weights like 50 or 45gr.
In saying that 55gr and you shooting 1" at 100 is actually a pretty good result as most newer shooters struggle to get that consistency without a lot more practise. But more practise will help and its fun too....
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