yeah, I was only referring to safety regarding bullet diameter, not necessarily accuracy. Accuracy is like anything else - some guns like some bullets, and dislike others. Regardless of the actual diameter, you pretty much have to try a selection of different bullets to discover which ones your particular rifles shoots best.
Only living creatures with a thinking mind can decide what they like or don't like.
Rifles do not fit this catagory.
If a rifle shoots better with a certain bullet, or a certain load, than it does with another bullet or load, there is a reason for it.
Where bullets are concerned, it is easier to figure out, why one works better than another.
As you state, trying out different bullets is the way to go.
Twist of the barrel is a very important factor in this. I'm not sure what the twist of the early Brno's were, but 40 grains was about as heavy as they would shoot, with about one MOA accuracy.
If the bullet was a normal shape and 40 grains, it didn't matter to mine, whether it was of .223 or .224 size.
A different shaped 45 grain fired almost as good, but other 45 grain weight shot much worse.
I was given a few 36 grain bullets to try. These were of a long design and they shot a pattern about right for geese!
As someone said, bullet shape is very important, when the weight for twist ratio is iffy.
When a group really opens up, like going from rifle and shooter capability of one inch, to 6 or 8 inches, the reason is almost sure to be stabalizeation. Small variations in group size can be attributed to slight bullet design change, or a change of pressure in loading.