Those "turrets" are sensor arrays, not artillery.
I wonder how artillery in space ouwl work anyway.
I also wonder why everyone looks at the ship and thinks "barrels = guns".

The entire Soyuz class line was retired from service before the time of Star Trek 6 (as was mentioned in the TNG episode), meaning the Bozeman was quite literally an anachronism when it reappeared from the temporal anomaly.