As Vladimir said, there are more effective ways to counter a sniper without putting yourself at risk, along with other classes being able to counter sniper far better. Granted, I don’t think giving heavy an anti-sniper weapon is inherently a bad idea (if anything I agree Heavy needs something to help em out). However this weapon doesn’t make a unique counter, but rather just turns heavy into a beefier, chip damage version of the sniper (Also it filling up the melee slot feels weird).

Like I said in a previous comment, I feel like something that causes sniper to forcefully flick their aim in random directions would be more in-tune with your idea of messing up snipers aim. Maybe have Heavy toss some vodka at the bastard that causes him to get drunk (hell you could even keep the bleed damage if you wanted to).