Against heavy weapons you are competing with the Vulcan RFG which is both sooner on the tech tree and has both unlimited auto range and 15 more shots in a burst. Similar accuracy. Vulcan has greater dmg per TU efficiency although it does pay a higher up front TU cost.
First up. It's still ages till I can get my hands on a RFG but I have had Bossars on my team for a month so the results may vay.
Second up. All the "bigger" firepower doesn't do squat if you can't apply it. You walk three steps and it's game over for the Vulcan/sniper rifle.
You need something that lets you move and shoot.
In the rifle mid-range slot i feel the bozzar loses out due to weight. IMO the midfield needs flexibility which often equates to more items types and extra weight. Spending 42 of max 90(before armor) weight on the primary gun is not particularly attractive. Smartrifles are available at a similar level of advancement, are slightly above 1/4 the weight and significantly greater volume of fire due lower TU costs particularly in aimed. Also more ammo per clip. The damage loss is tangible but i find anytime you need to handle a target that can ignore 40 base dmg your your probably already calling for your bombs and fire support anyway. There is just not a great deal of enemy units at 40 plus armor that are not either resistant to pierce or have so much armor that you need huge punch anyway.
Look. Reality of the situation is that you can not issue guns that can't pass 40 armor. You will be effectively issuing no gun.
Lets take Osiron Security as our baseline troop here (you do have to kill them):
https://imgur.com/7SvJQUCLets for the sake of simplicity say that his effective armor is 45 (50 front, 40 sides).
Bossar:
62.5% of the time you will deal damage to the target.
Average effective damage per shot is 37.5HP.
Expected damage per shot is 23.43HP.
Aimed 1 shot at 115% of 60 damage for 70% TUs
1 volley is expected to deal 23.43HP damage, killing the target in 2 volleys.
Auto 5 shots of 65% accuracy of 60 damage each for 42% TUs
1 volley is expected to deal 76.14 damage on the average, killing the target in 1 volley.
Smartrifle:
46.8% of the time you will deal damage to the target.
Average effective damage per shot is 10.99HP.
Aimed 1 shot at 115% of 46 damage for 48% TUs
1 volley is expected to deal 10.99 damage on the average, killing the target in 4 volleys.
Auto 5 shots of 50% accuracy of 46 damage each for 38% TUs
1 volley is expected to deal 27.47 damage on the average, killing the target in 2 volleys.
The 49 weight is a small price to pay for this.