https://www.youtube.com/watch?v=yY5y4l0wPsU

DISCLAIMER: I realize a lot of my points rely on having two tortoguns, or being able to single-switch effectively. Realising not everybody cares to farm for two of the same gun, don't say I didn't warn you.

Tortoguns are an interesting weapon type, and similar in style to the Winmillion. And, much like the Winmillion, are underused in my eyes. I've done some experimenting with tortoguns to see if they would be viable or not. As far as I can tell, my conclusions aren't effected by whether damage is innefective or neutral. Type innefective damage does seem to have negative impacts, though. Party size may or may not have an effect on flinching rates.

General Facts About Tortoguns
With dualing or single-switching, multiple monster families can be stunlocked.
The charge attack has a soft homing effect on enemies in front of you, especially noticable on turrets. The shards will fall in the general vicinity of enemies, rather than overshotting them.
Setting up a crystal wall with a charge attack and then using standard attacks to corral enemies into them is an effective strategy, and using a Tortodrone Shield Bash is the same thing, except it does more damage and stuns.
A stronger shield is generally recommended for using tortoguns, use a tortoshield for maximum punching potential.

With this being said, we can delve into the individual monster families.

Beasts
Chromalisks
Chromalisks are easily stunlocked by repeated punches via dualing or single-switching. Due to their slow speed, they are also incredibly vulnerable to the charge attack.

Wolvers
Admittably, tortoguns are not good at dealing with wolvers. Not as effective as toothpicks, anyway. Wolvers don't get stunlocked and tend to avoid the charge attack. Would not recommend unless you're real dedicated to tortoguns.

Constructs
Puppies
Also easily stunlocked by tortoguns, along with being immobile, puppies are easy to dispatch with tortoguns.

Lumbers
Lumbers, while not being stunlock-able, are very slow. Charge attacks work well against them, and after their attack is baited out you can get a couple cycles of punching in on them.

Mecha Knights
I honestly am not too sure. From what I can tell, if you land the punch, the bullet will also hit them. Being up-close to Mecha Knights also tends to have them attack, which will lower their shield. Charge attacks are ineffective due to their quick speed.

Retrodes
Slow and stunlockable. Punch them. Charge attacks also are effective against them. Due to flinch rates, especially vulnerable to being punched into the charge attack's crystals.

Scuttlebots
Stunlockable with low HP. Just punch them a few times, they'll be the least of your worries.

Fiends
Fiends, they're pretty annoying. I wouldn't recommend using tortoguns against fiends unless you're in a party where not all the focus is on you. However, I'll still go into specifics.

Devilites
If you can get up close to them, they're stunlockable. However, the other devilites may interfere with the process of punching. If you're not in a party, I don't recommend tortoguns for these guys.
*On the topic of Overtimers. They CAN be stunlocked out of their attack, but it's inconsistent. Another reason I don't recommend tortoguns for devilites.*

Gorgos
Surprisingly easy to dispatch with tortoguns. Basic attacks are ineffective, but a charge will do them in rather quickly, as long as you don't proc their biting attack.

Greavers
Another easy fiend to dispatch with tortoguns. In small groups, that is. One or two Greavers can easily be stunlocked to death, but if they appear in a massive swarm you're pretty much screwed.
*Silkwings will not attempt to fly to their patients if you are delivering consistent punches.*

Trojans
Charge attack can hit them from the front, as some will land behind, but in this time the Trojan can easily attack you. Treat it like you would otherwise, waiting for it to attack then using standard attacks from behind.

Gremlins
Oh man, Gremlins with tortoguns are a joke.

Thwackers
Stunlockable. Your constant forward movement will be enough to give the other Gremlins trouble attacking you.

Menders
They won't heal if you punch them a lot. If they put up their shield, punch through it. Not worth the trouble of doing any charge attack traps, just punch them.

Scorchers
Dispatched much in the same way as Thwackers and Menders. Stunlock them and they won't burn you.

Demos
Now, this is an exception to the "gremlins are easy" rule. If you try to punch them, they'll just blow you up. Try to stay at a distance spamming charge attacks until they die. If they ever fall down, you might be able to use the forward movement from punching to avoid the bombs they drop, but I wouldn't recommend it. Stun vials can be used as an easy way to get through their bomb walls and start punching them, along with freeze vials. A Maskeraith will also do justice.

Knockers
Pitifully easy. Low HP, stunlockable, with easily guardable attacks. They're quick, so charges wont do much against them, but there's no need to do anything except punch them to death.

Mortafires
The other exception to the "gremlins are easy" rule. They barely ever let you get around them to punch them in the back. If available, try to hit them with a freeze vial to start punching them. With any luck, they'll drop their gear and be stunlockable. Charges may also be able to hit them from the front if they land behind them. In some cases, this will cause them to fall over or even drop their gear. From then, you can punch them.

Stalkers
Punch them. Really. They can't cloak if you punch them, and they don't tend to fight you in swarms. They're not all that common anyways, bar Operation Crimson Hammer.

Slimes
It's sad how hard these things die to tortoguns.

Jellies
When you punch them once, they'll begin to wind up an attack. Even without any ASI, the second punch, weapon-switched or not, will ALWAYS interrupt their second attack. No fear, just punching.

Lichens
They will also begin to attack, but the second punch will interrupt them. Medium and Giant Colonies will not be stunlocked, however their large hitbox makes charge attacks extremely effective against them.

Polyps
Much like Puppies, they're easily stunlocked to death. Charges are also effective against them.

Undead
Half easy, half annoying.

Howlitzers
Again, easily stunlockable. Possibly less stunlockable than Puppies and Polyps, but I'm not too sure. Additional info would be appreciated. Charges are, again, effective against them. A bonus with Howlitzers is that if you kill them with the charge, the head will run into the floored crystals and explode without any harm to you or your party.

Kats
They don't get stunlocked and charges are very ineffective against them. During the brief downtime after their attacks, you can get one or two punch cycles in on them. Stun vials help immensely when fighting Kats.

Phantoms
Simple. Bait out an attack, then punch them. Too mobile for charge attacks, but they aren't needed. Not stunlockable, but they don't have to be. Bait out an attack from them and punch them a few times, and repeating.

Zombies
Contrary to my earlier belief, zombies do not get flinched often. Their attacks are very slow, however, so they should not be an issue.

Almirian Crusaders
It's really not worth bringing tortoguns to the missions these guys appear in. A simple Alchemer or Brandish will do much better in those missions. However, if you insist on bringing tortoguns, Crusaders will not be flinched. Dodge their attack and counterattack with punches.

Bombies
Bait out the explosion and run.

Minis
Minis are terrible. They are terrible, hellish creatures with no regard for human life. DO NOT use tortoguns against minis. Please don't. If you do, at least be type effective. But don't. Just don't, really.

With the standard monster families out of the way, we can move on to the Bosses.
The Snarbolax
Not much to say about Snarby, ring the bell and punch him. Charge attacks are too slow to be remotely worth considering.
*On the topic of Rabid Snarby, it's almost the same thing as normal Snarby, except there's two. Just punch them, take out the silkwing when you can. If you're in a party, take the role of silkwing disposal full-time.

The Royal Jelly
Royal Jelly is weird. Sometimes punching him will result in him doing contact damage, and sometimes it wont. Charge attacks shred him anyway, use those. If solo, I'd recommend starving the royal jelly instead of blitzing him, it's easy to be overwhelmed by jelly minis.\
*On the topic of The Ice Queen, it's almost the same as normal Jelly. Just use charges, or starve.

The Roarmulus Twins
I have not actually tested tortoguns versus The Roarmulus Twins. I'll further fill this section out when I have more info. For now, all I have to say is that the charge attack will not hit them. I think.
*Literally no clue about The Red Roarmulus Twins.*

Lord Vanaduke
Depends on if you're solo or in a party. Tortoguns will never be as effective as a Blitz Needle charge, but landing a tortogun charge in his center of mass will do at least a decent amount of damage. If you're solo, all his aggro will be on you and he'll nail you if you try to use a charge. In a party, take the role of managing the Zombies spawned and watering. Only attack Vanaduke if there's nothing else to do. Just don't do Vanaduke solo with tortoguns. Unless you're some sort of masochist. I'm not stopping you.
*On the topic of Darkfire Vanaduke, it's nearly the same, except your tortoguns can get cursed. Have fun.*

Warmaster Seerus
Battlepods are easily shredded, and you can do massive damage to Seerus once he knocks himself out. In a party setting, due to your single-target DPS with tortoguns, you should take the role of battlepod disposal full-time.

The Big Iron
Use the bottom right corner trick to avoid the tentacles, and blitz The Big Iron once his shield is down. Use standard attacks mainly, just treat him like any other Battlepod.

Maulos
Again, I'm clueless. Just punch him, I guess? He seems pretty big, maybe use charge attacks. Take the role of killing his adds.

Arkus
Quite simple, just punch him. Or use charges. It really doesn't matter, Arkus goes down quick.

The Collector
Wait for him to blow himself up, then use charge attacks on him. Why are you fighting The Collector with tortoguns?

Ironwood Sentinel
As we all know, the Ironwood Sentinel is the hardest boss in the game. Not even the allmighty tortoguns would be able to take him down. If you're some sort of immortal god and willing to try it, you need to look him straight in the eyes. Pure intimidation should be enough to scare him off.

Razwog
Pure intimidation factor. Stare him down.

Herex
Like other Gremlins, he's easily stunlocked in a corner. Though he does overwhelm you with adds. Punch them too.

The Dread Velvet
Treat him like a normal Retrode, and then treat him like a normal Jelly. Punch it.

Margrel
I'm too poor and unlucky to have ever fought Margrel, so, I'm clueless. I assume you just punch him when he's vulnerable.

Tortodrones
Just don't get close to tortodrones. Use a different weapon.

And with that, ends my book. I don't know how to end a thread, so I'll leave this open for discussion. Discuss why you think tortoguns are absolute garbage or if you don't think they're absolute garbage, talk about that too.