can anyone with experience of these guns tell me which is better? Or which they prefer?
Iron Slug or Callahan?
Currently I carry three weapons. A Blizzbrand, Graviton bomb, and Mega Magnus. I also have a Blackhawk. Is that a decent set up? And What if I had both a Callahan and an Iron Slug? Or is that not very useful?
I haven't actually made my Callahan yet, but, that's the one I'll make -because- it's piercing.
I already carry hail driver and umbra driver, giving me 2 of 3 special damage types. I use them to swiftly dispatch gun puppies and gremlin healers. With a piercing gun, I'd have all three (and a better way to shoot those pesky silkwings) and my sword for normal damage (unless I end up carrying one of DA or GF as my only sword, but i can always fall back on guns if I meet something resistant. Usually I prefer Leviathan anyway.)
For any given strata I usually only need two of three special damage types to be doing bonus damage to everything.
I would carry an Iron Slug if you plan to carry only one gun, basically, and Callahan if you're going to carry 2 or more.
(Or you could carry Gran Faust for shadow, Callahan for piercing, and Shivermist for elemental, or various other combinations)
Personally I think the Magnus line currently sucks and needs to be improved some way to be on par with the other guns.
Also there's a subforum called The Arsenal for these kind of topics now ~
As much as I'd like a 'Nail Driver' there's no piercing alchemer. Oddly enough there's only two pure piercing guns, and one is magnus line and one is autogun line. And the OP has a mega magnus and would have to start over to get Valiance instead if he wants Normal damage.
The magnus sucks and needs to be improved to be on par? What?
It has the highest base damage of any gun series in the game, and is available in two damage types. Not being able to move while firing sucks, but if you COULD move while firing one, it would be totally broken and easily the best gun in the game.
A level 10 Mega Magnus should do just as well as a Callahan. I have made Callahans for my friends and also have a level 10 Callahan. You want to keep that stun functional in regular firing and not rely on a charge attack. The charged attacks are rather annoying with the knock back effect (you land on your your bottom). The difference in damage up to the Core might not yet be worth the the hefty upgrade from the Mega Magnus to Callahan for piercing damage. I use the Callahan and Mega Magnus mostly for cornering Gremlins (especially Bombers and Menders). The knock back and stun effects of regular shots help interrupt those pesky Bombers and Menders. The charged attack is not worth waiting for as you want to keep firing rather than wait for a charge to keep the monsters from advancing.
When duoing with a friend in tier3 levels, I let him use his Argent Peacemaker while I use the Callahan instead of both of us using Argent Peacemakers. We stand close together and fire on Zombies or Gremlins to significantly reduce the advance of the monsters. We don't really worry about moving so much as the stuns and knock back help prevent monster advancement while we both fire away. As a duo team, also, only one of us needs to use a shield when we are that close together as the shield bubble protects us both. When my shield goes down, he puts up his shield so my shield can recharge.
I would work on getting your Sentenza crafted before considering upgrading your Mega Magnus as the Mega Magnus can really hold its own up to floor 23 when the damage difference between the Mega Magnus and Callahan gets a little more noticeable. When you start doing Vanaduke, you can upgrade to Callahan or make a Silversix/Argent Peacemaker. I haven't made an Iron Slug yet because I can't justify the CE crafting expense when I have a an Argent Peacemaker. I will be crafting a Sentenza to prepare for PvP, though. For normal damage, I really would rather wield a Leviathan than use a gun.
They have the same base damage, so the question you should be really asking yourself is, which would you benefit more from: Neutral damage that hits the same vs everything, or piercing, which is strong on beasts and fiends but weak on constructs and jelly. It mostly depends on what you find yourself using the gun on
Most people prefer to use swords on wolves and devilites, and guns on gun puppies and retrodes, so you might benefit more from neutral damage than piercing.
However, unless you already have a mega magnus that you're looking to upgrade, you might also want to look in to some of the guns that allow you to move while shooting/reloading, to give you an easier time.
I use nothing but guns so for me, callahan is the better option, since it's the best piercing gun, and I already have guns for elemental, shadow, and neutral. Most people use a variety of weapon types, though, so take what you want from this.