Title says it all
What's the best gun i can get at 2-star level?
Btw alchemer is awful at 2 star. You need to get it at least 4-star before you can get the feel of effective gun-slinging.
They give you a Calibur and Blaster for free while doing T1 missions, survive with those (it's good enough for starters) and save for 3* gear directly, skip buying and upgrading a 2*. It's unnecesary.
You shouldn't really skip 2 star. Learning the recipes for 3 stars is always useful and it doesn't cost any more to craft buying the recipe and 2 star then to buy it outright, so, unless you think that you'll play everyday, buy the recipe for 3 stars and craft it when you're not going to play that day.
Bzzts' advice applies to some players, but not to others. There are three basic cases:
A. If your main goal is not to get to the 5-star level quickly, but rather to get great unique variants, then you should certainly be crafting at the 2-star level as much as possible.
B. If you just want to get to the 5-star level quickly, and you frequently find that your mist energy is going to waste, because you don't have time or interest to play every day, then you should use your excess mist energy for crafting. You might as well craft both the 2-star and 3-star versions.
C. If you just want to get to the 5-star level quickly, and you don't regularly waste mist energy, but rather play it out every day like a good Spiral Knight, then you should indeed skip the 2-star level. Unless you waste it, mist energy has significant value, that you should include in your crafting costs. Buying a 3-star item is almost always cheaper than buying a 2-star item and upgrading it to 3-star yourself, or crafting the 2-star item and upgrading it.
I agree with Bopp on most of that, except that I recommend that some but not all new gunners consider starting with a 2-star Autogun.
A) If you're a "pure" gunner, any non-pierce Autogun is a top choice for Ironclaw and to a lesser extent Royal Jelly but the Needle Shot upgrade is mostly useless for those levels, and the Pepperbox is likely a dead end since apparently few people like it much. If you're one of those few who end up loving Pepperbox, using the Autogun early on will let you discover that sooner.
B) If you're not a "pure" gunner, a Calibur or especially a Brandish will probably do most of the Pepperbox' job better, so go ahead and start with Needle Shot and skip the 2-star Autogun.
If by "get," you don't specifically mean "buy," then earning a Pulsar is a safe bet for any gunner, pure or otherwise, since it's useful for getting past difficult missions if you solo and useful for Rocket Puppies and walls of turrets even in parties.
/emote does a trilobite impression:
"Another contender for best 2-star gun you can have is the one you get for free while clearing missions."
You should always plan in terms of 5-star items, because that's where everything ends up (unless you're focused on Tier-2 Lockdown). You don't want to work on a nice 2-star or 3-star gun, only to find that it can't be upgraded in any useful way. Instead, read the wiki and forums, figure out which 5-star gun you want, and then look back in its alchemy path. That's how you pick your 2-star gun.
So how do you decide on a 5-star gun? Perhaps the most important consideration is damage type. You'd like to coordinate your weapons so that you're carrying two non-normal damage types. Then you can inflict heavy damage against most monsters, and moderate damage against the rest. And, when picking damage types, there is an advantage to making your gun elemental, because elemental guns are very good against turrets. So which 5-star elemental gun do you want? Search Google for "spiral knights forum elemental gun", but here's the short version:
* Argent Peacemaker: Easy to use, decent damage, terrible charge.
* Polaris: Easy to use, decent damage, high knockback; really a crowd-control weapon.
* Nova Driver: Harder to use, but higher damage in the hands of an expert.
* Storm, Magma, Hail Drivers: Like Nova, but sacrifice a little damage for status.
My personal recommendation is Nova or Storm Driver.
To give you more specific advice, we need to know (A) how many weapon slots you play with, and (B) what your other weapon types are (swords, guns, bombs). While you're thinking, you may find my detailed sword guide useful. It has a section on mixing swords with guns and bombs.