As a means to make Hellgate easier in general, pack a few phases and warp your way to the other side. Even if you still plan on killing everything, avoiding the parts where everything gangs up on you is pretty useful.
On AoMr, you have the unfortunate disadvantage of not having a RL for the first part, though I suppose your question isn't directed toward the first part...I would like to note that, if you aren't aiming for MGK, it turns out a fair deal harder. Simply put, my favorite strategy is to shoot down the door on the right (the one you can't see; shoot off about 5 bullets, should do the trick), activate running on the tile before the walls come down, then run for the opening. Since it's a lot less crowded on the other side, you can weed out the enemies a lot easier.
Anyway, for the Bruiser Brothers. If you're hellbent on MGK, I wouldn't think about fighting them. Since this is HNTR, you won't get anything better than level 7 before Hellgate, and you'll end up using at least a stack of bullets on them alone (assuming you are even given the chance to do). The only simple method of fighting the Bruisers is to have a chance of knockback, which keeps them at bay indefinitely so that you can kill them. This means, at the very minimum, four more damage than a pistol's maximum output has. This can be accomplished with as little as SoGx2 and the power mod from completing Hell's Arena, although it's better to have more than a 10% chance (less per bullet if you're dual-wielding without both modded) against the impending march of the Bruisers.
The rest is just as rchandra suggests: SoGx3 is pretty important regardless of build, and SoB gets you toward a very reliable knockbacking attack. Since you're playing HNTR, where level 12 is for Conquerors, you don't have the luxury to go for everything, so I'll make your options clear.
Start SoG -> SoG, then either
- SoG -> DG (single pistol allows for better use of pre-game mod, faster attack)
- DG -> SoG (double pistols get more DPS, usually in a better position to reload)
depending on how you approach HA.
At level five, you have a few selections.
- Fin -> Fin -> WK( -> WK) is in hopes of super-modding. Additionally, it can be combined with the MGK build or SoB build, though is usually taken after either one.
- HR -> HR -> DM -> MGK is, obviously, for Gun Kata, which is great if you plan on running around shooting things in the open. This, however, is typically not a very good strategy when playing pistols. In the end, the benefits aren't all that great, and it blocks off SoB. Additionally, it can be combined with the Fin/WK build. If you have a unique pistol, however, get this (if only because reloading is much less of a hassle).
- SoB -> SoB ( -> SoB) is for unparalleled power. After the first shot you're definitely getting some knockback, regardless of mods, and the next two only increase your chances. It blocks MGK (but not HR/DM).
- EE, before (and combined with) any of the aforementioned builds. Since you aren't spraying your enemies with damage (ala shotguns or rapid-fire) every single shot counts. Even from the farthest range, +6-to-hit is usually enough to ensure that you're hitting with just about all your bullets. It's a personal favorite of mine, though on easier difficulties where you're strapped for traits, you may be better off ignoring it.
On higher difficulties where MGK has been blocked (ie, pretty much every AoMr UV game I've played), you sometimes mix Rel in there so Vile packs don't get out of hand. Otherwise, I stick to this script, throwing in Iro whenever it's needed.
In conclusion, Bruisers on Hellgate require knockback, and the only way you can ensure that on HNTR is to make a beeline for as much damage: SoGx3, DG, and as many SoBs as you can muster. If you really like MGK, by all means, play it: just be warned that it is not a YAAM-friendly build.