I saw PEEFSmash using this build (or something really near) this morning, and damn he is good! Note that this build can be used on all variants.
That's almost it, but the PPC should be on the LEFT arm (which allows you to twist and use your entire right side as a shield between shots). This is the critical thing. This specific feature is what makes the 2D2 best for the build. On the 5M and 2H you don't have energy hard points on the left arm so would need to use your original spec. There are better builds for those variants, IMO. Something more like this is better for the 2D2 (though you may arrange the armor a little differently this is pretty close):
Any reason you put a STD250 in there? You'll get another ton of ammo and another JJ when lowering the Engine size. 73 kp/h tweaked is more than enough to keep up with your average heavies or other poptarts.
Mobility is essential to getting in and out with this mech. I haven't tried it with a smaller engine but I suspect that it would be less effective. 21 shots is enough to get the job done if you make sure to hit all the time. It's definitely not a beginner loadout. To be effective in it you have to be spot on with your targeting of the enemy mechs and you have to consistently present your shield side between shots. It's all too easy to lose your PPC arm if you're not careful. I've been able to use it with mixed results (usually more good than bad), after considerable practice, but it's definitely not easy. Lingering in the line of fire is a bad bad idea with this mech.
With some 7k games under my belt I think I know how to do this snipe-&-turn thingy. This is first and foremost a mid-range sniper - the range is dictated by the weapons selected. This is also the reason mobility for 'getting in and out' isn't important at all for such a build. The speed granted by a STD250 won't get you out of trouble fast enough anyway, as any light or other medium will be faster than that. This simply isn't the right mech for hit-and-run tactics. You should rather move with the main group and provide fire support from the second line. Getting caught alone can be pretty nasty depending on which kind of opponent found you.
I guess this is something that's difficult to test empirically. I personally feel that a bit of extra speed is useful in many situations, particularly those where the "best case" doesn't happen (when pugging particularly, but also in pre-made situations where the unpredictable happens). If the tradeoff is only speed for a bit of extra ammo, I'll take the speed, even in the role that you've described. Still, as it's difficult to prove what the difference might be across a wide spectrum of different players, I must admit that you could be right here. I guess my advice to anybody looking at running this mech is to try it both ways and go with what works for you. Or try another build.
Not surprised to see this build here, but it's not really a pug game loadout, at least not one for a beginner. This build fills a specialized roll as a support fire mech in a limited drop deck, supporting the far flank in the murderball as it pushes forward. It does it's job well though, and for that it's 5/5 for me. My refinements to this excellent build.
Once mastered it's really a shame to put a single PPC, ER is much better imo (42% heat management is more then enough) also 28 shots are needed in most games if dropping solo. Quite fast and decently armored (considering that right torso and arm are just a shield, and as such, removing anything from them is better, and you want to lure for some component destruction with your arm and then the side torso, so the low armor on arm makes sure that it will be lost first most of times.) In a group I'd use SuicidalBaby's build, mine is more for PUG drop where speed and more ammo can help more then armor.