Theoretically the .45 is better.

round = same weight, same value. Personally I do not like Hollow Points and this is the only available option to 12.7mm. The .45 has hand load as a option.

.45 smg is affected by grunt. Have 50 ammo cap. with one mod. 12.7 only have a 27 ammo cap.

Bouth has almost the same DPS, without special bullets.

spread = 1,6 (12.7 smg) and 1,8 (.45 smg)

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that said, I have the impression that I'm achieving better results with 12.7 smg.

It's hard to explain if you have never used the two, but the .45 GORMANDIZE bullets. It's ridiculous, it seems I'm always having to buy more.

I believe this small difference between the spreads has made all the difference. Oh, there's also the criticals, but it is difficult to achieve with a SMG.

I'm a little upset because it seems like I wasted a perk (grunt).

Maybe I use as a third weapon the All American, just to not "lose" this perk. I like the fact that you can craft armor piercing.

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What about you guys? What is the favorite SMG of you?

Between the 12.7 and the .45 SMG I prefer the .45 SMG as I am taking the Grunt pick anyway. Also I prefer the look. Plus the handloaded .45 does better versus armor, the 12.7 JHP is really only good versus non armored foes. I've cleared the deathclaw cave using a .45 SMG with the handloaded bullets, couldn't do that with the 12.7 due to their DT. If I am using 12.7 ammo its going into the Survivalist rifle and aimed shots, the ammo weighs too much to spray it around on full auto.

Out of all the SMG my favorite is either the modded 9mm or Vance's 9mm using handloaded JHP it shreds anything without armor cheaply. The ammo is lightweight and abundant. These destroy cazadores when they close on you and are safe to shoot at your companions if they have decent armor in case you need to drop a cazadore or nightstalker that gets too close to them.

You might want to try 5mm early in the game and AP later on. You can still use the Grunt perk, and the ammunition weighs noticeably less.

Of all the submachine guns, my favorite is probably Sleepytime. It's great for unarmored or lightly armored targets, and also excels at infiltration/assassination missions as it is silenced.

I once used it to clear out the Fort, without raising an alarm.

I have also used the 12.7 SMG some, it needs a bigger magazine. With the silencer added it is also effective for stealth kills.

Don't much care for the .45 SMG. Grunt does make it better, but as you say it seems to really eat up ammo, which I would rather save for the .45 pistol.

And it weighs a lot. For full-on spray-and-pray mode I prefer the LMG.