One of my players was trying to decide between heavy weapons - eventually coming down to the two heavy single-shotters of the bunch: the man portable lascannon and the multimelta. It was at this time that I pointed out the errata which removed the multimelta's semi-auto rate of fire. The consequence of this was to make the lascannon a strictly superior choice of weapon... (apart from ammo - which isn't much of an issue for RT). So after a bit of brainstorming, I decided to add a slightly modified scatter quality to the multimelta to even up the choice between the two: the multimelta being allowed to get an extra hit in if you score 2 DoS at short-range. Thoughts?

Actually if you have any Dark Heresy books I would go with the autocannon.

I'd show your player pictures of the Imperial guard heavy weapons teams as well if he wants to run around with a multimelta or lascannon. These aren't guns you can just sling over your shoulder when not in use.

Even space marines versions look massive next to the marine.

I've tried to encourage my Arch-militant player to view heavy weapons as impractical personal weapons but he does love his Darloth Chain cannon so.

Aye, they are big pieces of equipment. The tech-priest in power armour is confident he can handle it if he needs too though (similar to how the SIsters of Battle handle theirs I would imagine). I've kept to the weapons in Rouge Trader and Into the Storm because...well, I love Autocannons on the tabletop because they're awesome. And this extends to the DH/RT rules as well. There is no reason _not_ to get an autocannon if you're allowed really so I've said no to that one...

Might steer them towards the heavy stubbers and bolters if you'd prefer them to use more 'fire on the move' style heavy gear. Or even a missile launcher.

However anyone who's had a glance at the supsensor upgrade will undoubtedly come to the conclusion that any heavy weapon is suddenly no more than a light machine gun instead of the 'predator mini gun' that they really should be portrayed of. In other words, sure it looks kewl, but in actual practise it's about as practical as hauling an artillery piece around as your standard firefight weapon.

OTOH if they specifically go through a lot of hoops to make a grav assisted snub nosed heavy death ray that's carried on a shoulder rig of their power armor I'd probably have no problem with it. Especially once I mention that it might cause problems should the fight get close and deadly. A reward for ingenuity with a potential penalty is better than just saying no.

Older marks (IE from earlier models for 40k) of heavy weapons were often shoulder carried by just about everyone, with the next series seeing wheeled carriages added for the normal humans, and then the tripod served versions most are familiar with. Though orks and marines still employ person portable heavy weapons. Other species either use special platforms or limit infantry heavy weapons to high tech limited issue specialty gear (Eldar weapon platforms, and tau rail rifles respectively)

So uhmm, yeah.

Just enforce encumbrance and unless your PC is freakishly strong/tuff many problems with having the PCs run around with a small artillary piece fix themselves.

Not sure it's been errata'd, but multimeltas also have Blast (1). Not much, but it has double the clip size, and you're hitting everything within 1m of the blast. Guess on the plus side, if someone was behind full cover, you could shoot the exposed spot 1m away from him, from a metagame perspective? And you're getting twice the shots before reload.

After having one of my arch-miliants running around with a multi-melta, the last thing it needs is something to make it stronger. On average 27 damage with 13 penetration with Blast 1 and a BS of usually over 100 is going to, and did kill anything short of a top tier daemon or xeno unless it's got a good dodge.