Khensu said:

Take the 40 clip as weighing 10% of the weapons weight. For ease and since I don't have a book for reference, say a Heavy stubber weighs 10 kg. 1 kg of that is a 40 round ammo box. If you use the ammo backpack you are carrying 5 kg of ammo plus the rest of the weight of the backpack, which I believe is in the 10 kg range, half your extra weight is in ammo.

Khensu said:

I believe only Space Marines get ammo backpacks by default for heavy weapons.

ItsUncertainWho said:

the nice thing about this is, that the stats for space marine heavy weapons are almost the same for normal weapons, so if they get, then all else get too XD

and I think it makes more sences that huge weapons get huge ammo packs, thats why most of the time they are held by 2 man teams

Khensu said:

Astartes get it as an option when they're requisitioning the kit from the chapter armory. For Rogue Traders it would either be a separate Acquisition or treated as an upgrade, incurring a further -5 penalty. The only heavy weapon that comes by default with a backpack is a lascannon.

I think that the +ammo for bolter is good on 25 kg, but it shouldnt be the same for every ammo type, sp is lighter as bolt, and huge energy packs are heavy as hell too, but fuel for plasma or flame isnt that heavy, even if its a few liter of it...

the problem maybe with the ammo vs ammo weight

Their are a fairly large number of shotguns with detachable magazines, although I have no doubt that in the imperium someone has made a revolver shotgun.

I was also leaning towards 1F for weapons with box magazines, but you seemed adamant about 2F being reasonable earlier on.

Engineers from the Death Korps of Krief use a revolver fed shotgun. I forget the name of the pattern used but it's fluffed up a bit in one of the Imperial Armour books, most noteably as being really good at chopping up traitors and mutant militia, not so great at dropping khornate berserkers astartes.

There are also clip fed shotguns, though the only one I recall is the vanaheim pattern from the Inquisitor's handbook and it's touted as an Adeptus Mechanicus weapon utilized by Skitarii. If you want the 40k equivalent of the AA12, that's the one you go for. My Kroot PC actually equipped several of his kindred with them since they become a veritable toolkit of carnage when given a fire selector. Executioner rounds, plus snare rounds and either incendiary or regular shot to round it all off.

AS for what ammo weights, I too go with the 10% rule for one load of ammo, unless the book specifies otherwise. I also treat ammo backpacks as separate items unless they too are mentioned as being a part of the weapon, and they weight an appropriate amount depending on how much more ammo they hold.

AS for reload times, not all 40k weapons are as simple as push a button, and slam a new box home. Not only do a lot of weapons require actions like unscrewing flasks, flicking switches, etc there's also the fact that there are actual reloading rituals many people in the imperium beleive are essential to keeping the weapon work.

So it's not bad enough you have to turn off your plasma gun, unscrew one or more bottles of potential explosive death, then screw in new bottles that also may or may not explode. You'll also have to remember to say the right words, tap the casing at the right points during those words, and possibly apply some manner of oil or fluid to the weapon to keep it happy. If you don't do all of that, you may bring down the wrath of the gun's spirit which is usually displayed in the form of weapon jams, or other malfunctions followed by a tech priest making you do penance.

Vandroiy said:

If my players wanted to question the reload times i'd offer them this option:

You may not dodge/parry attacks in the round and in return, you can take half the listed time rounded up to reload. Remaining aware of whats going on is worth the extra seconds. Tune out the combat around you at your own risk. A sniper in a secure location with no nearby hostiles can benefit from this, someone about to get charged might think twice.

Khensu said:

Of course old tabletop heavy bolters for astartes did have clips. I think it was 2ed over the shoulder types. This is an interesting alternative which I like because you can auto-stabilize or suspensor the HB and lug the clips around however you wish without a backpack - assuming you dont want to fire all day and just drop the bolter when you are out of ammo.

Errant said:

This makes me want speedloaders for shotguns. i think i'll include it as a option for my players as well as the revolver style feed for the shotgun if I already don't have it available in the armoury on the site.

If I read the rule on "extended action" right, than you already cant use parry or dodge when using reload...

No, it just means that if it takes more than one Round, dodging or parrying would cause the reload action to fail.