Has anyone considered changing the -20 attack roll modifier from lacking the required weapon training talent, into a +20 modifier to jam?

First off, what is a +20 modifier to jam?

Second, the -20 is a mix of factors. Not knowing the range/drop off of the projectiles, not knowing how to grip it right (spring piston air rifles for example need a specific grip) and all the little things that seperate someone picking up a plasma gun for the first time and not knowing the slower speed of the shot means they have to "lead" the shot VS an experienced gunner who knows that.

My guess would be Jamming on 76%+

Doesn't sound right to me. While I would admit someone not trained with a weapon is more likely to use it incorrectly and therefore more likely to cause stoppages and the like, I wouldn't see it as being that bad. I would say a +5% chance of jamming would be more likely.

The way weapon training talents operate are one of the oddities of the system, as it does seem a little odd that a character is so much worse with some weapons, no matter if they are familiar with very similar weapons, just because they are classed slightly differently. Yes, a penalty would be reasonable, but it is quite high for minor differences (how much different is using a power sword compared to using a normal sword, for example?). However, I just see it as a simplification compared to having a more "realistic" but more complicated system.

First off, what is a +20 modifier to jam?

I feel like I'm on Jeopardy and should be asking "what is a houserule?"

It's just removing the aim penalty for lacking the right weapon talent, and instead increasing the jam range by 20.

FX: You jam on a natural roll of 74+ on the attack test, if you're firing a Semi-Auto Burst with a SP weapon and you don't have the SP talent. With the talent you jam on a natural roll of 94+ as normal.

Second, the -20 is a mix of factors. Not knowing the range/drop off of the projectiles, not knowing how to grip it right (spring piston air rifles for example need a specific grip) and all the little things that seperate someone picking up a plasma gun for the first time and not knowing the slower speed of the shot means they have to "lead" the shot VS an experienced gunner who knows that.

I completely get that, I just happen to disagree with it, based on recent - though pretty minimal - personal experience.

My DH group visited the firing range recently. Only one of us do that sort of thing with any kind of regularity, so it would be entirely fair to say the rest of us knew just enough to point the weapons the right way.

Despite our proficient friend mostly not using weapons he was used to, he was significantly more accurate than the rest of us. Though the rest of us were actually a fair bit more accurate than I'd expected.

And the primary problem all we n00bs had, was trying to operate the weapons correctly. The lot of us n00bs jammed everything from rifles to handguns, each of us multiple times. A couple of us (totally not me... OK me) even managed to get our hands snagged in the infernal things. But we got Winnie the Pooh bandaids, so we kind of felt like winners

Basically, my very-very limited experience suggests that the main challenge with unfamiliar weapons tech would be keeping the weapon operational, while the ability to hit stuff wouldn't be drastically affected.

*Casts Summon Gun Nut*

Perhaps someone with significant practical experience could chime in? Pretty please?

That is actually a very good idea! I agree with your observations as well, there really isn't a good reason why you'd be less accurate with a Heavy Stubber than a regular Autogun, but keeping it working is a different beast altogether.

Well, for a power sword, the weapon itself handles differently, you use the powerfield, not the weapon itself. Similar to how a chainsword is another beast in of itself.

One issue with the "Jamming" increase is melee weapons, which don't.

Anyways, what has been happening the rules system is less individual weapon trainings and moving it to either massive groups of talents (pistol, basic, melee, etc.) or like in DH2e. Have each type be it's own group for pistol and basic, then have heavy be one group and you need both trainings to make it work (SP+Heavy = Heavy Stubber profciency, same with Launcher for RPGs/Missile Launchers).

Ideally there should be a penalty to both (perhaps -10), you don't know the mechanics of the gun (increased jamming), but you also don't know it handles. How do you properly angle a meltagun to get maximum penetration? Have you drilled at the ranges where meltaguns are most efficient? Do you know what every toggle, switch, trigger, etc. does on your gun? Hell, GURPS does it well, wiith, "You may know the category of gun well (shotgun, pistol, etc.), but you only know the specifics and are best in a handful of guns"

Yes, I know you are using the powerfield, but the field is projected along the blade so you use the weapon identically. It is just much, much more effective. It also doesn't have the issue of a lightsaber, where the blade is weightless, which could be argued to throw people off. I can see a penalty for some differences, but -20 is fairly harsh. Very few strikes you would use with a normal sword would be invalidated by the fact that it is a power weapon, just made much messier and deadly.

I can certainly see chainswords being used very differently, as the weapon works in a fundamentally different way (the blade is not cutting through the material, it simply holds the spinning teeth that do). I can see chain weapon fighting as being quite specialised, as the cuts would have to be comparatively slow to give time for the teeth to do their job. This could easily account for the -20 for the non-initiated.

The chainsword I might see more like "sawing", only being wielded like a sword until the weapon actually connects, so a different fighting style seems realistic. But how exactly would you wield a power sword differently from a regular sword? What's the difference between a shock maul and a club?

In contrast, the system tries to make us believe a shotgun with choke settings and spread handles the exact same way as a full-auto assault rifle. Huh.

However, I just see it as a simplification compared to having a more "realistic" but more complicated system.

Then again, one might argue the game is already so ridiculously overcomplicated at times that it makes little difference to come up with a small table of weapons sharing the same or similar (for a -10 penalty) talent.

One possible solution might be a combination thing based on weapon type (pistol, basic, heavy) and damage type (bolter, plasma, melta, ...), each proficiency negating 10 points of the usual -20 modifier: someone who knows how to aim a laspistol might not have too much trouble getting used to a ballistic pistol, and likewise someone who has experience with a boltgun would already kind of know what to expect of a heavy bolter.

Needless to say, this system would require splitting up weapon proficiencies into the aforementioned categories, though. A point of contention would be that most characters might end up buying only 2-3 weapon type proficiencies, at which point they essentially save XP as damage type proficiencies would be (1) cheaper and (2) carry over to "stack" with existing weapon type proficiencies (which is kind of the point), so perhaps the XP cost should be adjusted somewhat.

... but while we're at it, maybe even add that +10 bonus from Rogue Trader(?) for that one particular personal weapon someone has a lot of experience with? It seems such a characterful trait.

tl;dr:

No proficiency known: -20

On page 130 of the core rules, there is a sidebar entitled, "Using Weapons Without a Talent." The last sentence of the sidebar reads: "In addition [to the attack penalty from non-proficency], when a ranged weapon is used untrained, it counts as having the Unreliable quality, increasing its chance of jamming." I think that addresses the problem nicely

Also, the 2nd edition beta did away with Basic and Pistol proficiencies. You instead buy proficiency with the weapon type, allowing you to use both pistols and Basic weapons without penalty. There is also a single Weapon Training (Heavy) talent, which allows you to use heavy weapons of all types freely as long as you have the appropriate damage type proficiency. For example, a character with Las and Bolt training could use Basic Las, Basic Bolt, Pistol Las, and Pistol Bolt weapons without penalty. If that character bought Weapon Training (Heavy), he could use Las and Bolt Heavy weapons. Personally I like this option more than the one presented in DH1.

Yeah, the Beta of DH 2.0 may make some mistakes, but it also does SOOO much right.

Heh, I'm highly ambivalent. On the one hand, hundreds of pages worth of exception-based rules that do plug quite neatly into a very few places in a highly logical system, makes it very easy for me as a GM to simply make the rules I want to use, as I want to use them. That's usually the kind of freedom you sacrifice when you use a super-crunchy system.

On the other hand... Hundreds of pages of exception-based rules is why the world has tax lawyers, and I'm pretty sure most of them don't find their fairly well-paid jobs all that riveting either

Our alternative, so far, has been to turn the WS & BS Characteristics into actual Skills, divided into specific Uses based on different Characteristics like the Skill System in Living 2.3. We had thrown out both the Technology and Class Talents, but after our afternoon at the range we're probably going to re-introduce Technology Talents - though as a Jam modifier for Ranged Weapons, rather than a to-hit penalty.

- This, obviously, is a pretty major system surgery. That's why I didn't mention it in the OP.

On page 130 of the core rules, there is a sidebar entitled, "Using Weapons Without a Talent." The last sentence of the sidebar reads: "In addition [to the attack penalty from non-proficency], when a ranged weapon is used untrained, it counts as having the Unreliable quality, increasing its chance of jamming." I think that addresses the problem nicely

It seems the core rulebook (in some measure) already anticipated on your day at the range . I'd stick to this rule.