Ok I've read the rules to dark heresy and have a pretty solid feel for them I'd like to think, but I do have one question.

If a character is making a test what prevents their characteristic from reaching 100 from bonuses? I know this sounds kinda silly and dumb, but hear me out. Say you have some character with a BS of 50 that is using full auto (+20) on a bad guy at point blank (+30). Would they just auto succeed?

This seemed like a silly thought but when I learned Rogue Trader and Deathwatch were much higher powered I wondered if this issue came up more. Is there a limit to prevent this or some rule I'm missing or is it just THAT uncommon a situation that an auto success on the roll isn't an issue?

Thanks for hearing out a silly newby ^_^;;

Don't forget in Ballistic Skill tests the player has a chance of jamming a weapon.  So no, accruing a total over 100 doesn't guarantee a success.  Barring a jam, and assuming a player managed to get above a 100 on a BS test, then it's only a matter of counting degrees of success.  If the player rolls a 94 out of 101 an opponent could still easily dodge the only shot that hit.

Yeah that's not wierd, dude. No worries, and best place to ask the question. 

There is nothing to say that '100' is an auto-fail, but there is the chance of jamming on 91 (unreliable) OR 94(Auto/semi) OR 96(normal) to 100, which would result in a bad day. Max of +60 or -60, and count the degrees of success is what you're left with (up to your 100+  with added modifiers.)

My group has always played that 96-00 is an automatic failure, and 01-05 is an automatic success. Until just now, I never realized it was a house rule.

The Boy Named Crow said:

…Yeah, I did that. A 1/20 chance of auto fail/success might be a little more than you want to give them, but it's up to you. Try 1/100 auto pass, so a nat 1 is an Auto pass, like in Black Crusade? Or you can just be scrupulous and say NO CHANCE. (sticking one's tongue out at the same time, perhaps.)

Thanks for the replies guys, I've also considered the 1-5 as auto success and 96-100 as auto failure due to my first tabletop game being DnD and all but I cold see how that might be a little much in this sort of system. Main reason I asked about this rule in the first place was in case I missed something in the core book or if Only War changed this. Doesn't seem like that's the case though so I'm a lot less concerned : ) Cheers!