We've been using fate points in the standard way, including using it to re-roll an attack.

Yesterday, it came up that our Devestator with a Heavy Bolter rolled a jam. I asked if using the re-roll would allow a new attack and (as long as it wasn't similarly high) make it so the jam never happened.

Per the rules, would using a Fate Point to allow a re-roll make it so the jam never happened?

The GM ruled that we could use a fate point to clear the jam, but that we couldn't make a new attack roll. His feeling was that being able to negate the jam completely with a new re-roll AND get an attack was pretty powerful - and jams would basically never happen. Since they're such an iconic part of the setting, I think the GM is right - we'd basically never see them happen if you re-roll your attack that caused them. Is there an exception that doesn't allow you to use a Fate Point to re-roll an attack if it has some 'bad thing' attached?

Do other people allow Fate Point-Rerolls to make a new attack (voiding the jam)?

As a GM Myself... I would say a re roll is a Re roll. Which means it could be both positive or negative. If you re rolled and the Jam didn't happen that's fine. However if you re rolled a normal miss and ended up re rolling worse and ended up with a Jam, you would be stuck with that as well.

Generally you can use it to reroll any dice result. The trade off is that you must accept the new result, for better or worse. I know a psyker character who used theirs to make their phenomenon/perils roll a little better and even dodged a 00 result using it.

As written:

Spending one Fate Point allows a Space Marine to do one of the following:

- Re-roll a failed test once.

An attack roll is still a test and jamming is a failed test in the same way that failing a strength check means you cannot move that door/rock etc. You should be allowed to reroll it under the rules but then at the same time the GM's wording is final. If they have ruled that you can use it to avoid the really bad part of the effect but not the failure then thats their call.

Yes, it is powerful but then players have to be careful about using them. While the book says they renew at the start of each session, I played mine saying they dont replenish till the next mission. This was because some missions took extended sessions and basically the benefit of 6 or more potential fate points a session made people a bit oblivious to the risks of them. To balance out that potent benefit of it then, your GM may choose to override the rules and say that while you can use them to reroll the attack, you might not get those points back for a while!

If you use a Fate Point to re-roll a failed test, the original result (and any consequences thereof) are ignored. The result of the re-roll is taken instead, even if worse.

If your player decided to re-roll a ballistic skill test because his roll resulted in a jam, he re-rolls the entire test attack included. If the re-roll resulted in a successful attack, then he not only undoes the jam but also hits something as well.

Generally you can use it to reroll any dice result. The trade off is that you must accept the new result, for better or worse. I know a psyker character who used theirs to make their phenomenon/perils roll a little better and even dodged a 00 result using it.

As written:

Spending one Fate Point allows a Space Marine to do one of the following:

- Re-roll a failed test once.

Psychic Phenomena rolls are not tests and so cannot be rerolled. A Focus Power Test is a test and so can be rerolled, but only if they fail, not if you succeed and roll a double.

So a psyker cannot use it to "dodge" perils.

Psychic Phenomena rolls are not tests and so cannot be rerolled. A Focus Power Test is a test and so can be rerolled, but only if they fail, not if you succeed and roll a double.

So a psyker cannot use it to "dodge" perils.

House rule then... Makes up for when I throw other horrors at them. Besides, enemies get the same benefits as the players with that.

Most enemies don't have fate points though.

Anyway, matter of taste.

I would say that your GM sounds handsome and is probably a very sexual being with a great beard.

Generally you can use it to reroll any dice result. The trade off is that you must accept the new result, for better or worse. I know a psyker character who used theirs to make their phenomenon/perils roll a little better and even dodged a 00 result using it.

As written:

Spending one Fate Point allows a Space Marine to do one of the following:

- Re-roll a failed test once.

Psychic Phenomena rolls are not tests and so cannot be rerolled. A Focus Power Test is a test and so can be rerolled, but only if they fail, not if you succeed and roll a double.

So a psyker cannot use it to "dodge" perils.

This is correct.

I warn against house-ruling this out too, as psychic powers in this game can get pretty silly pretty quickly. The possibility of bad shite happening is one of the balances to this.