If a rule lets you reroll say 3 dice (precise 1) but you only have 2 dice to roll, can you re roll one of them twice? I presume the limit is whatever dice are in play, thereby making targeting scopes useless on scout sniper strike team above range 2 for example. Nothing in the rules that I can see which spells out re-rolls

Rules that allow rerolls are granting you one opportunity to roll that many dice. So if you only have 2 dice to reroll, the third "reroll" is indeed wasted. If you want to reroll any of those dice a second time, you'd have to spend another aim token. This applies to aim tokens as well as Han's Uncanny Luck keyword.

3 hours ago, Alan Noir said:

Nothing in the rules that I can see which spells out re-rolls

You can find that on page 13 of the rules, under "Aim", one of the last bullets:

"A unit can reroll the same die multiple times by spending multiple aim tokens; however, each die can only be rerolled once per aim token. "

When you say, "the rules," are you talking about the Learn to Play pamphlet that came in the box, or the Rules Reference Guide with the actual rules that's available on FFG's website?

59 minutes ago, Lemmiwinks86 said:

You can find that on page 13 of the rules, under "Aim", one of the last bullets:

"A unit can reroll the same die multiple times by spending multiple aim tokens; however, each die can only be rerolled once per aim token. "

Cheers. Couldnt find it under dice or attack. But it could also cause some confusion on uncanny luck too.

49 minutes ago, arnoldrew said:

When you say, "the rules," are you talking about the Learn to Play pamphlet that came in the box, or the Rules Reference Guide with the actual rules that's available on FFG's website?

Rules reference pdf.

1 hour ago, Alan Noir said:

Cheers. Couldnt find it under dice or attack. But it could also cause some confusion on uncanny luck too.

No, for Uncanny Lucky you'll need to check that entrance on the rules too:

"Any dice rerolled with the uncanny luck x keyword must be rerolled at the same time. Each die cannot be rerolled more than once with the uncanny luck x keyword. "

In short, there's no rule in the rulebook (at least that I'm aware of) which generalizes that a die cannot be rerolled more than once per trigger, but each possible keyword that lets you rerol have a bullet point under its rules clarifying this.

Cheers. Thats how we played it but my opponent queried it