m houseruling that if the player wants to decide how many ammo dice he/she rolls, they have to pass a CUF roll first
Your table, your rules. That being said sounds a bit harsh though. Also how do you decide how many dice he uses? To me this mechanic means one extra CuF roll with every attack and probably some random die roll to determine the amount of ammo dice used. What in it in your opinion makes it worth two extra rolls for the attack?
Also as for the use of sniper rifles, especially bolt action, I don't think this is beneficial representation of "combat stress" since situations where they are used are normally not as hectic as CQB situations. But even as a game mechanic this robs the players from the use of their telescopic sight bonus so I personally wouldn't house rule it that way.
Caveat: if it enhances the play experience in your table go for it!
You misunderstand, a bit.
Here's how I run it:
If a player wants to use anything but "all the dice" for ROF, they have to make a CUF roll. If they pass, they get to pick the number of dice they use. If they fail, they fire wildly and use all the dice they can.
So, ROF 5, you use all 5 dice unless you pass a CUF roll. If you do pass, you can use anything you want up to 5 (but if they want that, then they wouldn't have to roll anyway).
This is to represent the fact that less trained soldiers tend to fire more rounds at the enemy.
As for bolt action rifles, they still have a ROF of 1, so if they just want to fire one single shot during their entire 10-15 second turn, then they need to pass a CUF roll.
This is only during actual firefights, mind you, not if they're just sitting safely at a distance and nobody is firing at them, or they aren't under any pressure to make the shot.
For example, during my last session, two players (both snipers) set up an L shaped ambush on a town full of enemies. One sniper had a Barret, and the other had the PSG 90.
The .50 cal guy started firing first, drawing out the enemies and drawing fire (although largely ineffectual due to the massive distance). That meant he was under fire, and after the first initial attack, he had to roll CUF to fire just one shot (when he wanted to do that).
Meanwhile, the other sniper, firing from a side perpendicular to the enemy, didn't really get noticed until after a very long time (due to the enemy spraying wildly towards the first sniper, and the .50 cal being so loud, and both snipers being at their very maximum range), so she didn't have to roll CUF during that entire time, since she wasn't under fire and could take her time lining up her shots.
I'm also not running with the no ammo dice rule for scoped weapons, since I don't agree with that rule. Having seen plenty of people using scoped rifles getting several accurate shots during a 10-15 second period.
I suppose, if you use that rule, you'd just ignore the CUF roll during an engagement where people use telescopic sights.
EDIT: Just to add to this, I should point out that most of the time, my players don't need to roll for CUF since they're using all the ammo dice they can. It won't be until they're starting to run out of ammo that it will come into play a lot more. And at that point it works as a tension amplifier. Otherwise, knowing my players, they'd just start being super calm elite marksmen during the battle and only ever using one shot every time they shoot... despite all research about firefights pointing to the opposite for anything but the most well trained soldiers.