What is the not-proficient accuracy penalty?

Can’t find the answer to this - how much of an accuracy penalty do you take for using non-proficient weapon?

It looks like there is no accuracy penalty. Instead of accuracy penalty, the soldier will fail with the attack. So if you use jetpack, sniper rifle, melee etc without the related skill, there is a chance, the action will fail, the chance is around 50% in my observation.

There is penalty to accuracy and it is very easy to see, because the aiming reticle is much bigger. It could well be 50%, but TBH I don’t know: I do know it’s something you will notice immediately if you switch between proficient and not proficient operatives with the same weapon.

The 50% chance ‘to fumble’ only applies to using jetpack and attacking with melee weapons.

-50% accuracy is correct answer. Fumbling with ranged weapons was removed in one of the previous year updates.