You have the chance either to be successful or lose every time you try to upgrade a weapon.
In every upgrade try failed the 50% of the materials required will be returned to you. When you use a "Loss Reducer" the loss percentage is reduced by the concrete percentege from the standard 50%. (50% - (50% x 30%)).
When you use success-enhancing products, the success rate is multiplied by the percentage of the product you use. The materials lost in an upgrade fail will not be refunded. When your upgrade fails and depending on the level of upgrade you have failed the length of your weapon will be increased.