I would err on the side of caution and use the red guns. Red, like the orange, is a signal to all that the weapon is not real. I know, I know, who carries a blue gun? However, there is nothing wrong with training with a lightweight weapon.

Here's a revelaton: not all weapons weigh the same! Also, you cannot poll your adversary to see which weapon they are using so you can calibrate your technique to weapon weight.

When I would worked with a smaller person in karate on take-ddown techniques, I would just stand there until they finally performed it right. Being tossed to the ground, with authority and force, by someone who is only 5'5" 140lbs shows it is about technique. I was 6'1" 215lbs at the time. Technique, technique, technique...

The majority of training is about the perfection of the movement and technique. A few ounces of weight difference should not impact your abilities once said technique is learned.

All that said, I could still be full of a decent amount of dookie.