using my Pact model 1, nope I haven't shot it yet, but a "friend" did.
He took out both sky screen sensor boxes with a 180Gr .308 & I was 100% sure it was gonna cost a bundle to get them fixed.
Wrong! they are very well designed as the actual sensors are at the lowest bottom of the box. The total replacement cost was about $10.00 for the plastic boxes & cast plastic lenses.
The sky screens are to diffuse strong, directional light only, you can use them or not, but I always use them as they give me a frame of reference to shoot through & (for me) make aligning when setting up way easier.
A thought on the unreliable readings..........
Were you using either wads, lots of grease, or anything else other than the ball when checking BP velocities?
I ask because the only thing I've ever had effect my readings was the time I tried Cap & Ball with wads (the sensor can't tell a ball from a wad & so gets confused, thinking you fired 2 bullets almost together) or the smoke/burning powder particles does the same thing.
I had trouble with a muzzle device because of the side blast too,but I mainly had problems with some sabot rounds I was messing with.:barf:
Before you give up on the Chronograph, try backing the "START" screen off to 15 feet, this fixed most of the problems I had with multiple "projectiles" at 10 feet even though that is the suggested distance.