I am looking for someone who has had experience with the PVM-21 chronograph sold by NECO. I am having problems with my PACT reading .338 Lapua and larger. Even tried setting up a blast shield and shoot through a spider hole. This looks to be a well designed unit. Whats the consesus.

LSHopper

I do not own this brand of cono, I have a Corny. But I was wondering if you tried changing your distance from where you shot at it? The manual for my F1 states that for a rifle should be 10', pistols somewhere around 3'(if I remember right), muzzle loader out to 20' keeping out of the smoke and residue, and then goes on about testing distance to what works for you.

If your shooting large loads I would recommending moving it back and maybe checking you eye/lenses to see if they are clean too.
Another I found is light makes a huge difference! Not enough light will make it so it will not see the bullet in one or both the eyes.

If have tried such things, and or sound or think I m full of it.(only trying to help) contact the CO. and see what they have to say.
If all else fails contact them and have a work order done up and see if they can fix it if broken. (and I do hope its not broken)