I just tried my CED M2 today....
...with a .177 pellet rifle. It is sweet. I put twenty rounds through the traps and got a report every time but one when I knew I was shooting hi. I got about 640 fps and then after swabing the barrel it went up to about 710.
I did not use the sky screens. Bright shiney day. Got consistent speeds on the pellet rifle. I will probably take it shooting next week to measure some BP stuff.
The speeds I got on the ROA were with a Shooting Chrony which I have complained about in a different thread. This CED is already outperformaing that unit.
Don't mean to be critical. I know there are plenty of guys out there who get good results from the Chrony, including many who post on this forum. I just could not get mine to work...two different units, one of which had been rehabed by the factory. I never shot it 20 feet from the muzzle (I went out to about ten I think.) and never used blast shields. AND, I have not tried the M2 with BP so I may still be disappointed.