My experience is similar to that of those other respondents who've had little or no trouble - use off a bench with the Labradar on a tripod in front positioned a couple of inches to one side of the muzzle and maybe three inches behind. I never bother with trying to aim at the target - get the rifle set up aimed mid target frame, and position the chronograph looking down on it so that it's at 90-degrees to the barrel alignment.
Our (European export) version is permanently set on the 'low' power too. It'll read a 30-calibre bullet to 55 yards if the alignment is good.
I'm now on series #186, mostly 5-round contents, a few 3 and fewer still 10 or more shots. Apart from when I've forgotten to 'arm' the device and check the amber LED is illuminated, I've lost hardly any shots - probably count them on the fingers of one hand! Battery life - never bothered with them as I've used a USB powerpack from day one.
Problems, none really unless somebody with a really noisy muzzle-brake equipped rifle is on the next bench giving false sound/blast triggers. And yes, ergonomics could be improved. I've shot 223, 6mm BR, three different 6.5s, four different sevens and 308 Win past mine and it works equally well irrespective of calibre.
I used all three main models of the Magnetospeed and like it, especially the V3 which I've retained. It DOES affect barrel harmonics on most, but not all rifles though. See the pic for three groups shot in a session with the same 6.5-284 ammo, two without 'bayo' on, and one with. That's a Stolle Atlas action fully Devcon bedded with a 30-inch heavy profile Benchmark barrel on. Conversely, before I knew better in the early MS days, I did some basic load development on a Savage PTA based F-Class rifle with a 31-inch full F-Class / Heavy Varmint profile fluted barrel in 7mm-08 with relatively mild 162gn Amax loads. Every charge weight gave a tiny group over a 2gn range. Whizzo! thinks I, this rifle is going to be simple to get shooting well even if these particular loads were too slow. Took the MS 'bayo' off though and the rifle wouldn't shoot that bullet well with two or three powders and various other variables changed at any load / speed. (It convinced me that there is something in the idea of barrel tuners though which I'm about to play with in 90gn 223 Rem loads.)
I have a friend though on the GB FTR team whose 308 RPA Quadlock action and telegraph pole barrel aren't apparently affected at all by MS fitment. At a Bisley practice session just before the last FCWC at Raton four years ago, he strapped a V2 on and continued our shoot at either 900 or 1,000 yards - can't remember which now - and only adjusted sights by a click or two!
