On my factory Cooper 22-250 (pictured above) the POI did not change, and accuracy (at 100yds) was typical (.5 MOA)
I have a custom 338 LM with a broom handle thick barrel, and POI did change on this (at 200). POI moved upward about 2.5". Accuracy was also typical for this rifle.
I guess POI changes will vary from rifle to rifle, but accuracy seems to hold. I won't be using mine for ladder tests or for LR groups, but for confirming drops, keying in pn velocity, and testing a known load for ES it is awesome.
I really like mine. I read where some people have overtightened the strap and broke the bracket.I put mine on snug and check it carefully between shots.
I'd suggest just a little bit of butyl tape between the mount and barrel to eliminate that problem. You can get it at any builder supply or even most hardware stores. It's the tape used to secure the overlapping edges of steel roofing sheets.
Without the First and Second Amendments the rest of The Constitution is Meaningless.
Works as advertised. Has never failed to read a shot under various conditions. I use it for determining max charge and clocking promising loads. I never use it during accuracy testing.
I've never thrown a golf club in a lake but a chronograph that habitually fails to read a shot has got to be the same feeling. At this point I think it's fair to say I'm done with traditional chronographs.
I would be curious to know how that device strapped to the barrel affects point of impact VS point of aim or accuracy?
Any of you guys notice any problems?
I do get some POI changes and just don't trust any accuracy test with tool strapped to the end of the barrel. For me, the trade off of getting readings every time I expect them vs finicky tools that only sometimes get readings during accuracy testing is more than a fair trade off. Can't tell you how many times I've taken a trip out to the desert expressly for chrono data and been turned around due to finicky equipment. If I normally load 5 shots of each load, I might load 8 and when I done accuracy testing the first five, I'll strap on the magnetospeed and clock the last three of each load for a little data. I look forward to the last three because I can pick off ball targets like rocks or a broken clay pigeon I stuck on a branch and lob shots at them and still get good data because I'm not forced to shoot through sky screens. I can do more thorough testing on promising loads later.