I have a CED M2 chrono and sometimes the weather or the range itself precludes using it easily. So when the MagnetoSpeed chrono was announced I immediately bought one (V1).

The benefits are pretty obvious (works in any weather, no need to set up down range, etc) . . . so are the limitations (works only when you can attach it to a barrel). But because the bayonet's strap attaches to the firearm's barrel, I was concerned about affecting both POI and spread. So I've been running some tests.

The photo below shows the most recent test using a Remington 700BDL 30-06 shooting 123gr Lapua Scenars over 53.8gr of N-140 from the same batch of reloads at 100yds. The 9 bullet holes were transferred from three targets to a single target for comparison.



Three groups of three shots were fired . . . the first (Middle) using the bayonet, the second without the bayonet (Lower), and the third reattaching the bayonet 1/4" further back on the barrel and tightening the bayonet strap a little tighter than for the first group (Upper). Velocities for the 6 measured shots were ~3000fps and were all within 42fps of each other.

Compared to the base group, attaching the bayonet moved the POI 0.71" up and left; reattaching it in a different position and tightening the strap a bit more moved the POI 1.50" up and left. Anecdotally, this result is similar to results from previous attempts.

While YMMV, my own conclusion from several of these tests is that attaching the bayonet does cause a POI shift, and that the amount of shift depends on how and where the bayonet is attached to what kind of barrel . . . and maybe other factors. Importantly, the shift may change from use to use depending on how consistent one is in attaching the bayonet.

Initially I thought the bayonet also caused group size to change. However after several tests, as seen in this example, I can't be sure if the bayonet has a positive, negative, neutral, or variable effect.

I love the product - it gets me data I want when a regular chrono can't be used. However, the variable shift in POI may affect some uses.