How much do they effect bullet impact. I am curious how much it will effect load development
Just so you don't get misleading anecdotal information . . . this is from the manufacturer's web site:
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Can the MagnetoSpeed affect barrel harmonics (e.g. the location and size of my shot grouping)?
Last Updated: Dec 31, 2012 12:41PM CST
Yes, with most guns you will be able to see a shift in your point of impact. Some people say it has no affect on their guns so it seems to be a case by case basis. Group sizes seem to be relatively unaffected though by the MagnetoSpeed.
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(Gotta love the ". . . you will be able to . . . " language. Good writers there lol.)
I've seen POI shift on each of my four rifles (2 Rock River AR15s, Sako 223, Rem 700 30-06). Moreover, the POI will shift differently depending on where you attach the strap, and how tight the strap is. This leaves open the opportunity for the POI to shift during firing and from group to group. While I am 100% positive the MSpd has *always* changed *my* POI (vs without), in the half-dozen specific tests I've run I cannot say that groups are larger with the MSpd attached than without.
I continue to use my CED chrono whenever possible for load development. When it's not possible, or its too much hassle, I'll make up extra rounds in each test group and use the MSpd to get velocity separate from POI assessment.
While that deprives me of knowing what velocity the actual load development rounds achieved, it ain't a horrible way to go. MSpd setup is a dream, no waiting for the range to go cold, no worries about weather or light conditions, nothing to hit with a bullet
Those are the facts. The "best" approach is up to you.