Greg,
you are right that was not covered in his paper....i forgot that i had emailed him that question and he addressed it in the email. below is my question to him and his response. and again i will caveat with i have no way of knowing if his theory is in fact correct. but i havnt weighed the magnetospeed but it might fall into his caveat about 20 ounces or more, but if its close to that then according to what he says it affecting grouping could be contour specific, which would explain why some people see differences and some people do not.
Chris,
I was reading your OBT paper and found it so interesting I tried to explain it to my wife (though she did not find it as interesting for some reason) but I was curious. How would muzzle brakes and/or suppressors change those numbers? It seems like it would change how long the shockwave took to get from one end to the other but you would have to figure out when the wave would be at the actual end of the barrel not the end of the supressor. is there any data for this?
EJ:
I get this question a lot, and many Internetians dismiss the shock wave effect by saying that it ignores the bending vibration modes. Unfortunately, these people did not read the original OBT paper closely, particularly where I clearly state the that research I was doing was around the radial shock wave distortion and modeling, and that this effect was IN ADDITION TO the normal bending vibration modes that exist (Varmint Al has a good website that explores these modes). What my research has proven is that while a clamped or threaded mass on the end of the muzzle definitely affects the bending modes, it does essentially nothing to alter the timing of the radial shock wave. This is because the threaded or clamped connection is nowhere near stiff enough to transmit much if any of the shock energy into the mass, then back out into the barrel again for another round trip. The same goes for the barrel tenon threaded into the receiver – almost none of the shock energy gets into the receiver. Therefore, when calculating OBTs, use the bolt face to muzzle crown distance, and ignore any brake, tuner, or suppressor length.
So, both bending and radial modes are present, and you have to have both “in tune” for the rifle to shoot really well. Fine tuning the bending modes is where muzzle mounted tuners come into play. My initial research was all about investigating the radial shock effects, and only later did I do any research with adding mass at the end of the barrel (brakes and tuners). So, if you get a truly tuned load, on an OBT, and fairly intolerant to small (<0.5%) changes in charge weight, then the addition of a brake or suppressor will definitely change the point of impact (POI), but the group size will stay essentially unchanged. It would take a very heavy brake (on the order of a 20 ounces or more, depending on the barrel contour) to really change the bending mode tuning enough to see a marked difference in the group sizes in addition to the POI shift. Most brakes that I have used are on the order of 6 to 8 ounces in weight. A suppressor is also not that heavy, and while I have not personally experimented with one, I have corresponded with folks that have been tuning loads using OBT with suppressors, and they also see little groups size change with and without the suppressor.
Hope that this helps! Let me know if I can answer any more questions, I’ll be glad to try and do so.
Cheers,
Chris
