bludog,
I didn't detail any of the possible reasons for your low velocities, so will now.
Many other people have reported RL-16 velocities similar to those in Alliant's data, and in fact you're the first person I've read about who reported low velocities. Several possibilities exist for this to occur:
First, the assumption your chronograph was working correctly. Among around a dozen chronographs, I've owned two of one particular brand of popular chronograph that eventually proved unreliable, and seen the same brand causing trouble for other shooters at local ranges. My second one recorded velocities 100 fps difference depending on whether the sky was clear or cloudy. Low batteries can also cause problems. We don't know what chronograph you used, or if the RL-16 loads were the only ones you tried that day. But if you chronographed other loads during the same session and they all produced "normal," consistent velocities, we can rule out chronograph aberrations.
You happened to get a slow batch of powder. This can happen, but isn't common, and when it does velocity difference is rarely 200 fps. In fact I don't recall ever seeing as much as 100 fps.
You used a different bullet than anything listed in Alliant's data, and these days the pressures (and therefore velocities) produced by different bullets vary considerably. In fact different brass and primers can also result in lower velocities, as can seating bullets farther off the lands. I've seen as much as 250 fps difference in velocity when using different bullets of the same weight, with the same powder charge, in the same rifle.
MD (Brad, et al),
Thank you for taking the time to provide the potential causes. I appreciate it very much. And I apologize for the delay in responding, but we just returned back home from an extended stay in AZ, and I just now got to my reloading records.
This is a fairly new rifle, and was only the second time I've had it on the range, the first with a chronograph (a Shooting Chrony). The rifle produced "expected" velocities that same day with
120 gr NBT and 44.5 gr Varget of
3009,, 3009, and 2989 fps. So I would tend to rule out the chrony.
Velocities with 46.5 gr RL-16 and
140 gr NBT were
2726, 2710, and 2715 fps. Note that Alliant lists the
140 gr NPT getting
2952 fps with 47.2 gr of RL-16, with a 24" barrel. The Tikka barrel is 22.5".
I also shot some
140 gr Sierra HPBTs using 47.5 gr RL-17 and recorded velocities of
2873, 2852, and 2886 fps.
To me, the Varget and RL-17 velocities are very in the "expected" range and to me, the RL-16 velocities were "way slow". You can decide for yourselves.
Thanks again, and I will try this powder again, and let you know if I see some improvements.
V/R,
bludog
