Okay, so much for the paradigm shift WRT AA1680. I am officially declaring that is is a bad choice for the 275 XPB unless you super glue the bullets in. It's just too darn slow and besides, you'll run out of case capacity before getting into the velocity sweet zone.
However, lots of results with W296, that is slightly slower than Lil Gun.
I performed three iterations in this experiment. Some more extensive than others due to conserving my bullets. I want to emphasize that these 3-shot groups are not my method of choice, but until I find the right recipe, they do provide adequate data to make that determination and afford a limited glimpse into what to expect.
In this experiment I loaded up a series of powder steps approaching maximum case capacity using three different crimp options. I did a couple of runs with AA1680 before throwing the towel in, due to no improvement from the last part. The Lion's share of the work was with W296. I've already seen that Lil Gun will works with them, albeit probably a tad fast for the bullet weight.
1) Seat bullets utilizing only the TightNeck approach without a followup Taper crimp.
2) Seat bullets using a combination of the TightNeck and Hard Taper Crimp (.474)
3) One run using a shorter COL of 2.20 inches which allows driving the Taper Crimp into one of the driving band grooves.
Here's the results:
Yielding these 100 yard groups (note: 1/2 inch grid)
TightNeck Only
Tightneck + .474 (Heavy) Taper Crimp
Tightneck With a COL of 2.20 versus 2.26 to allow driving the (Heavy) Taper crimp into the groove
The Tightneck alone, while yielding similar velocities to the TightNeck+ Taper, yielded slightly looser groups. The TightNeck+ Taper yielded some excellent 100 yard groups, when I was doing my job. It was frustrating to throw 2-shots into less than a half inch, only to have a flyer ruin the total group. Admittedly, these are only one-time, 3-shot groups. All were however shot round robin to randomize any hot streaks. That equates to re-positioning the bag and rest every shot, which is distracting and a challenge to overall consistency. It is however how I do it.
Interesting Observations:
The TightNeck+ Taper Crimp seem to be synergistic to accuracy, though less so to velocity.
They didn't help one bit with the AA1680. As I said, I don't think AA1680 could ever be considered appropriate for this particular weight bullet, but I had to try.
If you look closely, you'll see that best velocity for the 41gr charge went to the shorter COL load that allowed the taper crimp to bite into the driving band groove. In my book, that equates to the greatest bullet retention of the three methods I tried. Not necessarily all that accurate though.
All in all a fun outing. Though the wind was gusting in the 20mph range occasionally from my front left, at 100 yards, I did not feel I could blame my occasional group flyer on it. These are heavy bullets and that's not very far. Typical TOF was probably in the range of .15 seconds, so the wind didn't have much time to act adversely upon them.. You could not hear the impact sound which was masked in the persistence of the muzzle report sound.
The jury is still out on whether the TightNeck benefit is worth the extra loading bench effort. It is definitely worth giving a try with lighter bullets where neck tension is more critical than heavier bullets. Just because they get moving faster by virtue of their lighter weight. That will be my next TightNeck experiment.
Yawn. Way past my bedtime after a busy day, which I got off due to having to work a double tomorrow.
Hoot