Here are some links to previous testing I've did last summer:
XPB Part 1
XPB Part 2
XPB Part 3
XPB Water Shots
A couple of weeks ago, having obtained some slightly slower powders in W296 and AA1680 and being obsessed with QuickLoad, I set out to continue where I left off last year, by characterizing real world results versus QL's predicted behavior. The idea was to attempt to calibrate QL and then see how subsequent load changes matched up with predictions.
The initial test was loading all three powders as close as possible to the QL predicted max SAAMI pressure and record the velocities obtained along with some accuracy assessment. In last year's work, I only used Lil Gun and judging from QL's prediction, took the loads a lot further than I begin with this year. So what follows is a bit of de-evolution, but it establishes a base line. Great accuracy from this bullet can be achieved and more so the higher the safe velocity goes. There's SAAMI safe. There's real-world safe and never the twain's shall meet.
The only default QL parameter for the 450B that I altered was the fired case capacity measured in grains of water. Mine were 59.7gr versus QL's 60.0gr.
Here's the baseline performance. Remember SAAMI recommends not loading the 450B past 38.5K psi.
The resulting groups were interesting:
35.9gr Lil Gun
36.6gr W296
40.5gr AA1680
Both Lil Gun and AA1680 flew close to the velocity predicted by QL, but W296 wound up flying a lot slower. I can not explain this. The higher velocity afforded by Lil Gun paid off in a pretty good group. Foot Note: I forgot to bring any fouling loads and had to utilize the first shot of Lil Gun. As is often the case with fouling shots, they can fly a lot differently than subsequent shots, even with my having patched all the Kroil out beforehand.
For those considering loading the 275 XPB, these can be starting guidelines. I am certain all three can be loaded hotter safely, based upon last year's experience. From those same experiences, I know faster translates to smaller groups. I'll leave determining what that limit is, to you. I intend to certainly up both the W296 and AA1680 loads until I feel uncomfortable and I will report in as I make more headway. We're in a weather pattern lately where it seems to be beautiful during the week and rainy on the weekends. The NWS has not been too stellar with their predictions and I will try to always have some loads ready to go, when a window of opportunity presents itself, as opposed to my normal "load 'em up as soon as it looks promising and rush over to the range."
Keep in mind that often there are two or more velocities where a given barrel will shoot the same bullet into small 5-shot, 100 yard groups as a function of Optimum Charge Weight, Optimum Barrel Time and Optimum Luck. Given the data already achieved with Lil Gun, my emphasis will be upon W296 and AA1680. The latter excites me as it can take better advantage of my full size 20" barrel as opposed to the carbine length 16". Proof is always in the pudding and Lil Gun certainly is up to the task, despite being the faster of the three powders. It's past and present results will serve as the rubric that I hold the other two powders up to.
Hoot
EDIT: Additional Tests further on in the thread.
Good luck with the 1680...should be interesting.