I've come along in my development efforts, and have had a couple of workup cycles and subsequent range trips.
I picked up some of the new IMR 8208 XBR powder a few weeks ago, and put together a set of loads using both the Winchester 55gr FMJ-BT bullets I've been working with, as well as Sierra 69gr HPBT Matchkings. I'd run out of Speer 70gr Semi-Spitzer bullets for my hunting load, and apparently no one in town carries them.
I was impressed that I got decent sets from each bullet using the 8208 XBR powder. In 55 gr, both 24.7 and 25.3 grains gave me decent grouping. Unfortunately, I loast all of my chronograph data for the day, so I cannot provide numbers. Please note, all targets were shot at a range of 50m.
In the 69gr loads, I got good groups in several of the charges, in both the low and mid ranges of the workup. I got good groups at 21.6, 21.9, 22.5, and 23.1 grains. As you may have noticed, some of the shots on these targets are far off to the right. This is due to a quirk in the operation of the Nikon VSD. I'll have a dedicated post on this topic in the near future.
Fast-forward to this afternoon. I got in on a bulk order with some other folks from Powder Valley a couple of weeks back, and was able to get a bunch of the Speer 70gr Semi-Spitzer bullets, so that I'll be able to finish out my hunting load development, and get a bunch loaded up for sighting and actual hunting. I got a bulk box of 1000 Hornady 55gr FMJ-BT bullets, which will replace the Winchester bullets for my normal range work. Hornady's bullets are nicer anyway, and the box of 1000 makes them cheaper.
I've also switched from using CCI #400 primers to CCI #41. The #400 primers don't seem to be made for .223 and 5.56 pressures. I found that the #400 primers would begin flattening even with moderate loads. The primer cups on the #41 are more stout, and are made specifically for 5.56 loading. Apparently the priming compound charge is different as well. My continuation of the 70gr TAC loads indicated a loss of around 80fps with the new primers.
I started out today's session finishing up the TAC workup, and found that 25.2 grains gave me acceptable results, with a velocity averaging 2740fps. I think I've settled on this as a hunting load. Accuracy is acceptable for hunting purposes at a high enough velocity for terminal effectiveness..
I did another workup using the 70gr using the 8208 XBR powder as well. Accuracy was good, but velocity was a little lower than I'd wanted in a hunting round. I may be able to push the charge a bit to get the velocity I want, I'll have to see. The best groups were at 22.1 and 22.7 grains, with average velocities of 2542 and 2610 fps, respectively.
Finally, I decided to try out Vhitavuori N135 with the 55gr bullets, at the suggestion of TxGunGeek. I ordered this powder along with the afore-mentioned bulk buy. I did a wide range for my workup, since I've never worked with the powder before. TxGunGeek uses a charge of 25.6 grains for his accuracy load, though our rifles are certainly different in configuration. I ran the whole gamut and came across a beautiful gem of a grouping at 24.7 grains of 7/16"! I'm quite impressed with the results using this powder so far.
I didn't get a reading from the chronographfor this string because it was getting dim out and I stopped getting readings about this time. Judging from the readings around this group, I'd say it was moving around 2950 fps. Not too bad for a plinking load. Next session, I'm going to run some of these at 100y and see how they do.
They Will Not Grow Old
6 hours ago