Happy 4th, Everyone
I made it out to the range today do to an OCW test for my 308. First a bit of backround: I'm was running 175gr SMK in front of 44.4gr Varget in Lapua brass. It is a pretty accurate load, and chrono'd around 2760 out of my 25" Bartlein barrel. But... pressure signs! Ejector swipes on the case head on almost all my brass, some really light, others pretty heavy almost obliterating the writing on the case head. Primer pockets were starting to get quite loose, not to the point of primers being able to be pushed out with a folded out paper clip, but very loose going in. This after only 3-4 loadings. On one occasion at an informal match, after 80+ rounds of this load, I was starting to get a very stiff bolt lift. So I felt that it was time to find a load that isn't so stiff.
For my test, I continued to use Varget and 175gr SMK with Lapua brass as my components, but I started at 42.6gr and worked back up to 44.4gr in 0.2gr increments. I shot 5-shot groups in a round-robin fashion at 100yd. I recorded each shot's MV at 15yd with my Competition Electronics chrono. Because they were shot round-robin style, I had to record the numbers manually and calculate average MV and SD/ES separately. I charted Ave. MV against charge weight and entered all the data into an Excel worksheet, but don't know how to add that to this post. I didn't measure distance from aiming point, because it was pretty small, and I'm not exactly sure how to find the center of a group (the point to measure from) accurately. Also, when I look at my groups, the elevation of the perceived center of the group doesn't seem to change as I would expect it to as the charge weight increases. Here's a picture of my targets:
Some of the data: (charge weight/average MV for 5 shots)
42.6gr/2623.4 fps
42.8gr/2634.6 fps
43.0gr/2657.6 fps
43.2gr/2656.6 fps
43.4gr/2680.4 fps
43.6gr/2686.8 fps
43.8gr/2711.0 fps
44.0gr/2717.4 fps
44.2gr/2718.4 fps
44.4gr/2739.6 fps
I have quite a bit more data (S.D., E.S., group size, and a graph) but it's on an Excel spreadsheet and I don't know how to get it in this post. Open to help here. I'm thinking 43.0 to 43.2gr or around 44.0gr, but the group at 44.0 was pretty big (0.962") and it is not that far from the high-pressure load of 44.4gr. What do you think?
Edited to add: Excel Screen Shot (thanks c_bass16)
I made it out to the range today do to an OCW test for my 308. First a bit of backround: I'm was running 175gr SMK in front of 44.4gr Varget in Lapua brass. It is a pretty accurate load, and chrono'd around 2760 out of my 25" Bartlein barrel. But... pressure signs! Ejector swipes on the case head on almost all my brass, some really light, others pretty heavy almost obliterating the writing on the case head. Primer pockets were starting to get quite loose, not to the point of primers being able to be pushed out with a folded out paper clip, but very loose going in. This after only 3-4 loadings. On one occasion at an informal match, after 80+ rounds of this load, I was starting to get a very stiff bolt lift. So I felt that it was time to find a load that isn't so stiff.
For my test, I continued to use Varget and 175gr SMK with Lapua brass as my components, but I started at 42.6gr and worked back up to 44.4gr in 0.2gr increments. I shot 5-shot groups in a round-robin fashion at 100yd. I recorded each shot's MV at 15yd with my Competition Electronics chrono. Because they were shot round-robin style, I had to record the numbers manually and calculate average MV and SD/ES separately. I charted Ave. MV against charge weight and entered all the data into an Excel worksheet, but don't know how to add that to this post. I didn't measure distance from aiming point, because it was pretty small, and I'm not exactly sure how to find the center of a group (the point to measure from) accurately. Also, when I look at my groups, the elevation of the perceived center of the group doesn't seem to change as I would expect it to as the charge weight increases. Here's a picture of my targets:
Some of the data: (charge weight/average MV for 5 shots)
42.6gr/2623.4 fps
42.8gr/2634.6 fps
43.0gr/2657.6 fps
43.2gr/2656.6 fps
43.4gr/2680.4 fps
43.6gr/2686.8 fps
43.8gr/2711.0 fps
44.0gr/2717.4 fps
44.2gr/2718.4 fps
44.4gr/2739.6 fps
I have quite a bit more data (S.D., E.S., group size, and a graph) but it's on an Excel spreadsheet and I don't know how to get it in this post. Open to help here. I'm thinking 43.0 to 43.2gr or around 44.0gr, but the group at 44.0 was pretty big (0.962") and it is not that far from the high-pressure load of 44.4gr. What do you think?
Edited to add: Excel Screen Shot (thanks c_bass16)
