Home Forums Reloading Big Game Rifles Powder charge or seating depth first?

Okay. My son and I got back out to the range yesterday with his .300 Winchester Magnum and we were able to fire a number of loads. The loads consisted of Hornady's 200 grain ELDX on top of varying charges of either IMR 7977 or IMR 8133 (yes I was lucky enough to find two pounds of each the other morning). I measured his maximum cartridge length using the highly scientific "sharpie method" and seated his bullets .015" off the lands.

I loaded four rounds at 74.5 grains of IMR 7977 to provide for a clean, cold first shot fouler and then a three shot group. Then three rounds each in 1/2 grain increments up to 77.0 grains. I then loaded three rounds each in 1/2 grain increments from 79.5 to 82.0 grains of IMR 8133.

As it worked out I was able to fire all of the loads of IMR 7977 without pressure signs and within what I think was acceptable velocity (being the #1 pressure sign) for a 26" barrel. With that said, the first two shots (fouler and 1st subsequent) listed higher velocities than anything else I fired with that powder. Those two shots went 2,999 and 3,031 fps respectively, then dropped for shots three and four to 2,909 and 2,926 respectively. I've not ever really paid too much attention to clean, cold bore shots, but it appeared that the bore needed to be "seasoned" if you will. Would value thoughts on that.

I was not able to fire all of the loads with IMR 8133 as I ran into a slightly sticky bolt lift at 80.5 grains. Interesting observation was that with nine shots fired with that powder across a full grain difference the low velocity reading was 3,003 and the high was 3,060. Another interesting observation was that the high reading was at 80.0 grains and didn't exhibit sticky bolt lift. It should also be noted that the primers in all loads fired still retained a fairly rounded appearance.

I gathered my starting load information from Hodgdon's website, but after reviewing Nosler's load data found online it is clear that I should have started the IMR 8133 at a lower charge.

Anyway, on to the results. First are the targets from the IMR 7977, with a composite of all the shots fired as if on one target.






I felt like there was a lot of positives about this powder/bullet combination and the velocity is acceptable at an average of 2,940 fps at the most accurate load of 76.5 grains.

Now onto the IMR 8133. I knew my testing would be short lived here as the first group at 79.5 grains averaged 3,026 fps, but very low deviation. I went up to the aforementioned 80.5 grains, but a little bolt stick and shiny extractor marks...so we stopped there.
Here is the target from the three loads that we were able to fire. As a caveat, I don't have great confidence in the size of the groups at 79.5 and 80.0 as my son was shooting them and he is still fairly inexperienced. As I thought he may have pulled the shot that is an outlier in the 80.0 grain group I asked if I could shoot the 80.5.


And the composite of these three:


On my way home from the range I kept thinking that the groups fired with IMR 7977 indicated a clear choice, especially given the upper end of the spectrum, pressure wise with the IMR 8133. However, after putting all the data together, especially the composite for the two powders (with the given that there are twice as many rounds included in one of them) I am wondering if the choice isn't as clear as it appeared.

My thoughts are to load up 9 rounds of each powder - 76.5 grains of IMR 7977 and 80.0 grains of IMR 8133 and see if there is a clear winner.

Would love to hear any feedback.

Thanks for following/helping me along this path.

300winnie