Originally Posted by ryguy00
you will initially see groups start to shrink with the changes and then eventually open back up. Refer to your notes to go back to where they were good and fine tune. Keep in mind that the throat will erode with use and lands move further away from the chamber due to wear. Eventually you will have to increase OAL to chase the lands and that "sweet spot"
I'm shooting a bolt action (Remington 5R), and what you described is what I was expecting to see. I was expecting to see the groups either open or close as I got closer to or further away from the right seating depth. I guess I just got lucky and the load that was .015" longer was the perfect load?
As for how I got to that point, I used a dummy round to find where the groves started. The groves in this rifle were way too deep and my OAL length where it made contact was at approximately 2.910". I then backed off .050" from that as a safety factor. A cartridge with the bullet touching when it goes off will increase pressure. Bench rest guys want the bullet right at touching but they are developing their loads for that and backing off on the charge to compensate for the increased pressure. So I backed off .050" from touching and then started working my way to that point stopping before I get too close. My longest loads were still .020" from touching.
In this case I'm way past the manual on OAL. I just didn't expect that much of a change from a .015" change in depth? I guess .015" really is a pretty big change in seating depth.
FMJ, I was shooting off a bench with a bi-pod and bag at the rear of the stock. I personally think most of use are capable of shooting great groups but our equipment is the biggest limiting factor? But I've also been shooting a long time and shot competitively on the rifle team in high school. And this still could have been pure luck? I will definitely load some more rounds at this length to verify my results.
I'm just trying to figure out how many rounds to load when testing a load. I don't want to load too many because at some point I'm wasting shots and time. In this instance I was trying 4 different loads with 5 rounds each. That's 20 rounds and could have been a lot more if I loaded more rounds for each load. At the same time I want enough shots to have confidence in my results. One 3 shot group could be misleading because you could get lucky and shot one good group, or one bad one. 10 shots per load would give pretty reliable results but that's a lot of shooting and time. In this case that would have been 40 rounds. So I'm looking for the bare minimum shots needed to have some confidence in the group. Right now five seems about right for me?
As for cleaning, I clean every 20 rounds as a general rule which is in part why I loaded 20 rounds to try on that trip. After I verify that I have found a great load for this gun I'll shoot more rounds and figure out at what point my groups start opening up or POI changes. I'll then change my cleaning to match what I need for this gun.