I am right at the end of calling my load workup for my new 6cm barrel done. Looks like I have 2 nodes one is a touch tighter but falls off faster. The other is not as tight but is almost twice as wide and falls off slower. Right off the bat I had decided on the smaller but after looking I think I'll use the other with the wider node for more forgiveness. What your thoughts?
Seating depth test. (Which one would u pick?)
- Thread starter Andrew863
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I say you load up 25 each of 1.73 and 1.85 and shoot some 5x5's to see if there truly is a "node".
Could be a fun exercise...
Could be a fun exercise...
or 2.160, allows more throat erosion without having to adjust. That said, I like 2.158 as it has decent groups either side of it.
I'd load up just a few those to those node configurations to verify, as that's always my the next step. Then, if they're confirmed being good still, it's easy to know what to do.
Thanks for the replies. I think at this time I'm going to load up 5rds of 2.164, 2.161 and 2.158 and which one of those that shoots the best call it my load. I have a couple primers I want to try after that then call that my load. But as of now powder is locked and one more trip the seating depth is locked in.
Maybe I missed it but velocity data would help here. Otherwise, theres no practical difference between any of them.
How does velocity help u decided a seating depth? Powder charge was the same on all loads?
Because seating depth affects pressure. There are two variables changing when you adjust seating depth, case capacity, and proximity to the lands. Land proximity tends to win in the ranges we work in. Closer to the lands equals more pressure. If you had velocity data, you’d notice that each increment you move away from the lands, the velocity drop becomes less and less. With a large enough sample size, you can see ES and SD changes as well.
The 2.182 (target #7) is impressive and 2.188" is quite good as well. Though I will make the observation these are only 3-shot groups instead of five. Since you moved in 0.006" increments, I'd recommend building some cartridges at 2.185" and see how they compare. Ideally you should shoot groups of five rounds from 2.188" down to 2.179" in 0.003" increments. Please let us know how it turns out.
Lol I knew the 5 shot group was coming. Last years barrel I worked up I tried both 3 shot and 5 shots. Still came down to the same seating depth so I changed to 3. I do agree the more data points the better but I'm just trying to conserve anywhere I can since I have had issues getting components. I am going to do another seating depth test with the data from this and that will be 5 round groups.
Reloaders try to interpret way to many conclusions from tiny data sets.
We also have a tendency to overthink and put too much emphasis on how a thou of seating depth changes precision.
As long as you have good components (and a chamber cut properly and to your specific projectile), you can load up almost any of those seating depths and it will shoot well.
I bet if you shot many 5 round groups of all of those seating depths (which you shouldn't unless you want to experiment, as that's a lot of time and projectiles), you would find that most of those seating depths average out to be approximately the same, precision wise.
I see the 3-shot groups working to get you in the ballpark. But now that you're close, I'd recommend the 5-shot groups. If components are an issue, I'd favor 3-shot groups at 0.003" increments instead of 5-shot groups at 0.006" increments for your next test.
I've found that 5 round groups don't really tell me any more than 3 round groups, when it comes to OCW testing. If one has perfected their precision loading, with a good gun/barrel a decent shooter can even get by with only a 2 round group. 3 round groups easily gets me to where I should be with close to a 100% success rate. Many times my first two rounds, when they're not touching or very close, don't warrant a 3rd shot since the group isn't going to get any better, so I move on to the next 3 round group.
Unless one is firing a really large magnum cartridge (like those holding 80-90 grs of powder or more), .006" increments is too much as it can easily skip over or miss a node. With that kind of increment, one can find a node, but I feel that's more luck than what shorter increments can show. So I agree with your recommendation of using .003' increments.
"Closer to the lands equal more pressure" only when you're really close to the lands . . . like within ~.010" or less. When one is that close to the lands, changes in seating depth with small increments causes higher pressure in the cartridge but the pressure spike caused by being close to the lands overrides what the seating depth changes produce. So, yes . . . one can actually see a drop in velocity as the proximity to the lands decreases, to only to a point.
Once one has moved far enough away from the lands, that decrees in velocity no longer occurs. If it did, one would have to constantly change seating depth as the throat erodes to maintain the velocity and accuracy. Once I've found a seating depth that works (usually, something between .015 - .030" off the lands to start with, I'll keep that seating depth fixed fixed for the life of the barrel with the particular cartridge configuration, even though the throat will be eroding. Though, I may make temporary changes in seating depth to address environmental conditions. Keeping the same seating depth produces the same velocity even when the throat has eroded a lot and my proximity to the lands isn't anywhere near the same (of course, I'm using the same lot of powder too
).
Thats what I said, with less words."Closer to the lands equal more pressure" only when you're really close to the lands . . . like within ~.010" or less. When one is that close to the lands, changes in seating depth with small increments causes higher pressure in the cartridge but the pressure spike caused by being close to the lands overrides what the seating depth changes produce. So, yes . . . one can actually see a drop in velocity as the proximity to the lands decreases, to only to a point.
Once one has moved far enough away from the lands, that decrees in velocity no longer occurs. If it did, one would have to constantly change seating depth as the throat erodes to maintain the velocity and accuracy. Once I've found a seating depth that works (usually, something between .015 - .030" off the lands to start with, I'll keep that seating depth fixed fixed for the life of the barrel with the particular cartridge configuration, even though the throat will be eroding. Though, I may make temporary changes in seating depth to address environmental conditions. Keeping the same seating depth produces the same velocity even when the throat has eroded a lot and my proximity to the lands isn't anywhere near the same (of course, I'm using the same lot of powder too
OK, then we're in agreement.
When I was reading what you said, I was getting the idea that with the jumps most people do for their loads they'd see less velocity as they increase their seating depth. So, I tried to clarify a little more and got wordy.
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