Some insight on jamming please

[BoydAllen]

I don't usually test that way. As I said, I would start where similar bullets had done well. But if I were going to do what you have described I would probably go with .002. Another thing, in order to minimize the effects of changes in the wind, I do initial tests as two shot groups, shot as rapidly as possible, over wind flags. If two shots look ugly, a third shot won't make it any smaller. If two shots look great, I can test with more shots in a subsequent group. I avoid loading five of each at home like the plague. Load at the range.

 

[6BRinNZ]

fayettefatts

an issue I found with trying seating depth changes of say .001" was - I couldn't maintain that level of loading accuracy (this is with non match bullets), i.e. for a group of say 20-40 loaded rounds the seating depth would vary by +- .001" for a spread of .002".

I suspect that neck tension plays a part in seating accurately as well, i.e. greater "neck tension" will be inclined to affect the seating depth more.

I measure every loaded round with the redding Instant indicator.

So depending on your setup you may find increments of .005" more meaningful.

 

[mikecr]

Boyd, have you tested bullets off the lands?

Maybe some amount into lands -vs- some amount 'more' into the lands tweaks timing, but that hardly relates to seating adjustments many need for best accuracy(like 8thou off -vs- 5thou, or 10thou or 20thou)
I've seen with every gun I put my hands on that seating adjustments OFF the lands produce bigger grouping deviations than can be caused by powder adjustments.

Test it for yourself. Take one of your jamming screamers and seat 5-10thou off for fun. Observe the ugly performance produced, then try to make your normal jammed load perform so bad with powder adjustments.
I don't think you can, and so then seating ain't timing.
It's something else.

 

[BoydAllen]

Yo Mike,
A fellow that is ever so much more experienced than I told me something that is not common knowledge. There are jump nodes, that are like powder nodes. The up shot is that when I pulled back an arbitrary distance from touch, and accuracy was reduced, i assumed that I didn't need to look farther, since I knew that that barrel/bullet combination did not shoot jumped. Now I know that there are jump nodes, and just like powder nodes, if you are in the wrong place, you won't get the best accuracy. Like powder nodes, they tend to be somewhat evenly spaced. I make no guarantees but the source was a good one.
Boyd

 

[fayettefatts]

BoydAllen:
How wide do you think these nodes are? .005, .010 or more? Or does it depend on the rifle and caliber used? I have already found a node for a powder charge using an arbitrary jam length while ladder testing, and would now like to tweak the load by changing seating depth.

 

[BoydAllen]

When seating into the rifling, if I am adjusting to see if I can gain anything, with a load that is already doing pretty well, I don't move any more than .003, and test, over flags, with a fast two shot group. Another thing to remember is that you will need to adjust for throat wear from time to time. I have seen friends go to a match with a seating depth that was working well in practice, but that they had not adjusted for some time, and suddenly find that they couldn't quite make it work. Seating .003 longer solved the problem. Another factor, this is with a double radius ogive bullet. For a single radius, around a 7 I would make smaller adjustments, because the ogive is is not as close to parallel to the throat angle.