Is it just bad luck that my largest groups are in the middle of velocity nodes?

[SuperBruce]

I'm trying to work up some 6.5 creed loads, one is 130 Norma golden + H4350 and the other 145 Match Burner + 6.5 Staball, and did a charge weight ladder the other day only to find that for each combo my largest groups where all in the velocity flat zone. Each grouped well on either side of the flat spot (~< 0.5 MOA) but in the flat zone they spread out to 1+ MOA with some a sizable vertical spread. These tests were done at 200 yards.

I haven't done a seating depth test and that is next but before I waste precious powder and primers I thought I'd ask for a second opinion as to whether this is just bad luck and can be corrected with seating depth or whether something else is going on.

 

[Olen_4504]

seating depth test should tighten it up. but a significant change in seating depth will also change your speed some. so you just gotta find that right combo

 

[redbullitt]

I'd test as far out as you can for vertical spread if possible. If you're in a node, like was said above, seating depth will modify when in travel of the barrel the bullet leaves

 

[SuperBruce]

I'd test as far out as you can for vertical spread if possible. If you're in a node, like was said above, seating depth will modify when in travel of the barrel the bullet leaves

'node' seems to be a somewhat overloaded, I presume you mean a powder burn node and not a barrel harmonic node. My understanding is that the seating depth should help tune the load to barrel harmonics while the powder burn node may shift a little if I dramatically change depths and may require a bit of fine tuning after the seating depth test.

 

[redbullitt]

I'd probably say bad luck, yes.

Example... subsonic loads for 300blk bolt rifle. Imr4227. I was loading for about 950 to 1000fps hopefully. At 950 fps, groups were very good at 50 and 100, but velocity spread was terrible and they made big vertical lines for groups further out. If I went to 1000 fps, the groups were poor, but the velocity spread through chronograph was VERY good, so the powder was happy but the barrel was not I think.

Soo, a bit of a balancing act between the two was next. Unfortunately with subs there is less room to work since I'm fighting speed of sound, but it's the same idea. I tweaked the seating depth on the loading close to 1kfps until it was acceptable. Kept the powder happy enough and got the barrel node good enough too. Depends on your goal really how far you go with it, and absolutely you may want to fine tune more after balancing seating depth with your favorable powder charge.

Just takes time and unfortunately primers... I've more or less suspended load work temporarily... if it shoots 1moa, it's done for now.

 

[918v]

If you are doing this on a new barrel then your “node” could be worthless. Probably is worthless.

 

[SuperBruce]

If you are doing this on a new barrel then your “node” could be worthless. Probably is worthless.

It's a factory barrel (Bergara HMR) that is about 300+ rounds in.

 

[Long Range 338]

I'll loosely quote David Tubb whom I saw in an interview state that for refining loads, powder charge to fine tune vertical dispersion and seating depth to fine tune horizontal dispersion (of course this assumes that the shooter/system is not suspect of being the larger problem).

 

[918v]

Then adjust your coal