Seating depth test analysis; would you even mess with this?

[TheGerman]

Shot multiple groups of 5 lots of seating depths for the 6.5CM because for some reason, I like splitting hairs and dicking around with things.

The results, other than the last 2 lots (the most jump) being really terrible, probably due to the 'hotdog down a hallway' syndrome, everything else was fantastic.

The thing that has me wondering if I should even change anything from my initial testing of rounds that are sitting exactly where the rifling begins, shoot almost identical to any other further seated (more jump) bullets. Would there be ANY advantage to having it jump more? The rounds that are touching the rifling are not jammed, so there is 0 change of a stuck bullet when ejecting a live round; so again, any purpose to jumping rounds if the accuracy is the same?

Lot 1 - 2.243 ogive measurement; sitting on the rifling - average of groups was .475
Lot 2 - 2.233 .10 jump - average of groups was .497
Lot 3 - 2.193 .50 jump - average of groups was .453 and then went to further shoot another 5 shot group in the .4s
Lot 4 - 2.153 3 groupings ranged from sub MOA to 1.25 inches
Lot 5 - 2.113 3 groupings all sucked

Lots 1-3 basically shot the same. There is probably more involved with trigger control and what fraction of an inch the reticle was on more than the actual bullet depth. Is there a reason to either stay with the round on the rifling, or go with one with a little jump? Or at this point it honestly doesn't even matter?

For anyone interested:

Barrett MRAD 6.5 Creedmoor
143g ELD-X
42.7 H4350
Hornady Brass
Federal 210
.002 neck tension

 

[PinesAndProjectiles]

I would go with at least a little jump. I would hate to chamber a round, just to have to pull it out and have a bullet stuck in the lands.

 

[SparkyHD1]

I think you would have less pressure if you would seat closer to the lands. Not touching, but close ?

 

[flyer]

Seating depth changes the pressure curve and if it shoots, I would prefer a bit of jump to on the lands.

 

[regency]

Splitting hairs, one of the top 5 PRS shooters in the country told me over the phone when I was pulling my hair out doing load development that, "A well made gun is going to shoot". I shoot a GAP rifle so I know I'm good there...

Then, he said to set that bullet .01 off the lands then do a powder charge ladder test. If the load has ES of 20 or less and can shoot a 1/2" group. Call it good and start practicing. This method has taken all the stress out of me and look at my results. I was doing ladder tests with gun powder in .2gr increments. These are 3 3shot groups going up .2gr on each one. ( I know 5 shot groups are king but again this is ladder test targets). Is their really an doubt...

 

[PinesAndProjectiles]

Splitting hairs, one of the top 5 PRS shooters in the country told me over the phone when I was pulling my hair out doing load development that, "A well made gun is going to shoot". I shoot a GAP rifle so I know I'm good there...

Then, he said to set that bullet .01 off the lands then do a powder charge ladder test. If the load has ES of 20 or less and can shoot a 1/2" group. Call it good and start practicing. This method has taken all the stress out of me and look at my results. I was doing ladder tests with gun powder in .2gr increments. These are 3 3shot groups going up .2gr on each one. ( I know 5 shot groups are king but again this is ladder test targets). Is their really an doubt...

View attachment 6917345

There's quite a bit of POI change. Is that intentional?

 

[Supersubes]

German, do you have velocity figures?


My testing of every creedmoor I’ve chambered or done load developement on has shown equal accuracy between ten to fifty thou off the lands. The velocities however show that pressure builds the closer you get to the rifling, with the slight spike coming at ten and under. If you’re velocity results match mine(as your accuracy does), I’d load around 20 off and forget about it for 2000 rounds or more. The window between twenty and fifty off showed no statistically significant change in average velocities with my tests. Kind of a sweet spot. I shoot the 140 and 147 elds exclusively now days.

 

[Supersubes]

I think you would have less pressure if you would seat closer to the lands. Not touching, but close ?

In the ranges most people are loading, the opposite is true. Backing off the lands always produces less pressure. There may be a point where intruding on the powder space creates the opposite effect but it would still have to compete with the effects of the lengthening jump to the lands as you seated deeper and deeper. Certainly some cartridge/bullet combos may be more sensitive to this, but in my experience, it’s a total non-issue when doing normal work-up.

 

[TheGerman]

German, do you have velocity figures?


My testing of every creedmoor I’ve chambered or done load developement on has shown equal accuracy between ten to fifty thou off the lands. The velocities however show that pressure builds the closer you get to the rifling, with the slight spike coming at ten and under. If you’re velocity results match mine(as your accuracy does), I’d load around 20 off and forget about it for 2000 rounds or more. The window between twenty and fifty off showed no statistically significant change in average velocities with my tests. Kind of a sweet spot. I shoot the 140 and 147 elds exclusively now days.

I will this weekend.

For the testing, I never put the magnetospeed on the barrel as it may have a chance of skewing the results. When I did the original OCW to get the charge first I loaded them all to touch/sit right on the lands but not be jammed as that will be the highest pressure assuming I didn't want to jam any (which I don't). Then I did the depth test and simply increased jump. Now that I have what is the best combination of everything, I am loading another batch of 50 of just that loading and will get velocity numbers as well as start verifying the data on my Nomad.

 

[regency]

There's quite a bit of POI change. Is that intentional?

The images may be misleading with how I cropped them. Group POI change is only about a .20-.25" difference across a .6gr load difference, that was to be expected. If there was no POI then I would be concerned.

 

[FatBoy]

all things being equal I would jump .015". You never know when one is going to grow under recoil or due to NT issues from brass fatigue. Plus, it's almost certainly going to drop pressure a little. shoot for the middle of your sweet spot so if you short stroke one, etc. you're still good to go.

 

[mdmp5]

There's quite a bit of POI change. Is that intentional?

That's not much POI change at all for ascending charges. Pretty much the same impact point. Take his charges up another .4 to .8, and you will likely see the group open up and shift to the other side of the bullseye or something similar

 

[TheGerman]

For those that asked about velocity, here you go:

Barrett MRAD 6.5 Creedmoor 24 inch
143g ELD-X
42.7 H4350
Hornady Brass
Federal 210
.002 neck tension
2.193 on the ogive (.50 jump)

106 degrees
6540 density altitude

2799 fps over 50 rounds; all 50 rounds 9.4 S/D

The only thing I noticed was some groups would get very obvious horizontal stringing which is usually tied to the seating depth. I'm going to seat them further forward to 2.233 and 2.223 and see if it likes the .10 jump (which it did on the initial testing) as well as the .20 jump and then settle on one.

 

[Gohring65]

I always go with the longest jump so I can chase the lands, slight adjustment in powder, but seating deeper allows me more bearing surface to use.

 

[TheGerman]

I always go with the longest jump so I can chase the lands, slight adjustment in powder, but seating deeper allows me more bearing surface to use.

I'm guessing the .50 jump initially tested well but ended up having quite a few groups that were very horizontally strung. That usually can be remedied via seating depth. I agree (and mentioned it in the OP) that I didn't necessarily want to have it touching the lands in case I wanted to unchamber a round, but seems that the final tweak will be either a .10 or .20 jump.

 

[Gohring65]

I'm guessing the .50 jump initially tested well but ended up having quite a few groups that were very horizontally strung. That usually can be remedied via seating depth. I agree (and mentioned it in the OP) that I didn't necessarily want to have it touching the lands in case I wanted to unchamber a round, but seems that the final tweak will be either a .10 or .20 jump.

Yea to clearify, I go with the longest jump that produced the best, or acceptable accuracy.

 

[arm017]

Seating depth changes the pressure curve and if it shoots, I would prefer a bit of jump to on the lands.

yep I agree - think I can squeeze a few hundred extra rounds in a 6.5 CM cartridge with this philosophy.

 

[nexusfire]

The only thing I noticed was some groups would get very obvious horizontal stringing which is usually tied to the seating depth.

I have never heard of this being the cause. Can you elaborate?

 

[TheGerman]

I have never heard of this being the cause. Can you elaborate?

Go onto 6BR or any of the heavy reloading based sites; its been mentioned for a long time that the effect of a 'bad' seating depth can be worse accuracy as well as horizontal stringing. Obviously there's other causes of horizontal stringing as well, but when you are testing and it never happens until it happens multiple times testing multiple groups of the same seating depth, its probably that.