Load vs Seating depth.

[Donkey]

Hi folks.

I am shooting a .308 Win Palma rifle and trying to figure out if I should be tuning for load or seating depth first and how to chose a node that builds in positive compensation for long ranges.

Does anyone have any slow motion video showing how variations in seating depth effect harmonics.

 

[Quickoz]

I always do powder charge and then seating depth. With my 308 I start with powder charge in 0.2gr increments in the MV range you wanna run. Ie for 155gr I'll work from 45.6gr to 47.4gr Varget with bullet 10 thou off lands. I did this with 155.5gr Bergers and got my magic load at 46gr but 46.4gr was also just as good. If you don't find a good load doing that, choose flattest vertical shooting load and test seating depth.

 

[dkhunt14]

I do load first but I always put the bullet in the lands about 10. Matt

 

[timeout]

I agree with the first two gentlemen. Start with a lower end powder charge and work up .2 gr. at a time. Start at .010" into the lands. Shoot at 300 yards, starting with the lowest charge. Mark all of your shots on target as to the charge weight. Keep working up until pressure signs appear in order to identify your max load. Examine your target to identify a pattern of shots with the same vertical height. If more than one node, I would choose the one from the heaviest powder charge or fastest MV. Finally, I would start shooting groups with varying seating depths. With a conventional style bullet, I would back off in .003" increments. With Berger VLD's I would go with their recommendation which uses much larger seating depth increment changes.

 

[BradY]

Erik Cortina started a threat of load development at 100yds in the reloading section. It works. Just follow the instructions. Easy.

 

[Alex Wheeler]

Good question. I believe seating depth has more impact on the tune than powder charge. In my experience when the seating depth is off it is hard to determine the nodes doing your powder test. I just tuned 2 barrels like this. Neither one showed me what I wanted to see in the powder test, so I picked a charge and went after seating depth, came back to powder and now they are acting like you want to see. What I want to see is a vertical group change to a flat group or a clover leaf then a nice little knot then go vertical again. When I see that I know I'm close, but when the seating depth is wrong you wont get that, you get random groups, some decent some not, but no pattern. I still do my powder test first, but if it donesnt show a nice pattern I go after seating depth and then return to powder. JMO.

BY1983, isn't Eric's method what they call Optimal Charge Weight, or is his somehow different? Either way you want your barrel to be "stopped" which is the purpose for looking at surrounding groups to see if they print to the same poi. Some methods look for that on seating depth first, then go after powder. It all works.

 

[Quickoz]

I should have added to test at 300yds/m. I always start my load dev there for 308 and for my 6mm aswell and it works well. I'll also use 500m club BR matches to tune aswell. Once it's good at 300m test at around 800yds/700m so you can see if there is any vertical at long ranges.

 

[Donkey]

Good question. I believe seating depth has more impact on the tune than powder charge. In my experience when the seating depth is off it is hard to determine the nodes doing your powder test. I just tuned 2 barrels like this. Neither one showed me what I wanted to see in the powder test, so I picked a charge and went after seating depth, came back to powder and now they are acting like you want to see. What I want to see is a vertical group change to a flat group or a clover leaf then a nice little knot then go vertical again. When I see that I know I'm close, but when the seating depth is wrong you wont get that, you get random groups, some decent some not, but no pattern. I still do my powder test first, but if it donesnt show a nice pattern I go after seating depth and then return to powder. JMO.

BY1983, isn't Eric's method what they call Optimal Charge Weight, or is his somehow different? Either way you want your barrel to be "stopped" which is the purpose for looking at surrounding groups to see if they print to the same poi. Some methods look for that on seating depth first, then go after powder. It all works.

Thanks, you hit the nub of the origin of my question.

I figure if I can understand which harmonic we are tuning with seating depth and which we are tuning with powder charge then I might have a better chance of working out which powder charge to use if adjusting seating depth or which seating depth to use when doing a ladder style of test.

Is is as simple as this:
- Load tunes compensation. (ie. bullet is exiting crown while barrel is moving up)
- Seating depth tunes pulse ring (ie. bullet is exiting while the crown is constricted)
- Or is seating depth more about trying to the phase of the burn pulse ring with the bullet hitting lands pulse ring to increase the crown constricting accuracy nodes amplitude? Or maybe trying to half phase this harmonic? Or maybe trying to stack these two pulse waves behind each other to increase the crown constricting accuracy nodes duration. I assuming that a large and small amplitude waves travel at the same speed in the barrel.
- I take it folks do not see big accuracy increases in adjusting from 0.005" to 0.020" jam. It is more of a factor when adjusting jump right?

The reason I am asking is that where I am at with my load development right now is that I mostly get 3/8" 3/4" (0.15 - 0.25 MOA) 4 shot groups at 250 yards with 0.6 MOA high or low flyers (depending on the load) with in a 7 shot string. The tight groups throw high flyers the looser groups throw low flyers.

I am currently using 155 Lapua Scenars (factory moly coated) Jamed 0.010 into the lands and adjusting load. I have a feeling my seating depth is off but it would be good to understand how this works so that I select the right load to work on seating depth with.

I suspect that the load will need to be adjusted as seating depth is increased and that barrel time and MV will also increase/decrease respectively. Hence my pondering on which load to use for seating depth work and vice versa. Maybe I need to increase the load I am using slightly as I increasing the seating depth to keep the barrel time the same?

Has anyone seen slow motion evidence of which harmonic seating depth is actually responsible for?
I would be great to have some clarity on this.

 

[Alex Wheeler]

- I take it folks do not see big accuracy increases in adjusting from 0.005" to 0.020" jam. It is more of a factor when adjusting jump right?

Wrong! Do a seating depth test like you would with powder, move the bullet .003 at a time, you will see the same thing as if you were tuning powder. It will go vertical, flat, round. Don't matter if your in the lands or not. I think the reason some don't see this is because they make changes that are far too big. As far as knowing what harmonic your tuning, good luck figuring that out, .

 

[Alex Wheeler]

Here is an example of a seating depth test. You can see where the rifle wants those bullets seated. This was do on a very windy day, 15-20. All my flag tails were straight out so it was not possible to pick up on small velocity changes which I am sure added some width to these groups. This is a new barrel and I will go back and test powder charges now. The reason I shot this test is because the powder test I did first at .010 off was erratic. I will seat at .009 in for now, and will tweak it .001 either way after I determine the correct powder charge using 3 shot ladders at long range.

 

[Donkey]

Here is an example of a seating depth test. You can see where the rifle wants those bullets seated. This was do on a very windy day, 15-20. All my flag tails were straight out so it was not possible to pick up on small velocity changes which I am sure added some width to these groups. This is a new barrel and I will go back and test powder charges now. The reason I shot this test is because the powder test I did first at .010 off was erratic. I will seat at .009 in for now, and will tweak it .001 either way after I determine the correct powder charge using 3 shot ladders at long range.

Thanks for that.

Interesting to see the groups tighten up near the lands as well.

I would dearly love to know which harmonics we are actually tuning here. I am sure we all would.

After settling on a load will you go back and redo the seating depth test?

 

[Alex Wheeler]

Yes, I will work it .001 at a time.

 

[Donkey]

Understood.

Will you then adjust for throat wear? eg move out roughly .001 each 150 rounds or so? How many rounds will you keep your barrel for? Do you touch your load over the life of a barrel? Assuming you have the same batch of powder/primers of cource.

I am trying to figure out if distance from the lands is the item we are tuning for or more projectile start position relative to the crown. (which wouldn't change over time) Also if we are tuning for harmonic amplitude/wave length (which should change little over time) with the load or more a barrel time/muzzle velocity (which should change as the barrel wears).

 

[Alex Wheeler]

I am not any type of authority on anything. So take what I am saying as just another guys opinion. I will follow the lands, but in the dasher they move pretty slow. But I wont worry about it untill the targets tell me to. I will keep the barrel as long as it shoots. I shoot long range br so as soon as they start getting bigger its done. Generally I wont mess with powder charge, but if I see the load wanting to go vertical I will tweak it. This barrel has 100 rounds on it and I dont know how it will act yet. I hope its a forgiving barrel and I dont have to stay on top of it.

There are some world class br shooters on here that know a heck of a lot more than me, hopefully they will ad their opinions.

 

[Donkey]

Thanks for the thoughts all the same.

With all the very limited slow motion video I have seen it looks like there is a deflection away from the front site of the muzzle at the first part of the recoil followed by a flick towards the the front site when the bullet leaves the muzzle. It looks like this is somehow the same regardless of where gravity is pointing. Which was opposite to what I had thought. I also noticed a downward deflection in the mid barrel and what looks like a pulse running the length of the barrel + other half and quarter harmonics running up and down. It would seem that the type of recoil eg. how tight you hold and the height of the but plate could make more of a difference to harmonic tuning than I thought.

Has anyone noticed that they have had to completely change their loads when moving to free recoil for instance?

Another thought is the choice between flat vertical and round groups. If you are shooting for score would you not want to set you groups to help with where you loose point most. ie. a vertical/round group if you mainly loose points to wind rather than elevation. (I realise your wind error does shrink when you have loose elevation) but something I hadn't considered until today. I too have always been chasing the cosmetics of a flat waterline.

I have to say that from watching slow motion video. I still have absolutely no clue as to what harmonic seating depth changes...

[youtube]http://www.youtube.com/watch?v=FaW_Hs0B79c[/youtube]