Charge weight tuning v seating depth tuning

[Northridge]

I appreciate that my own testing could jive me the answers Im looking for but like everything in life I have to balance my testing with time, cost etc so Ive never managed to do this yet, thats why I ask the collective from time to time if they have done what I propose?

Something that sill leaves me wondering right now is this;

I usually start by tuning my powder charge at a nominal seating depth, generally this would be 20 thou off unless I have historical data that showed me a particular bullet liked a certain jump/jam, all testing is then done and the powder charge is established. I usually use and OCW style test at 100, 200 or 300 yards to establish powder charges, depending on conditions. On small cases this will be 0.2gr increments or 0.1gr to fine tune.

Next I go on to seating depth tuning, I tend to load a batch of ammo long, say 50 thou past jam length and I then seat the bullets at the range at various lengths as I need them. If my OCW testing has shown the seating depth might be close, say groups in the 0.5" or smaller I will often start by moving 5 thou forwards or backwards to see what effect, sometimes adjustments will be more or less corse than 5 thou depending on groups sizes, I rarely see 2 thou making any difference. Often I will only fire two shots because if the trend is showing the groups are opening I will go the other way. Generally 30-40 shots is enough to get the groups tightened up and there will be enough ammo left for one or two 5 shot groups to verify.

I do wonder though if the original powder charge that looked so sweet at say 20 thou off has been affected if my final seating depth tuning that say now has me at 5 thou jam or any other length different to 20 thou off?

I guess what Im trying to find out is if the seating depth adjustments are affecting the harmonic vibration tune or if they are just timing the bullet exit into sync with the harmonics? Or in other words does one affect the other or are they working independently to achieve an optimum?

I suppose I could always go back to a fine adjustment powder charge test once the optimum seating depth has been found and that would tell me?

Curious, for me it is hard to say there is a "optimal" seating or powder or bushing .etc because every variable that is adjusted through fine or course adjustment can and does affect other values. what needs to be determined is if it as pushed me closer to the middle or have I fallen short or blown over the top. non of this is really hard most of the time after working targets long enough a guy often will know his rifles tendencies and how a adjustment will affect it but ladders will confirm results.

Shawn Williams

 

[Hengehold]

I enjoy hearing everyone’s methods and reviewing some old test targets. I used to load develop in the same manor for the NRA competitive prone 1000yd shooting. Over the years I have had less and less time to go test at the range. In some instances, I have not had access to ranges without significant driving involved.

In the past year or so I have maintained the “test powder charge first, then test seating depth” process. However, I have been able to use the Lab Radar chrono to find the node for the powder charge through the use of a velocity ladder test. This is a much faster process and I don’t need to shoot at a target to find a node for the barrel. I have done it for 3 barrels now and the test results have been repeatable when I duplicate the test on a separate day/time.

It is a very efficient process compared to shooting on paper if you do not have access to your own private range.

Thanks for sharing your experiences. I love this forum!
-T

 

[KenOath]

I’ll do what a lot of others do and that is find a powder charge that gives the smallest amount of vertical over a couple of different days of testing to make sure the first test wasn’t a fluke, using a seating depth that has worked in the past. Then run a seating depth test at the best powder charge usually in .005” increments then finer around the depth that looked best. Sometimes I’ll go back over the powder charges either side of my best charge with the final seating depth to see how well the window does either side. For me powder charge and seating depth are similar in terms of importance for accuracy, I have to work both a couple of times to come to a happy medium, sometimes a seating depth or powder charge is better than the one I’ve ended up on but it’s on the edge or isn’t any good either side, I prefer something consistent and in the middle, but once I’ve found a load generally the seating never changes I just chase the lands,but have found with most of my barrels that the powder may change by a few tenth over the coarse of the barrels life..

And some barrels I chase my tail round and round and get nowhere to, thankfully that doesn’t happen very often!!!

 

[alinwa]

Curious, for me it is hard to say there is a "optimal" seating or powder or bushing .etc because every variable that is adjusted through fine or course adjustment can and does affect other values. what needs to be determined is if it as pushed me closer to the middle or have I fallen short or blown over the top. non of this is really hard most of the time after working targets long enough a guy often will know his rifles tendencies and how a adjustment will affect it but ladders will confirm results.

Shawn Williams

I just realized that when I say "adjust powder charge first" I really mean velocity...... Jim Borden convinced me a long time ago that it's a VELOCITY tuning function and I just haven't ever looked back. He told of pre-loading for matches using different lots of powder and some of his loads needed 1.5 gr more powder TO MATCH VELOCITY for a given tune.

My "coarse adjustment" is dependent on powder charge, is generated and controlled by powder charge.... but while working up a load I will absentmindedly adjust this charge to stay within my velocity window. Perty much every time I post a picture of a shooting setup there's a chrono in there somewhere.

 

[lukehalee]

Few opinions:
- barrels have a fixed natural frequency.
- there are other variable vibration inducers tho.
- correct seating depth(s) is priority one.
- if .2 grains changes your perfect tune, your not tuned.

 

[BT1]

Few opinions:
- barrels have a fixed natural frequency.
- there are other variable vibration inducers tho.
- correct seating depth(s) is priority one.
- if .2 grains changes your perfect tune, your not tuned.

I especially respect and appreciate the comment regarding "If a .2 gn changes a perfect tune". I always get nervous when I review a "final" tune test to see that a .2 gn change, DOES pushes the group out. Like to see a wider powder tune node, then work on seating depth. Have seen barrels that just want that one powder node. For a one day match in the same weather conditions, OK with the narrow powder tune. But for multi day matches, will just take another "less fussy" barrel.

Steve

 

[gunsandgunsmithing]

Few opinions:
- barrels have a fixed natural frequency.
- there are other variable vibration inducers tho.
- correct seating depth(s) is priority one.
- if .2 grains changes your perfect tune, your not tuned.

I agree for the most part. The part about a barrel having a natural frequency is true too but is temperature dependent. IOW, it vibrates at a different frequency at a different temperature. This is NOT the most important factor to keeping the gun in tune though. Powder apparently changes more.

 

[Curious]

- if .2 grains changes your perfect tune, your not tuned.

Im told by shooters more experienced than me thats its quite common for the 6BRA to have a tune window of less than .2gr at 1000yds - if so what do you make of that?

 

[lukehalee]

Curious,

I don’t shoot long range, but do understand those guys are watching es on velocities. Maybe es dominates their view on tuning. I also think they go to matches preloaded. That said, I would have no confidence going to any match preloaded with no load window even if I had zero es on a knife edge.

Myself, I would keep moving seating depth. If that doesn’t yield results I would question my bullet to reamer relationship.

 

[Curious]

Curious,

I don’t shoot long range, but do understand those guys are watching es on velocities. Maybe es dominates their view on tuning. I also think they go to matches preloaded. That said, I would have no confidence going to any match preloaded with no load window even if I had zero es on a knife edge.

Myself, I would keep moving seating depth. If that doesn’t yield results I would question my bullet to reamer relationship.

I guess these thoughts are quite relevant to my earlier point.

ES doesn't appear to be the most important aspect of a good 1000yd load for a competitive LR benchrest shooter when working with long range ladder tests and positive compensation.

Lets not explore that here though as it will take us way off track and there are already threads about it