Charge or Seating Depth first on ladder test?

[rsplante]

I am developing a new load and am unsure whether to run a ladder test on charge weight first, or seating depth first. I usually end up alternating iteratively between the two for a few tests since each influences the other, probably wasting time and rounds, something that I cannot afford to do in this shortage environment. I am loading for F/TR 200yd prone competition. I am at a medium shooting skill level (600-42X best so far) but I am always looking to improve both my shooting and my ammunition. My last batch, with .224 80gr JLK VLD's registered an SD of 12 over an Oehler 35P Proof Chronograph. Unfortunately I have determined that my LaRue 5.56 OBR, 20" barrel 1:8 does not like 80gr. VLD bullets, but it is a tack-driver with 77 gr. Sierra Matchkings (SMK)(I am loading for single round, so I am not limited to magazine length.) (A friend of my son's, who is a much better shot than I am, got a 5 shot group of .78" at 200 yd.) I just got the Oehler and am starting from scratch with my load testing. I will be using LC11 brass, which I bought unfired (1000); however, they are currently on their second firing (thoughts on when to anneal?) I have skimmed the necks (checked with a Sinclair/Starrett Case Neck Micrometer), trimmed the flash hole, normalized the primer pocket, trimmed for length, chamfered the neck, and sorted in 0.1gr batches. I am using Varget, and plan on testing 23-25gr loads in 0.5gr increments (I currently use an RCBS Chargemaster). I'm using Federal 205M primers. I will be using 77gr SMK bullets w/o cannelure or crimp. I have trimmed the Meplats and pointed the bullets. I am using a Dillon 550b with a UniqueTek Floating Die Toolhead and Redding Competition Bullet Seating Die. I am using Redding's full length sizing die that also uses a bushing for the neck (245 bushing). I use a Hornady Concentricity gauge with a Starrett .0001" dial indicator, and usually settle for +/- .001".

I am constantly looking for that elusive 0.1moa improvement and will try anything. For instance, is it worth the trouble to sort my bullets by bearing length, or more accurately, ogive to base (for some reason the boattail seems to get ignored?) Secondly, is it more important to sort bullets by ogive to base, or by weight? I've given up on finding a Prometheus scale, but think I have found a better solution. Whenever I can afford it, I believe I will go with a Satorius GD503 paired with an Omega Powder Trickler (I saw a Youtube video where they were limited in accuracy only by the size of an individual Varget kernel.)

I know I've covered a lot of ground here. Again, my main question is whether to determine charge first, or seating depth first.

 

[pinsandpitons]

Holy rabbit hole batman! I will freely admit that while I understand the concept you're trying to clarify, I have no real insight into the real (if such a thing exists) answer. My 'thoughts' (for what they're worth) is that the charge weight will get you very close to the velocity with which your particular barrel is most consistent. Especially if you do that test with a seating depth very close to what you'll end up with. It sounds like you know far more than I about how far you should or shouldn't jump an SMK, so if it were me, I'd start with that and find the charge weight. Then stop messing with it and practice till you shoot like your sons friend. (see your second sentence) Sort your brass and bullets if that helps you sleep, that doesn't cost anything but time, (I have zero idea about ogive to base vs. bearing surface) but all that is cosmic minutia if the nut behind the trigger isn't a stone cold consistent quarter moa shooter. My .02...

I found that my 1:8 didn't like 80gr VLDs either. I think it's just a tad slow for pills that long.

 

[ChrisGarrett]

Start with charge weight first and play with seating depth second.

That's how I do it.

Paragraphs help, as well.

Chris

 

[rsplante]

Sorry about the long paragraphs. I actually can write (at least according to most of my MBA Professors), but I just got into a stream of consciousness mode and got carried away.

I need to make a decision by this morning, so I guess I will go with the advice to vary charge weight first. My concern has been that when I get to varying the seating depth, it will change the volume of the round which will in turn change the pressure, (which is what you are changing when you change the charge weight.) On the other hand, I guess iterative tests are necessary anyway to fine tune the load since the initial 0.5gr jumps are pretty coarse adjustments.

The reason, as I understand it, for sorting the brass by weight is to sort it for volume. The outside dimensions, with full length sizing, will remain constant. Therefore, with weight changes, you are indirectly measuring inside volume changes. Changing the volume of the container affects the resulting pressures. What we are looking for is anal-retenive control of all variables to ensure consistency.

A new question just came to mind. I understand how both seating depth and charge weight can affect pressures, so in that way they are interrelated; however, as I change the pressure, does that have any effect on the optimal jump distance? Maybe that contains the answer to my first question. If there is only one optimal jump distance for any combination of barrel/chamber and bullet, then you can determine the jump once and eliminate it as a variable. Then you can concentrate only on charge weight. Thoughts?

 

[ChrisGarrett]

Much better!

Wall of Texts are hard to read.


Find the harmonics first, the nodes, both high and low and those will have a more profound effect on groups size, IMO, than seating depth. Many bullets can stand long jumps (except VLDs,) so you're not backed up against the wall on that front. Fine tune seating depth at a latter date, while keeping things mag length safe, if you don't want to single feed.

Chris

 

[Graham]

Charge first. Seating depth second.

Try the 80gr JLKs to the lands to start. If they don't work there they probably won't work at all.

Start with 24.5 RE15 at 2.455 and 2.460 OAL.

 

[rsplante]

Actually, the 80gr JLK VLDs shot best jammed .015 into the lands, but it was still a much larger group than with 77gr SMKs. Why pay for hand made bullets if you get worse results? Believe me, I WANTED them to work, I still have 500 or so of them. I might try lighter JLKs sometime, but for now I am going back to what I know works.