I am currently developing a load for .308 which uses a bullet with a secant ogive.  This is the first time I am using a secant ogive bullet.  I have found the optimal charge at my starting seating depth (0.020" off the lands) but it didn't group as well as I had hoped / expected (0.70" @ 100 yards).  Having never fine tuned seating depth on a secant ogive load for accuracy, I am looking for recommendations regarding methodology or how to approach it...

Thanx in advance for your assistance and wisdom!  

Well I im using the hornady Comparitor tool to measure the seating depth. I started with a .040, and worked up in .010 increments just until it touched the lands. And look for accuracy and of course low SD and ES on the chrono.

Exactly

I would try and seat deeper by .010 increments. You'll find something that tightens things up.

OBTW - the bullet is solid and made from a non-lead alloy...  akin to something like a Barnes solid copper design.  I have read that "monolithic" non-lead bullet designs prefer more jump than lead core bullets...  Is this true and how does it effect the load development process?

Thanx again!

No black magic, just more work with a wider search dimension.

That was the thing about more common standardized bullets and reamers back in the day, it meant that the shared experience narrowed the search down.

With no other guidance, your dimensional sweep will take a little more work and a few more rounds.

I was often surprised by how deep some of these seated when they came to life. No complaints, but I can’t explain why they work when they do, or when they don’t.

Simple way to do this.

Set up a set of 5-10 shots with bullets JUST touching the lands, and a set each at .010, .040, .080 and .120 jumps. You'll definitely see a trend in the data. Once you see the trend, take the snuggest and go up and down on seating depth by .010 increments (so 2 more load sets of 5-10 rounds). If there's no useful change, call it a day. DO NOT GET INTO THE WEEDS with this. There's only so much you're likely to improve over a .7" load.

I recommend making 10 shots each as a minimum. You want a 5-shot group and then another 5-shot group. I fire the first group and then fire the 2nd group on top of it.

OP, here is what Berger says about it...

https://www.eabco.com/Berger_Seating.htm

Gentlemen;

I thank you all for your contributions and wisdom.  I am now confident that I will be able to get this done with a minimum of blood, sweat, and tears...

Best regards,

- Reorx -

Yeah, I am acutely aware of this.  If I can get down to 1/2 MOA, I'd call that G2G.

Nice article, THANX!

Seriously? .70" at 100 and you're disappointed......

You were expecting .50" I presume. You may already have your best load for that bullet. More testing will confirm it or not.

Anytime I group under an inch I'm good. A reliable sub moa load is all I need to have confidence to 600 yards, maybe further.

Many rifle/bullet/powder combinations simply won't shoot as well as your rifle is right now. I'd say your golden if that load holds up through several outings.

Yeah, I know!...  I'm very aware of the phenomenon > "The worse enemy of "good" is "better"!!!"

On the other hand, how likely is it that I picked the best seating depth to start my load development???  I have 70 more bullets (I bought 100 to experiment with) that I can use to fine tune this load...  I don't know if I will get any more, they're pricey...  if they perform exceptionally well, they might be "worth it"!!!

For most bullets (this is esp. true for tangent designs), I start .020 off the lands to find a powder charge that's stable. Once the charge is identified, load from .010 jam back to ~.050-.070 off in .010 increments. As someone pointed out earlier in the thread, you will usually find one depth that is much tighter than the others, and often you'll see it tightening as you work closer to that depth.

Once you've got a good idea as to where it likes the bullet, then go back and fine tune by loading in +/- .003 increments.

With a tangent or hybrid designed bullet, I've had lots of luck with this. With the more sensitive secant/VLD bullets, you're almost constantly chasing the lands, and that can be a real pain in the ass to keep in tune over the life of the barrel (at least for me).

Yeah, I thought about that too...  just one more factor against my using this bullet long term...  hmmmm...

Well, don’t give up so fast...

You see the issues clearly, but keep in mind that a .308 doesn’t wear out at the same rate as some of the bbl burners.

In a .308, your typical VLD seating depth holds long enough for the trouble to balance out with the distance benefits. This is why VLD bullets are still popular with the match crowds and distance shooters.

Say you check every 500 rounds or so, would that be too often? In many instances, that VLD seating depth sweet spot is wide enough to stay in the zone by just watching the throat wear on that kind of interval and following it out about every 0.005” as it goes. Then, if you do sense a decay in performance you check it out, but usually by then the bbl is done anyway.

If you are regularly shooting F-T/R or using .308 in Highpower matches, you will need every advantage the equipment can give since it gets down to this on still-winded days. Once the wind starts up, the VLD shows why it is worth the trouble.

Fair enough - good points...  more food for thought!

Thanx again!