Finding "sweet spot" with bullet seating adjustment

[MNbogboy]

Theory on why...just like some of you say...dont know...
There is a correlation between seating depth & neck tension (grip). A major change in grip most often changes seating requiring new tests...then powder charge may also be affected....
At any rate a few things come to mind and all may or may not be factors....
1. Bullet speed at first engraving
2. Rate of deceleration before acceleration at the moment when the bullet first starts engraving.
3. Pressures at first moment of bullet contact with lands.
4. The above all have effect on barrel time.
5. Angle of the lead including erosion.
6. Bullet shape, material, bearing surface, fore/aft balance, reaction to the gas propulsion due to shape at the stern.

There are probably 100 more things that will affect best seating...we need the formula and tools to solve this mystery..lol

 

[kolob10]

I am convinced that given a good barrel, maximum accuracy is a product of barrel harmonics. That can be accomplished by powder, powder charge, projectile, primer, stock bedding, or seating depth. Sometime all the above is needed or sometime minor tweaking of one or two of the above. I have a Remington 700 300wm that seems to shoot just about anything well without much load development. I have a Remington 788 .223 Rem. That is particular to a certain powder and charge but is not sensitive to a wide range of seating depth, primer, or match bullets. I once sat at a bench rest match and watched an old guy fill his case with powder, shake off the excess and seat his bullet. I inquired as to why when some shooters were more anal concerning powder charge. He said with this rifle, powder charge was not important (within reason). He shot with the winner that day. Maybe if I could still shoot in the 2's or .3's I would be more precise with my loads. If it shoots .5 " I am satisfied. I do not shoot game at 1000 yards so .5 is my goal at my age. Good shooting

 

[ThrdKllr]

I am convinced that given a good barrel, maximum accuracy is a product of barrel harmonics. That can be accomplished by powder, powder charge, projectile, primer, stock bedding, or seating depth. Sometime all the above is needed or sometime minor tweaking of one or two of the above. I have a Remington 700 300wm that seems to shoot just about anything well without much load development. I have a Remington 788 .223 Rem. That is particular to a certain powder and charge but is not sensitive to a wide range of seating depth, primer, or match bullets. I once sat at a bench rest match and watched an old guy fill his case with powder, shake off the excess and seat his bullet. I inquired as to why when some shooters were more anal concerning powder charge. He said with this rifle, powder charge was not important (within reason). He shot with the winner that day. Maybe if I could still shoot in the 2's or .3's I would be more precise with my loads. If it shoots .5 " I am satisfied. I do not shoot game at 1000 yards so .5 is my goal at my age. Good shooting

And thus is the quest for a wide stable node.

 

[Mike 338]

Been fiddling around with a Savage 6.5 Creed lately so I started working up a new load (Berger 140 gr. Hybrid Target). Loaded 8 bullets and determined max powder charge. Picked an arbitrary load a little below max load and went out to test rough seating depths. You can see how it didn't like the load closest to the lands. 5 shots per group really isn't enough data to say for sure what's going on but I see some vertical tendencies @ .130" jump, transitioning to diagonal tendencies @ .090" jump. I'll now do a powder charge workup using .100" jump. Hoping to blend the vertical and horizontal tendencies. It's just a 10X scope so some error is me.

 

[ThrdKllr]

Mine worked at .050 out with H4350.

 

[MNbogboy]

Been fiddling around with a Savage 6.5 Creed lately so I started working up a new load (Berger 140 gr. Hybrid Target). Loaded 8 bullets and determined max powder charge. Picked an arbitrary load a little below max load and went out to test rough seating depths. You can see how it didn't like the load closest to the lands. 5 shots per group really isn't enough data to say for sure what's going on but I see some vertical tendencies @ .130" jump, transitioning to diagonal tendencies @ .090" jump. I'll now do a powder charge workup using .100" jump. Hoping to blend the vertical and horizontal tendencies. It's just a 10X scope so some error is me.

I agree .010 looks like a scatter node but the inconclusive results with the other three groups would make me try again at .020, .030, .060, .070, .080 and .100 to make sure I'm not leaving anything on the table and refine the promising looking ones down from there. I have found some really sweet nodes that were only .003 or .004 wide.
Then switch to the powder tuning and finish off with final seating tests.
I may use up more components than some but it results in more confidence in my final loads before I head out for the hunt.

 

[Mikecr]

Seating as a harmonic adjustment (a tune) doesn't pass tests, and truths pass all tests.
You can easily counter a MV change from seating with powder, and it makes no difference to where best seating is. In fact you can find best seating with any load, whether grouping is large or small.
Also, with best seating determined to be off the lands (OTL), you don't ever have to chase the lands, with no load changes, for the accurate life of that barrel.
Chasing lands is merely synonymous with chasing your tail..

I couldn't declare law on it, but there is this hypothesis that passes tests:
If you've seen a lottery drawing on TV, then your familiar with ping-pong balls rattling into a tube. If you setup a lexan throat 1thou over ball diameter fed into a tube at ball diameter, and applied pressure to force the ball forward, then with a high speed camera you could see ping-pong bullets rattling into their bore/groove.
The ball lays in it's throat between shots at X distance from bore, and firing pressure pushes the back of the ball, but some goes around it (within that 1thou clearance).
At certain X distance increments the ball's transition is smoother, more consistent.

I don't think this is significantly affecting the pressure behind bullets(unless ITL), but is affecting deformation and the fidelity of eventual muzzle release. Notice during seating testing that grouping opens all directions and abruptly collapses to better or worse.
It's not like powder tuning. You couldn't shoot a seating ladder.

 

[jweigel]

Do you guys find ELDX bullets as seat sensitive (big changes in seating depth) as Bergers? I have mostly loaded VLDs and getting the best seating depth before powder charge has worked for me. Helping a friend with a Savage 300WM that has such a short mag box the 215 Hybrids woudl not work. Testing 200 ELDXs. Just wonder if seating matters much as the bullet is so different from a Berger?

Thanks for any advice

jjw
ND

 

[ThrdKllr]

I read somewhere that Hornady recommends starting at .030 out and going further with the ELD's.
They are supposedly more jump tolerant.

 

[MNbogboy]

Do you guys find ELDX bullets as seat sensitive (big changes in seating depth) as Bergers? I have mostly loaded VLDs and getting the best seating depth before powder charge has worked for me. Helping a friend with a Savage 300WM that has such a short mag box the 215 Hybrids woudl not work. Testing 200 ELDXs. Just wonder if seating matters much as the bullet is so different from a Berger?

Thanks for any advice

jjw
ND

Full seating tests work on all bullets whether seating sensitive or not so.
Mileage may vary!

 

[DUSTY NOGGIN]

ive always done powder first then seating. then verify at those seatings velocity ..

 

[Mike 338]

So now that I did a rough seating depth test and determined my gun likes a goodly jump, I decided to work up a powder charge with .100" jump, which was between my 90 thousandths and 130 thousandths test previously. I've found that generally, small incremental adjustments make little or no difference when your in the right depth ballpark so I picked a depth sort'a in between a couple of test groups that I thought might be promising. These groups were pretty lackluster till I started pushing things harder, which is a happy surprise. It started coming in on group #8. Wish I had loaded a bit higher but I'm not nuts for magnum speeds from a non-magnum cartridge. 4 shot groups really don't tell the tale so I'll re-test but it looks promising. The Berger method of determining preferred bullet seating depth has it's merits and may be worth a try is other ways aren't working for you.

I'll now re-test this load and maybe a couple other close powder charges. If I like the groups, I'll run the best group over a chronograph. If I think there may be some improvement to be had, I'll test some primers for both Extreme Spread and Accuracy.

 

[MNbogboy]

ive always done powder first then seating. then verify at those seatings velocity ..

I've done this both ways and it appears both methods work and one is no better than the other. End result is what matters.
Every barrel is different including the harmonics set up by its composition & physical atttibutes.
Having always respected mikecr's opinion there is disagreement on barrel harmonics concerning seating depth.
I believe contact with the lands is one of the first energies which set barrel "whip" in motion. Stretching in the chamber is happening simultaneously as pressure rises. Violent engraving as bullet accelerates from zero to thousands of feet per second seems to cancel out entry condition into the lands. Some top benchrest shooters have stated how concentricity of loaded rounds has little or no effect on group size. Seating "grip" at ignition sets up a pressure rise that eventually allows release of the bullet from case. The higher the pressure behind it the faster it will accelerate into the rifling. Momentum is the key to how hard this contact is made. Extremely low neck tensions allow for quicker bullet release and bullets contact at far less velocity. The farther from the lands the higher the velocity at contact. On the other hand a tightly crimped bullet will most likely be released with a higher pressure and obviously meet the lands going faster.
My theory, again without proof, is that seating is the biggest contribution to the setup & initiation of barrel harmonics.

 

[Mikecr]

I have no doubt the bullet transition affects pressure peak & burn timing a bit.
I just think it's an issue adjustment instead of a tuning adjustment.

On barrel vibrations, if significant vibrations were born from engraving then they could cause issue, or not. But there is no mention of this with OBT, nor in Harold Vaughn's book where he tested many vibrational sources during firing.
Whip is not vibrations, but straightening of a barrel, and seating does not straighten a barrel,, pressure does.

The reason so many see little affect from high runout is because their clearances are sloppy. This, preventing chambered tensions that would otherwise ensue with high runout. Chambered tensions affect barrel vibrations similar to thumb pressure on an action tang.
An engraving bullet runs out of clearance. At that point, it can't straighten much beyond what it had on it's way to engraving. So best or worst seating does not change with runout.