chicken or egg - seating depth or powder

[Diamondback]

MagnumManiac hit the nail on the head.

Every once in a while a rifle will like a fast burning powder pressure wave with less case fill.

I experienced this with a 270 Win shooting 150gr SPBT's. It liked Varget over H4831, H4350, or Hybrid 100. Every rifle is different on what powder it likes for what bullet you are using.

The Varget also gave a much faster softer recoil and I could tell the difference.

I do the powder ladder with a specific bullet I pick for what it designed to do / game I will be hunting, then the seating depths starting with SAAMI OAL till I capture the special powder for the bullet off groups and then move on to seating depth based off the Rifle's mag length capacity past SAAMI spec.


SAAMI bullet depth to find the most smallest groups off the powder ladder.
Dial them in, and then play with the seating. Usually 0.010 off the lands works on the majority of 700's I have shot. Each rifle is different on what it likes and pressure increased closer to the lands or slower back off them. That can change my powder loads to back off a little to tweak the combination where they meet for the best accuracy fps recipe for that round / barrel harmonics / pressure / timing.

If I get 0.75-0.50 MOA in a SAAMI spec length powder group load, I'm happy- Factory T3 Tikka's come to mind. I've got one and they don't give you a lot of magazine OAL seating choices in the magazine. I view it as acceptable accuracy with a functioning magazine capacity vs single loading long rounds for ultimate accuracy. I like having the use of a magazine in a bolt action. It depends on the accuracy variables though. A good gunsmith might be able to help you out if it can be modified. If in bear country, you want a functioning magazine and not hand loading single shot long OAL rounds that won't fit in a mag.


If I have plenty of magazine room- Rem 700's Long Actions... I dial it in ... I have one factory barrel shooting 0.30 MOA that is not a WSM or ultra anything, but it can shoot 150grs - 270 Win at around 2850fps. And it will do for my hunting uses just fine. It did for Jack O'connor shooting hot 130 loads with a 4x optic. What we have available to use as consumers today is incredible.

No Country for Old Men- Intro Hunting scene comes to mind when pushing your limits too far...

 

[benchracer]

It doesn't really matter which one you experiment with first. You will end up at the same place when you find your load.

IME, the optimum seating depth for a given bullet remains constant regardless of the powder used or final charge weight. If you plan to try multiple powders, it may make sense for you to establish optimum seating depth with your chosen bullet first.

Normally, I start by finding the distance to the rifling with a given bullet. Then, load 5 rounds touching the rifling, 5 rounds .040 off rifling, 5 rounds .080 off rifling, and 5 rounds .120 off rifling. Fine tune from there, if necessary. (This is all based on recommendations given on the Berger website.)

Given that you have decided to restrict yourself to mag length, you may need to improvise a bit. Using a starting load with your chosen bullet, treat mag length as the max "touching the rifling" length and shorten the OAL in .040 increments (go smaller if you feel the need) until you have four separate groups to test. At least one of the groups will shoot markedly better than the others. Do your powder workup from there.

Keep in mind that bullet design may be the most important factor in your success given that you are restricting yourself to mag length. Bullets with secant ogives (like VLD's) may or may not work well for you. I have gotten VLD's to shoot with a lot of jump, but have never tried them with .160+ of jump.

I can say that bullets like the Berger Hybrids truly are insensitive to seating depth. I have also had good luck with tangent ogive bullets like Sierra Matchkings when restricting myself to mag length.

Once you have found your seating depth, try this:

OCW Overview - Dan Newberry's OCW Load Development System

The above linked instructions work just fine before you find your seating depth, too. It doesn't really matter which one you do first. I have found that when I combine the seating depth instructions from the Berger website with the OCW method, I am usually able to find my best load in 50 rounds or less.

 

[Mike 338]

Powder first, OAL second.

I like this answer.

 

[Bart B]

J E Custom says, when ready to charge cases:

Then start loading 1 to 2 grains below max and work up in .02 grain increments.

1/50th of a grain increments? That's about one kernel of powder or less. Do you mean 0.2 grain, 1/5th grain? I think so. You can join the "Mistyper's Club." I'm a member, too.

MagnumManiac sez:

The sweet spot is generally somewhere very close to the lands or even into the lands, and then there is a second spot further from the lands that it will be in. What it is is where the barrel harmonics are in tune with the bullet barrel time.

This has often been claimed. Nobody has ever proved it timing barrel whip versus bullet exit. But it's been debunked time and time again when top competitors in international competition all using the same ammo in all sorts of barrels having different resonant/harmonic frequencies, chamber and bore/groove dimensions shoot it into 1/2 MOA at 600 yards. If you're basing this on the popular OCW theory, note that theory has several flaws in it. Biggest one is how fast sound waves travel in stainless steel; it ain't right. Second one is that high frequency sound speed stated in OCW theory (18,000 Hz) is not what causes the greatest amount of muzzle angle spread. It's a much lower frequency which is a harmonic multiple of the barrel action's low resonant frequency of 50 to 150 Hz.

Then there's this oft-time claim:

All rifles are different.

Get 100 rifle shooters with one rifle and its ammo that's been proved to shoot 1/4 MOA at 100 yards. Have those 100 people shoot a 5 shot group at 100 yards. Those groups will range from just under 1/3 inch to about 2 inches. Maybe bigger.