Those who start load development with OAL/BTO.
- Thread starter a1712
- Start date
There's some decisions to be make first, like. . .
Do you want to load to mag length or what? Or you want to seat at max length to near the lands?
What bullet(s) to use that meets you objective?
What powders work bests for the bullet, where case fill is at or close to 100%?
Once you answer these questions, then I feel it's when load development can start with seating depth testing.
But, I'm sure there's different approaches in load development that work just fine.
Main thing is to let the target tell you what's working or not. 
Do you want to load to mag length or what? Or you want to seat at max length to near the lands?
What bullet(s) to use that meets you objective?
What powders work bests for the bullet, where case fill is at or close to 100%?
Once you answer these questions, then I feel it's when load development can start with seating depth testing.
But, I'm sure there's different approaches in load development that work just fine.
Main thing is to let the target tell you what's working or not. 
Steve Donlon
Gold $$ Contributor
I start at the bottom node at .015"-.020" off and see where the bullet sits in the case, how much bearing surface is in in the neck at .015"-.020" and where the top of the powder column is. There is plenty of information about pet loads from max to minimum loads from people that have had success with the bullet you want to use. I have started in the middle and have had pressure signs right from the start. Better to go slow and use the BTO because at .015"-.020" off you could be pretty far off with the OAL length. It is not as accurate. Bullet length can vary a lot.
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Fast14riot
Gold $$ Contributor
I will typically use a known commonly accurate charge that is safely in range for the cartridge. If that doesn't exist, I will try calculated OBT from GRT then do my seating depth test. Or, if its just a new barrel, I typically know where I need to be within a few tenths on charge and maybe a .010"-.015" sweep of seating depths.
MikeRu
Gold $$ Contributor
Here’s what I do, ABC for each trip to the range, about 35-40 rounds for each trip to range, all at 200 yds wearing glasses and a smile, and some clothes:
A) 4 fowlers, if new barrel then start low and work up w 1 shot each load to check for pressure
B) find or confirm best seating depth with a moderate load or best guess load, about 8-10 rounds total, 2shots per depth x 5 depths, increment of 2-3 thou. Hybrids will start at 13off and test out to 25 off. Tangents start at 3 off. VLD start at 15 in.
C) reseat at the range to best depth from B, then shoot a powder ladder to find or confirm a load that groups. Early on shoot 20 shots w increment of 0.1 gn each shot, called 1 shot ladder, look for a group node meaning 3-4 shots with same POI, and also watch for a flat MV. If no group node, then switch powder/bullet for up to 3 total powders. Lately having good luck testing 3 powders w same bullet. To validate come back next time with 2 shots per powder load, testing across the group node. You should be able to get 0.3-0.4 gn wide that groups with flatter MV.
A) 4 fowlers, if new barrel then start low and work up w 1 shot each load to check for pressure
B) find or confirm best seating depth with a moderate load or best guess load, about 8-10 rounds total, 2shots per depth x 5 depths, increment of 2-3 thou. Hybrids will start at 13off and test out to 25 off. Tangents start at 3 off. VLD start at 15 in.
C) reseat at the range to best depth from B, then shoot a powder ladder to find or confirm a load that groups. Early on shoot 20 shots w increment of 0.1 gn each shot, called 1 shot ladder, look for a group node meaning 3-4 shots with same POI, and also watch for a flat MV. If no group node, then switch powder/bullet for up to 3 total powders. Lately having good luck testing 3 powders w same bullet. To validate come back next time with 2 shots per powder load, testing across the group node. You should be able to get 0.3-0.4 gn wide that groups with flatter MV.
TIFWIW but if I'm testing jump, I'm testing a finicky bbl. My best loads have almost always had some amount of jam. Yes, mag/action length can dictate things like this as well as it's based on your build and freebore. Best case scenario and a well planned build...and neither the action nor mag length are factors. Just that simple. IOW, I wouldn't build a 284 on a factory short action repeater....for example. Tikka maybe, but you get my point. These are just factors in what makes a gun good or great, among many others. I've done it but just wouldn't advise a customer to. There are tradeoffs, of course. If I have to jump due to action or mag length, that's on me.
I always start a new load with the bullet in the lands a bit. Then I start with the minimum charge of powder listed and work up looking for good groups and pressure signs,, then I’ll fine tune seating depth trying more jam or less. Most barrels I’ve had seem to like in the lands a little bit for those one hole groups and clean match 30-40x score’s
Is there a theory you find that explains this?
My own idea is that with jamming the variation in blow by before the bullet is fully engraved is almost eliminated, which produces more consistent Shot Start Pressure (give all other things equal).
tom
Gold $$ Contributor
If I start with seating testing it will be a proven load with that lot of powder, bullet and barrel manufacturer and configuration. The caveat being that i start every barrel at 1,000 yards, and you won't come close to getting anywhere if the powder is wrong.
Edit to add an example...in this case, how would I make head or tails if I'm not near 31.0(ish) on "powder c"?
Tom
Edit to add an example...in this case, how would I make head or tails if I'm not near 31.0(ish) on "powder c"?
Tom
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