stillquietvoice said:
if i understand you correctly. then the start load of the 308 should be close to an accuracy node.
The start load is not necessarily on a precision (smallest group size) node. My estimate just gives you another resource for looking for suitable candidate powders in an appropriate burn rate range. The OCW load development site I linked to is about a concept Dan Newberry has for finding loads that do well over a range of barrel lengths and chamber sizes. Those are the exception, though. For other loads you sometimes can take two identical rifles off the rack at the store and, due to tolerances, find they are different enough that they don't tune some bullets to best precision with the same charge weight of the same powder. So best precision and accuracy (where the group is centered; the result of your sight settings) have to be tested for. Also, be aware there are other things than charge weight that affect these. Seating depth is one. Cartridge concentricity is another. Priming technique, if done badly, can affect it adversely. So there's no simple guarantee some other person's load will shoot well in your gun. You have to do the work to see what it likes.
stillquietvoice said:
i have a speer #11 loads listed are considerably higher with magnum primers than hodgens web sight lists. the 308 175 listing for 760. is higher than listed weight for 139 7mm.
The Speer #11 was published in 1991. That's from back when many bullet makers did load development entirely by pressure signs and without pressure testing other than making estimates from brass and primer deformation, a practice that can be off by up to 50%. Since then, both powder manufacturing processes and primer formulations have changed. Pressure testing of maximum loads is now done by everyone, I think, for liability reasons. That 25 year old data is too old to be considered valid without retesting and careful workup. Some of it will be OK, but some will be obsolete.
In my Speer #14, the loads for 760 in 7mm-08 are the same for their 130 and 145 grains bullets (they don't make a 139 currently) and the load for the 168 grain 308 Winchester bullet are all the same; 45-49 grains of 760 over a CCI 250 primer. They don't make a 175 or 178, but their 180 grain load data is only 1 grain less (44-48 grains), so I think my estimate is still well inside the ballpark, as 1 grain is about 2% of the maximum charge, which is just one step in a pressure work up. If your #11 data is higher than that, you can expect it was worked up in a production gun without pressure testing, and that may well account for the difference. If so, it should be considered obsolete.
The Hodgdon data for a .308 with 175 grain bullet is 46-49 grains, so that's another validation of the estimate, to my mind. The only thing that's off is Hodgdon's 7mm-08 load, which is an unusually narrow 45.5 to 47 grains, with the top load pressure being just 44,100 CUP average, when the 7mm-08 is rated for 52,000 CUP average. So they seem to have stopped low for a reason. I'm going to hazard a guess that the fact they used a standard primer gave them a high pressure spread so they erred extra low with the maximum. You could call and ask them, but when they stay that far below the SAAMI standard maximum it is usually for a reason that came up during testing. It may or may not apply to your loads if you use the 250 primer.
