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Boys, I'd go middle or light .358 loads for a start, just to get a feel for your individual rifles. You should have and use a chronograph in your load development, watching for good SD's and leveling of velocity increases as powder charges increase which suggests gettingclose maximum loads, as the efficiency levels off for that powder.

I'd personally start with H4895 and 41gr. or 42.0gr. and with standard primers. 41.0gr. load is listed as 2,100fps in Hornady's 7th Edition book.

Another would be, with 40gr. IMR3031 - again with standard primers.

Another would be 42gr. BLC2 with a magnum primer, say CCI250. The mag primer becomes quite important in colder climates for good ignition.

Re#15 is listed - start at 39gr. It's maximum is listed at 45gr. at 2,300fps.

The .358 Winchester loads in Speers book are somewhat higher for starting loads, sometimes only 3gr. between start and max - just shows the differences, gun to gun as well as different loading practises, book to book.

Hornady notes it calls a load max when they lose accuracy in testing, which may or may not have anything to do with pressure. It's sort of difficult to surmise if your rifle shoots with better accuracy than their's did - is the load max due to their pressure, or lack of accuracy. Best to look at other books before proceeding.

The starting loads above will get you going in the right direction.

I like Barnes idea of picking a powder to work with.

Load several powders with bullets, from a starting load to near max, then shoot each powder's loads into separte groups, one powder with varrying charges per group. The best accuracy powder shows the powder to use, then experiment with that powder to find the best loads. Their reasoning is that with fluctuations in temperatures, your accuracy will be effected less than with a powder that has only 1 charge that shoots well. Better to have a powder that shoots a lot of different charges into a small group.

With that in mine, H4895 (or Varget-same loads for starting) will probably show the best accuracy, along with BLC2. The stick Hodgdon powders are Extreme Powders ie: not effected by heat or cold and are first choice for me in this type of ctg. I use a lot of BLC2 as it's just so dang accurate in these rounds as well, from my 9.3x57, through 9.3x62 and .375/06IMP. Highests speeds and bug hole accurate.

Watch your pressures. Measure web expansion increases per charge. Look for even measurements around the case. The amount of expansion will depend on your actual chamber dimensions.

If you measure base, ie: rims, you must mark the rim at two adjacent spots then measure the rim at those 2 spots prior to firing, then again same spots after firing. The allowable increase for modern rounds is .001" - apparently. Use a 1" micrometer readable to .0001" as calipers are not accurate enough, not even the digital ones.

I would not allow more than .0005" and probably none at all. If you get expansion of the rim, that means you've exceeded the elasticity of the case - already too far as far as I'm concerned.

Seat your bullets out as far as possible without them jamming into the lands. The longer the OAL, the better potential for accuracy and the lower the speed and pressure for a given load. The more deeply seated, the higher the speed for any given round and the higher the pressure, but less accuracy potential.

In my 9.3x57, this amounted to 3 gr. of ball powder difference with .150" deeper seating, ie: 50gr. with deep seating gave the same speed as 53gr. with long seating. Note, even seated long, the bullets had considerable jump to the lands. If they jam the lands, this also can raise pressure. Be aware of how your rifle is chambered. When developing loads, record ALL the data - including OAL.

Take care and go slowly. The only data I have for that round is for the 9x56 Mann. They went to 46.0gr. 3031 with the Speer 250gr. at 2,205fps and 46.0gr. 3031 with the same bullet in the second rifle gave 2,088fps.

LC mil. '06 brass used in the first rifle - gave higher speeds, ie: higher pressures.
Necked up RP 7x57 brass used in the second rifle, lower pressures and speeds. The article I have compares 9x56 Mann. with the 9x57 Mauser in Stoeger's book. Mannlicher ammo running 245gr. at 2,160fps from 22" bl. and the 9x57 Mauser running 245gr. at 2,296fps from a 22 1/2" bl., just about what we figured. The author of that book I just quoted, Big Bore Rifles and Cartridges suggests .358 Winchester starting loads + 5% as the place to start.

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Daryl

"a gun without hammers is like a Spaniel without ears" King George V