wadeb,

Have you tried stepwise regulating loads? You probably know this but it is done as follows. Take a plastic ammo box that holds 20 rounds of ammo. Tape a big piece of masking tape along the side of the box with the box top off. That gives you a place to write the powder charge for grouping pairs. Then load the following:

2 shots of 102.0 grains IMR4831

2 shots of 104.0 grains IMR4831

2 shots of 106.0 grains IMR4831

2 shots of 108.0 grains IMR4831

2 shots of 110.0 grains IMR4831

Then shoot each pair. But make sure to look through the spotting scope at each shot so you know which hole is the left barrel and which is the right. Mark the target with a pen after each group of 2.

The 2 shot groups should start off quite wide apart, then close in on each other. When they are close, you can go home and load up another regulating set that goes up in half grain increments across a 2 grain range. So for example, if 106.0 grains is not crossing, but 108.0 grains is, you could shoot 106.0 grains, 106.5 grains, 107 grains, 107.5 grains.

Then if you like you can repeat the proces with Reloader 15 (probably start at 88 or 90 grains, with filler). And you could repeate it with H4350 (probably start at 95 grains or so).

A couple of other important points. Use a fresh can of powder to eliminate the possibility that the powder is old nd degraded. Also, be sure to use Federal 215 primers ONLY. It is the hottest commercially available lare rifle primer.

Note that this load development is to find a regulating load, not to find the most accurate load. That is why only 2 shots are needed per powder level. If I had to shoot a 3 shot group per barrel to regulate, I would trade my .500 in on a .303 double.

One more point. I did not notice diddlysquat difference in recoil among the Reloader 15 loads, the H4350 loads and the IMR4831 loads.