I was not happy with the numbers I was getting with 66.5gr of RL19 behind a 130 gr Barnes xlc in my M70 270WSM, I know a few of you out there advised me to stay with this load because of the excellent extreme spread and standard deviation. I decided to try IMR 4831 powder with this bullet, so I loaded up 9 rounds with 9 different charges in order to check for pressure signs. This is what I got.

62.5 gr 3177fps
63.0 gr 3222fps
63.5 gr 3259fps
64.0 gr 3316fps
64.5 gr 3360fps
65.0 gr 3360fps
65.5 gr 3368fps
66.0gr na
66.5gr na

I did not shoot the last two rounds because I got a very sticky bolt lift and a heavly cratered primer, load only increased 8 fps, I am going to measure the cases for expansion and very carefully pick what I think is the safe load and will go out again tomorrow and fire a ten shot string and see if it is as good as the RL 19 loads. Barnes says the readings are a little bit high, their data shows 67gr is max with 3376 fps, I have almost reached that with 1.5 gr less powder, of course a ten shot string will give me a better idea of what I really have. I was going to pull those RL 19 loads but I am going to wait and see what happens.

Failure to increase velocity with increase in pressure is a high pressure sign in and of itself. Peak pressure depends on the total volume the propellant gases are expanding into. When increasing powder charge fails to increase velocity, it is because the chamber is stretching to increase the volume enough to neutralize the charge increase. Not a healthy condition.

Back down to about a grain below where the bolt first started to get sticky. Then fire a round robin (http://home.earthlink.net/~dannewberry/dannewberrysoptimalchargeweightloaddevelopment/id1.html) of loads from about 3 grains below that point back up to that point in 0.3 grain increments to determine which load in that range gives you the smallest group size? Shot placement matters more than velocity. A rule of thumb used by Harold Vaughn was that he wanted a rifle to group 3.5" off the bench at 350 yards for hunting. That is about 1 m.o.a. at 350 yards, and seems pretty tight. I would want to see 8" firing from an actual field prone position before using the gun out that far, though. So, the gun itself probably needs to make not much over 4" at 350 yards off the bench.

Please note that velocity variation doesn't affect group size at 100 yards much. At 200 and out, you begin to see the effect. For example, one .30-06 load I ran tables on recently showed a 50 fps muzzle velocity change only introducing 0.1" change in the vertical point of impact at 100 yards, growing to 0.5" at 200 yards, then to 1" at 300 yards. Approximately, 0.1, 0.25, and 0.33 m.o.a., respectively. This is assuming machine rest precision from the shooter. If you are looking to see the effect of muzzle velocity variation on group size, you should fire at the maximum range you actually expect to use the rifle at. This and the wind-caused group dispersion both grow with distance. A 1 inch group at 100 yards does not mean you will get a 4" group at 400 yards, not even from a machine rest in no wind.

I sent you a PM. Please check it.