A couple loads for the 300 mag

[irocbarry]

LOADS EXCEED PUBLISHED DATA, START LOW AND APPROACH CAREFULLY

I went and shot some loads today for mine and my dads 300mags today, had some great and some interesting results.

First the great. 
200gr AB, R-P brass, WLRM primer, 3.35 COL, 72gr H4831

Four shot .75" at a hundred, with a average speed of 2795fps.  Was very happy it the accuracy and consistency of the load, ES was 23fps for the four shots, the best of any load I've done to date.  These should wreak havoc on anything that gets in the way of them.  Would like to get it closer to the lands but the 3.35" is as long as the magazine will let me go.  The gun is a ~1974 Win. M70


Now for the interesting part.
In my rifle (MK77 300mag) going from 73gr of R22 up through 75gr i was getting in between 30 and 50 fps gain per half grain of powder.  When the load went to 75.5gr it jumped from 3035 to 3148 average for three rounds.
This was also my most accurate load, just under an inch.  Is that large of a jump in ave speed a sign I need to back off because of pressure? Everything looked fine on the brass, same as the other loadings, and bolt lift was same as normal.
Load info:
180AB, R-P brass, WLRM primer, 3.35" COL (magazine limit again) 75.5gr R22

Any input would be greatly appreciated, thanks in advance.

[Grumulkin]

Is that large of a jump in ave speed a sign I need to back off because of pressure? Everything looked fine on the brass, same as the other loadings, and bolt lift was same as normal.

I would say you are closely approaching maximum pressure.  Different guns have different ways of telling you pressure is high.  On some extraction may be a little sticky and on others you may get a pierced primer first.  Only you can be the judge of whether you should push the load further.  When you are near a maximum load, little things can make a lot more of a difference like increased pressure to dangerous level with increased ambient temperatures, different brass, different primers, etc.  Be careful.

I was working up a load for a 7mm/08 the other day.  As the load was increased, the groups started to tighten markedly but then case extraction started getting a bit sticky at about 2 grains over the published load.  I knew I had to back off a bit.  It's too bad, that bullet shoots great in a 7mm Rem. Mag. probably because of the higher velocity attainable.

[irocbarry]

with having no pressure signs that i can see, just the jump in speed, do you think i should back the load off a bit or just not try to go any higher?