Point of impact / pressure question

[mam4061]

I have a stainless steel Browning A-Bolt chambered for .280 Rem.  I developed a load this fall for elk using Win. 280 brass, 54.5 gr. of IMR 4831, Win. LR primers and Nosler Partition 160 grain bullets.  This load was 0.5 to 1.5 grains over max depending on which book I looked at, but I tried several loads ranging from 51 to 54.5 grains and the 54 grain loads shot just under an inch, but the 54.5 grain loads shot a four shot group just under 3/4 of an inch.  The hottest load showed no signs of excessive pressure to me (bolt opened easily after firing and primers were not flattened out).  So 54.5 grains is what I loaded and practiced with and they worked great!! killing my elk with one shot.   

In the past I have always used 140 grain bullets for deer hunting, but after killiing that elk so well, I thought maybe I should try some heavier bullets.  This last weekend I decided to try and load some Hornady 162 gr BTSP for deer.  I thought well since the Hornady bullet is two grains heavier, maybe I should back the powder down a little, so I loaded up five rounds with 54 grains of IMR 4831 and went to the range to try and duplicate the accuracy of my elk load.  The only difference was the brass I was using.  I necked some Remington 30-06 brass down and used that.   (when resizing 30-06 brass to .280, the shoulder of the case is about 10 thousanths of an inch shorter on the first firing.  This results in a slightly reduced case capacity for the first time the brass is shot in the .280)

At the range, the 162 gr. Hornady's shot about a one inch group, but the point of impact was 2 inches higher and 2 inches to the left of where my Nosler Partitions were hitting.  In addition, the primers were really flattened out compared to the Nostler Part load.  Does anyone have any ideas on why there would appear to be more pressure in this hornady load and also why the point of impact would be so much higher .  I also had brought some of my 140 gr. deer loads along and they were grouping well in the same spot as the 160 gr partitions.

[Graybeard]

First up you need to stop assuming you can judge pressure from the appearance of primers. That's just not the case.

Generally speaking a 160 PT should develop greater pressures than a Hornady 162 BTSP assuming both are seated with the same bullet base position thus giving same powder capacity in the same case. In your case you changed too many things all at once. Chances are your sized down '06 cases have enough less case capacity and perhaps the necks are too tight as well and thus higher pressures likely resulted

SAAMI pressure for the .280 case is less than either the .30-06 or .270 Win. so the slight over load likely should not have raised pressures to more than those rounds operate at but there is no way to know without pressure testing equipment. The difference between a safe load at say 58,000 to 60,000 which is high but not unsafe as compared to one at 80,000-90,000 which is blue pill proof load range is not noticeable in bolt lift, primer appearance or any of the other old recommendations. It is not reliable as an indicator of pressure differences between safe and unsafe.

My recommendation to you is to stick with pressure tested load data from reliable sources. Pressure has little to do with POI any time you change bullets or powder charges such differences in POI is perfectly normal and is to be expected.