I recently had an opportunity to help a friend reload for his .270. We chose the Hornady 130 gr. interlock as the bullet of choice, and settled on  Reloader 22 powder with Federal 210 primers.

we decided to load five cartridges of different powder charges and shoot for groups, figuring on setteling on the most accurate load that showed no signs of high pressure.

Starting with 56.0 gr we worked up in .5gr increments untill we reached 59.5 gr. which is 1.8 gr. below Hornadys listed maximum for that bullet/powder combination. This combination gave us the best grouping of all the loads tested.

This charge filled the case from the shoulder to 1/2 way to the base of the neck. When  we tested this load it showed no signs of pressure. (in a Winchester model 670.)

My concern is that my friend is going on a late whitetail hunt, which will most likely be in the snow and the weather will be very cold, do you think that the cold weather will make this load dangerous as far as pressure goes?

according to the Speer manual  (which i didnt have at the time) 58.0 gr is max. Hornady lists 61.3 gr as max, but I dont see how you can get that much powder in the case.

Any help would be appreciated.

Just some thoughts

1.8 grains below max should be fine,  newer manuals tend to lawyer/discount the max weight.

Regarding cold weather, most charts have taken the normal cold of hunting into account.  In cold weather the air is heavier, and that means more back pressure on the bullet.  So the internal chamber/barrel pressure behind the bullet can rise.  Sort of like trying to push a heavier object.  The same effect in in firing under water, but much greater.

The coldest I've been in and fired a rifle was minus 50 F.  The rifle and shells had been in a dog sled for 150 miles and many many hours.

The shells were my reloads that had been reloaded at 70 degrees F. and were at book max.  using 110 grains of 4831.

I had no problem (except some frost bite and a cold a$$).  Also I had taken my plastic stock off and was using a walnut stock and no cracks or brittle wood.

I will say that was extreme temperature and I did not even feel the recoil.

I doubt the deer hunter will be below zero and the shells are usually in your pocket or magazine where it is even warmer.

Just thoughts.

If you use a bow these problems don't exist.

BEAR 

You will have more trouble with increase of temp than cold.

The .270, 4831 powder and 130m gr bullets go together like peanut butter and jelly. It has been the premier load since the .270 came out .O'conner's load was 60 gr or 4831.