Freezing temps affecting loads? 7mm

[Mxracer532]

First off I bought a Sendero 7mm from a guy who give me the best load he had for it.
72 grains of Retumbo
168gn Berger VLD'S
Win LRP (standards)
Win brass.
3050 fps
COAL 3.345

So I load some up and went out to verify his load was good. Temp was in the 15deg range. At 100 I got 2 almost touching and the 3rd about an inch away. (Far from my acceptable groups)
Took it to 200 and shot 5 shots 3 almost touching hair left of dot 1 about an inch right of dot and 1 a good 3 in high and 4 inches left. (Terrible)

So last night I checked to see how far off the lands the bullets were seated. (I didn't have the ability at the time I loaded these rounds) and to touch the lands I would need to seat the bullets to a COAL of 3.453. So his (best load) was WAY WAY off the lands. I load VLDs for 3 other cals and none are that far off the lands. So I did some research and have read that their is mixed opinions on std primers vs Mag primers and in really cold temps Mag primers might be necessary. I really don't want a load for warm weather and one for cold if I can get away with it. This rifle could be shot in anything from 90deg to above to below freezing. Anyone got a recommendation? I know for sure I will be doing a seating depth change according to Bergers method.

 

[Barrelnut]

Re: Freezing temps effecting loads? 7mm

The mag prime may indeed help in 15 degree temps. The 72 gr. Retumbo load with standard primer would be is a little hot according to Berger published load data, which is 71.2 gr.

I would just back off 1 gr. and work back up with a mag primer. Then use the mag primer load for summer and winter. Cutting back the load and working back up is always best policy for component changes like this.

Few things:

* Most bullet makers publish loads for the 7mm with mag primers.
* Mag primer can help, even with non mag cartridges in very cold weather.
* Retumbo is temp stable. So a cold/hot weather load workup with it should be pretty stable both ways with the right primer.
* The long distance from the lands lowers pressures some or the hot load. So you might be able to work right back up to 72 gr. But safety is always best policy.

 

[4xforfun]

Re: Freezing temps effecting loads? 7mm

Affecting, not Effecting. LOL

Ok, that wasn't helpfull, was it?

For sure move to a MAG primer. I use 215's.

For sure load em longer. The VLD likes it jammed a bit.

Try H1000 if the Retumbo isn't working. 7MM MAGs love H 1000 with the heavier pills.

Good luck,
Tod

 

[Mxracer532]

Re: Freezing temps effecting loads? 7mm

Affecting, not Effecting. LOL

Ok, that wasn't helpfull, was it?

For sure move to a MAG primer. I use 215's.

For sure load em longer. The VLD likes it jammed a bit.

Try H1000 if the Retumbo isn't working. 7MM MAGs love H 1000 with the heavier pills.

Good luck,
Tod

Fixed it for ya!