Thread: Random pressure signs?

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See callums link he posted.


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Thats interesting that colder rounds have higher velocity. I remember years ago at a shoot when it was pretty chilly ( Waimate )
When the word went out that MV tests for power factor was going to happen, everyone that was doubtfull about their speed, stuck their ammo in their pockets........ shouldnt have bothered

Interesting regarding cold temps increasing MV! I always thought it was the the other way round...

Slightly interesting note though. Last weekends tahr hunts brass didn't have have sticky bolt lift (that I recall anyway) and cant see any ejector marks on the cases. I did only fire 2x rounds however. Air temp was below zero and ammo was sitting in mag all day. Maybe the Dunedin range is a colder hole than I thought!!! ;-)

Originally Posted by 338

I get this all the time in the cold. When I am hunting in the snow some of my loads stamp like a bitch! Keep them in your pocket.
I have actually tested this a few years ago with 2225 and 2217 powder using ice packs and hand warmers to heat and cool rounds.
Shot at 400 and had higher velocity’s,higher point of impact and pressure signs on the brass on the cold rounds


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Interesting. Cold shrinks metal. The relative differences in coefficients of expansion of the several metal involved, e.g. barrel, brass, bullet would change things like neck tension and case capacity, even headspace. Loaded close to limits, these combined factors may have a more noticeable cumulative effect than with a more mild load.

Originally Posted by Woody

Interesting. Cold shrinks metal. The relative differences in coefficients of expansion of the several metal involved, e.g. barrel, brass, bullet would change things like neck tension and case capacity, even headspace. Loaded close to limits, these combined factors may have a more noticeable cumulative effect than with a more mild load.

Had the same thought, will be interesting to try putting the remaining rounds thru when its a bit warmer and see if there is an issue.

I the mean time would folks keep using the load? slightly heavy bolt lift and light extractor mark. Or do I need to look for a different winter loading (would be a ball ache!)

If your bullet ogive is well off the lands, then you could extent coal say 5 thou which will increase effective case capacity and lower initial pressure. However, if by extending coal you are very close to, or into the lands you could dangerously increase pressure. Only you can carry out the required measurements and make the call.. If in doubt, drop a grain and start to look for the next lower velocity group node.