Random pressure signs?

I'm scratching my head some what....

Worked up a load for my 308 bushpig last summer with H335 and 150gr nosler BTs. Found an accurate load and loaded up 40 odd rounds. All components the same.

Have fired 30 odd rounds since without any pressure signs, chronograph them doing 2820fps.

Went to check zero yesterday after having the stock off and fired 3x of the handloads and had stiff bolt lift and slight ejector marks on all 3 rounds....

Any idea why this might happen?

Only things I can think of are:

- I fired 3 factory rounds 5 min beforehand and maybe the chamber was a bit hot? Was a cool day though. Also load was developed in summer and I went 1gr higher than current load without issue.

-rounds have been carted about hunting for a fair few trips. Could they have absorbed some moisture? They have been in a pack or the mag most of the time. Not sure if moisture would have this effect?

Any other ideas?

Carbon ring built up in throat maybe?

Where these rounds from the original batch loaded?

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Originally Posted by GWH

Carbon ring built up in throat maybe?

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Don't think so. Barrel always kept clean and a dry patch thru the bore before heading out. Had fired 3 factory rounds earlier so wouldn't be any traces of oil left either.

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Originally Posted by Link

Where these rounds from the original batch loaded?

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Yup all identical. Same mfg of brass, all preped the same. Same powder,primer and pills.

No issues with any of the earlier rounds.

Colder temperatures can create higher pressures, especially when the load is closer to max,

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Originally Posted by Callum

Colder temperatures can create higher pressures, especially when the load is closer to max,

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Explain?

carbon ring, or re-check the seating depth

are you jaming or off the lands ?

https://www.nzhuntingandshooting.co....ensitive-7447/

My edge also runs 50fps faster in winter compared to summer, just something I have noticed, might not be the case here with a different powder etc but seems silly not to mention it

Did the rounds spend a longer time than normal sitting in your hot chamber?

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Originally Posted by ebf

carbon ring, or re-check the seating depth

are you jaming or off the lands ?

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Off the lands, will recheck seating depth in case they got bumped somehow.

I read a thing a while back on some tests done on resized brass:
Basically the test was on measuring the down ward pressure on the bullet to seat in the neck of the case.
The pressure on the freshly resized brass was less than some that same batch of brass loaded a few weeks later.
It soundsg strange but it looked as if the brass hard hardened over time.
The article was on 6 mmbr.com I will try to dig it out.
One of them:
Neck Tension 101 — It Ain’t As Simple as You Think « Daily Bulletin

Point number 9

http://bulletin.accurateshooter.com/...e-time-factor/

This one is the better one

Im thinking warm ammo ie in the sun in little plastic box for half an hour before shooting?

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Originally Posted by rambo-6mmrem

Im thinking warm ammo ie in the sun in little plastic box for half an hour before shooting?

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Nah, straight out the daypack that was under the bench in the shade. Air temp would have been lucky to be in double digits.

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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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 :pacman:

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!!! ;-)

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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.

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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.

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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.