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Does the sun or temperature effect the round's pressure? How much? Here's something to consider.

Standard military issue 7.62x51 operate as lower pressure than typical .308 factory ammo, ie: -55,000psi compared to +60,000psi - considerably lower. How much does heat raise pressure?

The ammo box, sitting in the sun while we're prone shooting, if not protected from the direct sunshine (in Canada, not Australia's heat), will blow the primers - as -in the .416 Ruger rifle of this thread. What pressure is required, ie: how much can the sun's rays actually ioncrease the pressure inside a case?

To blow the primers, not just loosen, but actually enlarge the case head to where the primers fall out with a .470" head ctg. requires enormous pressure - with properly heat treated brass. A fellow on another forum with that computer program declared my .218Bee loads (40gr. @ 3,750fps) were running 84,000psi - yet my brass never dropped a primer - was loaded 14 times(and still going strong for the new owner, when Ken Waters could not get 5 loadings using his low velocity 2,800fps loadings(1,000fps slower). So, what pressure does it actually take to blow a primer? The .218Bee has only a .408" rim and much smaller body ie; much less strength than a .308, let alone the larger-yet, Ruger case.

The .416's larger case and rim diameter, has even more strength around it's primers and requires even more pressure than-does the .308 case. Strength increases exponentially with diameter.

As in the situation of the .416 rifle or any other, it is easy to jump to an erronious conclusion based upon limited know facts, or from a desire to solve a mystery quickly. Guesses are made as the fcts trickle in. I am guilty of this & for that, I'm sorry. Much of the time, a company is blamed for an error of the shooter.

With the information available, we don't know who's at fault and without proper equipment or 'being there' who'd to say? A simple mistake of shooting too quickly, overheated barrel and blooey - blown or leaky primers - blown is beyond leaking. The pressur spike occured prior to a leak.

As in any such cases, there are a lot of different facts & possible scenarios to take into consideration. At best, all we can do is to guess & probably wronly.

Consider this, a .45/70 case subjected to 70,000PSI in a Marlin lever action rifle shows normal pressure in expansion measurements - ie: Marlin's testing and measuring of primer pocket, rim and base diameters in an issue M1895 .45/70.

Brass strength is vitally important and comes down to proper heat treatment.

Ammo left sitting in a hot chamber prior to being fired, increases the powder temperature, in some instances, to the point of extreme pressure wave action. This depends on the type, and formulation of the powder. Some powders are more susceptable to pressure jumps with high temps than others. Many of the stick powders, commmonly used in large cases, are prone to big jumps in pressure with high temps, as-are some spherical or ball powders. Some aren't. with handloads, we can control this, with factory ammo, we are stuck with what the factory used.

ADI and Hodgdon Extreme powders are very much less suseptable to pressure excursions due to heat or cold.

Ctgs. like the British African rounds, loaded with cordite did not maintain their low, 38,000PSI or CUP when shot in Africa - their pressures jumped amazingly high - maybe scary high at times, so to keep their cordite-jumpy pressures safe they made them oversized for their actual performance - to keeping pressure moderate in extreme heat was important for the weak-compared to bolt gun actions.

When loaded with heat insensitve powders, high initial pressure rounds are just as 'safe' as low pressure rounds loaded with heat sensitive powders.

It would be interesting to put strain gauges on a DR to compute the pressures of the 1st and 2nd rounds, let alone the third and especially the 4th shot - when fired at 120F temp in the blazing sun-shine.

As an aside, I wonder what happens to regulation at extreme temps?

I see ammo carried in those pretty loops on the hunting shirt's pocket - directly in the sun - Hmmm.

The sun is NOT our friend.

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Daryl

"a gun without hammers is like a Spaniel without ears" King George V

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