Freebore and overpressure

[Buckys]

It doesn't increase pressure, so it's not a 'pressure' problem.
It's an oil in the chamber problem. Right?

If you oversize cases, leading to cracks/separations/flattened primers, again, that's not due to pressure.
It's due to a bad reloading plan.

If your cases won't extract due to bad bolt timing, or poor chamber/gun build, these are not pressure problems.

As each of these problems are separate and different, so is pressure itself.
If you have a pressure problem, the fix is to lower pressure. That is, fix the cause of overpressure.
You're not going to fix any of these issues with lowering of the charge, if the charge is not even the problem. Right?

Good point on the definition. I suppose for me 'pressure problem' is anything that might unexpectedly cause super-heated gas and/or metal fragements to erupt near my cheek weld

 

[243winxb]

IMR4955.... is it a risk for overpressure by detonation?

Unknown.

Powders containing nitroglycerin have been known to detonate, under certain conditions. Mostly takes a very high % of Nitro, like Alliants Bullseye powder, which is equivalent to C4.

In rifle cartridges, the firing of the primer pushes the powder column forward.

A standard primer may not compress the powder column fully. Powder burns from both ends. High pressure results.

A magnum primer will compact the powder column more fully. This powder only burns on the primer end. The burn/pressure moving forward towards the bullets base. As it should.

Bullets should have good neck tension/bullet hold of .002" to prevent early bullet movement.

Longer then normal free bores, add to the problem of pressure spikes.

Canada did a test on powders that can detonate. If i remember correctly there were 12? that could?

Our Goverment thought about issuing a license to buy smokeless powder, but it never happened.

https://discover.dtic.mil/

 

[Mikecr]

If the case can expand rearward (dry chamber) and stay within the case's elasticity, it would seem to reason that it could also expand forward (oily chamber) to the same extent and be within the same elasticity limits.

I imagine different results are possible depending on your chamber fit, amount of oil, acute or chronic issue, etc.
That as you go up in pressure, it will likely show up in 'some' regard.

And I'll concede that with enough oil in the chamber to cause a hydraulic solid condition, that pressure could go up a bit over well undersized cases expanding in a dry chamber. This difference would be similar to NEW -vs- FF'd cases with a given charge.
I don't FL size cases, so it wouldn't make any pressure difference to me, but I'd get an extraction issue like anyone else..

 

[assasinator]

dont forget that a shorter than minimum COAL can cause overpressure also.

that is probably the most dangerous thing a man can do. there is a limit to compressing powder. if a man is loading near max or max loads with compression, it is good to be careful loading shorter. i have done with with my old contender .223 barrel. i dropped the load, shortened it to get more jump to the rifling, then added powder until i had cratering, then backed down. shot accurate, and was .2 grains over max load from the 1987 lee manual.

 

[assasinator]

Mixing headstamps can do it.

OMG YES! every brand is different and have different load capacity. if a man is pushing the limits, it is advisable to use the same brass. for example, i use norma for my 350 rem mag, remington for the 375 taylor, and weatherby only for the 270BEE.