Dustyman wrote:Can someone clarify why ( in rifles using pistol calibres eg 44 , 45 , 38 etc ) if using a fast burning powder such as a pistol powder , there is an issue with dropping below the minimum load in the books ? The powder all burns before the bullet leaves the case in a pistol load because if it didnt it would be spewing sideways out of the air space between the cylinder and the barrel on a revolver if continuing to burn down the barrel as is the case with slow burning powders in rifles , rather than rifles using pistol calibres ?
Because the case 'obscurates' i.e. it expands under pressure to form a seal between outside the case & inside the chamber wall. Mess about with the rate of burning & you change the rate of gas evolution & that in turn changes the seal of case to chamber. A slow powder wont obscurate the case properly so gas is lost & that changes pressures. indeed the pressure peak can be before the round has jumped & that puts excess pressure on the neck throat & back down the primer. or across the revolver gap. There is more to it that that but thats the basics. Thermodynamics & reaction rates mate year 3 uni.
Dustyman wrote: Also the issue of an unfilled case , and being loaded without a packer , possibly allowing the powder to burn from both ends and upping the pressure seems to be unlikely with these fast burning powders because surely if there was a risk the reloading books would not be printing any loads that didnt well fill the case? . My 45 uses a load below the minimum charge cus i never shoot it further than 20 yards and i am able to get a inch to inch half group unsupported on open sights ( I think thats good enough for me ) , so why do i now need to up the load to someone elses minimum load printed in a manual and try and find a new sweet spot when this load works for me , which is what this NSRA C.O.P. is saying i have to do .
That's chemistry mate - the propellent has oxygen in its molecular structure it does not need air to burn. indeed excess oxygen can cause over burn & react with air / gas, moisture to form steam or nitrogen to form nitrous oxide all gasses that take up more volume, so an unfilled case can have excess oxygen & over burn & that increases pressures. there is a sociometry that is ideal for over burn & some people call that a detonation so it goes bang inside & can damage your kit / hand / eye etc so to avoid that use a low density faster powder or a filler to exclude the air volume & its oxygen. Add to that the gas laws dPdV=nRdT & reaction rates & you can get all sorts of effects.
Its also physics - tumble a live round & you refine the propellent powder, that makes the particle size smaller, that puts the surface area up, that makes it burn in more places at once, that makes it burn faster, that makes your round go quicker. but can also damage your gun if excessive.
The crap NSRA doc is giving advice that ignores this indeed as Dromia says is ignorant of it. Recipe for a painful cock up.
Quality control of Scottish Ethanol. & RDX/HMX
& my fav chemical is :-) 1,3,7-trimethylxanthine.......... used to kill frogs.... but widely consumed & in vast quantities by the French? Eh?
