disco stu wrote:Thanks guys.
Old Bloke: I know that's exactly what you have mentioned before, just wasn't sue if it was still an issue or what
BR: yeah, that's my concern-the fact I may be seeing over pressure while I'm still down on what I think should be my maximum. Not know what I'm looking at due to inexperience is also on my mind. Knowing that extraction will show signs is good to know also. I think the best method then is probably to shoot a few factory rounds before going into my reloads just so I've got the feel of what is normal.
I'm certainly not looking for the fastest round or anything like that, just want to make sure I'm safe in case my rifle is a bit different.
Still a while away though. Have to get let out of house arrest, the guy has to pick up the reloading gear I'm meant to be getting off him, and the shop has to actually have powder and primers for me to put into these mythical reloads.
Appreciate the responses, thanks
I think the easiest way to learn pressure indicators is to start low and inspect your brass and primers thoroughly. Then start increasing the charge and keep inspecting. Most likely the first thing you'll see is the rounded outer edge of the primer will start to square off at pressure increases. It doesn't indicate high pressure though, just that pressure is increasing. If you keep going the primer will flatten and completely close up the ring around it, you might also see the striker indent swelling into the striker hole in the bolt face. This still doesn't usually indicate high pressures, but if you have very hard primer cups it may do. The primer cup is _much_ softer than the brass case head, and the pressure in the primer is being funneled through the flash hole inside the case. If you are not seeing other pressure signs you can try a harder primer.
You should also see a faint ring around the case body, though with very light loads this will be imperceptible. As pressure builds, the heavier case walls start to flow (the walls of the case are thin at the mouth but taper down to being quite thick at the case head, requiring much more pressure to deform them) and expand to the chamber wall further down the case, leaving this discolouration. You can watch it move down the case as you increase the charge, but it is not necessarily indicating excessive pressure, just that there is pressure. If the ring stops moving down the case, and starts becoming more obvious you may be heading toward case head separation.
I also measure case length after sizing to see how much the brass flowed forward, with my light loads it can take several firings to even get .001" longer. Also measure the shoulder length if you can, and monitor that after firing.
Always look carefully for shiny spots around the base of the case after firing. As the brass flows under higher pressures it will start to mould itself into any features on the bolt face, like the ejector hole - this is an excellent indicator of excessive pressures, one that you really never want to see. With these you should certainly be able to measure case head expansion.
When you are starting out though I strongly recommend staying away from any pressure indications while you hone your loading technique. Pressure does not increase linearly, a 20gn charge might make 40,000psi, 22gn might make 45,000psi, but 23gn might make 55,000psi due to the reduced empty space in the case and other factors. As pressure increases you want to take smaller bites at it. Small discrepancies in technique can lead to significant pressure spikes, which can be nasty when you are already pushing the pressures. If you have a hottish load in neck-sized brass, then full-length-size it, you might see 100fps or more increase in velocity due to the reduced volume with the same charge. Or if your bullets creep out or in under recoil in the magazine until they jam into the rifling or reduce the volume of the case, you will also see a spike. When working with heavier bullets or higher recoil (due to a lightweight rifle for example) it pays to leave some rounds in the magazine through repeated firings, then inspect them to see if they are the same length as when you loaded them, if not you may want to crimp the bullets. Keep on eye on heavily-compressed loads, the bullets may creep out from the pressure before you get to fire them, so when you do the bullet might be biting into the rifling.
Spikes are usually fairly obvious because they are extreme, more recoil, more blast, more noise, and such. Any time something happens that feels "different", stop and try to determine what it was before you continue, including pulling the bolt and looking down the bore to be sure it's clear. Sometimes it happens for reasons you can't confirm, like a bullet moved in or out in a cartridge and you didn't notice.