Overpressure

[Mousegunzzz]

What are the basic signs of overpressure in a rifle other than a loud bang and parts flying all over the place .

[Nate1778]

Cratered primers, stuck bolts, stuck cases, Bolt in the eye.........

[GeauxTide]

If primers are flattened or cratered, measure case head. If it measures .005 greater than spec, it is maximum. If cases measure larger, back off. My old 700 had a tight throat and showed primer cratering before max was reached.

[Gbro]

I have posted this link before http://www.darkcanyon.net/john_woote...afety_tips.htm

Watch for signs of high pressure while working up a handload. This means extraction difficulty (however slight), flattened primers, cratered primers, ironed-out headstamps, polished headstamps, ejector marks, case-head expansion, and excessive recoil and muzzle blast. And anything else whatever that strikes you as abnormal about the load.

A good reloading manual like Speer or Hornady will give good information on pressure and other needed information.

[F. Guffey]

The first sign the case displays the effect of pressure is in the web, when fired the web is hammered, meaning the web shortens and expands. As pressure increases the hammering effect increases, the web gets thinner and larger in diameter, as the case web diameter increases the metal comes from where as in the theory of 'upset' or 'glupe making'.

This effect is explained as loose primers because brand X cases are softer than brand B cases.

The effect pressure has on the web (case head expansion) must be compared with an arbitrary? standard. Factory ammo will upset the head of the case 'every time' and is accumulative meaning every time the case is loaded and fired, the case head expands. Example:

The case head is measured first, loaded and fired and measured again, the difference is .001, the .001 should be expected every time that case is loaded if the same load is used, on the other hand if the bullet weight is increased with out reduction of powder or if the bullet weight stays the same but powder is increased, pressure will increase, if the head diameter increases .005 with one firing, other signs will be evident, flat primers, loose primers, bolt opening difficulty, etc..

Not a consideration, diameter of primer pocket, diameter of flash hole or thickness of web, but if the diameter of the case increases, where does the metal come from?

F. Guffey

[F. Guffey]

Because of case dimension variations between cases of the same lot, the web thickness must be know for each case tested. Catastrophic failure, could the web be crushed enough to allow the supported body of the case to become unsupported, if the thickness of the web had been measured before and again after failure we would know, or did the pressure down through the flash/primer pocket hole rip the head of the case apart? I have seen large flash holes and primer pockets, both are always associated with case head expansion and thinning of the web.

F. Guffey

[Mousegunzzz]

Thanks for the info.

[SL1]

Sorry, but I have to disagree with Guffey on one point:

The case head is measured first, loaded and fired and measured again, the difference is .001, the .001 should be expected every time that case is loaded if the same load is used...

The case head typically does NOT expand the same amount with each firing of the same load. Typically, it will expand the FIRST time its compressive strength is exceeded. That expansion will work-harden the brass so that it will have a new, higher compressive strength. If subjected to the same or even slightly higher load again, it usually will not expand at all. Somewhat higher pressure is required to cause more expansion.

Richard Lee's book has a good discussion of this, with an example of how much overpresssure you could get by looking for some standard amount of head expansion in a case that has been fired a few times with increasing loads.

So, please don't think that you can grab any old case and see if the head expands more than 0.0003" to see whether your load is still safe enough as you keep adding more powder.

PRESSURE RING measurements are a different matter. There, fired diameter should be ABOUT the same for each firing of the case with the same load pressure. But, there is work-hardening happening there, too, and how you resize the cases affects what you can do with that technique, plus it tops-out at some pressure (depending somewhat on chamber characteristics).

BOTH techniques take considerable study and skill to avoid unsafe assumptions and practices. There is a lot of MIS-information floating around the Net and in some gun magazines on these two techniques. If you are going to use either, I STRONGLY suggest that you do some experimentation to see what happens with these measurements with YOUR gun when you use repeated firings with WELL KNOWN, PRESSURE-TESTED DATA of various pressures BEFORE you start relying on it for other loads.

SL1

[F. Guffey]

Mousegunzzz, choices, which case is safest if any of what I said is true? I would go with commercial cases, the 30/06 commercial case web is TYPICALLY .060 thicker PLUS or MINUS a little than the web on military cases, the web on 30/06 TW, LC, SL etc., is TYPICALLY .200 + a few.

Typically it is said military cases are heavier because they are thicker, if what I said above is true the military web is thinner by .060 + or - a few. this leaves the body of the case, the military case has a thicker body, the thin web/thick body military case has a long column of powder that is smaller in diameter than the commercial case, the commercial case has a short column that is larger in diameter, does this make a difference? It does when comparing the 308 W with the 30/06.

Case head (web): The case head is not soft, it is not annealed, it is work hardened, hammering the web against the bolt face can compress the brass, if the web is compressed does the case shortens?

F. Guffey

[Dingoboyx]

LMAO.... that woz funny spot on too.... bolt in the eye....

[Gbro]

Mousegunzzz,

Its hard not to feel overwhelmed by the explanations given by some posters in this forum. I look at their level of knowledge in reloading to what could be viewed as a Masters Degree (if such were possible). I have been reloading for over 30 years and would claim to be close to an associates degree, as I am having a hard time following the posts of F. Guffey and SL1. They are most definitely very experienced reloaders and offer very good information/examples on why we should not push the pressure window. I myself used to try and get as much velocity out of my reloads as I could years back (Grammar School level). I do not do that anymore. I start low and work up slowly to find a load that will group well and shows no obvious signs of excess pressure in the -200 fps below the max if i possibly can.
Please pace yourself, and read, read, read, about this fantastic hobby.