Head space and pressure

[zap]

Does less head space (say .001- .002 ) create more pressure versus a headspace of .005-.006 ?
Will you see more pressure signs on the primer with the above question ?

[darkker]

No, amount of powder creates pressure. Amount of headspace can create uncontrolled pressure escape, as in not only out the barrel in the opposite direction of you.

We have ALL done it at one point or another, but please DO NOT READ PRIMERS. The fine folks who build ammo and rifle, that make-up SAAMI, found out quite a long time ago, that anything over about 45,000 psi isn't accurately reportable by copper crushers. They send the same lot of powder along with the same very carefully calibrated copper slugs to several different mfgrs, to test the reference load of some cartridge. Well with the same SAAMI min-spec test equipment, the reports varied in pressure by around 15,000 psi; so now they use strain guages.
So what does this mean? If the professionals who make billions of rounds a year can't accurately judge pressure with very carefully calibrated copper crushers, don't for one instant think that a NEVER calibrated primer cup, will report anything to a hobby reloader. Same thing with case head expansion. What alloy is your brass? What tensile strength is it hardened to? If you don't know, you would have now way of knowing when it even begins to stretch. Back around WWII lots of mfgs used an Olin alloy for 06 brass. That brass spec'd to be hardened to 89,000 psi. (Alloy C269, IIRC) So when you can measure that brass growing you know you are generally way beyond 60,000 psi...

Use your chronograph, or buy a Pressure Trace system if you want to know pressure.

[GaryB]

Soo, are you saying to the novice reloader not to watch for flattened primers as a sign of high pressure?

This gadget is kind of expensive.
http://www.shootingsoftware.com/mm5/merchant.mvc?Screen=PROD&Store_Code=RSI&Product_Code=PTIIBT&Category_Code=PT

[darkker]

That is precisely what I'm saying, for the reasons already started. A Pressure Trace system costs about what a rifle does, but if that isn't in your cards; use your chronograph. The standard in the industry is to use SAAMI minimum: Bore, Groove, chamber. Going to be highly unlikely that any mass produced rifle matches that, so you will bleed off more pressure than the rifle used in book data. So what that means is that if you are matching book velocities, you are over book pressures. I have been guilty of it to, thinking because my primers "looked good" my 308 had a fast barrel. The truth is no, I don't.

Testing H4350 & Superformance in the Creedmoor, 100 fps change took 10-12,000 psi extra. Don't think that is a linear deal, but within the listed loads (operating pressure) found in manuals, that's what was reported.
Here is a fun one for you, which illustrates the point of not reading primers. This load was done as some high pressure testing. The cases ejected perfectly, the primers were totally "Normal", the recoil and muzzle blast was normal.
http://i78.photobucket.com/albums/j84/Darkker13/Mobile%20Uploads/Screenshot_2015-01-31-15-00-18_zpsmopqcu83.png

As you can see pressures almost touched 70,000 psi, and there were some nasty secondary ignitions. Shows that even though there were no "classic " pressure signs, the powder was running away uncontrolled. Those types of events is what blows-up barrels and more. The thing with a chrono, as you can see from above, is that it is limited. By velocity that nasty trace wasn't fast.

[joeb33050]

Does less head space (say .001- .002 ) create more pressure versus a headspace of .005-.006 ?
No. Think of the chamber, it has a volume. For a given powder charge, primer, bullet, the pressure varies with case volume. Thick cases have more ressure than thin. But, headspace does not vary case volume, so no volume-related pressure change.



Will you see more pressure signs on the primer with the above question ?
Since the answer to above = NO, question 2 is moot.

[GaryB]

Darkker

You gotta love technology. Great info! Thanks.

and the chronograph/software is not a bad deal.

[darkker]

As a side note to the PT system. If someone buys one, be prepared to get out the cerrosafe and chamber cast. If you choose to fudge and not do that step, just keep in mind you will be accepting a much much larger fudge factor in the traces you record.