Pressure signs and the real world

[Sweetwater]

Guess I figure that anything that has the potential of helping us stay healthy at our chosen hobby is a worthy addition. That QL sparks an interest, as well as the Oehler Personal Ballistics Lab. I may have to forgo a weapons purchase and add that to my locker. I have a Chrony and it's been a wonderful useful tool and actually helped me tone down a load because I knew I didn't need the velocity being generated to get the performance that I wanted. Pressure signs that have been used for 40 years to keep me on this side of the hereafter were nil to nonexistent, I just like to maintain the least amount of noise and recoil necessary to get the job done. Plus my wife likes to shoot my stuff and doesn't appreciate needless 'macho-ness'. Guess I use her also to help me keep my pressures out of the twilight zone.

Though I can't say I really care what the actual value of the pressure in my load is, I do care that it is within the safety zone. I have also found that as powder charges get closer to their peak, their performance becomes more erratic. On the Chrony, SD's and ES's vary from one shot string to the next with no apparent explanation. The wide variance of pressure from shot to shot, even in great loads shot in ballistics labs, is enough to keep me tempered on the cautious side. Loads that created signs of casehead seperation were always less pleasant than loads backed off just a mite. This experience is limited to my stable of guns and may not work for your stable of guns. It's just another arena where we seek the best sources of information available and put it to use to serve our purpose as best we can - and stay alert. Sometimes our experience does not mirror that of the documented experience. 
For example; I have two 30-06's and two 257Roberts. The custom 30-06 is cut to minimum SAAMI specs and gives higher velocity with less powder than the Remington 700 with its factory chambering. Likewise, the two Remington model 722's in 257Roberts have very different chamber dimensions. I can necksize only all of the brass from one and it will fit in both, but the brass from the other must be full length sized to fit in both. The 'tighter' chamber takes a full grain less of IMR4350 to reach the same velocity as the 'looser' chamber. Just the way it is - nothing magic about it.
Someone else's experience may show different results. Doesn't make it right or wrong - just different.

Thanks for raising the question and sharing the opinions and experiences - all very interesting.

Regards,
Sweetwater

[steve4102]

Hey Sweetwater,  the Oehler Ballistics Lab is pretty spendy.  http://www.oehler-research.com/model43.html   There is another similar product out there called RSI Pressure Trace II.  It costs quite a bit less and may be something for you to consider. http://www.shootingsoftware.com/pressure.htm

[beemanbeme]

Castaway, you see, you said, "reliable load book", as you know, I tell new reloaders to get one or more load books and read them, cover to cover before starting out.  But now we are told the books we have used for years are worthless.  I knew exactly what you were saying.

I have found a Chrony to be very helpful in my reloading.  For instance, if I notice my velocity gains start to dwell or taper off even tho I'm within limits according to the book, I consider that the maximum "efficiency" for my rifle.  Also, if the hateful old book tells me that xxx grs of powder should give me 3000fps from a 24" barrel and I'm getting 3400fps from a 22" barrel, I don't come bragging about it in cyberspace. I get off the throttle.  And that brings me to a question:

Because of the difference between the lots of powder they order or even the types of powder they use to load their ammo, bullet factories  load their ammo to pressure. xxxx pressure equals xxxx fps.

  If my Hornady load book sez that xx amount of xx powder should give a 165gr Hornady bullet 2800fps at 50,000psi.  Now then, without nit-picking this thing to death about relative bore roughness and such, if I put that much powder behind that bullet and get that velocity, is it not reasonable to assume I am getting that velocity?  If I shoot several rounds and measure the case acrost the web and use that as a base line and then develop another load with a different powder and different bullet, using the same brand cases and the same rifle, when my web expansion reaches the base line measurement, isn't it reasonable to assume I have reached the same pressure?  If not, why not?