I started from the point of buying some 143gn bullets to load in .308, only to find that my 2 reloading manuals show 130gn and 150gn.

Okay so I can compare each powder's load data in the bullet weights either side of 143gn and take it from there.

But how, at the range with chrono in front of me, do I know what's a really safe "never exceed" load in practice in my rifle?

Take for example the powder I'm tempted to start with, BL-C(2) where the velocity of the "never exceed" loads are 3109fps for the 130gn bullet and 2835 for the 150gn. Is a straight calculation (2835/150)*143 valid and reliable, or what?

I accept the likelihood that my best groups will probably come in at under the "never exceed" load but apart from watching for the signs of excess pressure on bolt, case and primer, how can I determine my "never exceed" load?

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Pete:

The only way to ascertain the "never to exceed" load is to instrument the rifle with a strain gauge. It tapes on the barrel adjacent to the chamber and registers the expansion of the steel. Fischer Instrument and Oehler make them and they are used by afficionados. The other software and other instrumentation that is also available can and does get very exotic and detailed but that is for ballisticians.

You can begin to develop loads by using a ballistic loading software. Several are available for purchase but there is one free on the internet by John M. Knight. He has two sections - Win Load and Win Gyro. It has been around for quite a long time and it previously did not have all of the latest powders. But I suppose it is possible that he may have updated it. I think he has an E-mail address also and welcomed interchanges.

http://homepage.ntlworld.com/jmk/

Kendall

William,

Thanks, I should have added that I use Pointblank s/w but unlike say Quickload, this doesn't have a predictive capability but relies on muzzle velocity. Of course I could input a whole series of imagined m/v's but you can see the lack of appeal in such a lengthy process.

Pete:

You need an internal and external ballistic software, "Load From a Disk". It will give you exactly what you want. But you may find it a little bit conservative. I have it among several others and for what you get the price is very much worth it.

There is a demo unit that you can play with at this site:

http://www.loadammo.com/WhatIsBallistics.htm

Kendall

Pete......these never exceed values or max as we refer to them are totally rifle specific. A load that may lock up the bolt in my rifle will work fine in someone else's and even give widely disparate velocities. Other questions of course involve length of barrel, temperature, primer used, etc etc.

For ease of loading, use the 150 grain data that you have as the safe max.

Pressures, using the 150 gr data, will be within the safe range. For the 7 grain difference in bullet weight, "Safe Max" will be close enough to the 150 data, considering the lack of pressure testing equipment.
Direct comparisons aren't always accurate. Enjoy!

Safe Shooting!
Steve Redgwell
303british.com