Home Forums Hunting & Shooting Ask The Gunwriters Question about pressure signs when working up a new load?

Well, I fall in with the chrony pack. You are flying blind otherwise - no matter what data source you are using.

I will give my example of one that proves my point. Factory Dakota M97 300 Win Mag. Reaches Nosler #6 published velocity several grains before the max published charge weight...and no "signs" of pressure.

The reasonable man would look at his chrony and say...holy crap!!...I'm not even at book max and I'm 100fps faster than the book (a given we are talking the same components).

However, on this and other forums I would be led to believe I have the magical 'fast' barrel...and assured I could keep adding powder as long as I kept to the 'book' charge, and it was 'safe' in my gun.

Suddenly I would find that pressure 'sign' as my bolt locked up - being the lucky guy I am, I assume my bolt would hold. But who knows, as I'd be well over 70,000psi at that point.

WranglerJohn,

I am not (and never have) suggested that the average handloader ignore pressure-tested data and rely totally on a chronograph.

What I have always suggested is that the average handloader compare published, pressure-tested data with the chronographed results from the same bullet/powder combination in their own rifle.

Gotta say it....

+1

Having had to work up useable data where there was none available... I rely on a chrono... and I've watched the speed vs powder increases.. and it has pretty much summed it up that when the same amount of increase in powder fails to increase the MV the same amount as it was basically... IE you get less for more... then its way time to stop...

Doing it this way and then later having had things tested with a strain gauge it seemed to be that I was right where I figured...

Does a chrono lie? Nope, but then how often do you have exactly the same components to a T RE matching velocity then... There are way to many variables to say that in a certain cartridge.. IE like 130 grain in 270, that 3100 fpx is max period... and I'm not alluding to simple things like barrel length only.

I am also using a chronograph.
I usually like to shoot some factory loads first, to see what velocity that particular rifle will produce .
If velocity of my loads approaches or exceeds factory loads I will be measuring the cases very closely and comparing with the factory cases I previously shot.

I don't worry about trying to meet "Book" numbers, They weren't shooting my rifle when they clocked the numbers.

Pressure sighns?

When the barrel splits, you just exceeded max load - back off a little!

You're not serious if you don't have a chrono

I grew up reading Ken Waters' Pet Loads, where he measured case head expansion with micrometer, and I have used that approach for a number of years in judging pressure of handloads. I think in the books it is the first chapter.

On one batch of factory .25-06's I diligently loaded up and very slightly exceeded factory case expansion measurements. Then I bought a chrono and discovered the factory loads were a good 300 fps under spec! I was significantly under-loading the cartridge, based on the expansion measurement method alone.

Is the published max velocity in a manual still valid even if different primers are used. For example if the Barnes #4 manual lists a max velocity of 3003 fps with some powder and Fed215 primer. If I am using CCI 250 primers, is the 3003 fps max velocity still valid to use?

Great discussion. If pressure and velocity are tied together why do certain powders top out at a lower velocity than other powders? Aren't we forgetting another variable in the equation - such as burn rate?

"Aren't we forgetting another variable in the equation - such as burn rate?"

We might be, but burn rate is one thing that we shouldn't ignore.

A fast powder, by this I mean a faster powder than will give the most velocity, if velocity is what you are looking for.

For example, using a .300 Wby., you would be well beyond safe pressure if you tried to equal the velocity you can get with IMR 4831 if you substitute IMR 4895. Using a chronograph or not, a 180 grain bullet at 3100 FPS in front of IMR 4895 is going to give pressure out of sight, while this same velocity is feasable with IMR 4831 or H1000.

You have to match the chronograph with the powder and velocity you expect from that particular load. You cannot get max velocity and safe pressure with a fast burning pistol powder, regardless of what your chronograph is reading.

That is the point I was trying to make. I think pressure and velocity are related for an individual powder/bullet combination but they can't necessarily be compared between other powder/bullet combos in the same rifle. Just as some combos may be on the slow side for a given bullet weight, some are also on the fast side for the same bullet weight...even thought there may be a 300 fps difference the pressure may be the same.
So, do the newer powders modify the burn rate enough to give increased velocity over the old standard loads w/o exceeding pressure limits?

Any combustible fluid even water will vaporize at the chamber pressure. When you vaporize water -Oxygen and 2 parts Hydrogen are released into the burn, somewhat like adding water to a combustion engine to gain extra mileage. So you would see a pressure spike higher than a clean burn. Don't have to be Einstein to figure this out. Like throwing a cup of gas in your campfire.