Velocity as an indication of pressure

A question (or two) for all you highly experienced reloaders: I've heard many people talk about velocity as a sign of pressure issues, usually saying that velocities much higher than published for a given charge, are themselves, a pressure sign, even if there's no sign of flattened primers, cratering, extractor marks, etc.

1. Do you believe this?

2. Does it work the other way? In other words, what if you work your way up to a published, or Quick Loads max, see no obvious signs of pressure and your velocities are significantly lower than they "should" be? Do you take that to mean that you should feel comfortable going above the max load until you do get close to published velocities, or see other pressure signs?

Or, do you think that different barrels just shoot bullets at very different velocities, even if the pressures are the same?

1. Yes
2. Yes again but with caveats. I believe velocity (or speed) has a pressure equivalent. So I do work up until I find what I'm looking for accuracy wise. Although I get real cautious if I'm at or exceeding max book loads. I do a lot of wildcats and there isn't really a book for them. The accuracy being more important than the velocity, within reason of course. You can dope for velocity, crappy accuracy is crappy accuracy. I generally have an approximate end result in mind. 50-100 fps either way I can live with.
On your last part, do I believe there are fast barrels and slow barrels? Kind of but I think they can be explained. Quite a few new barrels need to be "shot in" and actually show increased velocities after 50, 100 or even 200 rounds. I have one that over 150 rounds picked up 100 fps. Same brass, primer, bullet and lot of powder. It also depends on the reamer used. Was it new, an older one, within specs or a couple thousandths out? Freebore. That will make perhaps a significant difference. How far is the bullet jumping or is it jammed? Then there are overbored barrels versus standard bores. There are just so many variables that it would be hard to have an etched in stone answer.

Dougfir,

I'm not what I would call an experienced reloader, but I'll give my 0.00342 cents on the subject.

Pressure and velocity are correlated, but I don't think as closely as we reloaders would like it to be, or in a fail-safe form for us...

Question 1. Yes I believe this.

Question 2. It might, but you have to be really careful here and for me it depends on the caliber and how much I deviate from the tested / book load. Quick Load and some testing methods don't fully examine rounds for secondary pressure spikes or other potential anomalies.

The best way I know to convey the idea is that there are differences between peak and average pressure. Difference in powder burn rates, illustrate the difference beautifully. A round using a fast powder has a high peak pressure but a lower average pressure and thus a lower velocity, than the same load using a slower powder. The slower powder provides a lower peak pressure but higher average pressure and thus higher velocity.

Realistically, peak pressure then looks to be un-correlated to velocity, while average pressure can be (I think) correlated to velocity. An old timers way of telling that they were in dangerous pressure was seeing the velocity drop with an increase in powder; the burn rate with some powders speed up as the pressure increases.

Also, there might be secondary pressure spikes which wouldn't show as increased velocity. Halfway down or so at: https://www.shootingsoftware.com/barrel.htm and https://www.shootingsoftware.com/pressure.htm shows some "data" on the secondary pressure theory.

Somebody like DrMike or DWH7271 will be along to clarify things as needed... I hope. Yup, I came late so just listen to DWH7271.

Dougfir":2zgwry4b said:

A question (or two) for all you highly experienced reloaders: I've heard many people talk about velocity as a sign of pressure issues, usually saying that velocities much higher than published for a given charge, are themselves, a pressure sign, even if there's no sign of flattened primers, cratering, extractor marks, etc.

1. Do you believe this?

It depends. Certain cartridges are already pretty well maxed out from the factory and even trying in some cases to match, no pun intended, becomes difficult to match if not impossiblr with the components available to us.

2. Does it work the other way? In other words, what if you work your way up to a published, or Quick Loads max, see no obvious signs of pressure and your velocities are significantly lower than they "should" be? Do you take that to mean that you should feel comfortable going above the max load until you do get close to published velocities, or see other pressure signs?

Yes, no, maybe. Sorry for the wishy washy answer but some cartridge/rifle combos can reap well past the 65KPSI level and not show one single sign of pressure. Then again, some cartridges are deliberately kept low pressure because of the weak or suspect rifles extant. The 93/95.96 Mausers and low number Springfield rifle come to mind. Another is the ,280 Rem. because Remington chose to use the round in pump and semi-auto rifles. For cartridges like the .280 and 7x57 careful load work can make a big improvement in velocity and accuracy. For the .280 and 7x57 yes, I am comfortable to comfortably work up somewhat. You can add the .257 Roberts to the list as well. I've done work with the three cartridges mentioned. I think the 6.5x55 can be worked up past boon values in a modern rifle like a Model 70 Winchester using load that might give an 1895/M38 Mauser a serious case of heartburn. Your choice on how to go with the matter.

Or, do you think that different barrels just shoot bullets at very different velocities, even if the pressures are the same?

Click to expand...

I'm not all that sure on whether fast or slow barrels exist. I know that in the 7x57, loads that work in my Ruger #1A and Winchester M70 FWT will lock up the bolt on a custom FN Mauser I have in that caliber. A load using the 175 gr. Hornady round nose loaded to duplicate the original 1893 load did 2300 and small change in the #1 and M70, but did 100 FPS faster in the Mauser. and showed some signs of higher pressure. Granted an example of one doesn't mean a hell of a lot but there is it.My though is it all boils down to each rifle is an individual and you just have to find out what it likes or dislikes rergarding not only accuracy but pressure.

Paul B.

Just another thought.
Many of the “improved “ cases don’t seem to give a pressure sign until you’re considerably over. At least that’s my personal experience learned by accident.

Interesting. I started thinking about it because I have noticed that my rifle always seems to shoot about 60-80 fps slower than books, or QL says it should. It's also very rare for me to encounter any major pressure signs. Only once have I ever experienced a sticky bolt lift and that just happened to be a load that was moving more in line with the published numbers... It's a factory M-70 featherweight that's seen about 500-600 rounds through the barrel.

Dougfir,

Don't forget that some chronographs will run fast or slow as well; and some models are better calibrated for pistol velocities while others are better for rifle velocities.

With my Shooting Crony using 30-06, 280 Rem, etc. I've seen 100+ fps changes come from setup variations (tilted chronograph and shooting at an angle through the screens) and I also see an average of 50 fps or so difference between sunny and cloudy results. I just got a used Oehler 35p this morning, so I'm trying to get a better handle on the chronograph variable.

Just FYI - my go to article on the wacky world of pressure is - http://kwk.us/chronographs.html. Check out the section on primers, some primers provided increased peak pressure but lower velocity. I'll give a quick quote that restates this so you don't have to take my word for it...

"...his comments found in the User's Guide to QuickLOAD:
Results of primer substitutions are thoroughly unpredictable. For example, use of a hotter primer is apt to raise pressure and velocity but it can produce the opposite result; worse, it might increase pressure and reduce velocity or decrease pressure and increase velocity! There are reasonable explanations for each of these potentialities."