Home Forums Reloading Big Game Rifles Velocity indicates Pressure???

Been reading through the reference section and had a question came to the surface. Consider a published load being tested.
The barrel of my gun remains the same (tightness, tolerances, wear etc.), throughout the load testing.
The bullet is the same as the published load (weight, point style, resistance).
The case is the same as the published load (mfgr., approx. weight etc).
Powder charge is the same as published load (same powder, same charge weight etc).
Primer is the same as the published load (mfgr.)
The COAL is the same as the published load.
Excluding manufacturing tolerances, etc, I am going to consider these items to be constants for my testing.
Now my question. I ‘m loading a 3006 cartridge with a 165 grain Sierra SPBT with 59.0 grains of H4350 powder, 3.300” COAL and a CCI200 primer and the book says I should be getting 2938 f/s velocity at 49,400 CUP (2011 Hodgdon annual). If this load in my gun gives me 2700 f/s velocity can I increase the powder charge and use the velocity as a general indicator of pressure until I am approaching the published velocity (observing pressure signs). Simply stated my question is if everything else is a constant, and a published load is used, it seems safe to say that the powder charge can be increased and still remain within indicated pressure.
I did this with an 8mm Mauser 98, using a published load it yielded about 150 -200 f/s less velocity than listed. I began slowly increasing powder charge until I got about 100 f/s closer to listed velocity. I am not getting any pressure signs and brass has lasted 7 loadings so far. If the above is correct, I am above the listed charge weight yet within the pressure constraints.
Before you begin thinking why am I asking this question now, I want to say I am only a sample of one and would like to hear what the experts say. I remember John B. touched on this subject in a past issue of Reloader.
Thank you in advance for any comments,
tj

The short answer is no. Rifle barrels are all individuals. Your rifle might give less velocity for many reasons, shorter barrel, differences in internal dimensions and finish. Not to mention different lots of powder, primers, bullets and brass.

I suspect the reason you got away with this approach with the 8mm Mauser is because most of the reloading data is consecutive for the 8mm in deference to all the old guns floating around.

Michael

Velocity is the best indication of pressure within reason of course. It should not be the only thing monitored. Barrels are all individuals, but as a general statement, using the same components/ barrel length, you can't get more velocity than published max and not have more pressure. Trouble is too many loading manuals do not have good pressure data and they may be estimating a little too much. I'd have to have a good reason to go over "book max" charges, the 8x57IS is one good reason, depending on the data source. "8mm Mauser" is not a recognized designation in Europe, the pressure for CIP standard 8x57IS loads is much higher than American SAAMI "8mm Mauser" data - velocity too. I load my 8x57 with 200 grain bullets to 2500 FPS with no trouble at all from my Brno '98's 23 " barrel, but I am using CIP data.

You seem to be saying that you can have less velocity with the same pressure, with everything the same, but not more. I don't buy that. You can have variations going both up and down, but only the up is dangerous, is my take, and you need to be really careful with that. miles

Generally the powder manufacturers test pressures in pressure guns with minimum saami standards for bore diameter, chamber dimensions, throat, etc, to find the highest expected pressure.

Rifle manufacturers make their rifles with looser dimensions in order to fit the largest ammunition within saami specifications that the rifle may encounter.

So one would expect that when using published data the actual chronographed velocity might be less, and so would pressure. If a chronographed load gave velocity in excess of published data for that charge weight, then pressure would be expected to be higher as well.

Since no one can ever be 100% sure of every variable they still recommend starting with the starting load and working up to the max load in your rifle, because you just never know how all of the 1000 different factors that will affect pressure will line up. Some rifles will tolerate more, and some a lot less.

And since you are being careful to follow the load recipe exactly, and to observe the accepted safety procedures, you are likely to be ok with your load development.

If your primer pockets stay tight, and there are no ejector marks or sticky bolt lift, those are good signs that you are on the right track.

Sorry that wasn't my intent - JB or other more experienced loaders than me could explain it better, but I think that to get more velocity with the same components / barrel length as a standard max load/ barrel length would require a short throat, or tighter bore, hence more pressure. If velocity is low for a given combination that is "same as the book", it would likely be from a long throat, loose bore or both. Pressure is likely lower too. But for most modern high pressure loads, it's not worthwhile going over max, in the book, book max is a reasonable end point in load development.

that said, I load for a 7x64 Breneke to a few grains over max as shown in a couple of good manuals, with brass that has gone 10 loads with no loose primer pockets. So just be careful.

There are at least couple of caveats to observe: As you add powder, perhaps half a grain at a time, does muzzle velocity advance linearly? Or does muzzle velocity standard deviation significantly increase? If muzzle velocity is advancing linearly, and if the load does not become erratic, then it's at least a reasonable bet that you can add powder. Not a sure bet, but a reasonable one.

In a well-behaved load, peak chamber pressure and muzzle velocity are VERY highly correlated. That is, one predicts the other very well.

I didn't see where you confirmed that your barrel is the same length as the test barrel. If they are not the same length, then you need to adjust MV expectations accordingly.

2700fps with that bullet and that charge seems really slow. Are you sure the chronograph is accurate?

I've had this happen more than once and it pops up with the 7 Rem Mag quite a bit. But in 30/06 I worked up to the Nosler manual max load of 63 gr RL22-165 Partition.This shows a velocity of 3002 from their 24" Lilja barrel. But in a couple of my 30/06 FW's the load gave in the low 2700's....there's a 2" difference in barrels but still I thought that was a big difference.

Since I was pretty well out of capacity I decided to try a faster powder and went to Rl19,which brought velocity up to where it should have been but the loads were almost the same as RL22(?)....I was using more than some manuals showed.

Finally I tried the exact load the OP mentions, 59-H4350-165 Partition and Sierra SPBT. My velocities were a bit over 2900 fps and so close to what Hodgdon says it doesn't matter.

A 7 Rem Mag with short box but longish throat was into 7mm Weatherby charge range with H4831 before it gave 3080 fps(over listed max charges)and simply would not shoot until it hit that sweet spot. Everything was fine.

Depending on the barrel and other factors I might not be concerned with cautiously going up a grain or two if velocities are sub par,but am less inclined to do it with double based powders.In other words I might do it with (say) H4831 or H1000 because you will see velocity flatten out as you add powder. This is an indication you have maxed out with that combination..

Like Denton alludes to above you can watch velocity "flatten out" with single based powders,but some double based powders will add velocity as long as you keep adding powder. This is one reason you see so many really quick loads for RL22 among a lot of hand loaders,and everyone thinks everything is OK.Might be until you hit the red zone.

I have learned to ignore most claims for extra velocity given by RL22 and similar....good powders but I get skeptical about pressures. I tend to judge a rifle by what it does with single based propellants these days,and with DB powders stick to the conservative side..

One other important thing: Make sure your barrel and ammo are maintained at 70 F. I tape a small thermocouple to the barrel just forward of the receiver. I pop off a couple of shots to bring the barrel above 70 F, and as the temperature drifts back down to 70, I fire a test shot.

As was mentioned, you may also have error in your chronograph. On mine, if I leave the diffusers in place, and a cloud passes over the sun, my readings drop. I try to do all my chronographing on days that I can see the shadow of the tripod.

Yes

Thank you everyone for the thoughtful responses. You have me thinking again.
I'll try to answer your points. Good catch on the barrel length, forgot to mention that, the lengths were not exactly the same as the sources I used. In averaging these sources it is a little over an inch shorter than average. That is why I stopped 50 - 100 f/s lower than average velocity. The 8 mm load development was not using SAMMI loads but other credible published data.
Never thought about the effects of differences in single and double base powders.
I have used 22 LR as a calibrating load but not during this particular load evaluation so there could be a chrono issue. The temperature issue could also be contributing some variables.
Sorry dogcatcher, the 3006 example has hypothetical results (2700 f/s) just to explain my issue. Should have stayed with the 8 mm load. I too have gotten very close to book results with this 3006 load.
The point of watching more than just velocity increases (rate of increase, SD, erratic behavior, etc) is good advice.
Again thanks everyone for the information.
tj

About half of the rifles I have owned shot considerably slower than the load manuals predicted. Often as much as 200 fps.

When working with new to me chambers, or when experiencing results which do not match the load manuals, I do velocity vs charge weight graphs. A notebook of graph paper is pretty cheap.

I usually start at the minimum charge weight listed in a manual, or perhaps an average of the minimum listed in several manual. Then I will clock two or three shots at 2 gr intervals in the light loads and then work with 1 gr intervals as I approach book maximum.

If my results produce a nice straight line I will continue increasing charge weight above book maximum until I approach the book listed maximum velocity.

If I had wanted to shoot a 308, I would have bought a 308. I bought a 30-06 because I wanted to shoot a 30-06!

If my data points are scattered all over the paper, or if the slope of the line changes as I approach maximum, I find a different powder and start over again.

I used to have dozens and dozens of such graphs saved, but finally decided they had served their purpose and tossed them all out.

Tjmga,
Don't think that you DO have the same powder as the loads listed. Hodgdon does not make smokeless powder, they blend/resell powder; always have. The old A-Squared manual is the only one I know that actually listed lot numbers of components tested. So was your source of info tested or re-printed and from when?
Hodgdon will not give any nominal info about "their" powders such as burn rate, bulk density, etc. So where your powder lines up verses the tested is also different. Same name does not mean thee same as your source. I've got some Pressure Traces of some wild differences from Hodgdon data, verses actual.

I think that this is way to simplistic. You seem to attribute to many things to the rifle being the culprit.
So here is a paradox. 2 rifles of the same caliber and manufacture shooting the same published load of Benchmark both go to published max velocity 1 grain lower than max. Same 2 rifles using a published load of LT 32 will be 100 - 150 FPS slower than published at max load, but will reach that velocity when going over max load without signs of pressure. Same 2 rifles will reach max velocity at max load using H-335.
Why would this be so considering barrel length and other components are exact, and rifles are exact except one has a 12 twist instead of a 14?

Because powder changes sometimes noticeably from lot to lot. For instance a load of 60 grains of reloader 22 in a 30/06 might yield 100 fps difference between different lots. In the end the achieved velocity is making a more accurate statement as to pressure than the actual powder charge.

Shod

I am not recommending people ignore reloading data, but those numbers certainly are a loose interpretation on reality sometimes. You need to safely find your gun's pressure zone, and work backwards. If realistic velocities are not achieved before hitting pressure, you can try and change powders. Some guns are just slow though, especially if throated long.

I don't really recommend people going over book without thinking things through completely.
That said I have another parodox question.
If I have a barrel that is 26 inches with a load using X powder and all components listed and my peak pressure is safe but velocity is not as published, but I take and chop off 2 to 4 inches of the tube shoot the same load and my velocity increases but chamber pressure is the same(which can happen) what is the cause?

I have heard of that happening in 22LR as there is insufficient powder charge to accelerate the bullet all the way to the muzzle with a long barreled rifle.

But the cartridge would have to be of very small capacity compared to bore diameter for this to be the true.

Your damn close to my point.

Among the things that affect the internal performance (pressure and velocity) of a given cartridge & bullet are:

Capacity of the powder chamber (a function of chamber size and shape, case construction, and bullet seating depth)
Relative burning rate and burning characteristics of the propellant powder used
Amount of propellant used and how much it fills the powder chamber (load density)
Diameter, weight, and the bearing area of the projectile
Length and interior dimensions of the barrel
Uniformity and speed of ignition of the propellant powder (Primer and loading density related)
Temperature of the propellant prior to ignition
Barrel freebore
Neck tension

The 2nd one catches it.
If I use a powder that has a steep rise and fall pressure curve is it possible that one runs out of gas at a point in the tube where it slows down the bullet due to friction and atmospheric pressure?
Where a powder with a more gradual rise and fall would have enough gas to keep accelerating the bullet all the way to the muzzle which in turn would give me more velocity at the same pressure limits?