Long story short, I worked up some loads 204 and
shot over the Chronograph today...here's the setup and results:

Savage M12 VLP 26" Criterion barrel stainless steel 1:11 twist

Remington 9 1/2 primers

VV N140 powder

32gr VMax bullets

Going by Hornady's Reloading Guide I worked up to their Maximum Load of 29.2 using the N140 powder and got this over Chrono:

4,226 4272, 4317, 4317 4370 Average of 4296fps.
Difference between High/Low is 144fps.

Seeing no signs of pressure, I decided to load up a bit and see what happens so I loaded 29.5gr of the N140, which is .3gr over Max and this is what I got:

4201, 4226, 4226, 4236, 4242, 4253, 4260 Average of 4,234fps. High to Low of only 59fps.

How is it possible that the heavier by .3gr load is actually SLOWER than the 29.2 Max Load??
Shouldn't is be a bit Faster since there is more powder?

The heavier 29.5gr load is more consistent with a difference of only 62fps than the 29.2gr load which has a 144fps difference between high/low.

I am definitely happy with the velocity I got with the 29.5gr load and so little difference I am getting between fastest to slowest shot so I am not complaining but it seems strange to me that the lighter by .3gr load is faster than the heavier load.

Have any of you ever experienced this, and if not how do you explain my findings?

Thanks Fellas!

You sure you're not reading the velocity of the muzzle blast?

I measured off 10 feet from the muzzle

Waters explains it pretty well. In short, there is a point of diminishing returns. Once you reach 'that point', more powder produces less velocity gains than the same increase did before(or decreased velocities).

No. More powder doesn't make less velocity. That's a myth perpetuated by looking at too-small samples of chronographed loads, uncontrolled for possible chronograph errors, temperature, or powder mass or moisture variations.

In addressing the apparent conundrum, first, the difference in the powder weights (assuming that the loads were weighed and not measured in some other way) of those two loads is only 292 vs. 295, or a difference of just about 1%. Further, only a weighing error of .03 grains -- less than most scales can reliably detect, represents a 10% error in the .3 grain difference. And if you consider that the .03 grains is plus or minus, then that represents a 20% possible error in the difference in the two loads. In other words, .3 grains in a nearly 30 grain load ain't much.

As a rule of thumb, a 1% increase in powder will on average result in about a 1% increase in velocity (at the expense of something like a 2% increase in chamber pressure.) One percent of the velocities listed is about 40 fps. The variation between individual shots is listed at 144 fps, or almost four times the anticipated difference in velocity between the lighter and heavier loads.

When the velocity deviation of a load is as great as almost 3%, then it is not possible with a limited sample (five or so shots) to say that it is not random velocity deviation which results in the apparent velocity discrepancy between loads only 1% apart. Doesn't that make sense?

Second: "Seeing no signs of pressure, I decided to load up a bit". Which is exactly the way to do it. But I am assuming that there was some kind of time lapse -- a day, three days, a week -- between the times that the two batches, 29.2 and 29.5, were loaded. Powder is "hygroscopic" meaning that it fairly readily absorbs moisture from the atmosphere. If on the day you loaded the first loads the relative humidity was fairly low and your powder's water content was at, say, 1%, then your load of actual fuel was 99% of 29.2 grains, or actually 28.908 grains of fuel. If on a succeeding day the powder had absorbed enough atmospheric moisture to raise its water content to 2%, then your actual fuel load would be only 98% of 29.5 grains, or 28.91 -- almost exactly the same as your "lighter" load (and velocity would also be influenced by the very slightly retarding effect of the extra water.)

Bottom line: I realize that the chronograph results seem counter-intuitive, but the possible factors I've mentioned along with a couple of others I haven't can easily create the unexpected inversion of chronographed velocities. Such unanticipated results sometimes make a handloader want to pull his hair out, but just keep fiddling and you'll eventually get where you want to go.

Thanks for the interest Fellas!

Stonecreek, once again your knowledge amazes me...

I did load the different loads on the same day, pretty much one after the other. I used a RCBS Chargemaster and weighed each and every charge.

I shot them all today too.

The only thing "different" that I can think of is barrel heat. After about 10 shots at a target with some factory ammo that I had lying around, I let the barrel cool down and then fired the 29.2gr load over the Chronograph.
After that, I let the barrel cool down (but not fully) at which point I fired the heavier 29.5gr(lower velocity-most consistent) so when I finished with all 8 rounds, the barrel was pretty hot.

Does this explain anything?? If not then I don't know what else it could be.

Sounds like the moisture content of the powder is not the source of the discrepancy.

I suspect that the apparent discrepancy is simply in the randomness of velocity variations inherent in that particular powder/primer/caliber combination. The sub-calibers have always been much more difficult for me to attain consistently small standard velocity deviations. If you ran the same test again, and the randomness of the order in which the shots deviate from standard happened to be different, your results might comport much more closely with the normally expected velocity gain of about 40 or so fps.

By the way, the 1%/2% velocity pressure rule of thumb has been shown to be reasonably (not perfectly) consistent when using the single-base IMR powders which most of us cut our teeth reloading. The rule seems somewhat less consistent with double-based powders and powders with certain additives like flash suppressant, retardant coating, etc.

By pooh-poohing the notion that more powder can yield less velocity, I didn't mean to indicate that there is not a point at which markedly higher chamber pressures add proportionately little velocity ("point of diminishing returns"). That certainly exists. But within the range of "normal" pressures, the addition of marginally more powder will, on average, result in marginally more velocity.

Stonecreek again, very interesting.

Before I got into Reloading I would have never thought that it was so technical and with so many variables such as those you listed above..
If you think about it, it's amazing that we hit anything at all!

With that said, I think that I will stop at what I am getting with the 29.5gr load and be happy with it. In spite of myself, it is dam fast and consistent as well.

I am not a Benchrest Shooter and the only thing I do with my 204 is blast Prairie Dogs so I think that I will just play with the seating depth and be done with it.

The average of the 2nd load falls within the extreme spread of the 1st.... Hmmm

Whatdaya mean Joe?

Your experience could be caused by a number of things or a combination of them.

First chronographs are sensitive to changes in light level, the direction that the light hits them, and false readings from the muzzle flash or blast.

Ammunition is sensitive to the temperature, case volume, and ignition quality. A more compressed charge can ignite slower due to the stifling of the primer flash.

The barrel of your rifle expands with heat and can result in less friction with the bullet which can affect the pressure rise time of the burning powder. Some powders respond to near maximum pressures differently and can cause very different results than one would expect. Without a piezoelectric pressure sensor it is impossible to know what is actually happening in the chamber. Some powders have a pressure curve with a "knee" near the top of their usable pressure curve where the pressure increases to over maximum and then drops to safer levels with the addition of more powder and then the pressure are extreme with the addition of more powder.

Sample size should be at least 20 rounds to get accurate information on extreme spread and average velocities. Ideally 100 rounds will give more accurate data but 20 rounds is considered accurate enough for statistical quality.

There are more than enough variables to get inaccurate results with only 5 rounds fired to make the resulting data look different even though it is flawed.

quote:

Originally posted by Stonecreek:
No. More powder doesn't make less velocity. That's a myth perpetuated by looking at too-small samples of chronographed loads, uncontrolled for possible chronograph errors, temperature, or powder mass or moisture variations.

In addressing the apparent conundrum, first, the difference in the powder weights (assuming that the loads were weighed and not measured in some other way) of those two loads is only 292 vs. 295, or a difference of just about 1%. Further, only a weighing error of .03 grains -- less than most scales can reliably detect, represents a 10% error in the .3 grain difference. And if you consider that the .03 grains is plus or minus, then that represents a 20% possible error in the difference in the two loads. In other words, .3 grains in a nearly 30 grain load ain't much.

As a rule of thumb, a 1% increase in powder will on average result in about a 1% increase in velocity (at the expense of something like a 2% increase in chamber pressure.) One percent of the velocities listed is about 40 fps. The variation between individual shots is listed at 144 fps, or almost four times the anticipated difference in velocity between the lighter and heavier loads.

When the velocity deviation of a load is as great as almost 3%, then it is not possible with a limited sample (five or so shots) to say that it is not random velocity deviation which results in the apparent velocity discrepancy between loads only 1% apart. Doesn't that make sense?

Second: "Seeing no signs of pressure, I decided to load up a bit". Which is exactly the way to do it. But I am assuming that there was some kind of time lapse -- a day, three days, a week -- between the times that the two batches, 29.2 and 29.5, were loaded. Powder is "hygroscopic" meaning that it fairly readily absorbs moisture from the atmosphere. If on the day you loaded the first loads the relative humidity was fairly low and your powder's water content was at, say, 1%, then your load of actual fuel was 99% of 29.2 grains, or actually 28.908 grains of fuel. If on a succeeding day the powder had absorbed enough atmospheric moisture to raise its water content to 2%, then your actual fuel load would be only 98% of 29.5 grains, or 28.91 -- almost exactly the same as your "lighter" load (and velocity would also be influenced by the very slightly retarding effect of the extra water.)

Bottom line: I realize that the chronograph results seem counter-intuitive, but the possible factors I've mentioned along with a couple of others I haven't can easily create the unexpected inversion of chronographed velocities. Such unanticipated results sometimes make a handloader want to pull his hair out, but just keep fiddling and you'll eventually get where you want to go.

__________________________________________________

Actually in some cases, more powder can mean less velocity.
I've done some pretty extensive testing with bullets and powders in several calibers for many years.
One extreme case was in four different .45-70 rifles.
With a 525 gr. cast bullet, anything over 45 gr. of 2495 actually produces lower velocities.
The more powder, the lower the velocity we achieved.
This was all done on the same day over the period of about an hour. No changing variables.

Welcome to the wonderful world of VARIANCE.

It is IMPOSSIBLE TO REPRODUCE the exact same parameters for every shot so as to eliminate all the variance's and reduce the variance to ONE parameter such as velocity.

The only way to do that is to use ONE case, ONE bullet(cant' be done because the bullet is expendable) keep EVERY parameter constant(can't be don because many of the component's are expendable, one time only use, and besides every time you fire a shot you coat the bore with a miniscule amount of fouling and actually wear the bore a bit, flame cut the throat...etc, etc, etc.

The fact that you get variations in the velos should give you a big clue of what is happening.

I've seen this happen in several calibers which caused me to ponder the phenomenon also, but here is something for you to consider and you can see the effects if you go to the reloading/testing section of AR and study the velocities of the various rounds...it shows just what you are describing, and it is probably the best teacher you can find for describing what you are experiencing.

Consider also that going a bit higher with the powder load can reverse the velocity numbers...an additional 0.3 gr OVER THE LOAD THAT LOWERED could just as easily INCREASE the velo by a substantial amount.

The phenomena is more evident with the smaller calibers, I think, because a very small increase in powder amount causes a large amount in velocity and you are probably more cognizant of changing conditions with small cases than with larger cases.

You might also study up on statistics a bit...SD, AVERAGE, MODE, MEAN,VARIENCE, ETC all have special meanings, but I can tell you for a fact that POPULATION SIZE means more than all the rest. If your population, the number of shots in this case, is small, less than 100 then all the rest's values drops of very quickly.

You might also consider that every time you fire a shot, the end of your barrel in relation to the first screen can change as much as 6" unless you have a stop set up for the rifles forend. Even as little as 1" can add/subtract a few fs to the velocity.

Example...I've developed several 17-22 cal loads for different rifles/bullet weights, that have a range of 100 fs and a SD of 50 that, with weight sorted bullets/cases (target prepped components) that are bugholers, but there are ALWAYS FLIERS now and then.


Conventional statistics say that SD's over single digits and ranges over 10 or so have to wide a variance to be "BEST", and of course this is true, but one flier outside a quarter inch group enlarging it to 1/2" for 10 shots will work great for sage rats...not the "best" for competition...so let the USE of the rifle determine the level of angst you have.

Chrono's are excellent devices for ammo development but they are NOT devices for measuring absolute velocity, just devices to give you a little more information to add to all the other information needed to develop well shooting ammo.

I had three chrono's at one time and I would set them up one behind the other and mix them up to see what was happening. Now I only have two and they both give different velocities no matter which is in the "first" position. I just average the two and call it good, or get lazy and only use one.

Luck

it is possible to get a lower velocity with higher powder charge.there is an efficiency that barrel length, cartridge, powder type, and bullet all play into effect.when you reach that peak efficiency,standard deviation should go down and when you pass that Point, velocity will go down a bit. now if you Lengthen your barrel, the parameters for peak efficiency have changed and you should be able to put a higher charge to increase velocity

Old timers used to speak of the "Balance Point"
where the velocity/powder stopped increasing.
When you are there changes in loading causes less
velocity increase and the results of two different loadings will overlap.
A quick check on muzzle blast effects is to move
the chronograph back and look for a change.
I do know that 10 feet isn't enough for a Krag
using 4350.

I have always been fasinated in all of the variables that come in to play that affect velociy. Lead , neck tension, barrel fouling, temperature, altitude etc.

Paul K