30-06 testing: Results and questions

M

MightyMO1911

New member
Having a TON to learn about handloading for rifles, I wanted to run a test on the effects of case capacity.

For this test, informal and preliminary though it may be, I sorted some mixed brass by headstamp and then by weight. I only loaded 5 of each which I know isn't really enough for definitive answers, but enough to begin forming a general impression.

I wanted to post these results and get some opinions from those of you more versed in this.

These first 2 are loaded with a 150 grain Sierra SBT being pushed by 54.7 grains of H414 powder. The engine was started with a winchester large rifle primer. All brass was treated the same. Tumbled then resized, trimmed and tumbled a second time. I should point out also that no attention was given to the primer pockets. COAL is 3.210"

First up is a Remington-Peters case that holds 193.5 grains of water. Results are:
2766, 2760, 2743, 2760 and 2777. The average is 2761 with extreme spread of 34 and a deviation of 12.

Second is a Winchester case that holds 183 grains of water. Results are:
2749, 2766, 2760, 2743 and 2749. The average is 2753 with a spread of 23 and deviation of 9.

Frankly, I was stunned at the consistency of both. While the differences are rather negligible, the Winchester case was a little better. Since the case capacity is less in the Winchester case, all be it only 10 grains, I expected the velocity to be higher due to increased pressure, not lower. But it was a tad slower.

So for the questions.

1. Is a 10 grain difference in case capacity enough to make any real difference?

2. Should I have expected the lower capacity case to have higher velocity?

3. Are these results about what you would expect?

As consistent as these were, I am going to consider this load as a possible hunting load for deer. I have a Nosler ballistic tip I would rather use, and at just a bit higher velocity, so I am going to test that bullet as well. But I did not expect such tight shot to shot consistency. I just assumed with higher velocities, wider spreads and deviation would be expected.

CORRRECTION: I MEANT TO SAY CASE WEIGHT NOT VOLUME.
 
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I think you may have confused case capacity w/ case weight.

The 30-06 'generally' holds 68 grains of water.
What you apparently measured was the weight of the empty case itself (~190 grains)

Since the outside dimensions are largely fixed, the heavier case (the Remington) has less
internal voulme and therefore produces slightly higher pressure/velocity -- as you witnessed.
 
You know what? You are absolutely correct. In my notes I even wrote down case weight but for some reason I had in my head volume and typed the wrong thing.

So. Correction. 193.5 and 183 are CASE WEIGHT, not volume capacity. Totally my bad.
 
I bet if you found the actual case capacity of all the cases, you'll find that most the cases have the same or around the same capacities based on muzzle velocities you received.

As mehavey stated, it appears you looked at case weight instead of the true capacity of the case
 
5 rounds is not enough to determine es or sd IMO. 10-20 would be a better indicator. Sound like you are off to a good start though.
 
I have 4 at my disposal to use. IMR4064, IMR4895, H380 AND H414. The only one I hadn't loaded wirh is the H414. I liked the numbers so I rolled with it so the short version is, I have plenty of it and just decided to start there.
 
What rifle are you loading for? If for the M1 Garand be absolutely sure that you investigate the restrictions on bullets and powders for the M1. Look at the web sites that discuss loads for it.
willr
 
H380 (canister grade WC852) is made for .30-06 ball ammo with the 152 grain (-3 grains tolerance) military FMJ ball bullet. Even it shows the start of secondary gas bump pressure further down the barrel. H414 will make that bump bigger. I don't know how much bigger (you'd have to strain gauge the chamber to see how much), but if a secondary spike is bad it's not impossible to ring a barrel 18-20" from the breech end with large secondary gas bump spikes. Going to faster powder or to a heavier bullet will eliminate them, and spherical propellants seem especially prone to behaving this way.

I'm not saying I know you have a serious problem with this because of using H414 with a 150 grain bullet, but I, personally, would want to check that with a Pressure Trace instrument before shooting too much of it. With a 180 grain bullet I wouldn't be particularly concerned.

Here's a trace from some M2 ball showing the small secondary gas bump spike. This was WC852, which was meant for the .30-06, but it is a slow lot. I wouldn't expect to see this with H380 that Hodgdon sells. Unfortunately, because they are transverse waves in the steel, a SAAMI pressure instrument doesn't show them.

Dads%2003A3%20and%20M2%20ball_zpsyfkytj0t.gif


William C. Davis, Jr. tried the case experiment with .30-06 in the 60's or 70's, IIRC. He concluded the brass weight had to be 16 grains different to justify 1 grain of powder charge adjustment in order to keep the peak pressure the same. And QuickLOAD thinks that's close, coming up with 15.6-15.8 grains, depending on the brass composition and assuming constant exterior dimensions. This is for H414 and a 150 grain bullet, but will be pretty close for other powders. For constant barrel time it gives 14.1-14.3 grains of brass weight to justify a 1 grain change in charge weight. For constant velocity it gets 22.2-22.5 grains brass weight change for each grain of powder change.
 
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willr I am loading for a winchester model 670.

Unclenick, you've given some very interesting information. I am gokng to studyvand research a little more on that, though I think your last paragraph may have been written in some unfamiliar language. Lol
Thanks for sharing.
 
Unclenick - I've always been somewhat confused by the terminology used with regards to pressure testing. SAAMI-type piezoelectric transducers measure pressure directly (albeit rather slowly). Strain guage setups measure steel movement. Propagation velocity in a hot gas is around 2200fps and about 18,000fps in steel.

So I'm always wondering how folks using a strain-gauge setup factor out the reflections propagating in steel, since they propagate much faster.

I'm not saying I don't believe in "secondary pressure bumps", I'm just wondering how folks focus on the real gas pressure events and filter out the metal-induced noise.
 
Remember that transducers don't measure pressure any more directly than strain gauges do. Both measure a different thing which is the result of a metal object moving (stretching or compressing) as a result of the interior chamber pressure. SAAMI's transducers don't even measure that directly. They require the cartridge case to deform (expand) in order to push on the transducer.

I'm interested to hear what Nick has to say, but from some limited conversations with the PT guy, I take it he's smoothing the high frequency variations you reference in the software.
 
Actually, Jim Ristow told me the opposite. The PT has limited filtering. His site shows output from the discontinued Oehler 43 which had a fair amount of filtering, but he didn't want to cover things up that much in his Pressure Trace instrument. If you look at the high speed oscillographs made by Dr. Lloyd Brownell from strain gauge readings in the mid-'60s, the PT plots look, if anything, faster and more detailed. There will, of course, be enough filtering to prevent RF interference and most system noise from registering as readings.

Look at my trace again at the waves circled in green. Those are the pressure wave reflections that happen at the speed of sound in the steel in its length-wise direction. You can tell by how short the time is between them. There are, however, actually at least two peak sets chasing one another. The wave initiated forward by the bullet impact with the throat—Dr. Brownell's theory of the event—followed by its reflection off the breech end of the barrel.

The secondary spike is another matter. This image from RSI is reproduced with kind permission from Jim Ristowe. It shows a very extreme secondary pressure. The giant secondary spike flattens near the top because the A/D converter's input range runs out of headroom. The actual peak value is higher. Texas gunsmith Charlie Sisk was able to blow the muzzles off .338 barrels on demand with a really spiky load and used to have photos of them up on either THR or 24 Hr. Campfire (I've forgotten which), but he stopped hosting them on his web site. I don't know why.

What we think causes the spike is a variation of the barrel bulging effect that BP muzzle loading shooters call "short seating". Actual short seating is when the powder is back where is should be, but the bullet isn't seated all the way. If it's more than a couple of inches out in front of the powder, the barrel will bulge or burst as the powder shoots its own mass into the bullet, which is then acting as an obstruction. Since secondary spikes like that in the plot tend to happen when the bullet is already on its way down the barrel, we think it happens because a light bullet is paired with a powder that burns too slowly to make gas fast enough to keep up with the bullet. The bullet scoots out ahead of the gas after the peak, then ceases to accelerate and may even start to slow until the powder burn catches up and propels the powder's own mass into the base of that bullet. Because the bullet is already moving, this isn't usually as catastrophic as a short seating event, but occasionally it can be.

Copied with kind permission from Jim Ristow:

Nosler.jpg


This doesn't show up on either SAAMI transducers or copper crushers. It is because what the strain gauge reads is steel strain (temporary elastic shape change in this case) that reflects a traveling wave from the actual pressure event further down the barrel. So actual pressure is not in the chamber or under the gauge at that point. The transducer and crusher are attached to the barrel and move with it, so they won't register the event. They can only respond to actual pressure at the chamber location.

So, what we think we have is a pressure indicator, remote from the actual pressure site, and that doesn't register on SAAMI standard pressure test gear. That doesn't mean it's not real pressure, even if not in the chamber, nor does it mean you don't want to know it's happening. Jim Ristow has identified barrel ringing caused by it in an AR, though not disastrous ringing. So it seems to be real enough. Also, the cure is simple. Use a heavier bullet with the same powder or use a faster powder with the same bullet. Either makes the spikes go away.
 
I must have inferred more than Jim intended, from what he was telling me about the very beginning of the firing event & trace. Thanks, Nick. Interesting that the strain waves from barrel 'ringing' don't show up noticeably until well after bullet exit. Are those sorts of strains not additive (as sound or pressure waves are, for example)?
 
I've misled you with my green circle. I was just pointing out where you can see the periodicity of the ringing most clearly. The ringing actually starts on the pressure rise side of the curve, and is what is responsible for the rest of the curve after that point being rippled looking. But in the trace that gets sharpened where the trace drops to zero because the unit can't read below zero, and I suspect the input coupling capacitor is getting its charge dumped into input protection diodes on the negative cycle, causing the upswing voltage to be "pumped up" for easier observation. They are less peaky in ripples above, though you can see the ripples quite clearly in the second image.
 
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Every time the graph is used on the Internet the explanation gets better. the first time I saw one similar to it I suggest someone had some bad habits and had never seen a graph that read pressure and time.

The other post had a secondary spike that matched the timing of the bullet hitting the lands. the spoke went from about 30,000 to almost 80,000 'straight up.

I can duplicate the reading on the graph you used by seating an 8mm bullet into a 30/06 case.

Sisk of Iowa Park, TX, he sold my older brother a container of powder that beat anything ever seen on a graph.

F. Guffey
 
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