I had to do a little searching to find this... maybe some of the rest of you will find it useful:

www.fabriquescientific.com

This is the place that you can buy strain gauges and associated electronics to measure pressure for your handloads. The electronics are $150, and strain gauges are $14 each. Epoxy a strain gauge to your barrel, under the forestock, and chisel out a place to store the lead. Make a few measurements on your barrel, reel out the lead, plug it in, and you'll be able to measure your load pressures for yourself.

Well it's good to see that they have their page up and running again. Did they lower their prices or is that just my hopefull imagination?

Turok

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Make it idiot proof, and some one will make a better idiot

Thank you so much for posting that! What a tool for reloaders! It'll make working up new loads SO much easier! A hell of a lot safer and more accurate than the "wait 'till you see an ejector mark, then back off a couple of grains" method. Measuring case head expansion...blah. For that price this is so much better....

I've been wondering why somebody hasn't sold something similar. Sure, the Oehler is cool but not many people are going to spend $800 on it. Most enthusiasts already have a chronograph and probably don't need all those fancy features...many don't have a laptop either.

This would do what most people want--help finding a safe maximum load for their rifle, quickly and easily.

Cool....

I've got my order in... electronics, plus 5 strain gauges. My wife thinks I'm half a bubble off level for wanting one of these for Christmas, but she is understanding.

I've done the stats on CUP based published loads, and am convinced that the fact that most of us still have our eyes and fingers is more because of conservative rifle design than the accuracy of the crushed copper method. Any load that I use that was developed in CUP rather than PSI is going to get reviewed.

My immediate question relates to .308 loads--If you make your COL .1" longer, how much more powder can you safely use?? The chamber is bigger, and the fundamental gas laws say you should be able to use more powder. I did a little digging, and did not get an answer that I felt sure of. With the new gizmo, I should be able to check that out very quickly.

I've also wondered if published loads have some kind of allowance for temperature? Or do they just assume that everyone shoots at 72 degrees? With a little testing, you can set a realistic safety margin.

Can't wait for the goodies to get here, and for a sunny day to go to the range!!

Denton
Do you have a phone # or Email for them.
All I saw was snail mail.
Rich

Try sfaber@mcs.net... I've exchanged emails with Steven Faber at that address, and he's the guy that did all the work on this.

Denton,

OKShooter did the same thing you were wondering about with the .308 except he used an 06 and the Oehler M43. From what he has in his manual, the pressures increased every time the bullet was moved closer to the lands.

At 0.164 away from the lands he had a pressure of 50,600 psi

At 0.059 away from the lands he had a pressure of 51,300 psi

At -0.021 into the lands (bullet jam), he had a pressure of 53,400

He has a bunch of other seating depths in the manual that I haven't included here, but I think you get the jist of it. My guess would be that the fundamental gas laws only apply in the sense you mentioned when the distance from the lands is proportional to the increased length of seating depth.

This is supported by the Weatherby line up and the extra long freebore so notorious in their rifles. Because of the freebore good 'ol Roy could add a few extra grains of powder. This can also be seen in the warning against using Weatherby factory ammo in rifles without the freebore like those found in special request custom jobs where people want to be able to seat the bullet out to the point where it is touching the lands.

Sure wish I was getting one of those for christmas!

Turok

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Make it idiot proof, and some one will make a better idiot

Turok...

That's really interesting data, pretty much the reverse of what I had expected. I figured that by lengthening the COL, I'd be lowering peak pressure. Of course, that doesn't occur until the bullet is a couple of inches down the bore, so it makes sense that if you postpone the "engraving force" for a while, you'll get lower peak pressure. I wonder if the graph of pressure vs. seating depth is non-linear, with a minimum somewhere between short-as-you-dare and touching-the-rifling??

I did a test on .223, and found that .030" difference in seating depth didn't produce a detectable difference in muzzle velocity. Wonder what it will take to produce a detectable difference in chamber pressure?

Denton __

Thanks for the heads-up. Shawna's ordered me one for Christmas (or my 74th, Jan. 6). What I'll do is "wring it out", 308 Win., 223 Rem. and 45-70, and see how it compares with the CUP vs. psi stuff we discussed. Maybe an article for the American Gunsmith? The editor's been gently nudging me for something new. Our fall season (like our spring) lasted just two weeks. 20's to 50's now. And windy. Not conducive to getting "generalized" ballistics data.

Good shooting.

Robert

Hey Bob...

Sounds like a lot of fun. We could run some cool stats on the measurement system... something sadly lacking in stuff I've seen published. This whole area seems lacking in measurement system analysis.

Gee, you've got 20-50 degrees? I've got a foot and a half of snow on the level.

I'm going to have to plan a trip down to St. George, to maybe get into the 60's.

denton,

The figures do appear to follow a somewhat linear line - notice that I did say somewhat. OKShooter has also included velocity and standard deviation in his chart as well. In this posting I will include them all. They are as follows:

Seating Depth---Vel.----PSI-----Std Dev. PSI

0.0164----------2608---50,600-------600
0.059-----------2620---51,300-------900
0.039-----------2621---51,200-------700
0.019-----------2624---52,100-------700
-0.001----------2622---52,100-------500
-0.021----------2633---53,400-------1000

There really doesn't seem to be much of a difference between seating depths in terms of pressure until you reach the point where the bullet is firmly jammed into the lands. However, I would like to point out that in this case the pressure is nowhere close to the maximum allowable of 65,ooo psi.

We should note that 65,ooo psi is the industry standard for all other modern high intensity cartridges, and that the 06 is held to 60,ooo psi due to the older model rifles out there. Modern rifles in good shape will have no problems handling the industry standard.

When dealing with seating depths combined with max loads, I would exercise a bit of caution, as the pressures may rise faster than those found here in the lower realms. At the same time, with the pressures close to max., the extra pressure generated by the 'engraving force' may very well be just enough to push you over the edge.

There could also be a difference in the particular powder you have chosen as well. OKShooter has chosen 4831. It could very well be a different story with the faster burning powders, or perhaps with straight-walled cases such as the 45-70. I guess now you will be able to find out for yourself.

If you want a little further information - pretty much what I have posted here - check out "Hornady Handbook of Cartridge Reloading" 4th ed. vol. 1., p 13-15

Turok

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Make it idiot proof, and some one will make a better idiot

Turok...

A really interesting set of numbers... it appears that the reloading books do give considerable safety margin for hot days, powder that has been vibrated into smaller granules, and general stupidity.

The right way to tolerance something like this is very different from what the industry has adopted. They say that your average pressure shouldn't be above some specified value. The right way is to aggregate the variation due to charge variation, seating variation, primers, powder lots, etc. and to make sure the mean, plus a comfortable number of standard deviations, still get you below the danger point. It's not hard, but it hasn't been done much in this hobby.

Denton __

It's a deal. I've got a few good years left. Once I see what the device is like, I'll make up a few preliminary loads for the Spring "season" and pass the data on to you. So don't hold your breath.

Turoc __

We'll be working with both straight-wall and bottleneck cartridge. Should be interestign.

Good shooting.

Robert