Pressure Trace II

[megasupermagnum]

Remember, it's is an absolute measurement but you need to calibrate your gun setup with a known load and by all means you can't depend on load data to give you a reliable pressure number for a particular load. Many component manufacturers use simulation data for their published loads and environmental conditions can change performance considerably unless you are shooting with the same conditions. In the same line, many load numbers are interpolations of the endpoints so a pressure number for 18 grains of a powder was simply calculated from the end points and maybe one interior point to create a curve.

The parts for PT2 are made to accommodate rifle loads of 60,000 psi and above. You are looking for pressure readings of about 1/5th that in a 12 gauge (11,500 psi max) and even down around 7000 psi to avoid bloopers so you will loose resolution when you are taking readings at 10% full scale.

I'm not knocking the system, in fact I was toying with the idea of getting some Omega strain gauges myself and home brewing my own pressure trace system because I am very interested in this stuff. I'm actually getting by quite nicely with Quickload, a chronograph and a grease patterning board for shotgun load development. Yes you are not supposed to "develop" loads for shotshells, you are supposed to follow the recipes to a "T". Well, it works for me and I 'mostly' interpolate "within the lines" and never extrapolate "outside the lines" unless it's on the low side like slugs that shoot like target loads or ultra light payloads such as 3/4 oz 12 gauge skeet and trap loads.

That's just the thing. If you are talking about 12 gauge lead shot, or common slugs like the Lee, Lyman, or round balls, you don't need anything but load manuals. When you are loading big slugs, there's no load data that you can even compare to, just some lead shot weights. Buffered shot data, lead birdshot, buckshot, or bismuth is surprisingly rare, and quite dangerous to mess with if you don't know what you are doing.

[rsrocket1]

What kind of slugs are you intending to develop loads for? 2 oz, 3 oz, bigger?

Don't get me wrong, I'm not criticizing the purchase. Getting something like a Pressure Test II system for me would be as much fun as getting a new gun in a new caliber. Modeling and predicting an outcome is incredibly fulfilling when you can test and validate your predictions.

I did a little more research on PT2 and the digitizer is an 8 bit unit (256 counts from 0-80,000 psi) and that one bit change translates to about 312 psi. In a rifle rated at 60,000 psi, one thousand psi (3 counts) is not that big a deal but with a 12 gauge shotgun with a max rating of 11,500 psi, one thousand psi is significant so be careful. Most shotgun powders like to burn at least 9,000 psi which gives you about 2500 psi margin between the low desired end and the top SAAMI max end.

FYI, here is some interesting reading on a user of PT:

http://www.ktgunsmith.com/straingauge.htm

I'm sure you could find more pretty easily.

Good Luck

[megasupermagnum]

770 to 943 grains in 12 gauge, although recoil seems to be the limiting factor. I have been on the edge of buying a Savage 220 for a long time, and a 500+ grain slug in 20 gauge would be a lot more manageable.

[W.R.Buchanan]

MSM: I was kidding, I wouldn't really ask that of you, or anyone else.

Randy

[303Guy]

I've pressure tested some 410 shotshells with the Oehler M43 PBL....interesting. Just haven't gotten around to 12 games yet

Hi Larry
Would you be so kind as to post those results?

[303Guy]

Strain gauge systems are much better than the crusher systems. The crusher gives a (fairly) accurate reading of the peak pressure only. (after measuring the flattened slug and doing the math). A strain gauge system will give an instant reading of the peak pressure. But it will also detect any pressure spikes on the pressure curve from erratic ignition. Those spikes could indicate a dangerous load with a SEE (Secondary Explosion Effect) waiting to happen. It would be nice to have a system like that...

The copper crusher may have an inherent inaccuracy in that it would also add the mean pressure to the reading - copper deforms over time under pressure. Not sure that the error would be of any significance though, especially with a fast powder as used in shotguns. Then again, we would be able to see the shock effect with a pressure trace. I'm actually more concerned with sudden pressure rise than peak pressure although both should be a concern.

[Cap'n Morgan]

I think the crushers used for testing shotshells were made from pure lead to allow for the lower pressure.

[rsrocket1]

^^^ Yes, I believe old shotgun load data used the term LUP instead of CUP.

[Petander]

770 to 943 grains in 12 gauge, although recoil seems to be the limiting factor. I have been on the edge of buying a Savage 220 for a long time, and a 500+ grain slug in 20 gauge would be a lot more manageable.

I'm interested in heavy 20 gauge slugs as well.

The thing is,I have not managed to get any shotcup size heavies fly straight out of a smoothbore 20. Tried a few molds, all keyholing.

Fullbore may be next but here we go... what size?

Anyway,Pressure Trace would be good when approaching full power loads. I shoot stronger loads in my modern 870 than,say, my 70's Beretta O/U.

And I've used Quick Load since it came out.

[megasupermagnum]

I'm interested in heavy 20 gauge slugs as well.

The thing is,I have not managed to get any shotcup size heavies fly straight out of a smoothbore 20. Tried a few molds, all keyholing.

Fullbore may be next but here we go... what size?

Anyway,Pressure Trace would be good when approaching full power loads. I shoot stronger loads in my modern 870 than,say, my 70's Beretta O/U.

And I've used Quick Load since it came out.

Now you've got me thinking about that Savage 220 more.

What I had in mind was a full bore bullet. The problem with 12 gauge is that to get a slug to look like an actual aerodynamic, balanced bullet, you are talking 800 grains minimum. In 20 gauge, assuming a groove diameter of .615", I would be casting a .617" slug of probably 550 grains (1 1/4 oz). With that, you can make a slug that actually looks like a bullet, and with this pressure trace system, I should be able to get to 1300+ fps, more if I go the Ed Hubel route. I know what 1 1/4 oz slugs at 1500 fps feels like, and it's still in my comfort zone. 770 grains at 1200fps is where I stopped in 12 gauge, and is just too much.

[longbow]

You can stretch out that 12 ga. slug by adding a "waist" like the old Paradox slugs, or by making them thick wall HB designs. So longer but not a lot heavier. Not sure where the commonly available 1:36" +/- rifled hits the wall with length though for stability. As weight increases velocity drops so unless you start going full on Hubel SFH loads the combination of low velocity and possibly slow twist for long slugs might be an issue.

The other option, though not as easy, is to do what the old Explora bullets had ~ a nose cone. Again, maybe a bit much for the home tinkerer but nowadays with 3D printers and castable Urethanes these things are doable without too much trouble:

https://revivaler.com/westley-richar...agnum-explora/

Longbow

[megasupermagnum]

The Savage 220, and many 20 gauge slug guns have a 1:24" twist, which should be faster than needed.

[nekshot]

You can stretch out that 12 ga. slug by adding a "waist" like the old Paradox slugs, or by making them thick wall HB designs. So longer but not a lot heavier. Not sure where the commonly available 1:36" +/- rifled hits the wall with length though for stability. As weight increases velocity drops so unless you start going full on Hubel SFH loads the combination of low velocity and possibly slow twist for long slugs might be an issue.

The other option, though not as easy, is to do what the old Explora bullets had ~ a nose cone. Again, maybe a bit much for the home tinkerer but nowadays with 3D printers and castable Urethanes these things are doable without too much trouble:

https://revivaler.com/westley-richar...agnum-explora/

Longbow

Not to stray from posts objective, but at what point in the 1x36 twist do you turn to hunkin big round balls?

[Larry Gibson]

Hi Larry
Would you be so kind as to post those results?

Testing was done with a Remington single shot. The strain gauge was mount over the chamber as per SAAMI location for a transducer. There wasn't a lot of muzzle blast so measure velocity w/o damage to the screens from the wads or errant shot I was able to put the Sky Screen start screen at 5' from the muzzle and did not use the diffusers. I tested 3 factory loads and the psi ran 7,700 (RIO 2 1/2"), 9,400 (Remington 2 1/2") and 11,000 psi (Federal 3") . The rest of the test were with loads a fellow was developing for a "Judge" revolver. Best load he developed was with 3 tungsten RBs (195 gr total) in shot cup loaded over 6 gr Unique. That load was running 1133 fps at 11,500 psi.

[longbow]

neckshot:

Not wanting to stray too far off topic but... in the case of 12 ga. a round ball wants about 1:110" twist according to both calculation from Greenhills and others and based on BP muzzleloader twist rates.

Round ball in any caliber doesn't take a lot of twist to stabilize. "Square" slugs are the same but being basically a shot fat cylinder if not hollow base weigh considerably more than a ball. Of course Foster slugs weren't around until quite late in the game and conversion to cartridge guns so round balls and shot were the projectiles of choice. for smoothbore muskets.

Having said that, PB muzzleloaders likely generate higher velocity that "standard" slug loads (not Ed Hubel loads!). Pacific Rifle Company shows .72 cal. ball at 1900 FPS muzzle velocity: http://pacificriflecompany.blogspot.com/

When I started my slow twist rifled choke tube I picked 1:72" twist as a "compromise" twist for round ball and slugs. I thought better suited to \lower velocities and would handle a short conical slug as well but still relatively slow.

Not sure if 1:36" is detrimental to slug/RB accuracy but it is faster than needed.

20 ga. would want a bit faster than the 1:110" twist just as round ball muzzleloaders see increased twist rates for smaller bore sizes but still slow compared to rifling for conical projectile.

On the pressure front, I'm not sure how much these twists would affect pressure, if at all. Shotgun twist rates are relatively slow and velocities are relatively low as well, say in comparison to .223 with 1:7" twist to 1:12" twists and velocities of around 3000 FPS. I can believe a 1:7" twist barrel could generate higher pressures than a 1:12" twist barrel with same load.

I'm sure Larry and others with pressure testing equipment can comment and whether twist rate significantly affects pressure for high velocity rifle or not and whether the slow twist rates shotguns have would affect pressure at all. It would be pretty easy to test same load in smoothbore and rifled gun. I'm betting bore dimensions and slug fit would have more effect on pressure than rifling twist rate. The extra squeeze of the rifling would likely have more effect... but then I'm just guessing.

Actually, I am hoping Larry gets caught up in this and does some testing because I am sure we will all learn a lot. With Larry and msm working on this I am optimistic that our learning database will grow!

Longbow

[W.R.Buchanan]

LB: my opinion is that you can't really over spin a round ball. 1:36 is one turn in 3 feet. If the target is at 50 yards the ball will turn 50 revolutions in that distance. Hardly rippin' around.

The whole idea behind rifling a round ball is to eliminate the "Knuckle Ball Effect," which causes the ball to wander back and forth in the wind thus altering it's flight path from predictable to random.

The rotation causes the ball to create a Central Axis to rotate around which presents all sides of the ball to the wind in a predictable manner. This works well as long as the ball is a perfect sphere. If the Sprue is protruding then it throws a wrench in the theory as there is something sticking up to catch the wind and alter the flight path from a strait line minus the trajectory to a slice. (golf term)

My Lyman .662 round balls have a prominent sprue sticking up.(See Pic) I try to load them with the sprue in front and as close to on the center line as possible. However at best this will vary to some degree and so will the flight path.

Incidentally The Pacific Rifle Company which I believe is now defunct made the nicest Large Caliber Hopkins and Allen Style Black Powder Rifles anyone ever made. 12 and 20 bore with Forsyth Rifling. They were true works of Art and I would love to have one.

Randy

[longbow]

Not sure about not over spinning a round ball or slug. Any imperfections (of which the sprue is a big one!) will cause imbalance and the faster the ball or slug is spun the more effect that imbalance will have. Point being is that any spin beyond what is required to stabilize could be detrimental in that way.

While 1:36" twist is not super fast, it is much faster than 1:110".

Another issue is potential stripping of RB's in fast rifling... though from the limited shooting I did from a rifled gun with 0.735" RB's I got good accuracy and recovered RB's showed good engraving. A rifled choke tube where the RB was at full throttle before hitting rifling might be a different matter. Fosbery did it though.

Hopefully I'll get to personally test the modern rifled choke tube shortly then draw my own conclusions. Some people report rifle like accuracy from rifled choke tubes and some report very poor accuracy so which is it? And why? As with any boolit, fit is king but that is one detail missing from any reports I've read. An undersize slug or slug wad combo could very likely skip rifling while a properly sized slug or slug/wad combo might do well.

What got me going was the Taofledermaus videos of the Moose .69 Minie and Lyman .69 Minie being shot accurately from both rifled choke tube and smoothbore. Rotation was very obvious from the rifled choke tube but what was really amazing to me was the stable flight from smoothbore.

As mentioned in another thread, I have modified one of my moulds to produce a smooth sided version of the Moose Minie. I cast a bunch up and now have to find time to load and shoot. While I am anxious to get this done, I have other commitments this weekend. I have to sort some yew tomorrow for bow staves and I have our annual archery shoot coming up in two weeks and desperately need practice!

I am looking forward to retirement so work isn't getting in the way of fun!

Longbow

[missionary5155]

Good morning
Experimenting would be more productive if sleep, eating, family responsibilities, work and all the other random issues could be set aside...

[W.R.Buchanan]

LB: I want a Long Bow.72" with 35-40 lbs draw should work. Where did you get Yew Wood in Canada?

Randy