Greetings,

This is based on my experience attempting to get traces with my .500 A-Square yesterday.

1. Do use the makers advice to use the silicone over the gage. It is Permatex 598-B "Ultra Black Hi-Temp RTV Silicone Gasket Maker", from the local NAPA. If you are careful when putting it on, the little smooth mound covering the gage will be almost un-noticable.

2. Point the gage connection down the centerline of the barrel, on top of the barrel. Hold it there using good tape while the silicone cures. Reason: you want it out of the way of your hand.

3. Use a rubber bicycle innertube cut in half and make two wraps around the barrel and forend. Place the lead to the module on this rubber pad and wrap two more turns around it, tucking the end in to keep it from unwrapping. Make sure there is no curve or slack in the lead between the wraps and the gage connection. If there are, the connection will pull apart.

4. Since it is very hard to take a trace and fire over a chronograph at the same time (unless you are at the range) take a couple of shots across the chronograph with the load and then forget it. Arrange the Pressure Trace module such that its lead can move and fire from the hip into a backstop, allowing the rifle to move. This assumes you want more than just 5 or 6 traces.

I found all this out yesterday out on the tundra. Fingers and hands rip the connections apart, recoil jerks the module all around and the whole session is simply for the birds.

I did get three very good traces.

Using 575 grain, cast gas-checked NEI 0.510" and 112 grains IMR-4350, 2250 and 2261 fps at ~38,300 psi.
A 600 grain Hawk with 0.035" jacket and 122 grains H-870 gave ~22,000 psi.

I thought I saved the traces but didn't. AAaarrgh!

If this helps those who have this equipment.

I am making a cradle out of 2x10 about 3 feet long and some section of black iron pipe (the cheep stuff) for legs. I will secure the rifles into it and use a lever to manipulate the trigger.

A suggestion...

I use the Oehler 43 to test for pressure and I would switch your setup to use regular telephone connectors as Oehlers does, not the RC model type connector which will pull apart. Another thing that will help immenselly is to make up an extension cord so you can set the PT unit off to the side well out of the way... like in the truck out of the weather, that's where my Laptop and Oehler 43 unit reside when testing. I made up a 20 foot long extension cord and all is well.

The wire is taped to the barrel with black electrical tape, or Scotch tape either one for strain relief on the gage soldered connection. Scotch tape turns to shit when it gets all wet, but works better when dry than black tape does.

No problems what so ever when testing my 416wby ever, the RJ11/14 type telephone plug connectors don't come unpluged and are inexpensive as are the tool to crimp them on.

Good luck.

No slam, but a 20 ft extension cord for the strain gauge is a bad idea. The signal the unit is processing is very small. Adding length to the cord will add to the pickup of stray signals, and limit the repeatability of the system.

I have both the PT and the Fabrique units... simply use electrical tape to make a temporary strain relief, so the recoil doesn't unplug the strain gauge. Works like a charm. I pressure test dozens of loads in some sessions, with no problems.

Denton,

Don't doubt what you're saying at all, makes sense, but still, I've never had a problem with mine in the pressure reading department. I did have it come unhooked one time when the clip broke off a connector at some point and I didn't notice it, it started plotting shot after shot until all ten indicated being fired and memory was full... had to fix it and start over. The other time I was shooting in heavy WET snow and the water running down into the forend turned the Scotch tape over the gage into a bag of water, I had to quit, go dry things out and replace the tape, the pressure was reading erratic at that point with familiar loads, 80-90kpsi etc. in the same string of loads that were 60kpsi.

Maybe the Oehler unit puts out a stronger signal, but I doubt it, might last longer with it's bigger battery tho... it still may be worth a try to compare the readings in your case, in mine it didn't change them at all and is a super convieniant...

Let me see if I can shed a little light here.

Long Cables:
If you want to use a long cable, I suggest making the serial cable longer. Since there is a "real" RS232 driver chip in the PressureTrace module, you should be able to use a serial cable up to 100' long. Making the strain gage cable longer adds resistance to the circuit. The algorithms make an assumption about the value of the wiring resistance. Changing that resistance will throw off the calculations.

Telephone Connectors:
Finding a useable connector was one of the hard parts of designing PressureTrace. The following factors had to be considered:
- Contact resistance
- Connector "lifetime"
- latching force
- Connector size

We considered telephone connectors early on. They were eliminated because of the contact resistance parameter. Not only do they have a slightly higher contact resistance, that resistance can be a little bit different every time you plug it in.

Make sure that when you glue the connector on the strain gage down to the barrel that no glue has migrated into the connector. If it does it can keep the strain gage cable from the module from plugging in completely. That defeats the mechanical latch in the connector.

Wire Tie Down:
If you're firing off hand, the weight of the cable can cause the connector to come unplugged under recoil.

Inside each PressureTrace box is a Velcro strip just for the purpose of tying the strain gage cable down to the rifle at some point. My favorite method is to run the strain gage cable up along side the scope tube then wrap the Velcro strip around the scope tube, trapping the cable.

Firing from a rest eliminates the problem for most folks. From the bench I fire over a chronograph and capture pressure traces at the same time.

Thanks Burt.

Oehler still uses the phone connector I think, must be calibrated for the extra resistance I suspect. No mention of max length in attachment cord in their manual but, the resistance *would* be higher no doubt. I wonder if I was getting 60kpsi on a load and switched to a telphone connector what the difference in pressure would be from the added resistance of the phone connector, not to mention the *stacking* of resistance a longer 10' to 20' extension cord would add as well.

Any ideas as to what the pressure error would be for a specific amount of added resistance in the circuit with the way it's calibrated? I can add up the extra resistance in both the cord and the connector, but how much extra resistance can be tolerated without being an issue and changing a pressure reading by more than a thou or two?

A side note;

Wires touching the barrel can cause shot stringing on the target, it happens frequently and groups are only being shot with mine now with them unhooked and off the rifle.

Brent, if you're out taking measurements in weather like that, you are one determined reloader!!

Burt and I do part company on one minor point: He likes the gauges on top of the barrel. I tuck mine under the stock, and drill a hole for the connector. Both ways have advantages and disadvantages.

The whole business of getting adequate protection from stray signals floating through the air is fairly tricky. Burt's design very carefully thought through those issues. That's why he gets much better repeatability than the Fabrique unit. The repeatability of Burt's design is as good as that of the best published reloading data.... assuming you are not underwater at the time.

Gentlemen,

My experience is with the esoteric end of firearms. With an '06 or a .375 H&H recoil really isn't going to matter.

The acceleratio is enough the velcro doesn't hold the cables so the connections pull apart. I almost had a heart attack when I saw this, my very carefully measured and applied gage (expensive) now toast. Well, the silicone held it fine and I later got some good traces.

After messing around for an hour I realized it wasn't going to work.

I have the self contained, mobile recoil sled and stand ready to try. Heavy at about 45 pounds but it'll work.

That is some serious recoil. I have to admit that I didn't take that much recoil into account. I'm not sure I even like to imagine it.

Try this. With the strain gage connector attached to the barrel, run your strain gage cable along side of scope. Then use a couple pieces of electrical tape to fasten the cable at two points to the scope. Keep the section of cable that runs from the scope to the strain gage connector as short as possible and don't leave any extra slack in it. This should make the cable move with the rifle instead of whipping around.

Someone asked if I could quantify just how much the extra resistance of a longer cable would affect pressure measurements. It can be done, I just can't give you a cookbook answer. Each module is slightly different, due to manufacturing tolerances of the electronic components, and the PC side software uses the actual values from that module to make calculations. I'll try to remember and see if there is some generality I can give you.

FYI when the PressureTrace software starts up, if a module is connected, the module sends necessary information about itself to the PC program. During manufacture we run through test routines that determine these individual values. They are then programmed into the microcontroller so that they are available to be sent to the PC program.

Shot Stringing Due To Wires

The method I outlined in my previous response about fastening the strain gage cable to the scope should take care of any wires that are touching the barrel.

Alternatively, Denton's method of mounting the strain gage under the barrel and running the wires out through the stock will fix that problem too.

Burt,

The method I use is like Denton and is under the barrel hidden, wires coming out between the forend and barrel. The aditional inletting made in the underside for the strain gage is maybe .100" - .150" deep in a small area and is tapered and opened just enough at the top of the forend to let the wires out without pinching them and touching the forend at all, the wires being on there undeniably have still been causing stringing even not touching, even with taping it up to the scope it didn't seem to help any.

What I do for strain relif, so as not to break loose the gage from the barrel or the leads soldered to the gage itself, is to run the wires down toward the muzzle from the gage about an inch, inch and a half or so, then double back to the gage with them, then double back again toward the muzzle another the inch or so. Now I take this "S" turn section of wire ahead of the gage and completely tape it to the barrel with a few wraps.
The "S" type strain relief won't pull the gage or connection at the gage loose, where as it will pull it through the tape if just run straight.

I'm a bit puzzled about those light wires, back near the action, causing stringing. I'm certainly not denying it. I just haven't seen it. I have to ask. Is there any evidence of the wires being trapped between the barrel and stock during recoil? That could change the vibrations and cause it.

The "S" turn in the wire will certainly give plenty of slack for movement. It seems like overkill, but, if that's what it takes then that's what it needs.

Burt,

I'm glad you have not seen it with your testing, that's nice to hear. The 3 rifles in question were "not" pinching the wires between the bbl and the forend, or contacting the forend on recoil, as they were taped up to the scope, that's definitely what's perplexing and unusual about it. I've had them pinched before and one had problems, the other "may" have, could not tell for sure but it was relieved so it didn't touch too, still haven't been back shooting it tho so, I can't say.

The "S" turn or "U" turn, whichever works best, just assures that if the wire is tugged on for what ever reason, it doesn't initially pull directly on the gage connection. At the price and time putting one on, it's worth it IMHO.