Range Report Experiments in OBT

[Bearwalk]

I have sold under a lucky star and have been granted access to some very nice high speed data acquisition equipment for the summer.

My thoughts are to design some experiments around OBT theory.

My initial plan is to instrument the chamber and muzzle with strain gauges to detect the travel of the shock wave. I have a couple of donor rifles that will stand in as test subjects. My plan is to detect any muzzle growth and the relative timing of the bullet exit. Using various loads, hopefully I can time the exit with max muzzle growth and min muzzle growth and see the corresponding effects on accuracy.

I also have access to accelerometers, but my thought now is to focus on the shock event/impact and not so much any vibration analysis. The size of the accelerometers would likely affect the barrel harmonics anyway rendering results with dubious or limited value.

So far, I have come up with zero on my research to see if anyone has done this, yet.

In any event, looking for input as to the design of the experiment and/or a donation of strain gauges - just kidding.

 

[MALLARD]

Re: Experiments in OBT

Whats an accelerometer ?

and your "high speed data acquisition equipment" isn't a pressure trace II machine is it ? because , it sounds like, and there is a sticker on top of the PTII that says just that.

the pressure trace manual says to locate strain gages 7mm away from metals of different thickness. So if your putting a gage on the muzzle , i imagine your machine and gages must be different then the pressure trace machine( unless your going to put the gages on a brake.. or something). And , the PTII only has one cable, unless you have two PTII's , then it must be a different machine, since you speak of of putting gages on both the chamber and muzzle.

 

[bohem]

Re: Experiments in OBT

Bearwalk, I'd like to see if we can do something to benefit us mutually, if you want please get in touch with me.

The potential sounds pretty cool.

 

[Bearwalk]

Re: Experiments in OBT

An accelerometer is a sensor that measures changes in speed (and direction). Pretty much like it sounds. They are useful in vibration analysis. Unlike strain gauges, they usually have significant mass compared to a strain gauge, thus, if attached to a barrel, they would likely alter the harmonics and not provide a true measurement of the native vibrations resulting from firing the gun. Conventional "wisdom" says that vibrations are secondary in importance to other phenomena going on in the barrel during combustion, but I would love to know for sure one day.

As for the system I am using, it is not a PT system. As you pointed out it would not accomplish what I am trying to do....even if I had two or more. The strain measurements need to be synced so that I know when and where the shock wave is relative to the start of combustion. I will pin down combustion start by gauging the chamber area and then place one or more gauges in the muzzle area.

To do all of this, I need a multi-channel system capable of several thousand samples per second per channel....which is why I am using an Inet system by GW Instruments. I will also use their software as well as Labview for measuring and analyzing the traces.

I haven't yet decided how to share results. It may be beyond posting here, in which case I will likely set up a web page.

Bohem....pm inbound.

 

[AR4U]

Re: Experiments in OBT

You should run ocw tests with several different bullet and powder combinations and have that data worked up independently. If you have a multichannel instrument you should put strain gauges along the length of the barrel.