Pressure Traces/ observations?

[alphaburnt]

I know that there are several fellas on here that have been using PT equipment. Other than the obvious of checking for safe loads and pressures, are there any correlations that can be drawn from a PT graph alone?

a) Does it tell you if you are getting efficient use of powder/ map of power burn?

b) Can you look at a trace and assume it is going to be an accurate load?

What about using the PT in conjunction with a chronograph? Can you know an accurate load if you see low ES on the chrony and a sharp rise and gradual fall of pressure on the PT?

I assume the ideal PT would be a sharp rise to peak pressure of less than 30-35K and a gradual fall until the projectile exits the bore.

[alphaburnt]

The reason I ask, for a bow- you can look at the "force-draw curve" and get a fairly accurate representation for how fast it will shoot and the effort you have to put into drawing it to make it shoot. I was wondering if the PTs are somewhat of a FD curve. For a bow, this can only tell you how efficient it is, not how accurate it will shoot. A lot of variables go into that.

[ET]

Alphaburnt.

A pressure trace unit is designed to first show amount of bore pressure and will show the characteristic response of powder burns by pressure curve generated.
A viewing of a trace/s does not guarantee or foretell an accurate load. Too many other variables in play.

A fairly sharp pressure rise may be good for certain bullets for obturation but not necessary beneficial to a sabot. A gradual fall to a point is considered beneficial for resulting velocity.
Traces showing repeatable outlines that are close to being the same might be a good indication of best powder choice for consistent response.

Still a lot of learning going on as to what a pressure trace can reveal but the main point is to avoid going into areas of unsafe pressure with load development.


Ed

[edge]

Too slow a drop off will show that you probably have a lot of unburnt powder too.

edge.

[Savage Shooter]

Feb 22, 2011 22:51:15 GMT -5 alphaburnt said:

The reason I ask, for a bow- you can look at the "force-draw curve" and get a fairly accurate representation for how fast it will shoot and the effort you have to put into drawing it to make it shoot. I was wondering if the PTs are somewhat of a FD curve. For a bow, this can only tell you how efficient it is, not how accurate it will shoot. A lot of variables go into that.

This basic principle works with shooting any projectile. anytime you keep the projectile under equal pressure for longer time the fps will increase.

So short description is IMO it is desirable to see the peak pressure farther out in time (.35 to .5 ms) and also try to balance burn rate enough to keep under pressure for max time.

Rounder the curve, longer the time under pressure.

And as Edge has pointed out get back close to zero (I use 10K max for rule of thumb) at bullet exit, which will indicate burning all powder and not just blowing unburnt powder out of barrel.

[rangeball]

As testing progresses it will be interesting to see if the readily duplicated "perfect" looking traces also prove to be the most accurate, since they should have the most similar affect on barrel harmonics assuming consistent bullet/load sizing.

[Richard]

This goes hand in hand with low Extreme Spreads in velocity. Loads that spike high pressures real quick are the ones (IMHO) that cause the most problem with blown sabots and are not necessarily the most accurate. The PT's that I have done probe that lower "drawn out" pressure curves can and do produce higher velocities will less pressure..........this also means less felt recoil as most have experienced when shooting duplex loads. The same can also be said for the triplex load.
Richard

[edge]

IMO, for sabotless bullets you need a fairly fast pressure rise or you won't seal the bore.

edge.

[Richard]

I would have to agree with you also on that Edge.
Richard