Thread: POWDER LOAD RELATIONSHIP TO FPS & PSI

Just a WARNING. Reloading can be dangerous & I'm not recommending you actually try these loads. Always follow manufacturers recommendations. (sorry)
Remember these numbers are generated by a computer program. NOT measured by a chronograph.


A couple of years ago I was working of a project for one of my 30.06s. Doing a bit of research gave me the impression that there could be a linear relationship of powder increases to FPS. That is,,, say increase the powder charge by one grain always gives you a fps increase of say,,, 50 fps. (example only)

One of the reasons I came to this conclusion was that Hodgden are now providing data for subsonic loads using AS2206H at a rate of about 30% of the Max recommended load!
Yet, ADI’s advice is that you should only reduce loads to 60% of the max recommended load!

And as most are aware there are many warnings on the www that light loads of slow powders in large cartridges may cause very dangerously high pressures.

Well that project is currently on hold. Ill get to it next year I guess.

However a few weeks ago this subject came up in one of the threads and I cant remember which one. Anyway I think it deserves it’s own thread. I have recently loaded Linux onto my laptop and it’s great. However I've been unable to get GRT to work. So having waited patiently,,, today I managed to make use of my grandsons laptop and these are the results.

I simply modified three files I had saved loads for loads I already had. (I run GRT off a USB drive)

Starting at approx max ADI loads stepping down to 30% in convenient increments.
However in each case at about 40% GRT refused to provide additional data saying the powder load was too small/light.

Each load is using AR2208. I have not investigated other powders.

Make what you like of it.
It certainly appears that at least with AR2208 from 40% to 100% the Velocity is very close to linear, if not exactly.
However max chamber pressure is NOT linear.

There is also a near enough to darn near straight relationship if you change projectiles weight of similar type of 130-140-150 GRN projectiles to the order of SOMETHING LIKE every ten grains of projectiles more you take off two grains of powder....depending on case of course.... This is helpful if you have projectiles of weight in between published data weights or a SMALL step outside either up or down.... But if your looking to hot rod your loading all bets are off....

@Micky Duck

That makes sense.

I was just reading a reloading book which was giving the relationship between loadings and pressure. One particular cartridge went up 19% in pressure for a 1% increase in powder this from the Hodgsons testing laboratory.*

Originally Posted by nor-west

I was just reading a reloading book which was giving the relationship between loadings and pressure. One particular cartridge went up 19% in pressure for a 1% increase in powder this from the Hodgsons testing laboratory.*

I think this happens when you are effectively above recommended max. Pressure spikes. That why the max is set where it is, to avoid that exact scenario. Also more likely with a fast for cartridge powder. A good reason to do your research and stay within the manufacturers recommendations.

I presume these charts are only based off grt calcs and do not include any actual chronographed data?

In that case any linearities or non linearities merely are a reflection of grts models.

GRT only

So to really be able to come up with any conclusion regarding linearity of charge weight vs velocity you would need to chrono test actual loads

I have high faith in grt and think its an excellent program, but i would not be surprised if velocities would be off with very low charge weigts.

Well, to confirm what GRT say, yes. I thought that would be automatically assumed. However, let me post something else.

From another forum. Sounds like actual fps. But I've asked the qn.

Just noticed I didnt up load the 223 data/image. My bad.

Originally Posted by Oldbloke

From another forum. Sounds like actual fps. But I've asked the qn.

These were actual using a Labradar LX.