Handy tables and charts.

[Harry's Lad]

Being the original author, let me say that I am and was at the time aware that the maths were simplified and ignored the Van Der Waal issue, rather like the earlier versions of Chairgun and other ballistic software had simplified approaches to residual energy and trajectory.

The first ChairGun version, as it evolved through several iterations, was an adequate model of airgun ballistics as used in the context of airgun usage at that particular time. ChairGun2 evolved from a different ballistic model that more accurately met different (and more challenging) criteria – mostly driven by the requirement of long-range shooting in Oz and the USA. In both cases, the software operated accurately within its stated restraints.
That’s the difference; your spreadsheet is capable of giving results that, because of the known and ignored oversimplification, are erroneous. I was simply pointing out that, given the deficiencies of the simple model used, the 232 Bar + results may be seriously in error.

There seems to be little point in re-releasing number-of-fills as pretty well everyone these days will choose a 300 bar bottle over a 232 so long as they can get it refilled relatively easily. The cost of getting to the filling shop is for many the largest single factor, so it makes sense to buy the biggest and highest pressure bottle you can manhandle.

Perhaps that’s a good reason for re-doing/releasing the spreadsheet since it is the > 232 Bar predictions that are in error. The conjecture was, on acquiring a 300 Bar bottle on the basis or your spreadsheet, that the punter could be very disappointed in the number of fills realised.

If I were to update it, I would not bother with a true Van Der Waal correction, but simply use the present elementary maths substituting an arbitrary value of something like 285 bar whenever the user thought they were selecting 300 bar. That would give a closer approximation.

You could do that . . . or you could do it properly although writing an accurate working algorithm in VBA could be quite challenging.

In any event the accuracy is affected by whatever allowance is made for dead volume in the hose and gauge, and experience has shown me that some decant sets are far more wasteful than others. The other factor to consider is that number-of-fills has a look-up table with the reservoir capacities for several popular rifles (and that's out of date now too.) Readers may think that getting the reservoir capacity from the manufacturer only requires a phone call. In practice one firm steadfastly refused to let me have the information declaring it was a trade secret. I ask you, how can it be a trade secret of any worth when firms such as Theoben specify the size of the buddy bottle? The example of the S410 with 200cc is actually incorrect as later information has shown this reservoir to be 216cc. The carbine and export models have also been amended.

True. But then, we can only use the data that we’re sure of. Otherwise it’s just GIGO again.

ATB
Dave