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Old 12th March 2015, 01:15 PM
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Brian.Samson Brian.Samson is offline
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Join Date: Jun 2009
Member of: Pontefract, Doncaster Airgun Range
Location: Doncaster
Posts: 2,332

Originally Posted by scutter View Post

I look forward to reading Tench's findings, both he and Brian will probably forget more about the internal workings of airguns then I will ever know.

This is a genuine question for Brian, how does reg pressure affect the pellet, does a shorter blast remove turbulent air etc?

That's a really interesting question actually ( well it is to me, some readers might want to stop reading this thread before it descends into a very technical ballistic theory type thread )

This is a thread about ballistics though, so I make no apologies

First off, what I should say is that there are very few cast iron known facts when it comes to airgun ballistics (which is what makes it so interesting), there are lots of unproven theories though - just be very careful not to quote an unproven theory as a fact and then make assumptions based on those 'facts' - that leads to ******** theories

So my short answer to your question Gary is - I don't know the answer for a fact, but I have theories....

What I do know to be a fact is that a pellet doesn't leave the barrel exactly the same as it went into the barrel - some of the changes are caused by the barrel itself (such as leaving rifling marks on the pellet) but some changes can be caused by the air delivery mechanism itself.

In a PCP I don't think the air release is a single short burst of air (Tench or Jon Harris could probably confirm this), I think it's more a pulse of air or you could think of it as a wave of air followed by smaller waves as the hammer oscillates against the valve. I think that the shape of that oscillating waveform can have an effect on the changes to the shape of the pellet when it leaves the barrel and also on the final stability of the pellet in flight. (Which could be something to do with turbulent air, I have no idea)

Just coming back to what Rich said, it's something I hear a lot of... "If the BC is so much better that you notice a gun takes less wind... wouldn't you also notice that the trajectory is much flatter too?"

I've spent a bit of time playing around with the equations in the past year or so and what I've discovered is that it's quite possible to have a very noticeable difference in wind between two 'systems' (pellet/barrel/gun), with pretty much the same trajectory.

Going back to the 40 yards, 40fps example that was given earlier, the windage difference is nearly half a mildot (quite noticeable) but the difference in impact is less than 4mm - not so easy to notice. That's in a 4mph wind, if you tested at say 6mph, the difference in drop would be the same (less than 4mm) but the difference in windage would be even more pronounced.

Here's an interesting video that someone has posted on the Yellow Forum today :

The first shot is the most interesting, it looks almost like 2 pellets have been fired, but in fact it's only one.
That's an 8.4grn JSB shot at 965fps. I suspect, that if the MV was dropped you might not see such a pronounced spiral (or none at all) but what caused it? Was it the twist rate, the muzzle break or the air delivery system?

I dunno
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