Skout Skout .177...

Well that was interesting, just put the gun back together with the manifold/TP reducer and only done a couple of 10 shot strings to test, but it seems there is an instant tightening of the FPS constancy, now getting 5-6fps total vernation with 8.44 and 10.34, so I would say that's a win, obviously subject to more testing but so far so good!
 
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Curious what size ( I.D.) you choose to test with ?
I used 2mm at the valve face end with a sort of taper to 5mm at the barrel side haven't got a taper drill of the right size, so it's stepped with a large chamfer at either end, I originally intended to contour both sides with corresponding surface match, but this proved too much of a pain so contented to contour the barrel face to avoid the insert being pushed up enough to hag up on the barrel TP and the result was a gap at the valve end, but it's a resounding success!

I have now put around 100 pellets through the chrono of two different weights, and I am now getting total FPS variations of 3-6fps and no odd spikes and can now have stable FPS down to 100bar bottle pressure whereas before I was seeing gradual drop from 160bar down, I always had a bit of suspicion that the manifold pre expansion area before the barrel was not a good thing and the fact that you have done similar with good results clinched it,

To compare with the previous non insert results, I was seeing FPS variation of anywhere from 20-35fps with odd spikes of more than 60 fps!

It could certainly solve the problems with the restricted small calibre versions for counters with restrictions like the UK, I now have to wait to see if it may have any positive effects on accuracy which would ice the cake for me.:)
 
Well :unsure: ... while that may be be working and a reduction in transfer area .... If I read correctly you have used a tapered transfer path Opposed / Switched to what I was doing and testing.
When you have a Larger seat than caliber, The taper is placed to be larger and matching seat area end and terminating smaller at the barrel. * Sonic choking so expansion happens behind projectile.

With an already Small seat, the transfer path ideally should just be straight at say @ 3 to 3.5mm threw the manifold.
* As you have done, the energy of the HP air is expanding as it leaves the seat and it results in less energy once this pressure pulse is at the barrel.
You want the release of the energy of the pressure to happen once behind and pushing the projectile and not before hand. This is exactly whats wrong about the OEM configuration in that the same thing happens as what your trying now and is IMO not the correct technique to achieve what I thought was stated on earlier & referenced threads.
 
The size of the outlet from the Valve seat into the manifold on the restricted sub 12 .177 is around 1.3mm so as I couldn't match the valve seal contour I just chamfered it and then 2mm opening out to 5mm to get it near the barrel TP which is around 4mm by 6mm also much too large with a fillet across the centre so a compromise for testing, but it works very well!
So may make some other prototypes, but it seems that it's just the area/volume that is causing the FPS problems.
 
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