Bigger breech seal O-ring

[Archer50]

In the comparatively short time I have had my .177 S400 Classic I have had quite few problems with the breech seal coming out or not sealing properly. As an experiment, I have fitted a BS 008 0-ring which is a bit bigger and fatter at 4.47 x 1.78 mm than the normal 4.5 x 1.5 mm. It fitted easily enough, is still in place after about 1000 shots and the pellets feed in perfectly despite the slightly smaller hole. It increased the speed of an AADF 8.4 grain pellet by 6 to 8 fps, and reduced the average shot-to-shot variance of a 100 pellet string - which I find a more useful measure of consistency than SD for an unregulated gun - from 2.8 to 1.7 fps. The effect on my HFT 500 was much the same.

I'm not sure how much this matters in practice, but the theoretical improvement is pretty clear. Anyone else tried this? Am I just reinventing a well known wheel?

Alan

Edit: I have changed the velocity figures as I was reading the wrong spreadsheet, sorry. However the overall picture is still the same.

[gdavison]

interesting findings TY for sharing

dunno what size these are, but these are what I use now in all my S510's and Ultimate Sporters

http://spares.bagnallandkirkwood.co.uk/product/two-air-arms-upgraded-breech-o-ring-seals/

[Archer50]

interesting findings TY for sharing

dunno what size these are, but these are what I use now in all my S510's and Ultimate Sporters

http://spares.bagnallandkirkwood.co.uk/product/two-air-arms-upgraded-breech-o-ring-seals/

Just looking at them, I think they are the standard, metric size. The other difference is that the Bagnall and Kirkwood ones are nearly 5 quid for 2, the BS 008's are just over 5 quid for 100 (if you want that many!)

[TenMetrePeter]

I might get 10 for £1.99 just to have in.

It must be possible to have a slightly oversize machined o ring groove especially if the seals tend to come out. I have used BS sizes on a FAS604 as improvement over the metric ones

[gdavison]

interesting findings TY for sharing

dunno what size these are, but these are what I use now in all my S510's and Ultimate Sporters

http://spares.bagnallandkirkwood.co.uk/product/two-air-arms-upgraded-breech-o-ring-seals/

Just looking at them, I think they are the standard, metric size. The other difference is that the Bagnall and Kirkwood ones are nearly 5 quid for 2, the BS 008's are just over 5 quid for 100 (if you want that many!)

I like the 100 for 5 quid idea

[TenMetrePeter]

I just got 5 for under £2. Should last longer than me.

[TenMetrePeter]

Photo std breech seal FP121 left. BS008 right. Noticeable difference.

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