Scraper ring on Airsporters - what does it do?

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I'm no Airsporter expert, but I haven't heard of a scraper ring being present before? Is it, perhaps, a home-brewed addition?

No this does not look home made. The gun has lived a rough and abusive life, but does not seem to have been opened.

I believe it adds support to the Oring.

How? It is quite far away from the O-ring?

never seen one in an airsporter or merc...

Probably short lived as other posts say, I belive this is an early mk6

I've found three now on both guns. They were a short-lived alteration which I believe did not work.
By the time I bought my Mk6 Airsporter in 1977 BSA had changed to a Nylon head without the ring. I'm sure Gunshop would know more.

Hopefully he'll chime in. This is a nylon head with steel "scraper" in front of the usual rubber O-ring.

The Mk4 has the scraper ring and it is rubbish ! but also the aftermarket Ali one is rubbish and your best option is long stroke by shortening the spigot, leaving off the buffer washer and having the O ring undercut 1.5 mm set back from the face , not 10mm as is and it will shooter better .

Yeah, the gun is running an aluminium after market head at the moment, and it is not great.
I cant really remember if my other later mk6 Airsporter has the steel ring but it has a nylon head and performs surprisingly well. (but my expections for an Airsporter is really low).

The stroker may be a solution in the future, but for now I'm not too keen on making a new piston head.
I did something like that on my Franken-Mercury that worked out quite well in the end, just maximizing the stroke and compression without cutting down the spigot.