O-ring sizes (for cartridges)

Guys,

Do you maybe know what are correct o-ring sizes for use in various modelgun cartridges?

I'm in particular after these for Hudson Skorpion, MGC 1911 .45 and Hudson Desert Eagle (same as MGC 1911 I believe).
Tried to measure ones for Skorpion - a tricky task, they get deformed while measuring.

Not sure what should I measure for ordering - thickness (for sure), but then it's inner or outer diameter?
Skorpion o-ring seems to be 2.4mm (internal), 1.2-1.4 (thick) and 5.1mm (external).
5.1mm is approximately 13/64"
2.4mm is approximately 3/32"
1.2mm is approximately 3/64"

Not sure how to map it all to size for order from o-ring/seal company. There seems to be a few standards for o-ring sizes: HNBR, SAE and Metric. Skorpion o-ring does not correspond to any standard size listed here:
http://www.allorings.com/size_cross_reference_framed.htm

This company in the UK were able to help me out

http://www.altecweb.com/home.asp?cat=RangeB05

I sent them a sample 7 and 5mm 0-ring with a descrption of the application they're used for.
They were able to measure them far easier than I could at home and sent me details of their recommended rings.
They'll happily sell small quantities to the public

The 7mm version is a fraction smaller on the o/d once placed onto the piston but they work fine during firing there's no appreciable difference that I can see.

Could be worth sending them samples if you can't get exact dimensions.

Also, there's a link on here to Lucifer's Blog pages... mentioned here https://mp40modelguns.forumotion.net/modelgun-videos-f2/marushin-mauser-m712-english-version-from-lucifer-t1497.htm If I remember correctly there are dimensions quoted with his drawings for the Skorpion 0-rings
Get onto Lucifer's youtube channel, follow link to his blog. I found Google translate useful

Cerwyn, thank you for very useful information :-)

I did not think of providing a sample to a company, that should make things simpler!
I found a (almost) local company advertising a full range of o-rings, also sold in low quantities - will get in touch with them.

And watching Lucifer's work again in pretext of searching for information is just a pleasure ;-)

http://lucifer7922.blog.so-net.ne.jp/2009-08-08

7mm cartridges seem to use Japanese JIS 2401 norm P-3 size o-ring, which is 2.80x1.90 (inner diameter x thickness).
The closest corresponding ISO size is 2.8x1.8, American size is 2.9x1.78 (11A039).

However for 5mm cartridges he seems to have chosen SS3.5 (?) 3.0x1.0 o-rings, and I'm not sure if this is for his own design, or original cartridge. There is such a size in NBR o-rings.

Further references:
Morisei Kako list of standards
Maryland Metrics list of standards

smootik wrote:

http://lucifer7922.blog.so-net.ne.jp/2009-08-08

7mm cartridges seem to use Japanese JIS 2401 norm P-3 size o-ring, which is 2.80x1.90 (inner diameter x thickness).
The closest corresponding ISO size is 2.8x1.8, American size is 2.9x1.78 (11A039).

Is this size you've found true of all 7mm type cartridges regardless of manufacturer (ie: Marushin, MGC, et cetera)? And if so, were you ever able to find an online dealer/distributor that carried these O-rings? The reason I ask is because as I've been sitting here assembling some Cal.9mm cartridges for my Marushin Beretta m92FS (they came in a kit I recently acquired), I've discovered that I'm 2 o-rings short of completing all of them.

lowlight wrote:

Is this size you've found true of all 7mm type cartridges regardless of manufacturer (ie: Marushin, MGC, et cetera)?

Probably not. Size I provided was measured for MGC .45 cartridges (for Colt 1911).

smootik wrote:

Probably not. Size I provided was measured for MGC .45 cartridges (for Colt 1911).

I see, well, I went ahead and ordered them from Francky, as I didn't want to figure out where and how to find a maker/retailer of these little things. Based on my invoice, he charges about 23 cents (about 16p in the UK, I reckon) per O-ring; not too bad I suppose given the application.

Here you go, this thread gives details of 0-ring suppliers:

https://mp40modelguns.forumotion.net/modelgun-caps-cartridges-and-magazines-f6/7mm-0-rings-t439.htm

Replacement (similar, not exactly the same size) O-rings that I found locally cost about 33 cents + shipping, so you got a better deal :-)