O-Rings & Things

Looking to just buy a kit. They are cheap enough. I do have a couple of questions, though:

1) I've found that the kits are sold in metric, as well as regular or conventional. Which one or both do I need? Does it matter where the gun was produced?

2) Does Harbor Freight have decent quality rings? They have kits for $7.99 each ... all sizes in large numbers.

Thanks, shooters!
 
Well it isn't just size but also the firmness. Too soft is no bueno as they get over compressed or stressed and don't function well. I wouldn't buy from harbour freight if they had any, as the rings are not probably designed for anything above 300psi. I would go to a hydrologic supply store like a tractor supplier or specialty o-ring site dedicated to PCPs or even maybe Miners depending on the firmness of the rings. 
 
I recommend The O Ring Store, or, O Rings and More. Both have a comprehensive selection, and an interactive web site for selection. And they have the correct compound of hardness. You can't just get a "kit" of various sizes and hope to have your needs covered. As you will see, there are thousands of sizes, and to pick the correct ones by chance would be nearly impossible. Find a parts drawing of your rifle that includes the O ring sizes. They will probably be metric, and the sizing is stated as the ID X thickness. For example, a .22 breech seal might be shown as: 5.50 X 1.37 mm. 

Ed
 
The problem with measuring, you have to have each one off the rifle to measure, which could be a problem. Also, I've found that trying to measure these things to the 0.01 mm is difficult. But a parts diagram can be found for most rifles. If not, a call to the maker might be productive.

Ditto if you are off even a slight amount it increases as a o-ring failure point many times over. Firmness or hardness is important too. Feel the hardness of the stock o-ring and compare. If yours is much less firm or hard, the air can push around it. I see a lot of guys with the Impact platform using sub-quality o-rings and while I think the complexity of that rifle is a problem in itself, to FX's credit they don't count on people placing soft o-rings from various bargain shops. If you can send in a OEM o-ring to an o-ring specialist they could probably match it and give you the part/order number and then you can buy in bulk. I have a hydrologic store I go to that works exclusively with high pressure, so I can go and take in an o-ring, match it up, and then buy a pack of them (they have some massive o-rings pretty crazy). 



Well cheers on that note
 
I've used Horror Fraught o-rings quite a bit (the shame!), with good luck. The manufacturing process is so mature that it's hard to make a lousy one (there's always the chance of a QA defect though). 

That said, I'd recommend either buying the manufacturer's 'kit' (easiest way to get what might be a dozen different sizes and several materials), or at least getting the 'real' spec and ordering the right thing. Aside from size and durometer (hardness), there are many different materials that o-rings are made from which will affect how well the ring works under pressure, with friction, or in the presence of lubricants. Figuring out the full spec of an o-ring is well outside the wheelhouse of most of us duffers - it's one of those things best left to the pros.
 
I recommend The O Ring Store, or, O Rings and More. Both have a comprehensive selection, and an interactive web site for selection. And they have the correct compound of hardness. You can't just get a "kit" of various sizes and hope to have your needs covered. As you will see, there are thousands of sizes, and to pick the correct ones by chance would be nearly impossible. Find a parts drawing of your rifle that includes the O ring sizes. They will probably be metric, and the sizing is stated as the ID X thickness. For example, a .22 breech seal might be shown as: 5.50 X 1.37 mm. 

Ed

I've had excellent service from TheOringStore personally. Usually have everything I need and ship quickly. I've ordered from ORingsAndMore as well with good results also.