Rubaga wrote:Ah ok many thanks - Thats helpful.
Please pardon my ignorance as a newbie but An alternative question - is it possible to get replacement commercial cylinders for the 831 and swop them over ( so I can keep these military ones with their keys in case I want to put them back to original state)?
They take a special cylinder (the way the back is shaped) which isn't the same as any of the Medeco commercial cylinders. Ordering original cylinders is incredibly difficult, some of us tried for years, even going through Medeco dealers. Medeco will only sell them to certain dealers, and even then the factory will sometimes want to know who the end user is before they will decide whether or not they're willing to ship the cores to the locksmith. In the unlikely event you can find a locksmith who can get them, retail is ~$200 apiece, their dealer cost is about $100. Even then, they will come with 1 control key and 2 user keys and they won't be keyed alike. Blanks are not available even to the locksmiths who can order cylinders. You'd need to collect several pairs of keys, then figure out a deeper bitting that all the keys can be cut deeper to accomodate.
Your best bet is to either do some metal work and modify a commercial cylinder to fit, or try to find someone with a Keyway King key machine that can make custom blanks by cutting the warding grooves into some brass stock. I'd expect to pay around $10 per blank, give or take, if you can find someone to help you go that route. Then you'd have to pay the cost of having a locksmith code cut your bitting onto the blanks. Common fees for that tend to run between $15-$25 per key, but they might discount that a little bit since you'd be providing the blanks.
You can also look for surplus cylinders on eBay. They don't come up very often, typical price is around $75, but every once in a blue moon you'll see one for $50 or so.