The Colt was described as sand cuts, now how they function compared the the KAC ones I have no idea.
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Silly Rabbit! Sandcuts are for FALs
http://imageshack.us/scaled/landing/801/imageqyk.jpg
In broad strokes, here's how it works;
The DoD sets the minimum standards it wants for equipment. The providers submit samples, and if/when something is submitted, that whatever, in all of the details that can be nailed down, is cast in stone.
That's mil-spec.
A manufacturer can, if the spec does not deny it, submit something that is actually superior, provided;
It is absolutely interchangeable with the existing interfaces
Does not require any difference in maintenance, inspection, gaging, etc.
Is not rejected by the issuing authority
And does not cost any more than the specified price in the contract.
Example;
Carpenter 158 was a really good steel in 1959. Since then we've found better steels. Could Colt substitute a superior steel? Maybe;
If it requires no change in maintenance, gaging, eyc.
No-one objects to the change
And Colt sells the new bolts at the same price as the old ones.
Can Colt convince DoD to re-write the spec? (Not that they haven't tried.)
Sure, but;
They'd have to convince DoD that the new steel is actually superior
That the new bolts will have a service life greater enough to warrant the cost of testing to prove it (You don't think DoD is going to take Colt's word for it, do you?)
And finally, that the improved product is worth the hassle of having two different bolts in inventory, until they can use up all the old bolts.
Glaciers move fast, compared to mil-spec changes.