casually changing BCGs?

[hotcha223]

I have a spare Bravo Co bcg I have thought of trying in one of my Bushies. Haven't as I grok the 'if it ain't causing problems don't fix it' advice from the "Oh, no, I bought a..." thread. Searching turned up a few threads mentioning swapping out bcgs pretty casually, like it is no big deal. However, I was reading an Army manual covering what to check for, what to fix or replace and what to send back to support to repair or scrap, and this manual made a big deal of not putting the bcg or bolt from one rifle into another, that consequences could range from property damage to death! Is this because of possible headspace diffs from rifle to rifle?

[Oscar 319]

Putting the BCM Bolt Carrier Group into your Bushmaster Carbine(s) would be considered a reliabilty upgrade.

The only "property damage and death" should take place downrange, where your improved carbine is firing.

[Iraqgunz]

I think it has been discussed a dozen times in just the last week.