I've shot full auto plenty of times - it is nice to have access to a range that allows it and a buddy with a tax stamp collection.

But I've only shot "pure" full auto - never anything set up with a burst mechanism.

So I'm a wee bit curious as to how it works, especially when dealing with numbers of rounds available where X%3 !=0

For example... I can usually manage to get single and 2 round bursts off when shooting my buddy's M16.  If he had his set up for 3 shot burst instead of true FA, would such a "quick" pull and release of the trigger only give 2 rounds, or all 3?  And if only 2, what happens next time I pull the trigger, assuming it is "slow" enough to allow 3 cycles of the action?

Or, you load a fresh 20 round mag, pull trigger 7 times.  Obviously the last trigger pull will only result in 2 rounds before bolt locks back.  Reload, release bolt, pull trigger again.  How many rounds?  If different from above, why? Does bolt lockback reset the burst mechanism?

Almost done -  from what I understand, the military changed the M16 to burst (on a1 or a2 maybe?) due to training issues and soldiers doing mag dumps instead of short controlled bursts.... true?

And finally, is it possible for a M16 type to be set up for 4 selector positions? Safe, fire, burst and FA ?  Was this ever a issued M16 config for the US or other countries?

This link has all your answers:

https://robrobinette.com/M16_4-Way_Selector.htm

The US went with a burst trigger that doesn't reset to 3 every time if the trigger is released early.

Topic Moved

The M16 burst trigger does not get alot of love, not just for the whole "fire 2 you get 1 next pull" issue (and thats regardless of lock back and mag changes, so yes if you fire a 20 round mag on 3 round burst, the first trigger pull on your reload will be 1).

No, it also gets alot of hate as it will give you different trigger pulls in semi auto!  6 to 9 pounds depending on 'where you are'.

In "The Black Rifle" on pages 358-359 there is a brief discussion of an alternative burst control that does recycle back to the initial position, independent of the number of rounds fired in each...burst - U.S. Patent No. 4,004,496.