Damn, was the goat pretty? I sure hope the goat was pretty. I’ve got some standards, ya know. 
That would only be true of blowback operated weapons, mostly handguns these days and older submachine guns.
Machineguns and assault rifles are gas operated. In simple terms, when the bullet gets close to the muzzle, the gas *behind *the bullet is piped backwards to push the bolt back. The amount of time the bullet spends in the barrel wouldn’t have any effect at all that i can see. If the bullet is spending enough time in the barrel to cycle the mechanism, then it will have the same stroke regardless. And if it’s moving so fast that it can’t cycle (probably physically impossible), then it won’t cycle at all.
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It’s not physically impossible. Auto-loading weapons are designed to use a specific range of bullet weights and operate within a specific range of muzzle velocities. Additionally, some bullet shapes (ogive and length) can cause feeding problems. Auto-loaders can also be affected by how efficiently the propellant burns. Some powders are “dirtier” than others. These are not problems encountered with revolvers or bolt action rifles.
.30 caliber bullets, AFAIK, are available from 110 to 240 grains, which is the broadest selection of any caliber’s bullet weights. (7mm is the next largest.) It’s possible that 110gr bullets would exit the barrel before there is sufficient gas pressure to operate a particular gas-operated, auto-loader design, and a 240gr bullet could repeatedly allow excessive gas pressure that could jam, or destroy, the gas-operated auto-loader mechanism.
Not your original question but a lesson that you won’t find in the -10 for the 240B (or at least didn’t used to be there). The BFA is less sturdy than the rest of the system if you are using blanks.
I seem to recall the -10 for the 240B having a number of rounds that was a maximum before barrel change ( in a short period of fire.) It didn’t specify service versus blanks being fired. ISTR something between 1000 and 1200 rounds. I can tell you that blank firing adapters don’t seem to agree with the manual’s number. In the one case of attempting it… small chunks of the adapter flew off and the rest became one unmovable lump. It made an interesting show in the night training event as it self destructed. The NCO working for me that day was initially getting threatened with having to pay for the barrel before he pointed at the manual. They later were able to cut the BFA off without damage to the barrel anyway. It’s easier to avoid the hassle.
If I’d worked for a living I’d probably have a clearer memory of the exact details of what the manual said. 
Hey OP, welcome. And why the hell have you not introduced yourself and added your 2¢ here, where all the cool kids are?
Then you haven’t been in the bush long enough.
When I read or hear about people firing a 700 rpm auto weapon for 3 minutes of sustained fire, I can’t help think of the poor schlubs who had to lug around the 2,100 rounds of ammo that got expended during that burst. And since the loader probably has 2 spare barrels in his pack, some more schlubs are lugging around another 4,200 rounds.