General Discussion
In reply to the discussion: Many people may not know this about the AR15. [View all]aikoaiko
(34,159 posts)and many semi-auto rifles have detachable magazines too, but there are a lot of large capacity magazines made for AR15s. Standard issue magazines for ARs is 30 rounds. Magazines that are larger often jam. If I recall correctly, the Autora theater shooter had a 100 round magazine but it jammed.
Most nonAR semi-auto rifles come with magazines in the 5 - 10 range and there aren't many larger magazine aftermarket choices.
Also, there is the issue of bump stocks and bump firing (eg Las Vegas shooter). Bump firing harnesses the natural recoil of a semi-auto gun to shoot faster. Folks are focusing on bump stocks because they make bump firing easier but they are not necessary for bump firing.
Bump firing any firearm brings the rate of fire up almost to full-auto M-16 rate, but they are more difficult to aim. That's why I'm sure the Las Vegas shooter choose a massive group of tightly packed people (outdoor concert goers) to shoot at.