[elmer fudd]

Most machineguns and subguns do fire with an open bolt, but assault rifles do not. An open bolt is bad for accuracy since you have a very long locktime and the gun is being jostled by the closing of the bolt as you fire. It's my understanding that the BATFE also bans any open bolt guns since they are much easier to convert to full auto.

[tet68]

Some open bolt guns like the Suomi are very accurate,
the Suomi rate of fire is controled by a check valve in
the end of the receiver, since tolerances are very close
the feed stroke is retarded, also the round fires slightly
before chambering completely.
The great Finnish sniper Simo Haya made many kills with his Suomi.

Kids, remember, the ATF has NO sense of humor and that
you're NEVER too old to go to prison!

[tet68]

YOu can see the check valve on the end of the receiver. the lower model was adapted to fire from tank loopholes. The machine work on these is very fine, hardly cost effective now adays, to see the ATF torch cut the receivers breaks one's heart.