The barrel extension pinned to the chamber end contains the interrupted threads
that mate with the angled lugs on the bolt head.
Most takedown rifles use an interrupted thread
system, but interrupted threads
can wear out over time," says Dobler.
Those full threads also handle the rigors of disassembly much better than the old interrupted threads
With the interrupted thread
method, portions of the circumference of both barrel and receiver have no threads.
Roden's actions are available in right- or left-handed patterns, and he's even making some interrupted thread
, takedown actions for a well-known European firm.
Also note the mag tube, like the barrel, has interrupted threads
that must be disengaged before either can be withdrawn from their shared block.
M2A1 barrels have interrupted threads
on the receiver side of the barrel, a barrel lock pin (or lug), and a carrying handle assembly.
This extension contains three floating steel rings in a machined recess, which act as a seal to help prevent debris from coming back into the interrupted threads
and gumming up the works.
An obvious problem with this design would be powder fouling getting into the gaps of the interrupted threads
and locking the breech in place.