Winchester Repeating Arms 1300 (Historic Manual) - Manual (Page 9)

FIGURE 3
7
Choice of barrels. Choose standard ventilated rib models with the
WinChoke ® system; rifled barrels with rifle sights for shooting slugs;
smoothbore barrels with rifle sights; or models with shorter, smoothbore
barrels with the WinChoke system.
Most Model 1300 hunting models are fitted with the
WinChoke system. It allows you to change choke
constriction to the demands of the game being hunted.
You can easily change the pattern size and density by
simply switching tubes. A variety of accessory choke
tubes are available.
Model 1300 field guns feature a fully floating
ventilated rib. On all barrels, as the barrel heats
with shooting, dimensions can vary slightly. The
1300's floating rib design allows the rib to move
without distorting your sight plane.
Faster, inertia-assisted pumping. The rotary bolt disengages
from the barrel fractions of a second after the shell fires.
The bolt is forced rearward by inertia, actually assisting you
as you pump the forearm rearward for the next shot.
WinChoke ® threaded choke system.