When the Remington 870 shotgun was originally designed, a shell could become jammed in between the bolt and the carrier without an easy way to remove it. Old timers report having to either take apart the gun or mortar (drive the stock into the ground with the muzzle up in a safe direction) the gun into the ground while engaging the slide release (similar to the method sometimes taught with the AR-15/M16 M4 series of rifles).
The jamming problem was addressed with what Remington calls the Fleixtab system. The Fleixtab is sometimes referred to as the Remington 870 anti jam system, or the Flex tab system. According to the “The Remington M870 and M110/11-87 Shotguns, A Shop Manual” by Jerry Kuhnhausen the Flexitab kit was originally developed for the law enforcement shotguns. The Flexitab became standard issue on Remington 870s in the mid 1980s.
I asked an experienced and well known instructor for a large federal agency about the Flexitab conversion, and this is what he said:
“It was not a common occurrence with the gun as designed, BUT if the shell stops became loose over time (staking wore out with use), or a shell was not fully seated into the magazine tube (operator error), a shell could exit the mag tub at the wrong timing and be caught between bottom of the bolt and the shell lifter. At that point it would jam the mechanism as there was not enough clearance if the bolt was in battery or close to it.
Funny that it didn’t come up as a problem until the LE guns stared getting older and worn out, and the “new generation” of police recruits that had no gun experience started coming into the profession on large numbers. For many years, Remington only offered the modification to LE agencies, saying it wasn’t a problem with the sporting guns.”
The Flexitab system uses a modified bolt, carrier and slide assembly (sometimes called a slide plate).
The Flexitab bolt is notched at the bottom.
The Flexitab carrier has a “U” shaped notch in the bottom.
The Flexitab slide assembly (plate) has clearance cuts on the side.
If you work on Remington 870s, being able to identify Flexitab parts and guns is helpful. If you have an old gun, and would like to upgrade the parts, Brownells sells a carrier conversion kit that contains the necessary upgrade parts.