new Remington "Rem Choke" system of screw-in chokes (also fitted to Remington model 1100 auto-loading shotguns at the same time). Initially, the Rem Chokes were offered only in 12 gauge in barrel lengths of 21", 26", and 28". The following year the availability was expanded to the 20 gauge and included other barrel lengths. The 870's production for over 30 years had a design whereby a user could fail to press a shell all the way into the magazine when loading - so that the shell latch did not engage the shell - which could result in tying up the gun. This was caused by the shell slipping out of the magazine under the bolt in the receiver to bind the action, requiring rough treatment of the action or even disassembly. The potential issue was resolved with the introduction of the "Flexi Tab" carrier. Guns with this modification can be identified by the "U"-shaped cut-out on the carrier, visible from below the gun. The cut-out, combined with a modified machining on the underside of the slide assembly, allows the action to be opened with a shell on the carrier. Variants There are hundreds of variations of the Remington 870 in 12, 16, 20, 28 gauges and .410 bore. In 1969 Remington introduced 28 gauge and .410 bore models on a new scaled-down receiver size, and in 1972 a 20 gauge Lightweight ("LW") version was introduced on the same sized receiver, and all of the smaller gauges today are produced on that size receiver. From the original fifteen models offered, Remington currently produces dozens of models for civilian, law enforcement, and military sales. 870 variants can be grouped into: Express – Matte blue/black bead-blasted with hardwood, laminated hardwood or synthetic stocks and chambered for 2 3/4" and 3" 12 or 20 gauge shot shells. All Expresses have been chambered in 3" in 12 and 20 gauge, but markings have varied. Express Tactical – Matte blue/black bead-blasted with a synthetic stock and chambered for 2 3/4", 3", or 3 1/2" 12 gauge shot shells. FieldMaster – Matte blue/black with walnut stock and chambered for 2 3/4" and 3" 12 or 20 gauge shot shells. Mark 1 – adopted by the United States Marine Corps in the late 1960s and saw service into the 21st century. The Model 870 Mark 1 has a 21-inch (53 cm) barrel with an extended magazine increasing total