M4 motorway not signed, European route E30 includes most of the M4. The M4 has two sections of smart motorway. The one between junctions 19 (M32) and 20 (M5) north of Bristol has variable speed limits and a part-time hard-shoulder. Completion was in summer 2014. The section between junctions 24 and 29 in Newport has variable speed limits. In 2010 it was announced that a smart motorway would be constructed between junctions 3 and 12, with work starting in Autumn 2018. This will be the longest smart motorway scheme in the United Kingdom, with a length of 51km (32 miles). Work is
M4 carbine Marine Corps Infantry Automatic Rifle testing, the Colt IAR displayed a MRBS of CLASS I/II Stoppages of 952 rounds, with a MRBEFF of Class III Stoppages of 60,000 rounds. An array of firearms accessory makers have offered gas piston conversion kits for the M4. The claimed benefits include less needed lubrication for the bolt carrier group to run reliably and reduced fouling. The argument against it is increased weight and reduced accuracy. The Enhanced M4 uses an articulating link piston operating system. Complicating the Army search for higher reliability in the M4 is a number of observations of M4 gas