The Daniel Defense MK18 RIII SBR is a 5.56 NATO short-barreled rifle with a 10.3-inch barrel and a 1-in-7 twist (Daniel Defense part no. 02-088-10401-047). Daniel Defense builds the MK18 RIII by taking its MK18 and adding a fully ambidextrous lower, so the bolt catch, safety selector and magazine release all work from either side. Up front, an RIS III rail with M-LOK attachment points replaces the older quad rail, cutting weight while keeping room for a light and grip. This configuration has a 30-round capacity, a manual safety and no factory sights, so the top rail is ready for the optic you choose. It is a compact semi-automatic rifle built for close-quarters training, vehicle carry and home defense.

Key Specifications

• Chambering is 5.56 NATO, the cartridge the MK18 pattern was built around.
• Barrel length is 10.3 inches, the classic MK18 length used on CQB uppers.
• Rate of twist is 1:7, which stabilizes heavier 5.56 bullets.
• The barrel is cold hammer forged, Daniel Defense’s process for accuracy and service life.
• The handguard is an RIS III rail with M-LOK attachment, which saves weight compared with a quad rail.
• The lower is fully ambidextrous, so the bolt catch, safety and magazine release work from either side.
• Capacity is 30 rounds, the standard AR magazine count.
• The safety is a manual safety selector, part of the ambidextrous control set.
• The action is semi-automatic, firing one round per trigger pull.
• The rifle has no factory sights, leaving the top rail open for an optic and backup sights of your choice.

Frequently Asked Questions

What does the RIII add to the MK18? Daniel Defense adds a fully ambidextrous lower receiver and an RIS III M-LOK rail, so left- and right-handed shooters run the controls the same way.

Does it come with sights? No. The rifle ships without sights, so plan on mounting an optic and backup sights on the top rail.

Do I need ATF approval to buy this? No. As of October 9, 2026, ATF no longer requires Form 4 approval, registration or a tax stamp for short-barreled rifles. It transfers on a Form 4473 with a background check through a Class 3 (SOT) dealer. State and local laws still apply. Taking an SBR across state lines still requires an approved ATF Form 5320.20.

Buy the Daniel Defense MK18 RIII SBR, 5.56 NATO, 10.3-Inch

As of October 9, 2026, this short-barreled rifle transfers on a Form 4473 with a background check at your Class 3 (SOT) dealer, with no Form 4 or tax stamp; state and local laws still apply. Order through Daniel Defense‘s short-barreled rifles lineup and our Lubbock, Texas team will handle the transfer, and it ships fast to your Class 3 dealer. It is the MK18 layout updated with ambidextrous controls and a lighter M-LOK rail.