The ProMag RM40SL is a 40-round 5.56x45mm NATO magazine built for AR-15 platforms that demand higher capacity without the weight and bulk of multiple standard mags. If you're running drills at the range, setting up for three-gun competition, or just want extended trigger time between reloads, this polymer magazine delivers the round count without breaking the bank. ProMag engineered these with heat-treated chrome silicon springs and DuPont Zytel polymer construction—materials chosen for durability and long-term reliability in the field and on the bench.

The RM40SL is made in the USA and backed by a lifetime guarantee against manufacturer defects, which speaks to ProMag's confidence in their assembly process. Every magazine goes through multiple quality checks during production to ensure consistent performance, so you're not gambling on feed reliability or premature wear.

At 40 rounds, this magazine sits in a practical sweet spot: more firepower than standard capacity, but still manageable for most shooting scenarios. Whether you're stocking up for high-volume range sessions, competitions, or just want the option of extended capacity in your magazine rotation, the RM40SL is a straightforward, no-frills choice backed by domestic manufacturing and a warranty that doesn't expire.

The ProMag RM40SL is a 40-round 5.56x45mm NATO magazine built for AR-15 platforms that demand higher capacity without the weight and bulk of multiple standard mags. If you're running drills at the range, setting up for three-gun competition, or just want extended trigger time between reloads, this polymer magazine delivers the round count without breaking the bank. ProMag engineered these with heat-treated chrome silicon springs and DuPont Zytel polymer construction—materials chosen for durability and long-term reliability in the field and on the bench.

The RM40SL is made in the USA and backed by a lifetime guarantee against manufacturer defects, which speaks to ProMag's confidence in their assembly process. Every magazine goes through multiple quality checks during production to ensure consistent performance, so you're not gambling on feed reliability or premature wear.

At 40 rounds, this magazine sits in a practical sweet spot: more firepower than standard capacity, but still manageable for most shooting scenarios. Whether you're stocking up for high-volume range sessions, competitions, or just want the option of extended capacity in your magazine rotation, the RM40SL is a straightforward, no-frills choice backed by domestic manufacturing and a warranty that doesn't expire.