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Custom 40-Round AR-15 PMAGs — Magpul GEN M3 Extended 5.56 Magazines
Run more rounds between reloads with custom 40-round AR-15 PMAGs from My Southern Tactical. Built on the genuine Magpul PMAG 40 AR/M4 GEN M3 in .223 Rem / 5.56x45mm NATO, these are true factory extended-capacity magazines — not 30-rounders with a bolted-on baseplate.
That distinction matters. Aftermarket +10 baseplate extensions add length but reuse a spring that was never calibrated for the extra rounds, which is a common source of feeding failures and last-round hang-ups. A native 40-round body has factory-matched spring tension and a continuous internal curve designed from the ground up to feed all 40 reliably — exactly what you want in a high-volume range, competition, binary, or full-auto setup.
Then we make it yours. We apply full-color, high-definition direct prints to both sides of the extended body — flags, camos, custom text, or your own artwork through Design Your Own. These are true direct prints, not monochrome laser engraving, and the taller 40-round body gives your design even more canvas to stand out.
Shop our custom 40-round Gen M3 PMAGs below and personalize your high-capacity loadout without sacrificing reliability.
Advantages of a True 40-Round PMAG vs. Magazine Extensions
- Factory-calibrated spring tension — a native 40-round magazine uses a spring engineered for the full round count, avoiding the weak-spring feeding failures common with +10 baseplate extensions on a 30-round body.
- Continuous internal curve geometry — the body is molded with one uninterrupted feed curve, eliminating the binding and round-stacking issues that occur where an extension meets the original magazine.
- Reliable to the last round — purpose-built geometry and spring rate help prevent the last-round hang-ups extensions are known for.
- Impact-resistant polymer construction — Magpul’s polymer shell resists cracking and deformation under the heat and rough handling of high-volume shooting.
- Built for high-volume fire — ideal for range, competition, binary, and full-auto setups where reload frequency and reliability matter most.
- Durable, heat-tolerant custom print — our premium UV-curable inks are bonded to the body and built to hold up to the high heat and repeated handling of long range days.
- More design canvas — the taller 40-round body offers extra surface area for bolder, more detailed full-color graphics.
Custom 30-Rd PMAG vs. Custom 40-Rd PMAG
| Feature |
Custom Printed 30-Rd PMAG |
Custom Printed 40-Rd PMAG |
| Capacity |
30 rounds |
40 rounds |
| Base magazine |
Magpul PMAG 30 AR GEN M3 |
Magpul PMAG 40 AR/M4 GEN M3 |
| Caliber |
5.56x45mm / .223 Rem |
5.56x45mm / .223 Rem |
| Approx. length |
~7.6 in |
~9.4 in (taller) |
| Ideal use case |
Home defense, carry, general/tactical use |
High-volume bench, range, competition, binary/full-auto |
| Graphic surface area |
Standard |
Larger — more room for custom designs |
| Print method |
Full-color HD direct print, both sides |
Full-color HD direct print, both sides |
| Reliability |
Proven Gen M3 performance |
Proven Gen M3 performance (factory 40-rd spring) |
Frequently Asked Questions
Are these true factory 40-round magazines or modified 30-rounders?
True factory. These are genuine, unmodified Magpul PMAG 40 AR/M4 GEN M3 magazines — built as 40-round bodies from the factory with a matched spring and follower. They are not 30-round mags with an aftermarket baseplate extension.
Are these 40-round PMAGs engraved or printed?
Printed. We use a high-definition, full-color direct-print process — not laser engraving — for vibrant, multi-color designs on both sides of the magazine. The taller body gives even more room for detailed graphics that engraving can’t match.
Will a 40-round PMAG fit in standard AR-15 magazine pouches?
It depends on the pouch. The PMAG 40 is noticeably taller than a 30-round mag, so it seats deeper and sticks out more in standard pouches. Open-top or adjustable/elastic pouches work best; some fixed 30-round pouches won’t fully retain it.
Do you ship 40-round magazines to capacity-restricted states?
Some states and localities restrict standard- and extended-capacity magazines. Orders are subject to applicable local laws, so please confirm your area’s magazine-capacity rules before ordering.
