S&T M249 MK2 SAW Sports Line AEG - Complete build

[nathan13n]

Building the Ultimate Lightweight HPA LMG: My S&T M249 MK2 SAW Project

Going through my airsoft collection, I realized I was missing one key piece — an LMG. Naturally, I thought: why not? I didn’t expect it to become one of the most frustrating builds of my airsoft life. From the start, I knew I was going to HPA it, especially since I had a Backdraft Phoenix engine lying around — a solid engine, though a bit inconsistent in DMR roles.

---

Why I Picked the S&T M249 MK2 SAW

Let’s be real — the S&T M249 is just a rebranded A&K Featherweight (also sold under Cybergun), but with a few advantages:

• V2 gearbox (sounds great at first… more on that later)

• Lightweight — only 4kg, compared to 5.5–6kg for most other M249s

• Cheap — cost me just £200

At first, the V2 gearbox and light weight seemed like a win. But that big proprietary nozzle and body flex quickly turned into a massive headache.

---

Out-of-the-Box Performance

Running a 7.4V battery, it gave me:

• 12 RPS

• 1.1J

• 30m accuracy with a torso-sized spread

Not bad for £200. Decent compression, a metal rack piston, basic MOSFET locked to full auto. It worked — but it wasn’t good.

---

Goals for the Build

1. Fix the weak plastic stock

2. Tighten up the shot spread

3. Increase rate of fire

4. Get consistent mag feeding

---

The Build Process

Body Flex & Rail Replacement

Because the gun is so light, body flex was a huge issue — even minor misalignment can cause major problems with HPA. I replaced the plastic top and bottom rails with metal ones and added bracing plates. This significantly stiffened the gun and improved alignment.

---

Engine & Electronics

Installed the Backdraft Phoenix HPA engine and wired it to a Gate Aster II for better control.

Problems started immediately:

• Sporadic shots

• Inconsistent feeding

• Laser shot followed by a 2-meter fart

Hop-Up & Feed Ramp Hell

The stock hop-up is garbage — cheap, flimsy plastic with lots of flex.

Swapped to:

• Bullgear Featherweight M249 Hop-Up — improved consistency, but feeding issues remained

Tried:

• Drilling stock feed ramp — BBs jammed

• Anttech feed ramp — flimsy 3-part design, reintroduced flex and made things worse

Final Solution:

• Found a 3D model of the original feed ramp by Gazadonf77

• Printed in PA12 nylon (MJF) via 3D People

• Game changer — fixed all feeding issues

---

Bucking & Barrel Testing

Bucking Results:

• Prometheus Purple: Good but had flyers every 5 shots

• Quantum: Best range (50–60m), but overhopped everything and grouping was meh

• Maple Leaf 60°: Winner — torso-size grouping at 50–60m with 0.30g BBs, great price-to-performance

Tip: With Bullgear hop-up, use high elasticity buckings. Stiffer ones perform worse.

---

Barrel Results:

• XT 6.00mm: Tight bore, low PSI, bad consistency

• ZCI 6.02mm: Better, but still not quite there

• Stalker Morpheus 6.03mm: Extended crown = more range (70m), but groupings were wild

• PDI 6.05mm: Winner — 55–65m range, best consistency, 2–3 inch spread. Uses more air but totally worth it.

---

Magazines: A Comedy of Errors

The stock S&T mag (9V battery) fed only 12 RPS — upgraded to 7.4V LiPo, gained speed, then shredded the gears (poor plastic internals).

Tried:

• Lonex 200rd & EPM1: Fed great, but too low capacity for an LMG

• Classic Army M249 mag: Worst of all — inconsistent, weak, loud motor

• Novritsch M249 mag: Winner — actually a rebranded A&K 2000rd box mag, fed up to 30 RPS on both 7.4V and 9V. Responsive mic, auto shutoff, and only £75.

---

Stock Upgrade

The original SAW stock is huge and ideal for batteries, but looks awkward and feels cheap.

Didn’t want to pay £50 for a CNC adapter, so:

• Found an STL file by CitrusPers - Stock adapter

• Got it printed by 3D People

• Now using M4 buffer tube + compact stock = lighter and more ergonomic

---

Final Build & Cost Breakdown

Part	Price
S&T M249 MK2	£200
PDI 6.05mm Barrel	£60
Backdraft Phoenix HPA Engine	£250 (already owned)
Gate Aster 2	£65  (already owned)
A&K 2000rd Box Mag	£75
Bullgear Hop-Up Unit	£60
Custom Feed Ramp & Stock Adapter (PA12)	£50

Total: ~£760

---

Final Verdict

What I have now is a lightweight LMG, feeding 0.30g–0.32g BBs reliably, with:

• 55–65m effective range

• Consistent grouping (~2–3 inch spread)

• 30 RPS at 1.1J

• 3,500–4,000 rounds per 48ci tank @ 70 PSI

Great for suppressive fire, fun skirmishing, and surprising people who think it can’t reach them.

Would I do it again? Probably not.
Am I happy with it? Hell yes.

 

Little video of the bad boy shooting