What Is the Airsoft M870?
The M870 is a gas-powered, pump-action airsoft shotgun modeled on the Remington 870. The two most common versions are the Tokyo Marui (TM) original and the Golden Eagle (GE) clone. Both use a shell-less, magazine-fed gas system where a pump cycle loads BBs and cocks the internal valves, and most models fire three or more BBs per trigger pull from a multi-shot barrel cluster. A stock gas M870 typically chronographs between 260 and 350 FPS on 0.20g BBs using green gas, depending on temperature, gas type, and barrel count. The GE version is based on the TM design but uses a proprietary gas reservoir and stock assembly, so it is not a 1:1 clone and some TM parts do not transfer directly.
Best Value M870 Upgrades
The M870 responds best to a small number of high-impact upgrades rather than a full internal rebuild. This table ranks the most effective upgrades by value, cost, and difficulty.
| Upgrade | Approx. Cost | Impact | Difficulty |
|---|---|---|---|
| Heavier BBs (0.28g to 0.32g) | $10 to $20 | Highest: fixes overhop, improves range and accuracy | None (ammo change) |
| Gas O-ring / seal set | $8 | High: restores lost gas and consistent FPS | Moderate |
| GE polymer stock with integrated reservoir | $20 | High: adds gas capacity and shot count | Easy |
| Internal reinforcement (Wii-Tech / Army Force) | $20 to $50 | High: durability under heavy use | Advanced |
| Tight-bore inner barrel | $30 to $60 | Moderate: minor accuracy gain, fitment risk | Advanced |
| Upgraded trigger set | $13 | Moderate: crisper trigger pull | Advanced |
Why Heavier BBs Are the Number One Fix
The single most effective upgrade for a stock M870 costs almost nothing: switching to heavier BBs. Stock M870 hop-up units tend to over-apply backspin to light 0.20g and 0.25g BBs, causing them to climb sharply and lose range. Moving to 0.28g, 0.30g, or 0.32g BBs balances the hop, flattens the trajectory, and noticeably improves both range and grouping. Because this requires no disassembly and no tools, it is always the first change to make before spending money on internal parts.
M870 Upgrade Path (Step by Step)
Follow this tiered path in order. Each tier builds on the previous one, and most players never need to go past Tier 2.
- 1
Tier 1: Switch to heavier BBs
Start with 0.28g to 0.32g BBs. This corrects overhop on the stock hop-up and gives the biggest range and accuracy gain for the lowest cost, with no disassembly required.
- 2
Tier 1: Refresh the gas O-rings and seals
A fresh gas O-ring set (around $8) restores lost gas pressure and returns FPS consistency to a gun that has started to leak or feel weak. This is the highest-value internal fix.
- 3
Tier 2: Add a reservoir stock
On Golden Eagle guns, the polymer stock with an integrated gas reservoir (around $20) increases onboard gas capacity and shots per fill. Confirm stock compatibility for your specific model before buying.
- 4
Tier 2: Reinforce the internals
For players who shoot heavily or in cold weather, internal reinforcement parts from Wii-Tech or Army Force improve durability of the loading system and valves. This is an advanced install best done by someone comfortable opening the gun.
- 5
Tier 3: Consider a tight-bore inner barrel
A tight-bore inner barrel ($30 to $60) can add a small accuracy improvement, but fitment varies across the multi-barrel cluster and it is not a guaranteed gain. Treat this as optional fine-tuning, not an essential upgrade.
- 6
Tier 3: Upgrade the trigger set
An upgraded trigger set (around $13) sharpens the trigger pull. It is a comfort and feel upgrade rather than a performance one.
- 7
Chronograph and test
After any change, chronograph the gun with your chosen BB weight and confirm it is within your field limit. Test feed and cycling across all barrels before taking it to a game.
M870 Upgrades to Avoid
Some popular-sounding upgrades cause more problems than they solve on the M870 platform:
- •Aftermarket hop-up chambers: these frequently cause BBs to roll out of the barrel or feed inconsistently, and rarely improve on a properly set stock chamber. Avoid them.
- •Aftermarket loading nozzles: these are a common source of feeding failures and jams on the M870. Keep the stock nozzles unless a trusted tech specifically recommends a replacement for your model.
- •Very light BBs (0.20g to 0.25g): these make overhop worse. They are the opposite of what the platform wants once you are tuning for range.
- •Mixing TM and GE parts blindly: because the Golden Eagle uses a proprietary gas reservoir and stock, not all Tokyo Marui parts transfer directly. Confirm compatibility before buying.
Golden Eagle vs Tokyo Marui M870
Both platforms share the same core pump-action gas design, but there are practical differences that affect upgrades:
| Aspect | Tokyo Marui (TM) | Golden Eagle (GE) |
|---|---|---|
| Design origin | Original design | Based on TM, not a 1:1 clone |
| Gas reservoir | TM system | Proprietary reservoir and stock |
| Price | Higher | More affordable |
| Parts compatibility | Widest aftermarket support | Most TM internals fit, but confirm gas/stock parts |
| Best for | Players wanting the reference platform | Budget-focused players who accept some parts limits |
Frequently Asked Questions
What is the best first upgrade for an airsoft M870?
The best first upgrade for an airsoft M870 is switching to heavier BBs, in the 0.28g to 0.32g range. The stock hop-up over-applies backspin to light BBs, causing them to climb and lose range. Heavier BBs flatten the trajectory and improve both range and accuracy for almost no cost and no disassembly.
How much FPS does a stock gas M870 shoot?
A stock gas M870 typically fires between 260 and 350 FPS on 0.20g BBs with green gas. The exact figure depends on temperature, the gas used, and how many barrels the model fires per pump, since gas is split across multiple BBs.
Should I install an aftermarket hop-up chamber or loading nozzle on my M870?
No. Aftermarket hop-up chambers and loading nozzles are the most common causes of feeding failures and BBs rolling out of the barrel on the M870. The stock chamber and nozzles are reliable when properly set, so these parts are best avoided.
Are Tokyo Marui and Golden Eagle M870 parts interchangeable?
Many internal parts are shared because the Golden Eagle M870 is based on the Tokyo Marui design, but it is not a 1:1 clone. The Golden Eagle uses a proprietary gas reservoir and stock assembly, so gas system and stock parts may not transfer directly. Always confirm compatibility for your specific model before buying.
Is it worth putting a tight-bore barrel in an M870?
A tight-bore inner barrel can give a small accuracy improvement, but it is optional. Fitment across the multi-barrel cluster varies and the gain is not guaranteed, so heavier BBs and fresh gas seals deliver far more value first.