Gas blowback maintenance: fixing leaking magazines

Gas blowback maintenance: fixing leaking magazines

if your gbb magazine is leaking that's annoying but almost never the end of the magazine. in the vast majority of cases it's an O-ring worth a few cents or a valve that's worked a bit loose.

below: how to find where it's leaking, how to fix it, and how to stop it happening again.

first: where are the valves

a GBB magazine has two valves that can leak.

the fill valve. at the bottom of the magazine, where you seat the gas can. usually a small brass or steel valve with a thread, tightened with a dedicated valve tool (a small flat key) or sometimes with a flat screwdriver.

the output valve (or knock valve). at the top, this is the valve the hammer or striker hits to release gas. often unscrewable too.

on top of that there are O-rings around the valves and sometimes around the gas route.

step 1: where is it leaking

fill the magazine and submerge it in water, or coat it with some dish-soap water. look where the bubbles come from.

bubbles at the fill valve at the bottom. most common. usually a dirty or worn O-ring around the valve, or the valve is loose.

bubbles at the top at the output valve. valve is loose, or the O-ring around it is worn, or there's dirt under the seat.

bubbles from the seam of the magazine body. bad news. usually a crack in the reservoir. that's mostly not repairable.

no visible leak but bleeds down within an hour. often a very small leak at a valve. repeat the test for longer, or use thicker soapy water.

note: a little gas escaping while filling is normal. that's the overpressure venting.

step 2: the simple fixes first

A. tighten it. this fixes a surprising amount. valves work loose from the vibration of shooting.

• use a valve tool that fits. a screwdriver that's too small chews the slot round and then it gets hard
• hand tight plus a small amount. not with force, you'll strip the soft brass thread that easily
• do this only on an empty magazine. loosening a valve on a magazine under pressure launches that valve with force. vent the gas first by pressing in the output valve with a screwdriver, with the magazine pointed away from your face

B. clean it. dirt under a valve seat holds it open. valve out, clean with a cotton swab, back in.

C. silicone oil. dried-out O-rings shrink and lose their seal. a few drops of silicone oil on the fill valve and then a short burst of gas, so the oil travels into the magazine, makes the rings swell again. often the problem is gone with that.

do this about every three to five fills. not every time, because too much oil ends up in your barrel and on your hop-up rubber, and then your accuracy is gone.

step 3: replacing O-rings

if cleaning and oil don't help, the rings have to come out.

what you need:

• valve tool
• new O-rings. often there are magazine-specific sets for sale, otherwise you measure the old ones with a caliper
• silicone grease or silicone oil
• a wooden or plastic pick to lever the old ring out without scratching

the material of the ring matters. NBR (nitrile) is standard and works fine for green gas. for CO2 magazines you usually want a ring that handles higher pressure. don't use random rubber rings from the hardware store, because those often aren't gas resistant.

method:

1. magazine fully empty. really fully
2. unscrew the valve
3. lever the old O-ring off with something plastic
4. lightly grease the new O-ring with silicone grease
5. valve back, hand tight plus a small amount
6. fill and repeat the soapy-water test

step 4: when it's beyond repair

• crack in the magazine body. replace
• stripped thread in the valve housing. sometimes savable with a tap one size up, mostly not
• deformed magazine body after a drop
• on CO2 magazines: cracks around the cartridge housing. retire it immediately. a magazine under 800 to 1200 psi that lets go is genuinely not a fun event

the maintenance schedule

this prevents the bulk of the leaks.

after every game day:

• store the magazine under pressure. not fully full, but a short burst of gas so there's light pressure. then the O-rings stay under tension and dry out slower. this is the most important rule in this whole piece
• wipe the outside clean, especially the feeding lips
• look for dents and cracks

every three to five fills:

• two drops of silicone oil on the fill valve, followed by a short burst of gas

every season:

• valves out, clean, inspect O-rings
• check the magazine spring
• tighten the valves

never:

• store fully empty for months. that's exactly how O-rings dry out
• leave it in the sun or in a hot car. pressure rises with temperature
• hold it up to your face right after filling to see where it's hissing
• loosen a valve on a magazine that's still under pressure

bonus: the magazine that suddenly won't feed

not every GBB problem is a leak.

• BBs keep jamming: feeding lips damaged, or magazine spring weakened
• slide doesn't come fully back: too little pressure (cold gas), or the slide runs heavy and needs lubrication
• slide won't hold on slide lock: usually cold gas, sometimes a worn follower
• the nose of the BB pokes out but nothing happens: output valve isn't opening, or the hammer has too little force

and the cold

this belongs in every GBB piece: green gas loses pressure at low temperature, and the magazine cools itself down while shooting. around 5 degrees C (40 F) a green gas replica works half or not at all. a magazine that "leaks" on a cold day sometimes doesn't leak at all, it just has too little pressure.

so always test at room temperature before you conclude something is broken. more on that in my piece on CO2 and green gas.

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Also on Airsoft-FOB

• also available in dutch: Gasblowback onderhoud: lekkende magazijnen repareren