M4A1 Gen 9 or New Blaster

Hi I would like to know what would be the best upgrades for my J9 because I am looking to get a higher FPS and for it to shoot straighter or should I get a Whole new Blaster?
Tying to keep it under $250Aud

Higher fps doesn’t always benifit accuracy tho,
What fps u aiming fir o.o??

around 300-400 fps but I don’t know what to upgrade apart from the gears to metal

J9 is a good platform, I like the gearbox, but that’s probably because I have a few of them (and Gen8s as well, less experience with V2s/LDTs).

What I’d do for accuracy:

  1. teardown the gearbox and get all the seals as good as can be. Check Low Guidos videos on YT for howtos, get new o-rings for the plunger (“brown” or “green” from the gelblaster stores if you’re not savvy on this stuff), consider a new cylinder head and nozzle (but not easential)

  2. metal inner barrel, I like the 7.3mm ID ausgels but a lot of guys like the stainless barrels you can get from CHGBBS or Bruisemaster better. Get the inner barrel fitting tightly in the outer barrel by putting an o-ring (or just wrapping electrical tape around it a few times) right at the end where the inner barrel comes out of the outer barrel (you want 10mm or so of the inner barrel coming out the end of the outer barrel for hopups)

Beyond that you can replace the outer barrel with a metal one, but you probably don’t need to. Notice I haven’t said upgrade the spring - a J9 box should get you into the high 200 fps just with a decent seal and barrel. I also wouldn’t go below a 7.3mm ID inner barrel, I’ve never got 7.0s or 7.1s to work satisfactorily but that might be to do with my gels and that the box is heavily overvolumed for those type of barrels…


Also changing the gears does nothing for FPS or accuracy until you start dealing with really big springs - and I wouldn’t recommend those in a J9 box unless you’re willing to break a box finding out where the limits are. If you really want a bigger spring an Ausgel 1.18 is fine with the stock gears and gearbox case (remembering that nothing is forever and all machines break eventually) - but you’ll be over 300fps with one of them if your seals are any good…

so if I upgrade the spring and put better seals on the piston with maybe new head and nozzle and alloy barrel, I should get above 300 fps?

Yes, pretty easily I would think. Air seals are going to be the issue, not spring power.

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I found the nozzle in my gen9 didn’t seal very well with the cylinder head because it doesn’t have an o-ring so I would definitely replace that if yours is the same.

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ok thanks
How long should the barrel be when i change to alloy

I think 335mm for a Stock Gen9? That could be wrong though…

should i change the outer barrel and make it longer and should i do 7mm inner and 9.5mm outer or 7.5mm and 9.5mm

Ok, well that’s up to you - in theory the 100% cylinder that the J9 comes fitted with can handle a 360 inner barrel just fine, greater than 400mm is getting to be a stretch but still OK. Over about 450 is too long.

That said, anything longer than stock is more for looks or for extreme tuning that I don’t recommend you do until you’ve got this one under your belt…

And I don’t recommend going lower than 7.3mm unless you’re grading your gels and paying particular attention to their size and growing times.

ok thanks so much

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If you’re sticking with the stock outer barrel then 9.5mm is the correct outer diameter. But you can go smaller and just bulk it up with tape or an o-ring to keep it stable :+1:t3:

Hey welcome to the group! :+1: Gen 9s are pretty decent to start with if you’re just getting into modding.

Pretty much everything Torc’s mentioned, for sure. I get about 310 -320 FPS out of my Gen 9 and all I did was make sure the t piece was sealed, 7.5mm X 350mm alloy barrel, 1.18 Ausgel piston spring, green o ring and an upgraded cylinder head and nozzle.

I tried a 7.3mm barrel but was punching 350 - 360 FPS and spraying everywhere :joy: dropping it back to 7.5 dropped the FPS about 40, better accuracy. Oh, stock nylon gears too.:+1:


Actually that’s a good point that @Friendly-fire raises - the 7.5 ID is far more tolerant of gel size than the 7.3, particularly if you’re not using the AKA or carefully grown milky white gels …

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Well, I changed the barrel/cylinder volume ratio a bit with the larger ID of the barrel, so the VE is probably not optimal, but when you pull the trigger, it shoots straight and hits hard.

That’s good enough for me :+1:


does anyone know what website sells it all or i have to use more that one site

Is there a big difference between 1.18 and 1.28 spring?