Another J10 mod list 'check my lack of knowledge' thread

Hey hey from VIC, me and a couple of mates have bought a blaster each (1x SCAR2 and 2xJ10) and I’m chasing a little more FPS and more importantly, some accuracy/consistency with my J10.

I’ve done as much reading as I can but it’s a deep pool and not hard to get a little crossed up!
I’ve got the list of upgrades below chosen - does this basically cover the ‘low hanging fruit’ starter pack?

1.3mm Steel Spring
Stainless Steel Cylinder
Brass Cylinder Head w/ Double O-Ring (is this or does it include the o-ring upgrade I understand is almost necessary?)
Piston w/ Full Metal Rack and Head
Fighting Bro Barrels 350MM / RED

I’d appreciate any advice from you more experienced hands! Loving it so far and keen as mustard to get onto a field (even if it’s a ‘private property definitely-not-a-skirmish’ meet up, thanks victoria…)


solid starting point.
if you want a good reliable blaster that out performs all your friends go a little higher.
i’d chuck some metal gears in it, and a bigger battery.
runnin a higher rate of fire and a 1.3 spring your stock gears wont last too long.
also get a green Oring for your piston (i’m assuming thats what you meant by the oring upgrade)
and a hop up for good measure for accuracy purposes.
if you do these you’ll have a reliable beast that should make your friends hate you.
then prepare to be addicted and fall deep down the rabbit hole.


i’d do away with the 1.3 and get an M90

the M and SP series springs are more consistent in what you get.

i’ve also started replacing my FB 7.2ID barrels with stainless 7.3ID barrels to get around what has been a really bad time for gel consistency


Thanks for your input guys! Given the advice I’ve changed my list to:

$14               SHS M90 upgrade spring
$8                Stainless Steel Cylinder
$15               Brass Cylinder Head w/ Double O-Ring
$20               Piston w/ Full Metal Rack and Head
$3                Green o-ring upgrade for piston
$12.50            350MM Red Fighting Bro Barrel
$20               DK ACR J10 Hopup
*Total  $92.50

$10               WARINTEREST HARDEST 3.0 RED GEL BALLS 7-8MM (10,000 PACK)

The stainless barrel seemed a bit overkill…for now. I’m going with a 35cm x 7.5mm (ID) barrel shooting the red hardened 3.0 milkies, which apparently suit 7.5mm pretty well.

Now the shipping wait! I’ll post back here with my results for any future similarly inexperienced J10 searchers. :+1:

piston from ebay is problematic. you may find you need to grind out the 14th tooth. I use the kublai single piece cylinder and head and use a LDT mozzle. I would have taken the advice and used a stainless barrel. Cheaping out on the piston and cylinder head will undo the good work with the o ring and spring


have you got a metal gear set because with a metal rack on the piston, the nylon sector gear could strip more easily

Thanks for the tips! Thankfully hadn’t completed the checkout (was waiting for a mates OK to order the same for him) so was able to change a couple of bits

I ended up getting a 1.2mm and a 1.3mm; I was about to order an M90 spring given your advice but couldn’t find a size down, and got scared off by the threat of damage to some internal parts that are still stock. I couldn’t find reliable info on the force output in comparison to the standard 1.2 & 1.3.

That and the battery is still stock and if I’ve understood correctly it might require a more powerful one?
I figured springs are cheap as and I can always throw it in later without harm.

I tried to get a 40cm stainless barrel but I couldn’t find any in Aus! Had to go with 35cm alloy for now but will upgrade in the future. It’s pretty hard to find info on ‘Alloy vs Stainless Barrels’ by the by! Would love to see how much it effects fps and accuracy.

I need to do more reading on metal gears, I’ve seen some comments on it being a bit more stressful on the gearbox or case/shell, but not educated enough yet.

I don’t really want a higher RoF, it’s high enough for me from stock, and it chews more battery right? So I’ve put off a new battery for now.

I took your advice and got a hopup - the DK10.

I’ve already rabbit-holed for probably a dozen hours and I still feel bloody uneducated. So yep this is definitely gonna suck me in chasing accuracy :joy:

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The piston is this one here:
Nozzle is

Are they no good? I haven’t got any parts off ebay, not confident enough to navigate that cluster***k yet!

On the barrel point, yeah I tried to get one in the end, couldn’t find any in stock though :frowning_face: Going with the 35cm alloy for now.

Nah I didn’t - but I didn’t think of the metal rack point!
Crap I hope it holds up :persevere: - whats the honest likelihood within the next 100-150 mags?

If not I suppose it just means I get metal gears when it happens right? It won’t knock-on destroy the gearbox I presume? (maybe just an adjacent gear or two, which’d be replaced anyway)

m90 is loosely comparative with a 1.3. its just that an m90 is an m90 is an m90 and a 1.3 will vary between springs and providers and material…

metal gears - don’t in an of themselves create box stress…its the heavier springs we pair the metal gears with that does that.

on that front, GLUE your metal ladder in

SS vs ALU: its all to do with the internal finish of the barrel

ROF is a function of battery voltage and gear ratio, doesn’t really play too heavily into battery life perse but double the ROF, halve the battery run time, same number of gels come out.

battery life is a function of torque required to drive the gearbox. increase the torque and reduce the battery run time. heavier spring + more aggressive gear ratio == shorter run time at higher amps == better battery required. heavier spring + slower gear ratio == less amps needed, m90 + 18:1 would not be considered a high amperage box.

torque and run time is also linked to the motor design - but thats a topic for a whole other day

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yup thats the piston I got for my first build. had to grind out the 14th tooth. that brass head didnt fit into the cylinder. You may not have the same problems (I hope not).

sorry for the useless reply but aren’t blasters illegal in Victoria


judging by your spring they wont strip

Yep, they are for now - that’ll likely change ‘soon’ I gather.

Don’t forget to buy a dk barrel stabiliser. It’s a must for accuracy. You can even put 2 of em in.

Or if you want to pay way too much but get a better product that needs to be filed down to suit. The masada barrel stabiliser. I have one of each, the second pic is the masada. .

and the last pic shows where a 40cm barrel ends up. I have ordered an outer barrel extension. Come on Australia post.

Thanks for the input guys, I’ve got halfway through writing a reply about 3 times and been pulled away by work/life, flat out.

@zeHamish Nice tip on the ladder glue, and yeah that’s what I was thinking with the battery, shoots fast enough - I want more playtime! Less shots in a burst won’t hurt me I reckon.

Yep, I had to grind that bloody tooth down as well @spectre720 - absolute pain in the arse!!! Took me 2 assembles to figure it was that (and JESUSCHRIST that bloody ratcheting gear arm thing on the lowest gear makes assembly a prick). I tried filing (only had wood files), hacksaw (barely dented it), and eventually just took a bloody anglegrinder to it (with only minimal collateral to the plastic!). I had to clamp it down to do that of course, and I did hear a crack…inspection came up alright though so I put it in - ordered a new one though.

I had trouble with the trigger fouling the single hemisphere toothed gear up top, caught me a couple of times, not immediately obvious when it’s out of place.

Screwed the screws in the pistolgrip into the wires going to the motor, so had to pull it out and whip out the soldering iron. Then the wires going from the gearbox to the battery stripped and mostly broke when sliding the stock on. So more soldering and plumbers tape (no sparky tape handy). Managed to break the handle on the (as I understand it, cosmetic) cocking slide thing along the top of the ■■■ trying to get it to slide all the way shut smoothly instead of sticking 10mm before fully closed.

I pulled it apart and reassembled about 7 times I reckon…and that’s when I tried the 1.2mm spring instead. Then it worked fine, immediately.

So I guess the 1.3mm spring was just too stiff for my motor/battery. Godamn I spent 8 hours on the bloody thing.

Some winding of more plumbers tape got the inner barrel captured tightly in the outer barrel, gotta find some grommets/orings to do that job I guess.

The DK10 hopup doesn’t fit with the 35cm alloy barrel, so don’t know what to do there.

I ended up using some motor oil and some ‘personal lubricant’ since I only had filthy grease handy.

I tried shooting both gold pack milkies, and standard blues once I had it assembled & working. 90% of shots barely made it 10 meters. I’ve got some red pack milkies on the way in the hope that it’s just a barrel + gel size issue.

What a learning experience, shout out to the missus for putting up with the swearing. :face_with_symbols_over_mouth:

@LYSURGIC_ACID I’m gonna have a look at those tomorrow, keen - accuracy is what I’m after!


Well gotta say I did have a bit of a chuckle to myself reading your saga! Sounds like it was a whole heap of fun. These bloody toys!! Just put some metal gears, motor, oring spring etc into the wife’s (my 2nd😉) ACR and has some fun with the anti reverse ratchet too, it kept wanting to jump up and out so I managed to hold it in place with a thin Allen key and carefully put the housing back together. Then for some reason when on single shot the trigger would click🤬. I thought bugger it and continued to reassemble and see if it was noisey before pulling it back apart. Ran it for a quick burst and you little beauty, clicking went away, no gear noise and no pulling back apart.
Fluked the shimming process to. Got it all stripped, shimmed and back together in 2 hours. Happy days!!

Use a magnet or spring bend on the AR latch lads

Bend the box side of the spring 90deg down so it presses flat against the box wall