Try growing them for less time. Measure them as you go if you can around the 1.5-2.5hr.
Strange if the GBX came standard with a 7.1mm id barrel.
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Barrel swap would be the easiest answer, but another possibility would be trying out some xforce predator v2 gels.
From the bit of testing I’ve done with them, an unagitated grow of 4 hours had a teaspoon worth of gels completely within 7.1-7.3mm (as long as you ignore 3 outliers either side). A grow at 2-3 hours could be perfect for your blaster.
I’d recommend a 7.5mm barrel though, so much less mucking around
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Always loved the simplicity of 7.5.
No issues, no fecking around trying to control grow gels…… just load up whatever is in the bottle out of the fridge and everything would just work 
I only used 7.3’s as a method to fine tune certain sized blasters…… but even then, 7.3 was a world of difference from the pain in the arse 7.1’s 
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These are decent blasters, and considering the price are fantastic. I have done up countless of the long and short version, and they always come up great.
I will apologise for the long post, but it is worth it, as it contains all I know of these!
Definitely swap the deans connectors from battery to blaster, as that is the connector the gel lords intended to use.
If you want to get them going well, and not spend a boat load of money they are an awesome option, the bonus is the motor is good decent magnet and balance of speed and torque, with good pinion and motor tower so shimming bevel to pinion makes for a very nice clean sounding and long lasting blaster. In my experience they are not perfectly shimmed, but not terrible either.
List of mods I normally perform:
Change piston to a shs or equivalent, retain the piston head and oring, cylinder head and nozzle. They have a great airseal as is.
Aoe correction, usually around +2mm. My preferred method on these gearboxes is to remove the cylinder head pad, and glue a 2mm rubber washer on the cylinder head, then glue the stock pad on, I use a rubber that is not really compressive, but the stock pad is more impact resistant and wont decay, this way they last longer than the almost two years I’ve been doing this. I have seen a couple “wells” the front end and break gearbox in stock form, all were the long version, with the stock ported cylinder. I am yet to see one I have modded do it but time will tell. (mine is nearly two years old)
Shorten return spring 2-3 loops, or replace and shorten with a better quality one.
13:1 gears (shs)
If you have the long version, replace the cylinder with a 100%, will require you to file the lug on the gearbox shell but it only takes a couple minutes with a file.
choose a spring, M100 usually gets 330fps on the short and 340fps on the long.
M110 usually gets 360fps for the short, and 380fps on the long.
And that’s it! Stuff all changes really, more work than parts 
If you want you can change the oring for a brown one, but the stock thick black one holds up for a very long time if kept lubricated every few months.
The only other potential mod is to swap the stock bushes for good quality low profile ones, but I have only seen one “keyhole” the bushes with all the modifications, and that one was drum mag full auto’d mag dumped empty a titan in a day abused, a normal player wont have a need for the change.
If you aren’t happy with the 24-25 rounds a second on 11v at this power, Trim 2-3mm off the bottom of the tappet wing, and change the motor. I have one with an X-force red 480 18k, and it rips just under 30rps. Though once doing this, you may want to grab and shs spring kit, and take the cut off lever spring, feed it inside the stock one making a doubled up spring and return it to the gearbox… or get a mosfet, though it will reliably semi at this speed, and be very snappy but you will still have the trigger pull and reset of a standard trigger.
I don’t really recommend going much beyond 30rps, as I have not tested much above this (did one with 12:1 and the xforce motor hitting 31rps) as the gen9 style tappet design will make it fun to seal and feed, as it has a longer travel than the typical v2 gel style, and you’ll be trimming quite alot of tappet plate with a really short tight return spring. My experiences with the MK h92 (similar gen8/9 tappet design) is that beyond 30 rps is doable, but your performance will plateau and you will either feed, or seal; not both, and motor heat and battery punishment becomes huge.
with good shimming and quality grease etc, these last a long time. Friends have shortened the inner barrel and used the aztech hellfire hopup, with really impressive results. My personal one has an AKA long, and it works well too.
All this said, for 70-80 bucks (115 if you do the brown oring, bushes, return spring and cutoff spring kit and get ripped off full price) of parts and a few hours of work, getting this sort of performance and reliability is 100% wicked and hard not to recommend. Even paying a decent tech to do it, you have this blaster at this performance for around 400 bucks. Impossible to beat really.
Also worth getting a titan nunchuck, and a stock that fits it, you will be able to use it all day without a battery change. If you use ultra hard gels, dont oversize them, as at this rof it will fill the barrel quick and bust the ladder, as the air seal on these especially with a shortened return spring is absolute!
Sorry for the massive post, but thought I would impart the knowledge upon you all.
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Hi , I’ve used the hellfire on my GBX , it transformed its performance.
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Awesome info! Appreciate the time you put into that and for sharing. Now to just find all the parts you mentioned. 
Update on the barrel. I swapped out the stock 7.1mm for a polished alloy 7.5mm. Works a lot better now! Luckily the local store(One Shot Gel Blasters) I bought the barrel from also have a lathe and offered to put in the groove required by the T-Piece and cut the barrel down. 
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HI my JG GBX gear box just broke, , metal box, Iam unable to purchase another JG WORKS one , will a JG SLR v2 box fit , or any suggestions which v2 g/box that will fit, UAV,ME AUSTRALIA had some replacements, out of stock.
m4a1 sell JG v2 gearboxes, they don’t list them on their website though for some reason, have to go in store, or maybe ring them? They are $149. I would recommend at least loctiting the piston head before dropping in.
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Thanks ROKSOLID , I’ve contacted them about the gearbox, I wonder if th JG SLR V2 NYLON BOX WOULD FIT🤔
I think you mean a JingJi SLR nylon box. I actually don’t have a spare one here to test, however, I do have an Slr that I fitted a JG metal box into. You may be able to just use the JG nozzle in the SLR box and have it work…
For my blaster that is the JG box in the SLR I used the SLR nozzle, to get it to seal I had to space the nozzle tip forward with a oring but is otherwise straight forward.
The other challenge you will face is JG use a 6mm buffer tube bolt, that bolts into the spring retainer. The SLR uses a 5mm bolt that secures to the lower receiver. The spring retainers don’t fit each other, so you will have nothing to screw the buffer tube in to.
So while the box will fit and work, it also won’t as you can’t secure the buffer tube.
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Never knew that there were different buffer tube bolt sizes…… but at the same time, not surprised considering the stupid lack of standards and extensive use of proprietary parts purposely used by different manufacturers 
At least a Spring Retainer with the required buffer tube bolt size should be pretty easy to find, or alternatively being able to buy an aftermarket bolt from the local Bunnings/Hardware to suit the job
Yes when I put the JG box in my SLR, it was easy, 6mm bolt to suit, and drill out nylon lower receiver. Done a few now and it is a nice conversion.
This gear box from eBay ???
It is NOT a JG, it is a JingJi. Please see this from a reputable seller
Hi , ROKSOLID , will it fit .
Please read my earlier comment from 16 hours ago dude. It will fit, it won’t work. You will have no way of putting on your buffer tube. The nozzle from JG will fit in the SLR box but I don’t know if the tpiece will.
Your are going to spend 80 bucks on downgrading gearbox, and $20-25 on a spring retainer, and get a 5mm bolt that is long enough… then you’ll need to hope the nylon box holds a metal spring retainer that is holding a buffer tube on… and this is if you get the nozzle and tpiece working.
For the extra 50 bucks… please just get a JG box. Sure the SLR is probably the best nylon box, but the JG generally is one of the better cast boxes. I have upgraded heaps… well over 50 to 340-380fps and only seen a couple break… it’s rare but it happens. It is unlikely to happen to you again is what I am saying.
Hi , no worries, I’ve contacted m4a1 , about a JG BOX .
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