Has anyone had issues with accuracy using a 7.3 barrel with 7.1-7.3 gels? I later tried 7.5 gels and at 15 meters the spread was 10cm, with 7.1-7.3 gels it was 30-40cm.
Im using a grey wolf stainless 7.3mm x 450mm with integrated hopup, 100% cylinder
Tightbores around 7.3mm and smaller are a bit of a thing of the past these daysā¦ too problematic, cause too many jams since the huge variation in gel quality. Okay if you size sort, but most cannot be arsed doing that. 
Accuracy and grouping variation usually comes from different sized gels.
A decently set up (for VE) and stabilized 7.5mm barrel with a functional hopup gives very good accuracy and grouping and is much easier to live with. At 45cm barrel length your VE would be less than ideal for a 100% cylinder, but just something you have to live with if you want a long barrel. 
Iāll agree with @Friendly_Fire on that, tight barrels worked and made sense prior to ultra hard gels.
Not so much now. I would rather a drop in accuracy to get less risk of jams, but generally speaking Iāve never had any loss of accuracy between inner barrel sizes.
Volumes play a big role to accuracy, what length barrel are you using, in what blaster with what cylinder? And how is the seals?
I dont really have an issue with accuracy using 7.5 gels in the 7.3 barrel, shoots dead straight with an average spread of <10cm at 15 meters,
Iām just curious how you can achieve great results using gels under 7.5 with a tight bore as from what Iāve found testing anything under 7.5 the accuracy gets worse.
My setup is a DB m4ss
ā¢100% cylinder
ā¢alloy head with double o-ring nozzle
ā¢green O-rings throughout
ā¢eshooter v2 mosfet
ā¢450mm 7.3mm Greywolf barrel integrated hop up
So doing the calcs, your current setup with a 7.5mm IB would be give you a volumetric efficiency ratio of about 1.37:1 thereabouts.
The figure generally accepted as optimal VE is around 1.77:1
Youāre current setup with the 450mm 7.3 IB would give you a VE of roughly 1.55:1. Not horrendous, but if youāre chasing perfection, not ideal either.
Shorten that 7.3 IB to 400mm and your VE would be about 1.8:1ā¦ pretty much what you want. Of course, that may be something you canāt do due to the blaster design.
I wouldnāt get too hung up on the math thoughā¦ itās an interesting exercise, but itās gels weāre talking about here. Expectations for accuracy and grouping are rarely ever acheived.
Not sure how you are fitting 7.5mm gels down a 7.3mm barrel, but that might be an issue regarding accuracy and performance.
Golden rule of thumb is to control the growth of your gels to be 0.1mm undersized to the barrel you are using.
7.5mm barrel = 7.4mm gels
7.3mm barrel = 7.2mm gels
7.1mm barrel = 7.0mm gels etc.
I know that this is good in theory, but it takes a LOT of time having to put every single batch of gels through a size sorting system.
Donāt overlook stability of the inner barrel in the outer and the outer in the hanguard as a major factor in accuracy.
A beeās dick of movment equates to a shit ton over 20 metres.
I always prioritise in this order if Iām looking for accuracy :
Stability and solid setup of barrels.
Optimal Volumetric Efficiency (if possible).
Realistic FPS. 300 and under is usually fairly accurate, high FPS like 350+ often causes erratic gel flight. I prefer to aim for target FPS of around 280.
Effective hop up, although high FPS often negates any hop up effectiveness.
Gel hardess and consistent size.
Get it all right and you generally end up with an accurate unit. 
As a general guide, 7.5mm barrel ideally max length of 380-400mm.
A 7.3mm barrel seems like a better thing for VE, though it usually only allows an extra 20-30mm over a 400mm 7.5mm barrel for the same volume. The bones length you can theoretically achieve is so insignificant it really isnāt worth the control growing and gel sortingā¦ and jams.
Definitely barrel stabilisation helps, and a good hop up set up well will help with accuracy and distance.
There is a lot of choice of gels, and do not discount the value of trying different gels. Some gels just perform better in some blasters than others.
And always grow your gels with as few variables as possible. Water temperature, time, water hardness all play into how a gel grows and the size it achieves over a given time.
I donāt really grow mine for a set time, I just grow until they average 7.3mm- measuring a handfull with vernier calipers. And that is for a 7.5mm barrel.
The odd 7.4mm, and even 7.5mm will generally be okay through a 7.3mm barrel, but it is not a friendship you want to test. Especially if you have good seals, full stroke, long barrel, and weaker springs.
Letās face it, Iāve bought supposed 7.5 IBs that have measured from 7.4 through to 7.6, so the accuracy of productionās on a par with the randomness of gels sometimes. 
I once picked up a 7.1mm IB from Vipertac out of their bargain bin once for $5ā¦ totally useless. No wonder it was in the discount bin.
Should have spent the money on a Snickersā¦ 
Always amazes me how we expect to get accuracy and consistency from a sphere of starch that deforms with age, with pressure, with temperature and the quality of the growing medium. Then add variables like volumetric efficiency, friction in the barrel quality of the backspin and environmental factors like wind and humidity - not to mention the effectiveness of the operator
Just an exercise in managing variables
And the most consistent, effective and accurate blaster I have was a freebie Steyr that I have no idea how it was built but have immense respect for the builder
If itās the one Iām thinking off, Iād tell youā¦ but then Iād have to kill youā¦
Seriously, that was just tuned VE, optimal FPS, excellent barrel stability and a whole lotta luck.
From everything i have read 7.5 gels in a 7.3 barrel is wrong, but it is the only size gel that gives me crazy good accuracy, Like I mentioned 15-20 meters back and my spread is <10cm
I have no jams for feeding issues either
When I try 7.4 to 7.0 the accuracy is all over the shop