Tight Versus Wide Bore Barrels

[Adolf Hamster]

so i had a bit of an idea fairy moment after i woke up this morning and i figured it merited discussion.

 

one of the things i've spent a lot of time in my airsofting career doing is chasing accuracy, and one of the debates that comes up for this quest is that of barrels, specifically tight (eg 6.00 or 6.01) versus wide (6.05 or 6.23) bores.

 

now i kind of went with the tight bore side as i figured given a large part of what you spend a lot of time doing in an accuracy build is killing every last possible chance for an air leak, why then re-introduce an air leak to the gun by having a wide barrel?

 

but the thought that struck me this morning was one of tolerances, specifically bb tolerances.

 

lets assume we have a gun that has perfect seal and consistency everywhere and the only room for a leak is between the bb and the walls of the barrel as it travels.

 

going by most bb's branding they claim a nominal 5.95±0.01mm which if we skip all the statistical stuff for a second and take it literally means an individual bb could be 5.94 or 5.96 mm

 

if we again for the sake of simplicity assume a barrel is exactly nominal and perfectly consistent along its bore then the question is this:

 

is the noted "accuracy" of a widebore barrel due to shot-shot consistency supposedly being better because the change in "leak area" (ie the gap between the bb and the barrel that allows air past) is smaller percentage when the barrel is a wider bore?

 

so i ran some numbers just to see:

a 6.01 barrel has a CSA of 28.36866mm², a 6.23 barrel has a CSA of 30.48358mm²

 

our 5.94mm bb has a CSA of 27.71167mm² and our 5.96mm bb has a CSA of 27.8986mm²

 

if you work out the air gaps for these combinations it works out that the difference in area remains the same (ie the smallest bb has 0.186925mm²  more air gap than the larger bb) however if you take this as a % of the barrel (ie air gap/barrel CSA for both bb's) then work out the difference it's interesting.

 

the tight bore has an 0.66% difference between the 2 sizes of bb, whereas the wide bore has 0.61% difference.  (ie 0.05% between them)

 

what's interesting is if you widen the tolerance of the bb's to say ±0.03mm then this gap increases, with the tightbore having 1.98% difference, the wide having 1.84% difference (ie 0.14% between them)

 

so i'm thinking, with all other factors being equal, the widebore's "accuracy" comes from slightly improved shot-shot consistency as the difference in air leak between a small or large bb being fired is a smaller % of the overall leakage. the same would apply not only to different bb sizes but also variations along the barrels length meaning it's going to be slightly more tolerant of imperfections.

 

 

now needless to say this is quite literally academic, whilst i get excellent results running a 6.01 PDI i've not done direct comparison with an equivalently marketed wide-bore. i'm also not sure if i've picked the best numbers to analyse as tbh the differences above are so incredibly small compared to the myriad of other factors that affect accuracy (for example bb weight differences and the fact no system is going to deliver perfectly consistent air pressure each shot). there's also the factor of the whole "air cushion" argument, which i suspect is going to need a hell of a lot more analysis than can be acheived in 10 minutes on excel.

 

i might have a crack at seeing if there's a larger effect from the weight difference of the different sized bb's (assuming constant density and just the volume change) under these same conditions.

 

also inb4 i've finally lost it due to lockdown....

[PopRocket123]

Nerrrrrd! Seriously though that's some interesting maths. You're probably right that it's too small of a difference in an imperfect system to make any real difference but it's interesting none the less

[Adolf Hamster]

9 minutes ago, PopRocket123 said:

Nerrrrrd!

 

have you read my other analysis threads, this is lightweight

 

9 minutes ago, PopRocket123 said:

Seriously though that's some interesting maths. You're probably right that it's too small of a difference in an imperfect system to make any real difference but it's interesting none the less

 

well this morning i didn't know the numbers, but you can see why i thought the idea was valid.

 

always want to learn more, see if there is an actual proof that can sway the argument one way or the other when it comes to things like this where so much in this hobby is either horrendously subjective or "science" only by the loosest definition.

[EDcase]

The only way to really test is to try two barrels in the same gun and then crunch the numbers.

There are several videos on YT where they did this and it still came out uncertain which is better.

Here's one

 

[Adolf Hamster]

1 minute ago, EDcase said:

The only way to really test is to try two barrels in the same gun and then crunch the numbers.

 

yeah, although eliminating the variables (particularly wind) is gonna be the fun bit of that.

 

anyone got a warehouse handy?

[EDcase]

This one is kinda flawed because they changed the hop unit but still interesting

 

[Steveocee]

PDI did testing on their own barrels and claimed that there was an accuracy improvement from their 6.05 over the 6.01 and a barely slight improvement from 6.08 to 6.05.

 

It's all much of a muchness, as long as the finish is good and the thing is straight your accuracy won't waiver far from those 0.04 or so mm.

[Adolf Hamster]

21 hours ago, EDcase said:

This one is kinda flawed because they changed the hop unit but still interesting

 

6 hours ago, Steveocee said:

PDI did testing on their own barrels and claimed that there was an accuracy improvement from their 6.05 over the 6.01 and a barely slight improvement from 6.08 to 6.05.

 

this is a problem with a lot of the "tests" you hear about, there's either a relatively high chance of bias (ie a manufacturer toting it's own products) or some fatal flaw in the testing regime that invalidates any result (especially as we're talking about the higher end where everything else has to be perfect for this to really matter)

 

there's also the question of if PDI proved conclusively that the 6.05 was superior why would they still sell the 6.01 (or other sizes)?

 

6 hours ago, Steveocee said:

It's all much of a muchness, as long as the finish is good and the thing is straight your accuracy won't waiver far from those 0.04 or so mm.

 

this is absolutely true, i'm kind of basing this discussion on the presumption that the fundamentals of quality are already there and equal between the options at the high end.

[Davegolf]

Taking it right back to the OG explains why most standard barrels are 6.08.... BBs used to be 6.00. (Diff = 0.08mm)

 

These days they are 5.95, which leads to the coincidental reason that 6.03 is the new go to. (Diff remains 0.08mm)

 

Im sure the like of Marui did extensive testing, and in my own testing 6.03 or 6.05 (if you have the volume) work best.

 

Likewise what I would consider widebore these days is a STD 6.08.

Run in a sniper setup with massive volume at your disposal they work well, but there are not many SS options.

 

As you say the air gap / cushion is the critical part here and allowing for tolerance deviation, both aiding in preventing the BB from touching the inner surface and affecting its backspin and/or trajectory.

 

This is the main contributing factor in barrel lengths below 350 being optimal - less time in the barrel = less chance of contact.

And that's not even thinking about the user moving slightly whilst firing.

 

Following that explains again why most rifles run 6.03/5 and pistols can run 6.01

[Adolf Hamster]

interesting, didn't think about the motion element but it does make perfect sense.

 

volume wise i'm not too worried, my aeg's get a much looser tolerance for accuracy so i'm pretty much entirely focused on hpa so volume isn't an issue.

[Davegolf]

You building a HPA DMR or somthing then?

[Adolf Hamster]

2 hours ago, Davegolf said:

You building a HPA DMR or somthing then?

 

built

 

basically i've been obsessed with range and accuracy almost since starting this game, and my m4 has evolved over the years to the point where it's the focus of this project (basically so i can justify not being quite so zealous about doing the same as my other gats)

 

given we're at a flat 1j limit it's sort of a "battle dmr", insofar as whilst it's a short barrel and could absolutely be at home in a speedsoft arena and can still use full auto (because why the hell not) i mostly use it in the dmr role.

 

at this point it's not really about practicality so much as seeing what's actually possible.

[Davegolf]

So you are trying to get the most effective range from 328fps?

 

Whats the full spec on it?

 

Diminishing returns 😁

[Adolf Hamster]

1 hour ago, Davegolf said:

So you are trying to get the most effective range from 328fps?

 

Whats the full spec on it?

 

Diminishing returns 😁

 

well, 1j, it's a bit under 328fps when you're lobbing .48's

 

currently it's running a gen3 fusion engine with low flow poppet, MAXX hopup chamber (with tracer which i'm looking forward to having a go with), using the standard MAXX R-nub and maple leaf macaron 40° (i think, might be 50) with the aforementioned PDI 6.01 barrel.

 

rest of the shell is tightened down, homemade carbon free float handguard that has the double whammy of being cool but annoying purists who hate the missing gas block/tube. i do like the balance, got it to the point the centre of gravity is slap bang in the magwell.

 

oh yes and a big can because why not have it silent

 

diminishing returns pretty much sums it up, i passed the barrier of worthwhile investment a loooong time ago

[Davegolf]

What barrel length you on?

 

To clarify you're pulling 1J on 0.48s?

 

PS where the pics!?

 

[Adolf Hamster]

1 minute ago, Davegolf said:

What barrel length you on?

 

To clarify you're pulling 1J on 0.48s?

 

PS where the pics!?

 

 

275 iirc, and yeah i am although normally i run ~.3's because man are .48's expensive.

 

it's not as bad as it sounds, everyone else is stuck at 1j so it's a case of edging out every tiny improvement in practical range.

 

pics would mean digging through the pile as i've been doing a lot of tinkering recently

 

 

[Davegolf]

Oh I wasn't say 1J is bad, just wanting to understand the build.

 

Yeh fuck speedballing 48s!!

 

Thought about Rhop?

[Adolf Hamster]

15 minutes ago, Davegolf said:

Oh I wasn't say 1J is bad, just wanting to understand the build.

 

Yeh fuck speedballing 48s!!

 

Thought about Rhop?

 

tried rhop, but it's an awful lot of ballache and tbh the ml setup gives basically the same results.

[Davegolf]

What is your effective range / target size at 60M?

 

Years ago when all the R hop hype started I gave it a good few goes and - like you by the sounds of it - found it a PITA, consistency crap and a general waste of life.

 

Fast forward and I revisited it with an engineering approach, install is a breeze, results are amazing.

[Adolf Hamster]

4 hours ago, Davegolf said:

What is your effective range / target size at 60M?

 

Years ago when all the R hop hype started I gave it a good few goes and - like you by the sounds of it - found it a PITA, consistency crap and a general waste of life.

 

Fast forward and I revisited it with an engineering approach, install is a breeze, results are amazing.

 

Ive tried a few approaches to rhopping, tbh i still reckon the ml macaron gives the same contact patch.

 

Also here's a pic of the heresy i'm using: