DMR inner barrel diameter

[R4IDER]

So researching this topic it seems to yield mixed results some say for any long range weapon you should be using 6.01 or smaller inner diameter barrels and others say it really doesn't matter and its just about barrel quality and a small group state that 6.08 barrels are the way to go and interestingly PDI actually recommend this size for longer range weapons.

 

No doubt about it barrel quality is the most important aspect of a barrel but I wondered what difference the different inner diameter sizes actually made. When I first thought about this problem my thinking was that you would want a barrel with the smallest size inner diameter because this would mean that the BB will be kept as straight as possible where as something wider would actually allow the BB to move around and the only thing a larger inner diameter would be good for is reducing your FPS.

More research into this I think that it might just be the other way around with a smaller inner diameter the BB will be hitting the sides of the inner barrel which will cause the spin of the BB to be reduced slightly and that resulting in less range and accuracy. Where as the 6.08 gas will create a cushion around the BB which will mean that the BB never touches the sides of the barrel.

That's the theory anyway if this is actually true I don't know but I want to find out. I have two 455MM PDI inner barrels one which is 6.03 and another which is 6.08 and I plan to test both to see which one will offer the best range and accuracy. I am still trying to figure out the best way of testing this as I don't have access to any large areas indoor or out so my only real way of testing would just be to use the gun for the day and watch the scope cam footage back and see what the accuracy was like that way.

I wondered though what others thought about this and which size barrel is thought to offer the highest accuracy?

[gavinkempsell]

I asked a similar question but about bb weights a few weeks ago, I'm sure lots of the replies I got will answer any questions you have.

 

 

[Pseudotectonic]

I subscribe to the school of thought of wider barrel has a better buffer zone for "more dampening of oscillations", and in the real life environment because of dust or other minute imperfections of the BB or vibrations or other factors I think the wider bore is more capable of better consistency, because the same speck of dust might have affected the tight bore more than a wider bore.

 

And I think the inside surface finish (factory finish vs mirror polished) is probably going to have a bigger impact on the aerodynamics (thus consistency/accuracy) than say the nominal diameter.

[Badgerlicious]

The imperfections is probably the only difference, if it is a difference, besides power adjustment and volume. 

 

Though, with an aeg it will be easier to get enough volume in a longer barreled rif with a tighter bore. And you should probably clean your barrel regularly if you're trying to do anything approaching precise for airsoft. 

[Chev Chelios]

This guy uses visual aids and explains stuff very well 

 

[Cr0-Magnon]

Luke/Negative Airsoft built me a G&G GR25 DMR using a Maxx hop unit and 6.15mm widebore Orga barrel. It dropped the power significantly, but the range was seriously epic. This is airsoft though, so there's never going to be one definitive universal answer.

[Lozart]

1 hour ago, Cr0-Magnon said:

This is airsoft though, so there's never going to be one definitive universal answer.

 

 

There is an answer as it is all still governed by the laws of physics. The sheer number of variables however, make it at least impractical if not almost impossible to find the right result for every combination of parts. 

[MrTea]

4 hours ago, Cr0-Magnon said:

Luke/Negative Airsoft built me a G&G GR25 DMR using a Maxx hop unit and 6.15mm widebore Orga barrel. It dropped the power significantly, but the range was seriously epic. This is airsoft though, so there's never going to be one definitive universal answer.

 

What spring is it using and FPS it's producing?

[Cr0-Magnon]

I can't remember the spring but with a tightbore barrel it was pretty spot-on 2.2J (circa 315fps with a 0.48g), the widebore dropped that to something like 1.5J. Luke's mentioned a few times that it's the longest ranged rifle he's ever built (although that may have changed by now). I regret selling it but he's since done me an MBR556 (cue the "not a DMR calibre!" crowd) which is nice and consistent at 1.85J on 0.36g's and much easier to shoulder. That's with the stock hop unit, Maple Leaf 70 rubber, black macaron nub and 455mm ZCl 6.02mm barrel.

[MrTea]

Thanks for the info. I'm just gathering more info as i'm getting ready to order parts for my DMR build. I'm likely to go for 6.08 or 6.05 depending on what I can actually find in stock

[Fatboy40]

47 minutes ago, MrTea said:

I'm just gathering more info as i'm getting ready to order parts for my DMR build.

 

To throw a spanner in your works what's made the biggest difference for me, for range, was not barrel width etc. but how the BB was being hopped.

 

I use 0.40g BB's in my DMR with a Maple Leaf 410mm AEG inner barrel + 70 degree MR bucking + Maxx Model M4A-PRO hop unit using the solid concave nub, and with this I can put just the right amount of spin on the BB and rob it of as little energy as possible. I specifically went with the Maple Leaf barrel as it's designed to take full advantage of the MR bucking (the unique patch and extra internal ring, with the barrel having a cut out for the ring and a slanted window for the patch, so an "out of the box" R-Hop).

 

I've hit the point now where 3x magnification is not good enough for me, the BB can travel way beyond me being able to see clearly at distance, so I need to buy for example an LPVO that can do at least 5x.

[MrTea]

19 minutes ago, Fatboy40 said:

 

To throw a spanner in your works what's made the biggest difference for me, for range, was not barrel width etc. but how the BB was being hopped.

 

I use 0.40g BB's in my DMR with a Maple Leaf 410mm AEG inner barrel + 70 degree MR bucking + Maxx Model M4A-PRO hop unit using the solid concave nub, and with this I can put just the right amount of spin on the BB and rob it of as little energy as possible. I specifically went with the Maple Leaf barrel as it's designed to take full advantage of the MR bucking (the unique patch and extra internal ring, with the barrel having a cut out for the ring and a slanted window for the patch, so an "out of the box" R-Hop).

 

I've hit the point now where 3x magnification is not good enough for me, the BB can travel way beyond me being able to see clearly at distance, so I need to buy for example an LPVO that can do at least 5x.

Can't ever have too much information to look over!

As for hop unit, I'm a bit stuck because i'm DMR-ing a A&K Masada SPR/DMR. The standard hop unit is crap, I know this because I have the carbine length Masada from A&K and it's hilariously crap and the nozzles break a lot. I installed a Begadi rotary hop into it and while it works well, it makes the assembly/disassembly a bloody nightmare as you have to change the way it's designed to be stripped/built. The other option is Wiitech make a CNC version of the stock hop unit including loading ramps, nozzles, hop arms and brass nubs. The hop adjustment is stepped on a sliding scale rather than a rotary hop but i've heard good things. AirsoftPro make a CNC copy of the stock hop unit but they're difficult to find in stock.

I was planning on using Maple Leaf MR 70°. I've seen the Omega nub recommended all the time but might try out these brass ones that Wiitech supply.

Barrel choice is an interesting one as it depends what I can find in stock at the time while being in the length I want based on the discussions i've had with Leo Greer about cylinder/barrel volume ratios. I'm looking about the 380mm area with a range of +-50mm.

[Sewdhull]

My view is that bore size cannot be viewed on its own.

Having said that let me view it on its own.

If your bb it stabilised down the bore it won't matter how wide the bore is, it's still going straight, and being passed by air creating a force keeping the BB off the barrel walls.

 

So you must have enough air passing the BB to keep it off the walls, the hop must impart spin without creating too much bouncing about in the bore, and the barrel must be long enough to allow the BB to stabilise in the bore and smooth enough to not disturb the air flow.

 

Ppl who know thier stuff will have a good hop unit etc in mind, know which barrels are good quality and understand how to get enough air down the barrel.

 

All things being otherwise equal enough air down a wider bore will work.

 

I think so anyway