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King03sh

King arms m4a1 cylinder:barrel ratio

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Hey guys, as the title says, im looking for assistance with cylinder:barrel ratio on my ka m4a1 firing 1.3J on 0.2 bbs, I have tried the search function and googled more than I care to recount, essentially I am looking to increase the effective range and accuracy of my rifle (i will be fitting a weaker spring to bring me below field limit). Due to previous non-airsoft related injuries I cant play up close and personal very effectively so wish to take a kind of support role, not quite to dmr distance but mid field as it were and retaining full auto function. I have been looking in to longer barrels and came across the hk51 barrel extension which I love the look of, the issue is this would take my inner barrel length up to 595mm which I dont mind, however im finding contradictory info on google. Apparently the type 0 cylinder in my gun is suitable up to 500mm and I know ideal cyl:barrel volume ratio is somewhere between 1.7:1 and 2:1 so I considered a bore up kit as I want to upgrade my internals shortly anyway, however all the bore up kits iv found seem to be rated for around the 400fps mark. As I intend to keep full auto im limited to 1J on the field and wondered if this would be detrimental rather than an upgrade? Obviously I will be checking air sealing and probably installing an r hop as well as the other upgrades. Thanks for the help

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Why do you want a longer barrel? Barrel length has no impact on accuracy or range over about 200mm. Key drivers for accuracy and range are hop, BB quality and weight, and quality of the barrel bore.

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I will be dmr'ing this rifle in the not to distant future, once iv developed my skills a little more, however  our local site will only allow you to run a dmr once they get to know you a little better which I guess is understandable, I dont want to spend to much on upgrading right now just to have to upgrade even more once im allowed to run a dmr, id rather have a good base line now then just install a heavier spring and cut off the full auto at a later date as im on a limited budget

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A longer barrel is about the last thing you want to be installing if you intend to build a DMR. Once you are running heavier BBs, say 0.36g then for maximum efficiency your cylinder ratio wants to be somewhere closer to 2.3:1. Once you have lost a bit of piston stroke to adjust the angle of engagement it means that a full cylinder has about enough volume to support a standard M4 length barrel (368mm).

The accuracy then comes from the combination of your quality, heavy BBs, the ability of the hop to lift them completely consistently, the bore quality and the consistent power output of the rifle.

Your hop needs to have any slop removed by shimming, and then the hop and the barrel assembly need to be stabilised in the upper receiver /outer barrel. R hop will allow the use of heavy BBs and a quality hop rubber will ensure a good air seal, as will making sure the hop is perfectly aligned with the gearbox.

 

For your barrel look to Prometheus, PDI or EdGi, with Prometheus being good and EdGi being best. The PDI and the EdGi have a hop window shape that is less R hop friendly, but it can be done.

 

All of this will still work with running your current full auto set up with 0.28g BBs for enhanced range and accuracy, although check the power as you may well have improved the efficiency to the point where your stock spring has taken you over your current energy level.

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Barrels can help a bit, but your biggest area to look at right now is your hop. Creating a good seal could see your FPS increase slightly, but more importantly a straight/flat hop is relatively easy to do and will usually see some marked improvements over the stock hop unit. Range is really more defined by the consistent backspin that you can get off your hop, and this is especially true in the UK where the limits are relatively low compared to certain continental countries. That's why you see so many TMs being used - until recently they were about the only manufacturer who made guns with hop that were too good to bother messing with.

 

There is the option of the R-hop too like Hangtight says, though these are a little daunting if you've not done one before.

 

Agree with locking down the barrel too. I've found aluminium tape to be great for shimming the gap between inner and outer barrel as - unlike electrical tape - it doesn't compress at all over time. There are also Hunter Seeker Armouries lock-down kits that include some o-rings to push the hop unit back against the nozzle, a wedge to lock the barrel in place and a piece to stop the barrel wobbling inside the hop unit. However, the former (o-rings) are generic and can be bought for a couple of pennies and the latter (to lock the barrel into the hop unit) isn't really a problem if you have a good hop unit like a ProWin one anyway. Really the wedge is the only decent thing there and again the same results can be had from aluminium tape if you take your time.

 

Anyway, I think the main problem for OP here is that he's shooting way too hot, and that's something that can only be remedied really inside the gearbox or with a shorter or wider bore barrel.

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