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I don't know if barrel flex or handguard flex is causing the contact between the gas block and the handguard. I suspect it is the handguard.
Maybe the vibration occurs after the bullet has departed.
But this obviously would contribute nothing to accuracy.
It would be interesting to mill a slot in the handguard so that the gas block cannot make contact, and retest for accuracy. This would be a simple modification to a lower cost component that would eliminate one variable.
If the the rifle is loaded on the bipod or on a sandbag, the handguard ( especially a thinner handguard like this ) will bend upwards and touch the barrel gas block if it is too close. First hand experience, this will destroy accuracy even with a thick handguard. This can be tested by applying pressure to the handguard where the rifle is rested.
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Wasn't there a class on exterior ballistics in the military about this?Originally Posted by greentips
Not really. The key is not to put the gas block too close to a free floating handguard, or do some weird semi-quasi touching free floating. Either it is free floating with space for the handguard to deflect, or do what FN in SCAR16 and PWS in their old MK series did, ie, bolting the gas block in at least 1 axis to a rigid handguard.
One way to get around this is to adjust the location of the bipod to avoid touching that sweet spot. The handuard is more rigid near the receiver, so putting the bipod closer to the receiver may cut down the deflection.
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The BRN-180 has a cutout for adjusting the gas system. I wonder if they designed the gas block to have more height in the vertical, up in the slot, thus preventing the gas block from bottoming out on the handguard when pressure is applied with a bipod or rest.
Would a carbon fiber handguard be less likely to flex and touch the gas block when heat and pressure applied?
Another way to test this is to use a split Mlok bipod that mounts each leg on the side of the rail -> amazon dot ca/Feyachi-M-LOK-Adjustable-Compatible-Hand-Guard/dp/B084Z5KN2C/ref=sr_1_2_sspa?keywords=side+bipod+mlok&qid=1638464283&sr=8-2-spons&psc=1&smid=A211XTRG8Z1K1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExNkZPR1ZBRlRHTjM4J mVuY3J5cHRlZElkPUEwMDc5MjkzUjY2SE1ORFFWSExVJmVuY3J 5cHRlZEFkSWQ9QTA0NjAwMThNTzZSSzIwSzhRTE8md2lkZ2V0T mFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3R Mb2dDbGljaz10cnVl
That’s good in theory except the forces are downward so regardless of where the bipod is mounted the handguard will flex upwards countering gravity. Moving the bipod closer to where the handguard is attached will minimize the amount of upward flex. The best solution is going to be a smaller gas block or larger ID handguard to ensure maximum clearance to the free floated barrel.
All of this theorizing about whether it is the Handguard flexing upwards or the Barrel "whipping" during firing due to barrel harmonics is all well and good, but we pretty much eliminated the Handguard theory by firing the rifle with the Handguard removed. We balanced the rifle on the Barrel Nut to avoid interference with harmonics. The results were effectively the same, meaning that Barrrel Harmonics primarily account for the large group sizes due to "fliers". This is why I believe that the thin Barrel diameter, in conjunction with the violent movement of the Gas Piston, is primarily responsible for the random deflection.
No doubt the effects of the thin Barrel and Gas System are exacerbated by Gas Block contact with the Handguard. I strongly suspect that it is the Barrel whipping into the Handguard, and not vice-versa. I say this because the handguard is very rigid when tightly screwed down to the Barrel Nut. I can easily "bend" the barrel to touch the bottom of the Gas Block against the Handguard, and can do the same with upwards pressure on the Barrel. The barrel is not moving where it is sandwiched by the Upper Receiver and Barrel Nut - it is the barrel actually flexing that is causing the problem. Hence the requirement for a slightly thicker barrel.
The fact that the R18 Barrel is .1" thinner than the original AR180 is indicative of the likelihood that the SAI engineers went too thin between the Chamber and Gas Block where the flex is clearly occurring. I strongly suspect that a thicker barrel is required in conjunction with a reduced-size Gas Block to avoid contact with the Handguard. The combination of improvements should eliminate the "flier" problem, resulting in far better accuracy results more in line with the potential demonstrated by the R18 when fliers are discounted.
Last edited by Bartok5; 12-02-2021 at 03:16 PM.
Mark C
^
Thanks for the clarification!
Most float tube hand guards are made for ARs so they tend to interfere with anything larger than a gas block designed for the DI system.
That barrel, while likely being too thin, could also just suck for accuracy. For the expected price, the manufacturer really should be getting their barrels from a known, quality supplier (IBI?), especially since, as we all know, that is where the rubber meets to road.
I went out on a limb with the other (first) rendition of a re-worked 180b clone some time back and could get 10 rounds into 2". That was at a $1K price tag. This thing for the price should be kicking' it's a$s.
Life Member CCFR and CSSA
Posts made by the pseudonym "Beltfed" may not accurately reflect the beliefs and opinions of the Registered User.
And I suspect that the R18 will kick the competition's arse accuracy-wise once it is fitted with a stiffer Barrel. The R18 is a work in progress, whereas the WK-180 and (now $1600) WS-MCR are production rifles with several years of rolling improvements under their belts. The R18's demonstrated grouping potential (less fliers) varies from 1 to 1.5 MOA, ammo dependant. That ought to give the competition a run for their money.
Note that the WK-180 and WS-MCR are both fitted with stiff, medium-weight barrels. The down-side is that they are both ill-balanced, front-heavy beasts in factory configuration. SAI went with the "Pencil"-profile barrel from the outset in an effort to minimize weight and improve the rifle's handling characteristics and balance. The SAI engineers evidently went a bit too far in terms of the lightweight Barrel profile and wil have to stiffen things up somewhat. Watch and shoot as we see what changes a heavier-weight barrel brings to the ongoing R18 development.
The new Barrel is being manufactured as we speak and will ship from Ontario, so expect 2 weeks before we have new accuracy results. In the interim I will continue to ramp up the round-count with the existing barrel, which has more than enough practical accuracy for banging steel!
Mark C
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