Adams/Voodoo barrels

[JonF]

So i just put together a rifle with the 16.5" barrel (free floated), a voodoo LTW bolt, SLR gas block, JP extra power polished carbine spring and Taccom delrin buffer. First test outing at the range, i'm having every problem you can possibly have. Cycling, lock back and accuracy are all terrible.

My first goal was to get the gas system dialed in. With only PMC 55gr 223 and some PRVI m193, i could not get the thing to stop short stroking. Opened the gas block all the way up and it would eject empties, but not feed. I tried putting in a standard carbine buffer but still chronic short cycling.

I had a Wolff reduced power spring on hand so i put that in there with the Taccom buffer and now it will actually cycle and feed ammo on setting 11 from closed. The wolff is something like 10% reduced and the JP is like 7% increased so thats about 17% spring rate reduction if that adds up like that. I guess that was enough resistance removed to let the bolt slide back far enough to strip new rounds from the mag. Still though, i cannot get it to lock back but i think its for a different reason. The Wolff spring is a bit longer, specifically in full coil bind, so basically with the thick spring seats of the TACCOM buffer and the Wolff spring all stacked up and bottomed out in the buffer tube, there is virtually no room to let the bolt catch rise up. In contrast, when i put the JP enhanced spring back in, i can hand cycle it and there is physically plenty of room for lockback (though it doesn't happen) so the Wolff spring is definitely longer.

I double chekced the gas block alignment and it seemed fine, i guess this system is on the ragged edge of low rifle length gas pressure and shorter dwell but the lighter reiprocating mass should be helpful, no?

So "Fine" i say and accept the fact that i may not be able to get lock back as long as cycling is reliable. Now i want to zero my scope and shoot some groups.

I get the scope (vortex PST 1-4) on paper and shoot a few groups of the PMC, M193 and some handloads (69gr SMK over 25gr Varget) at 50 and 100 yards from the bench on a bipod and rear sandbag. None of this grouped well at any range. The PMC 223 shoots a bit softer than the rest but groups pretty big. M193 hits harder but no improvement. 69SMK load feels like M193 but is a bit tighter in grouping. All of them are stringing wildly and there is some semblance of a shot group center, but the barrel is acting so hinky its not reliable. In general, the groups were about 3-4 MOA with so many fliers in various directions, it just cant be me. I have shot sub moa groups with good rifles in heavier calibers before, i can't imagine i'm pulling shots that bad. No matter what i do, shoot it repeately hot, let it cool for several minutes between shots, its still all over the place. Wish i would have saved some targets but they were such crap, i pitched them.

Looking at the barrel and how thin it is, i also noticed that it will physically deflect with just mere fingertip pressure up, down, left, right, ect. I checked my BCM 16" .625 LTW barrel and it does NOT budge at all. The Voodoo barrel will deflect up to 3/16" in any direction just lightly pushing on the muzzle. I know its thin, but is that right? I double checked the barrel nut at home and its at least 30+ ft/lbs per my torque wrench. If the barrel can tweak that easily, then it could certainly be deflecting substantially from heat soak and other factors. Anyone else notice the overly flimsy nature of this barrel?

[waktasz]

I am running a wolf reduced power spring too...and I don't think my barrel flexes that much. Mine has been 100% once I got the gas tuned to my liking. Maybe you got a lemon. I'd send it back and try again. I've had really good luck with mine. (I'm not affiliated with them in any way, fyi)

[Hunter660]

My barrel flexes, but maybe not as much as you suggest yours does.

I have only been to the range once with mine and had the same problems with not locking back. I also have the Voodoo bolt. I have discovered that the bolt is very tight in the carrier. I have another BCG I am going to try later today. My fingers are crossed.

[Shooter115]

Mine functions just fine with a full weight carrier, carbine buffer and standard spring after getting the gas block adjusted correctly. At first I was having all kinds of problems with short stroking with the gas wide open. Pulled the gas block and going by the carbon marking on the barrel determined the gas block was too far rearward. This was the first time in quite a while I'd seen a barrel/GB combo that I wasn't able to just run the GB all the way back to the step in the barrel and have it run just fine. Moved the GB out just a touch towards the muzzle and it ran like a top. As far as accuracy goes mine seams to shoot right about MOA with a 1-4x optic and 55gr FMJ handloads. I'm in the process of doing a complete write up on the build, but am still testing and tweaking on it. I did run it through one local match and didn't have a single issue.

[JonF]

I am running a wolf reduced power spring too...and I don't think my barrel flexes that much. Mine has been 100% once I got the gas tuned to my liking. Maybe you got a lemon. I'd send it back and try again. I've had really good luck with mine. (I'm not affiliated with them in any way, fyi)

Matt,

after you got yours all set, do you get lock back with the Wolff spring and taccom buffer (And if so, what ammo are you using)? What setting did you end up on the SLR block?

I'm running mine at 11 clicks from closed and it will cycle my PMC, PRVI and handloads, but none lock back no matter how much i turn up the gas. But again, i think its a spring/buffer stack height issue for me.

[Steve RA]

Try a slightly shorter buffer, or, shorten the spring slightly.

[JonF]

i may try to take a little material off the delrin buffer. Also see if i can screw the buffer tube out one rotation and still retain the plunger. But will clipping a coil or two be detrimental to the spring weight? Only one way to find out i guess.

[gdcguns]

If there is plenty of room for lockback with the JP spring and it's still not locking back even with the gas wide open I would focus on the gas block and tube first. Something is definitely not right with your gas. Port could be too small or not aligned properly.

As far as the accuracy, I would take a good hard look at my mount and optic. Make sure it's torqued down properly and not moving?

Just saying this is where I would start with trying to diagnose the issues.

[JonF]

All good suggestions. Gonna re-align the gas block tonight with a home made version of this.

http://hbindustries.net/products/hbi-22-cal-pins/

Should tell me if mounting straight to the shoulder is off axis or not.

The Optic is torqued down in an AD mount to specs. Double checked that and ran it on another carbine with much better success so thats good.

[waktasz]

I am running a wolf reduced power spring too...and I don't think my barrel flexes that much. Mine has been 100% once I got the gas tuned to my liking. Maybe you got a lemon. I'd send it back and try again. I've had really good luck with mine. (I'm not affiliated with them in any way, fyi)

Matt,

after you got yours all set, do you get lock back with the Wolff spring and taccom buffer (And if so, what ammo are you using)? What setting did you end up on the SLR block?

I'm running mine at 11 clicks from closed and it will cycle my PMC, PRVI and handloads, but none lock back no matter how much i turn up the gas. But again, i think its a spring/buffer stack height issue for me.

I'm using a syrac gas block. With the stock spring and the gas block wide open it would fail to lock back about 10% of the time. With the reduced power wolf spring I have the gas turned down quite a bit from wide open and it always locks back now. Taccom ULW buffer, JP LMOS bolt carrier and the Wolff reduced spring. Shooting PMC or Freedom Munitons 55gr reman that chronoed at about 2860

[JonF]

Well, I took the whole thing apart to see what was going on here.

First i looked at the gas block situation and it seems that for 100% alignment of the SLR block to the VDI barrel, it cannot be flush against the shoulder. Spaced off .010-.020 is probably the necessary amount just eyeballing the gap once aligned.

Also discovered that there is some slop in the tolerance between the receiver extension and the Balios Lite upper receiver im using. Receiver ext mic's about .999 and the receiver bore about .101. When inserted (But not fastened), thats .004 of play and there is definitely perceptable "wobble" in the fit. Checked a BCM M4 upper and the fit is TIGHT, no wobble. Not sure if this is contributing to the accuracy issue, but may need to shim or bed that for optimal interface. Though for the cost of this receiver, i'm none to pleased at the loose tolerance there.

Lastly, I measured the coil bind length of the WOLFF reduced power spring compared to a JP carbine spring and found that it was and it was nearly was an A2 RIFLE length spring. :facepalm: Coil bind length was about 1 inch longer than the JP so thats definitely not gonna work. I bought this off Brownell's and thier description was vague, only mentioning .223 cal ar-15 application and assuming that meant carbine length. PArt number for that was 16505 and confirmed on Wolff site that was A2 length. P/N 16502 is for CARBINE length and not available from Brownells. Guess i'll have to get a proper spec spring to try out. Perhaps that will solve my lockback dilemma.

[waktasz]

You dummy.

The spring I have is 16505. I have a rifle length buffer tube. Next time buy direct from Wolff. They are in easern PA.

[gdcguns]

Sounds like you are definitely on the right track to getting this thing solved. Once you get that gas block alignment set up you should be able to get it to lock back with the JP spring. The proper wolff spring will let it lock back with even less gas. Sounds like you and Shooter115 have the same issue with the gas block spacing. That's good info to have for anyone else who is planning to use one of these barrels.

I also have to wonder if the slop you mentioned is creating extra friction as the carrier is cycling, slowing it down. It seems minimal, but when you're talking about fine tuning with this kind of system, maybe it could have an effect. I don't know if it is enough to matter, just a thought.

[Hunter660]

I bought a set of the plastic pins like listed above. My gas block seems to work all the way against the flange. I have not yet made it to the rage though. Will head that way in an hour.

[gdcguns]

Which gas block are you using, Hunter? Do all gas blocks have the same size hole for the gas port? Maybe some are larger than others, so on those you would be able to run the block all the way down to the shoulder and still cover the whole port?

[Hunter660]

Which gas block are you using, Hunter? Do all gas blocks have the same size hole for the gas port? Maybe some are larger than others, so on those you would be able to run the block all the way down to the shoulder and still cover the whole port?

SLR Rifleworks

[Steve RA]

On the original AR there was a piece of sheet metal between the gas block and the shoulder. Not on new guns but some barrels are still made to the original specs for distance between the back of the gas block and barrel shoulder. Other new barrels have deleted that amount of spacing. Easy way to tell is to measure from shoulder to center of gas port, then measure the gas block from the back to center of hole. That way you can tell whether or not to space the block off the shoulder by the amount needed to center the hole in the gas block over the gas port. Or use a spacer of the correct thickness.

[gdcguns]

On the original AR there was a piece of sheet metal between the gas block and the shoulder. Not on new guns but some barrels are still made to the original specs for distance between the back of the gas block and barrel shoulder. Other new barrels have deleted that amount of spacing. Easy way to tell is to measure from shoulder to center of gas port, then measure the gas block from the back to center of hole. That way you can tell whether or not to space the block off the shoulder by the amount needed to center the hole in the gas block over the gas port. Or use a spacer of the correct thickness.

That's some good info. Thanks.

[gdcguns]

Which gas block are you using, Hunter? Do all gas blocks have the same size hole for the gas port? Maybe some are larger than others, so on those you would be able to run the block all the way down to the shoulder and still cover the whole port?

SLR Rifleworks

So you and Jon have the same gas block. That eliminates my theory I guess. Please let us know how your trip to the range goes.

[JonF]

I went and mic'd the gas port on both the VDI barrel and the SLR .750 gas block and there is a bit of a difference that would account for some fudge factor. The barrel port is .098" and the block is about .125 (hard to get the calipers in there so I used a machinist drill index). If the gas block port is completely centered over the barrel gas port with it standing off the shoulder .010 - .020., that .025" of wiggle room port size differential means you're still lined up over the hole even if you're off kilter. Basically, whether flush or backed off a few thou, you're GTG and not blocking the port.

That said, when mine was mounted flush, I was still able to get it to cycle with a reduced power spring and the block at setting 11 (I think ~16 is max open) so I still had gas to spare. I just couldn't lock back because it was too long a spring.

[MickB]

I have the VDI barrel and SLR SA7 adjustable gas block.

The gas block is installed 0.020" away from the barrel shoulder to align the gas port.

With JP LMOS bolt carrier group, TACCOM ULW buffer assembly and TTI reduced power carbine buffer spring, the gas block is locking open on an empty mag at a setting of 5 from fully closed.

Mick

Edited August 3, 2014 by MickB

[Bam Bam]

Has anyone shot these for groups yet? Just curious how well they shoot with 69gr and above ammo.

My 16" Ultra Light Barrel shoots .5in groups with Black Hills 69gr SMK.

bgc

[JonF]

I had tried shooting for groups with some PMC 223, PRVI M192 and 69gr SMK handloads that print .5 moa from a rock river varmint. None of these grouped under 2-3 moa but i suspect i had an issue with barrel to receiver fitment. I have shimmed the barrel extension with a 360* .001" shim but haven't had a chance to test it out yet. I hope that helps since others seem to get better results. I think the biggest issue with this barrel will be heat stringing due to its thin profile.

[Hunter660]

I am getting to the point where I'm thinking of getting another barrel. I'm not convinced this 16.5" barrel can work.

[waktasz]

Sorry for you luck. Mine has been 100%