Gas Block Identification

[MNtadpole]

Hey,

Can someone please educate me on my Daniel Defense's "adjustable" gas block? More specifically, can someone please tell me what this Allen screw does?

The instructions and a DD tech-rep had told me that my DD5V5(Ar-10) features a 2-position gas block, meaning that its adjustable for suppressed and un-supressed. Bellow is a photo of the 2-position Allen key:

Long story short, I'm wanting to tune my DD5V5 rifle, since I'm having cycling issues with some reloads. I was interested in doing so with a true fully adjustable gas block. I was curious to know if there is a slim chance that this unidentified Allen screw might be related adjustability? I haven't really messed with it other than checking if it has indexing points or not. It does not.

It would be very unfortunate if I paid for a fully adjustable gas block when I already have one installed. Thanks in advance!!!

 

[357Max]

I don't own one, but educated guess is that the allen @ the front just captures detent ball & spring.
Looks like 2 position only i.e. full gas/reduced gas. If your going to replace it I'd highly recommend an SLR Sentry adjustable block.

What are the symptoms your seeing now?

 

[MNtadpole]

I don't own one, but educated guess is that the allen @ the front just captures detent ball & spring.
Looks like 2 position only i.e. full gas/reduced gas. If your going to replace it I'd highly recommend an SLR Sentry adjustable block.

What are the symptoms your seeing now?

Hey thanks for the feedback. So I have been trying to work up a load that provides be approximately 2650~ fps velocities for 6.5CM. I know it's on the low side, but my primer pockets only survived 3-4 reloads with hotter powder charges before expanding too much to hold primers.

I most recently did a ladder load test using 140gr SMKs, Hodgdon H4350, WLR primers, Hornady brass, and a COAL of 2.80". Starting on a low side @ 2530 fps and finished at 2631 fps

I have tested Hornady 140gr Match, which cycled fine with a velocity of 2574 fps. I have also tested Hornady 140gr American Gunner, which cycled fine with a velocity 2622.

To answer your question, I'm getting jammed rounds, appearing as a "bolt over base" as the round tries to chamber from the magazine. It's not happening to every round, but occurring at least 25% of the time. I tested whether the BCG would be locked back on a single round fired, and it failed that test. The BCG did not lock back. That is why I feel like my gun was operating near or below under gassing.

I'm thinking that maybe opening up the gas port size and throwing an adjustable gas block on there might give me better results. More importantly, giving me the option to actually tune to my loads.

 

[357Max]

Hey thanks for the feedback. So I have been trying to work up a load that provides be approximately 2650~ fps velocities for 6.5CM. I know it's on the low side, but my primer pockets only survived 3-4 reloads with hotter powder charges before expanding too much to hold primers.

I most recently did a ladder load test using 140gr SMKs, Hodgdon H4350, WLR primers, Hornady brass, and a COAL of 2.80". Starting on a low side @ 2530 fps and finished at 2631 fps

I have tested Hornady 140gr Match, which cycled fine with a velocity of 2574 fps. I have also tested Hornady 140gr American Gunner, which cycled fine with a velocity 2622.

To answer your question, I'm getting jammed rounds, appearing as a "bolt over base" as the round tries to chamber from the magazine. It's not happening to every round, but occurring at least 25% of the time. I tested whether the BCG would be locked back on a single round fired, and it failed that test. The BCG did not lock back. That is why I feel like my gun was operating near or below under gassing.

I'm thinking that maybe opening up the gas port size and throwing an adjustable gas block on there might give me better results. More importantly, giving me the option to actually tune to my loads.

So to confirm with gas block on un-suppressed setting it's not locking back? If so then it sounds like probably under gassed as you suspect.

Have you changed stock buffer tube?
The DD5 apears to be a rifle +1" gas length & the BCG has a tungsten weight in it.
I'd double check your gas ring before opening the gas port. Factory block could also be missaligned a little. Check it if you have access to a bore scope. You could also try removing the the weight from the back of the BCG.

 

[MNtadpole]

Everything on the rifle is stock except the trigger, so nothing was done to the buffer tube. I do have an electronic bore scope, so I'll look to see if something looks off. Are you suggesting to just check the gas rings for proper operation and condition?

 

[357Max]

Everything on the rifle is stock except the trigger, so nothing was done to the buffer tube. I do have an electronic bore scope, so I'll look to see if something looks off. Are you suggesting to just check the gas rings for proper operation and condition?

You should be able to look straight up the gas port & see no gas block impeding the port.

Weigh your buffer on your powder scale and go 1-2 oz lighter if you can't remove the tungsten weight from the BCG. To save some $ you can knock the pin out of the buffer and swap one of the tungsten weights for an aluminum plug. Shaving a little weight from the reciprocating mass has a similar effect to more gas.

Yes check gas rings for tension and to see what kind they are. For example JP uses a single 3 turn spiral ring that they call their "low friction" ring. They aren't gas efficient. I had to change rings on a brand new JP bolt. You want the regular mil spec 3 pc ring set. For a quick check you can just remove the BCG group, extend the bolt out, and stand it up on the bolt face. If it collapses then tension is low & there's probably a lot of blow by.

 

[MNtadpole]

You should be able to look straight up the gas port & see no gas block impeding the port.

Weigh your buffer on your powder scale and go 1-2 oz lighter if you can't remove the tungsten weight from the BCG. To save some $ you can knock the pin out of the buffer and swap one of the tungsten weights for an aluminum plug. Shaving a little weight from the reciprocating mass has a similar effect to more gas.

Yes check gas rings for tension and to see what kind they are. For example JP uses a single 3 turn spiral ring that they call their "low friction" ring. They aren't gas efficient. I had to change rings on a brand new JP bolt. You want the regular mil spec 3 pc ring set. For a quick check you can just remove the BCG group, extend the bolt out, and stand it up on the bolt face. If it collapses then tension is low & there's probably a lot of blow by.

Thanks again!

I think the mysteries get deeper.

So here are some pictures from the gas port. I wasn't able to get a clear view deep inside, but I don't feel like I saw any obvious concerns.

If my memory serves me correct, I believe my stock buffer is like 3.91oz. I'm pretty sure I should be able to remove the tungsten BCG weight. So if I'm understanding you correctly, you're saying to remove the BCG weight, but if I can't to lighten the buffer?

Concerning the gas rings, they appear to be the regular mil-spec 3 split ring type. Here's where things get interesting, the internal BCG components were absolutely filthy! There was a mud-like wet residue caked on the bolt's gas rings area. I was able to wipe my finger across it to remove the gummy substance. Here's a photo:

Most of soft caked on filth was removed by my finger. I think you can get the point here though. After seeing this, I feel like its kind of hard to believe that the gas system is operating under gassed. It was embarrassingly dirty that I'm surprised it cycled at all. What do you think? I think there were no more than 200 rounds, tops, that were fired since the last time I put the BCG in an ultrasonic cleaner.

 

[357Max]

So if I'm understanding you correctly, you're saying to remove the BCG weight, but if I can't to lighten the buffer?

Yes exactlyto the above question.

If you shine a pen light in front of the gas tube in upper while bore scoping you may see alignment better.

That bolt is filthy damn! I'd pump the breaks before swapping buffer weights at this point.

What really jumps out to me is the fact that the ring faces are crusted over. They should be shinny. All the blow by appears to be going forward right past the rings. Bolt tail is clean so not much blow by out the rear. This is just a hunch but I suspect the carrier ring bore might be big & possibly out of spec. I'm basing this on what I just read that DD just started applying DLC to their BCG's. If they didn't adjust bore size from Chrome lined spec to DLC it'd be to big. Try some new rings. If it runs good for <100 rounds and starts acting up again then the bore is off.

If it were mine I think I'd contact Daniel Defense and question this. See if they'll swap out the BCG. I'd also ask if their bolts are interchangeable with Std DPMS. If their CS is crap then I'd consider switching the bolt & or the whole BCG. Rubber city HP bolt/group would be a solid choice.

 

[MNtadpole]

[/QUOTE]

What really jumps out to me is the fact that the ring faces are crusted over. They should be shinny. All the blow by appears to be going forward right past the rings. Bolt tail is clean so not much blow by out the rear.

When you say "ring faces", are talking about the exterior circumference of the rings or the surface area of the rings where they are sandwiched to another ring on the inside? I'm wanting to make sure I can communicate these concerns to DD customer service...lol and not sound like a delusional idiot.

If you're talking about the exterior circumference, I did happen to wipe a huge amount of build up nearest the scalloped section, in front of the gas rings, on the other side of the boat tail of the bolt...if that makes sense. I would wonder if the wiping might have placed some filth on the exterior.

Thanks again!

 

[357Max]

When you say "ring faces", are talking about the exterior circumference of the rings or the surface area of the rings where they are sandwiched to another ring on the inside?

Yes I'm talking about the circumference or the wear/sealing surface that rides on the carrier bore.
That wear face of the ring should always come out shinny if it's attempting to seal.
It makes more sense if you smeared goo on the rings when wiping it. FYI- the rings don't need grease. I use light gun oil or even ATF. After 80-100 rounds mine looks nothing like yours. Just wipe light carbon of with a paper towel & some alcohol.

Still, one would think DD has the port size matched to buffer weight & gas length. I remain suspicious of the carrier bore size & ring tension.
Your Chrono speeds aren't out to lunch so this thing should be running reliably & if anything slightly over gassed when gas block is in the open setting.

 

[MNtadpole]

Yes I'm talking about the circumference or the wear/sealing surface that rides on the carrier bore.
That wear face of the ring should always come out shinny if it's attempting to seal.
It makes more sense if you smeared goo on the rings when wiping it. FYI- the rings don't need grease. I use light gun oil or even ATF. After 80-100 rounds mine looks nothing like yours. Just wipe light carbon of with a paper towel & some alcohol.

Still, one would think DD has the port size matched to buffer weight & gas length. I remain suspicious of the carrier bore size & ring tension.
Your Chrono speeds aren't out to lunch so this thing should be running reliably & if anything slightly over gassed when gas block is in the open setting.

I will try shinning a light down gas tube when I get home tonight.

As far as BCG lubrication goes, I only would lube the bolt lugs, the ejectors, extractor pivot points, and maybe a few drops on those rings. I have never put grease on the BCG bolt or in general. I honestly don't know what the build up is from. Most of the lubrication on the BCG is where the BCG rides in the upper...thats it.

 

[357Max]

As far as BCG lubrication goes, I only would lube the bolt lugs, the ejectors, extractor pivot points, and maybe a few drops on those rings.

Gotcha - Post updates when you here from DD & let us know what the resolution ends up being.
Hopfully you can rule out miss aligned gas block via the light.

 

[MNtadpole]

Gotcha - Post updates when you here from DD & let us know what the resolution ends up being.
Hopfully you can rule out miss aligned gas block via the light.

Well no joy on the gas port check. I shined a light down the gas tube and zero light made it to the bore scope. I didn't check, but I'm betting that there was a bend in the tube, which scattered the light too much.

I didn't yet call DD because I was thinking about running a test first, just out of curiosity.

After taking apart the BCG and seeing how dirty it was, I was thinking that maybe all that crud in there was causing the rifle to short stroke. With that being said, I was thinking to take the rifle back to the range and test fire it dirty again (I haven't cleaned it yet) and then clean it and test fire a final time. I was going to bring a thermos of hot water, simple green, and my ultrasonic cleaner.

In my limited experience, I feel like there are many indicators showing more than enough gas being introduced to the BCG. All that crud on the front side of the gas rings and also there is crud on the exhaust ports. Look:

Kind of a blurry photo, but that main gas weep port on the left side is caked with a similar build up to that of the bolt.

Do you think this is worth an investigation or a waste of time?

 

[357Max]

Do you think this is worth an investigation or a waste of time?

I'd just clean it, check ring tension like I described above (pictured below) & then take it to the range. I'd still follow up with DD. It shouldn't gunk itself into malfunctioning that quickly.
The gas port on the left vents leakage from the small tail portion of the bolt. The 3 on the right are the main vents that open once the bolt is forced open.

Also I'm no reloading expert, but I'd search around on here for gas gun specific recipes. Since they tend to have shorter barrels and a gas system I'd think clean burning & maybe a slightly faster powder might work better.

For reference, I just pulled my AR 10 bolt with about 100 rounds of 168 FGMM on it pictured below. I didn't wipe it at all. These rings are sealing well & you can see why I'm suspicious of your ring seal/carrier bore spec.

Ring tension test. These rings have about 300 total rounds.

 

[MNtadpole]

Okay I went ahead and cleaned it. Here it is fully cleaned out and lubed:

I'm curious to see which direction the brass flies as it is ejected. Apparently, that is a telltale way to determine under gassing, over gassing, or ideal gassing. I loaded up 20 handload and have about 20 factory loads as well.

 

[MNtadpole]

Gotcha - Post updates when you here from DD & let us know what the resolution ends up being.
Hopfully you can rule out miss aligned gas block via the light.

Here's a follow up to the issues mentioned before. So after cleaning the rifle out and bring it to the range noted noted issues occurred.

1. My reloads chrono'd as expected, ejected at approx. 40-45 degrees, but failed to cycle far enough back to lock the bolt.
2. Hornady 140gr Match chrono'd slower than the handloads, but also failed to cycle the bolt far enough back to lock, ejected at 40-45 degrees.

I did take note that the outdoor temp was approx. 28 degrees on the evening I shot.

Daniel Defense customer support said they would look at it since that's obviously not supposed to happen.