Frequently Asked Questions

Dolos and Prometheus

What handguards are compatible?

Click here for a list of compatible aftermarket handguards. We also have our own handguards that can be seen here.



Can I use the handguard I already have?

If your handguard is not on our list of compatible aftermarket handguards then you will not be able to use it with your Dolos (the list is updated as new compatible handguards are found). Our Prometheus kits come with one of our handguards and is typically less expensive than purchasing a Dolos and handguard separately.



How do I line up the rail on my handguard to my upper receiver?

With our handguards you will want to use the three Allen screws that were included. Thread the handguard all the way down the lock collar, attach your barrel assembly to your upper and loosen the handguard until the rail aligns with your upper. Tighten the handguard to the lock collar by evenly torquing the Allen screws. There should be a gap roughly 5/64" between the two sides when the handguard is sufficiently tight. If you have a torque driver, shoot for 26-30 in-lbs. For YHM and other handguards that use a jam nut, attach your barrel to your upper with the lock collar as tight as you can by hand (loosen the collar and tighten again a few times to be sure it's tight). Thread your jam nut onto your lock collar, then the handguard as far as you can to the point it aligns with your receiver rail. Tighten your jam nut against your handguard slightly, pull the release and loosen your lock collar, then give a good firm twist to tighten the collar. Check the rail alignment, verify that the lock collar is tight against your barrel extension, adjust the rail if necessary. For the anti-rotation screws included with YHM handguards, you will need to cut off the nub at the end of the threads to act as a set screw, or pick up set screws from your local hardware store to use instead (1/4"x28TPI). A piece of rubber or soft plastic can be placed under the set screw to prevent marring of the lock collar threads. Be careful when tightening your jam nut as excessive torque, especially rapid application of torque, on the lock pawl without pulling the release can cause damage to your pawl. Do not drill holes in your lock collar for the anti-rotation screws.



What calibers can I use with the Dolos?

Any caliber that uses a standard AR15 upper receiver can be used with the Dolos. This includes, but is not limited to: 5.56x45mm (.223REM), 5.45x39mm, 300BLK, 6.5 Grendel, 6.8 SPC, 7.62x39, 9mm, 40S&W, 45ACP, 10mm, 450 Bushmaster, 458 SOCOM, 50 Beowulf. For 450 Bushmaster, 458 SOCOM, and 50 Beowulf you will need an upper where the ejection port is enlarged to allow the casings to eject. The Dolos is not compatible with 5.7x28mm (FN 5.7) uppers.



Can I use the Dolos with a billet upper?

The Dolos was designed based on mil-spec tech drawings of upper receivers. Since most billet uppers have external dimensions larger than mil-spec, the tabs on the back of the tri-lug assembly, or the receiver, would need to be modified to fit. It is possible to install the system with the tabs removed.



What gas system lengths work with the Dolos?

Pistol, carbine, mid-length, and rifle length gas tubes are all compatible. You are not limited to a specific gas length; however, direct impingement 45ACP uppers require the gas block to be placed too close to the upper to be compatible with the Dolos.



Can I use a piston gas system with the Dolos?

Short answer: no. We have found that the height of the gas block with many piston systems does not allow enough clearance for a handguard to be installed.



Will my barrel work with the Dolos?

If the diameter of the barrel is 1.000 inches or less, yes.



Can I use the Dolos on a Ruger Precision Rifle?

No. The barrel threads into the upper on this firearm and is not compatible with the Dolos.



What parts do I need to add a second barrel to my Dolos equipped upper?

You will need a Dolos standard lock collar and a handguard. We have barrel kits available which include one of our handguards, or check out the list of compatible handguards from other manufacturers on our support page.



Can I use the Dolos with a blowback pistol caliber?

Yes, you can. Since there isn't a gas block or tube to retain the lock collar, we recommend using our Barrel Stop-Pistol Caliber specifically for blowback builds to provide an index point and limit the collar movement when it's not attached to your upper.



When do I need to replace my lock pawl?

Several factors play into the effective life of a lock pawl. Ultimately, if you begin noticing the lock doesn't hold as well as it used to then it may be time to replace it. To replace the lock pawl, just remove the nut on the bottom of the tri-lug assembly, then the two screws from the plate. The lock pawl will slide out with the spring, and replacement lock pawls can be purchased from our retailers, which include a new spring. Insert the new lock pawl, replace the plate and screws, apply a small drop of medium threadlocker (Loctite 242 or similar), replace the plate and nut. Stop tightening the nut when the slightest resistance is met.



Can I use the Dolos with an A2 front sight post?

Yes, you can. If you are using a carbine length gas system the Prometheus SC or Prometheus MC will fit behind the post. The installation instructions will change just slightly where you will need to install your handguard onto the lock collar prior to reinstalling the gas tube and sight post.



What if I rotate my lock collar all the way and the barrel still isn't tight?

If you've made sure there is no more rotation available by pulling down on the release and attemping to rotate the lock collar further, you may need to add barrel shims between the barrel extension and lock collar.



Kentri Short Buffer

What do the profiles mean?

We have one tube profile that is specific to SB Tactical (Sig Brace) pistol braces (SKU: KTRSB), and one that is tailored to the Shockwave Blade (SKU: KTRSH). The SB profile is 1.203" and tapers up to a larger diameter to allow the soft rubber to slide on more easily and still secure the brace. The Shockwave is 1.240" and has a shoulder that stops the brace roughly an inch from the rear of the receiver.



What is the diameter of the tubes?

The SB profile is 1.203" and tapers up to a larger diameter to secure the brace. The Shockwave is 1.240" and has a shoulder that stops the brace roughly an inch from the receiver.



Is the Kentri compatible with the Law Tactical AR Folding Stock Adapter?

No. Since our buffer system replaces the standard buffer and buffer spring, and omits the buffer retaining pin, it would not function properly with the Law folder.



Can I use the Kentri with the SB Tactical PDW (SBPDW)?

No. The SBPDW uses a proprietary pistol buffer tube to retain their collapsing mechanism so the Kentri cannot be used in its place.



Does the Kentri work with 9mm and other pistol caliber ARs?

Yes, but your bolt carrier will need to be open-ended like a standard M4/M16 bolt carrier (no pinned weight) since our buffer system inserts into the open end of bolt carrier.



Can I use the SBA3 on a Kentri?

No, the SBA3 uses a proprietary buffer tube and the Kentri cannot be used in its place.



Why can't I lock the bolt to the rear right after installing?

The springs are not pre-stressed to increase the duty cycle. Over time the springs will wear in and allow the bolt to be locked to the rear (typically 60 rounds or so).