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What is roller-delayed blowback?

Click here for a video introduction to the system.


I have a problem with my firearm. What should I do?

Please reference your owner’s manual. If your question is not answered there, e-mail [email protected] with your concern. If you do not have access to your owner’s manual, select “Manuals” from the drop-down list in the Products top menu or click here: https://zenithfirearms.com/manuals/ to download it.


Can I use +P ammunition in my Zenith roller-delayed firearm?

Yes. These are military-grade firearms designed to withstand and operate with +P ammunition. However, we do not recommend the use of +P+ ammunition.


What kind of ammunition should I use in my Zenith roller-delayed firearm?

During the 500-round break-in period for your new firearm, we recommend you use NATO-spec or other high-quality, high-pressure ammunition having a bullet weight of 124 grains. Following the break-in period, while we still recommend you use NATO-spec or other high-quality and high-pressure ammunition, you’ll probably find that most commonly available brands of newly manufactured target ammunition will work well — to include steel-cased offerings, in our experience. Of course, it is of critical importance that you ensure you are using the correct caliber of ammunition for your firearm.

For those interested, here are Zenith’s make-and-model-specific recommendations:
During the 500-round break-in period:

  • Winchester NATO FMJ (124 gr.)

After the break-in period (FMJ):

  • Speer Lawman FMJ (115 gr. – 147 gr.)
  • Winchester White Box FMJ (115 gr. – 147 gr.)
  • Remington UMC FMJ (115 gr. – 124 gr.)
  • Sellier & Bellot FMJ (115 gr. – 124 gr.)
  • Fiocchi FMJ (115 gr. – 124 gr.)
  • CCI Blazer Brass (115 gr. – 124 gr.)

After the break-in period (JHP):

  • Winchester Ranger T-Series (124 gr., standard and +P)
  • Speer Gold Dot (124 gr., standard and +P)
  • Federal HST (124 gr., standard and +P)

Lastly, we recommend you always avoid the following types of ammunition:

  • Federal American Eagle (all)
  • Magtech (all)
  • Maxxtech (all)
  • Remington Golden Saber (147 gr.)
  • Any remanufactured product

What is the recommended break-in period for a Zenith roller-delayed firearm?

We recommend a 500-round break-in period, during which a high-quality firearm lubricant should be frequently and liberally applied to bearing surfaces of the bolt carrier assembly and receiver, and occasionally, sparingly applied to moving parts in the trigger pack assembly.


Are Zenith roller-delayed firearms compatible with parts from H&K?

Our firearms are compatible with most H&K parts. However, please consult your local gunsmith before purchasing or installing any aftermarket parts or accessories.


Can Zenith remove the full-auto bolt carrier block from my privately owned Zenith roller-delayed blowback firearm?

In 2018, Zenith requested from BATFE a corroborating opinion, on the basis of an argument that we set forth, of the lawfulness of our company engaging in the post-import removal of full-auto bolt carrier blocks. In an August 15, 2018 letter to FTISB Chief Michael Curtis, we contended as follows:

If under its U.S. manufacturer license Zenith Firearms were to remove the full-auto carrier blocks from its upper receivers, after importation, and then sell those upper receivers either as stand-alone parts or as components of partially or fully assembled firearms, provided their metal shelves were still in-tact, Zenith Firearms would not have sold any machine gun receivers, just as other U.S. manufacturers that sell roller-delayed blowback firearms without full-auto carrier blocks but with metal shelves are not considered by BATFE to be selling machine gun receivers.

On May 17, 2019, Mr. Curtis sent BATFE’s formal reply, several excerpts from which are reprinted here (bold and underline are BATFE’s emphasis):

Previously, importers requested ATF allow a forward pin-hole in semiautomatic firearms, in order to give their firearms a more authentic appearance. These semiautomatic firearms continued to incorporate a “blocking shelf” in order to prevent the installation of an unmodified machinegun trigger pack. However, this “blocking shelf” was smaller than the original full shelf; therefore, a secondary blocking feature was required to prevent a semiautomatic firearm from being easily converted into a machinegun.

ATF has permitted semiautomatic receivers to include a forward pin-hole only if the receivers contain both:

  • A smaller blocking shelf, still preventing actual attachment of an unmodified machinegun trigger assembly; and
  • An internal blocking feature which prevents the installation of an unmodified machinegun bolt assembly.

Any HK-type receiver that contains a “blocking shelf” that is insufficient to prevent the installation a machinegun trigger assembly, constitutes a machinegun receiver, and will be classified as a “machinegun.”

Zenith semiautomatic firearms also incorporate a blocking bar in the rear of the receiver, which prevents the installation of an unmodified machinegun bolt carrier. This is consistent with other semiautomatic HK-type receivers, where the presence of a forward pin-hole and the smaller “blocking shelf” require a second blocking feature.

In your correspondence, you request permission to remove the secondary blocking feature in order to install unmodified machinegun bolt carriers. FTISB cannot approve this request because the Zenith Firearms without the necessary blocking features is a “machinegun” receiver.

Accordingly, it is clear that in the BATFE’s opinion, Zenith cannot lawfully remove the full-auto bolt carrier blocks from privately owned Zenith roller-delayed blowback firearms. Neither can it do so from its firearms that have yet to be sold but are destined for private ownership. And the reason is because Zenith roller-delayed blowback firearms incorporate in their design a forward pin-hole and “blocking shelf,” the BATFE approval of which is conditional upon Zenith firearms also incorporating in their design a full-auto bolt carrier block. Hence unambiguously, in BATFE’s judgment, removal of the full-auto bolt carrier block from a Zenith firearm would constitute manufacturing a machinegun.


My charging handle is stiff. What can I do to make it easier to operate?

Operation of the charging handle in a roller-delayed firearm compresses the recoil spring, which is often stiff in a new firearm. After tolerating this stiffness through the recommended break-in period, your firearm should become easier to charge.


What are the advantages of a roller-delayed blowback firearm in comparison to a gas-operated firearm?

Several tangible advantages are worth noting: 1) The engineering of the roller-delayed blowback system is very simple and reliable. While gas-operated systems can also be engineered to a high standard of reliability, the roller-delayed blowback system is at least their equal and arguably superior. 2) Roller-delayed firearms tend to run cleaner than direct impingement gas-operated firearms, since there is no recirculation of gas by which debris can be introduced into the chamber area during the cycle of operation. 3) Especially when firing suppressed, the far-forward position of the roller-delayed system’s charging handle will limit or eliminate the blowing of gas directly into the user’s face. 4) Due to the lack of requirement for a buffer tube, roller-delayed blowback firearms can be made more compact in pistol form than their gas-operated counterparts (e.g., a Z-5P, K, or even RS pistol, with their receiver end caps, vs. an AR-15 pistol with its required pistol buffer tube). For further information about the roller-delayed blowback operating system, click here for a video introduction.


How do I submit a warranty claim?

Select “Warranty” under Quick Links at the bottom of our website or click here: https://zenithfirearms.com/warranty-form/ to complete and submit our online warranty return form with as much detailed information as you can provide. Following your submission of this online form, we will contact you within 48-72 hours with further instructions.


Can I use a suppressor with my Zenith roller-delayed firearm?

Provided you own a Zenith roller-delayed firearm capable of receiving a suppressor, you can use a suppressor with your firearm once you have completed the legally required paperwork and are in possession of the resulting approvals (tax stamp, trust, etc.)


My suppressor either will not mount or mounts too tightly on my barrel’s 3-lug device. Is that normal?

Yes, that is sometimes the case due to the coating on many of our 3-lug devices. However, the problem is easily remedied as follows:

If you’re unable to mount your suppressor on your barrel’s 3-lug device, or if you’re able to mount it but the fit is too tight, use steel wool or acetone to remove up to 1 mm of paint from the circumference of the barrel immediately forward of the 3-lugs and up until the start of the thread protector, as indicated in the photo above.

Once you remove this extra paint, while some suppressors will still be very tight when they’re new, after a short break-in period you should have no problem mounting your suppressor.


How do I properly unload my roller-delayed firearm?

Verify that your firearm is on “Safe” and pointed in a safe direction, and that your finger is not touching the trigger. Detach the magazine, and then pull the charging handle rearward and to its upright and locked position (lock the bolt in its open position). A chambered round may eject. Verify that your firearm is now empty by looking through the ejection port. Insert a chamber flag if necessary. Please consult your owner’s manual regarding proper and safe handling of a firearm.


Can I ship my firearm to Zenith Firearms for repair?

Yes. However, not without first receiving an invitation from Zenith’s warranty/technical team to do so. If you would like for Zenith to repair your firearm, please contact [email protected] to explain the problem, and then await our reply with specific instructions. Whether or not a needed repair service is covered under warranty, we do not accept unexpected shipments of firearms.


What kinds of services can the Zenith Custom Shop provide?

For more information see our Zenith Custom Shop section.


Zenith FirearmsFAQs