The Endcap Guide Every DonnyFL Owner Needs Before They Order

Every week our customer service team fields the same handful of questions. Wrong endcap ordered. Moderator does not fit. Cap shows up and the thread pitch isn't right. These are not complicated problems, but they are completely avoidable ones, and the only reason they keep happening is that most of us have never had occasion to dive into the twisting world of threads and thread pitches. A screw is a screw...but there is more to it!

This page is that explanation. If you already own a DonnyFL moderator and need a spare or want to run it on an airgun with different threads, this is your guide. If you are shopping for your first moderator and trying to figure out what to order, this is your guide. Read it once and you will never have to call us about an endcap again.

BEFORE WE BEGIN

In order for you to attach a moderator to your airgun, the barrel or shroud covering the barrel must have a threaded end. Many manufacturers build their airguns with the customer's desire to add an aftermarket moderator in mind, some do not. If your PCP does not have a threaded muzzle, DonnyFL offers adapters for over 100 different models of airguns.

Want That 10-Second Swap? The fastest way to remove a stubborn DonnyFL rear cap is to use the DonnyFL Moderator Endcap Remover Wrench. It keys into the basecap lugs so you can break the cap loose with controlled pressure, then spin the matched endcap on by hand. It is the cleaner choice for maintenance, inspection, and swapping caps between rifles without chewing up the finish.

Get The Wrench

A DonnyFL moderator has three main pieces: the shell, the monocore and the endcap.

The shell is the large cylindrical section that holds everything in. It contains the monocore, the screen and the felt wrap that slow the air coming out of your barrel behind the pellet. The shell is the same on every moderator within a model. All Tatsu shells are the same regardless of caliber.

The monocore is caliber specific. DonnyFL small bore monocores are sized .177/22. .22/25 and .25/30. If your airgun has a shroud or uses an adapter, we recommend you go a half size up to avoid a pellet clipping the inside of the monocore. The monocore determines the caliber size of the moderator and is not meant to be changed, though the screen and felt it's wrapped in can be as needed.

The endcap is the part that screws onto the base of the monocore. This is the only part that physically contacts your airgun. The threads on the endcap determine which airgun the moderator can mount to. That is the entire job of the endcap: to connect the moderator to the  threads of your airgun.

Because different airgun manufacturers use different thread pitches when designing their barrel systems, DonnyFL built the lineup to make the endcap swappable. You do not need three separate Sumos for three separate air rifles that have different threads. You need one Sumo and three endcaps. That is the whole idea. A spare endcap costs $35 and takes about ten seconds to swap in the field. It is one of the smartest parts of the DonnyFL design that most newcomers do not even know exists.

Before anything else, look at the front cap of your moderator. DonnyFL's latest generation of Ronin, Emperor, Sumo, Tatsu, and Shogun moderators has machined grooves on the outside of the front cap. These grooves are part of the locking mechanism that holds the swappable endcap system together.

If your moderator has those grooves, you are running a current-generation unit and the interchangeable endcaps will work with it. If your moderator is an older model without the grooves, the swappable system is not compatible. The endcaps for the current lineup will not seat correctly on the older bodies.

This trips up a lot of people who bought a DonnyFL years ago and are now trying to add caps for a second rifle. If you are not sure which generation you have, check the front cap. Grooves mean you are good. No grooves means reach out to us before ordering.

Thread size is where most wrong orders happen. Every airgun manufacturer uses a specific thread pitch at the muzzle, and they are not the same across brands. An endcap threaded for a. 30 caliber FX Impact will not fit on a Karma Red Panda, and vice versa. There is no adapter workaround here. The thread either matches or it does not.

Threads come in a variety of sizes. When airgun manufacturers choose to thread the end of the barrel or shroud, they have to pick a thread size and pitch. There are both metric and imperial threads to choose from. With a metric thread, the first number, 14 in M14x1.25, is the outer diameter of the threads in millimeters. The second number is the distance from the peak of one thread to the next...in this case, 1.25mm. With imperial threads, like 1/2x20, the 1/2 is the diameter of the threads in inches, so a half inch. The 20 is the number of threads per inch. The 1/2x20 used in the airgun industry is further described as UNF which is a finer cut for better holding power.

DonnyFL makes products exclusively for the airgun market. The industry tends to pick from a few standard sizes not traditionally used by the firearm industry. DonnyFL does not make endcaps for moderators threaded in the pitches commonly used in the firearms industry.

Here is the quick reference for every thread size you will see across the DonnyFL endcap lineup:

If you are not sure which thread your rifle uses, check your owner's manual or look up the specs on the manufacturer's website. You can also contact us directly. We might not know every rifle off the tops of our heads, and some manufacturers change specifications from time to time, but we can figure it out together. This is a one-minute question and it is worth asking before you place the order.

DonnyFL currently offers eight standard endcap products, plus one Great Kami special case worth calling out because it does not follow the same shopping logic as the smaller moderators. They are not interchangeable across moderator families. Ordering a Sumo endcap for a Ronin will not work. Here is a breakdown of every option in the lineup and exactly what it fits.

This section applies specifically to the KOI and Tanto endcap line, but understanding it matters for your overall understanding of how DonnyFL moderators mount to different barrels.

When you shop KOI or Tanto endcaps, you will see two style options listed alongside the thread size: bolt and cone. Most people guess. Most people who guess get it wrong at least once. Here is what each one means...

Bolt Endcap

A bolt endcap is what you need when your barrel is shrouded, or you like the look of a flat, 90° transition between the end of the barrel and the moderator. The encap is flat, like a big, thick bolt. 

A barrel shroud is an outer tube that encloses the barrel along most of its length. The barrel usually ends within the shroud, and may be unattached -- AKA Free Floating, or may be physically attached to the inside of the shroud by way of a spacer, air stripper or adapter screwed into the inside of the shroud. 

Cone Endcap

A cone endcap is designed for rifles with a thin, unshrouded barrel. The cone shape on this endcap is specifically machined to provide a tapered look between the shell of the moderator and the end of the barrel's threads.

One of the most common misunderstandings from newcomers is the assumption that the endcap determines the caliber of the moderator. It does not. The caliber of a DonnyFL moderator is determined by the bore diameter of the monocore and its integrated front cap, specifically the exit hole the projectile passes through. You select the caliber when you buy the moderator.

The endcap has no effect on caliber. It only controls the mounting thread. A Ronin in .30 caliber will always be a .30 caliber moderator regardless of which endcap you put on it. You are not changing the bore by swapping caps.

This matters because some shooters try to solve a caliber mismatch by ordering a different endcap. That will not fix anything. If your moderator bore is too small for your projectile, it can result in a dangerous situation. Reach out before you order anything new and we will get you pointed in the right direction.

The red tube that ships with DonnyFL moderators is not just packaging. It is a purpose-built protective storage and transport tube with a tightly fitted inner diameter. Your moderator fits inside with the standard flush endcap installed, snug and secure.

The ribbed endcap is designed differently. The ribs extend outward from the cap body to give you a better grip for hand removal without tools, which is useful if you swap endcaps frequently in the field. But those ribs add diameter at the rear of the moderator. With a ribbed cap installed, the moderator will not fit back into the red tube.

This catches people by surprise because it is not obvious from the product photo. If you transport your moderator in the tube regularly, know this before you order. If you leave the moderator on the rifle and do not use the tube for daily transport, it is not an issue.