Action Markers

What do you think?
Add your comments in WARPIG's TECH TALK FORUMS.

Action Markers Sentinel
by Bill Mills

The Action Markers Sentinel is a blowback paintgun that’s not just another blowback.  Functionally the Sentinel works on a stacked tube blowback principle, the same as most lower cost semiautomatic paintguns on the market today.  However, at first glance, it more closely resembles a stacked tube electropneumatic paintgun than it’s low cost cousins, and this is largely due to the attention Action Markers has put into their choice of materials and metal finishes.

Tippmann Pneumatics put Fort Wayne, Indiana on the map when it comes to paintball, but they are not the only manufacturer to hail from that town.  PEC produced the Master and Combat in the 1990s, and now in the new Millennium, Action Markers has joined the ranks of manufacturers in Fort Wayne.

Functionally the Sentinel semi is so similar to stacked tube blowback semi autos like the Illustrator, Spyder, Rebel and others that its operation and maintenance will present few hurdles.  A single valve in the lower front section of the Sentinel is struck by a spring driven hammer from the rear.  Linked to the hammer is a bolt in the upper half of the receiver.  When the hammer strikes the valve gas is released up and into the bolt where it is directed forward to propel a ball out of the barrel.  Another, smaller burst of gas comes out of the back of the valve, and forces the hammer back, compressing the mainspring until the Sentinel’s sear catches and holds the hammer until the next shot.

The main functional difference between the Sentinel and other blowbacks is velocity adjustment.  Most blowbacks have a screw adjustment in the rear that changes the back face against which the mainspring rests.  When the adjuster is screwed in, the hammer is under more pressure when cocked, and hits the valve harder, holding it open longer to release more gas, and firing at a higher velocity.  The Sentinel has a reversed approach.  The valve spring in the front of the paintgun is affected by an adjustment screw.  Technologically speaking this is a more difficult approach, as the adjuster screw must be airtight since it lies upstream of the valve.  Unlike the hammer adjustment, the valve spring adjuster is backed out to lessen the spring pressure on the valve and increase velocity.  Performance wise this arrangement has an advantage in that adjusting the valve spring has less effect on the hammer’s ability to recock properly.

The Sentinel’s receiver is billet machined (cut from a solid block) of Aluminum, and the TS models feature a number of decorative cuts.  A teardrop near the front echos the milling in the original basic Sentinel, while a tribal pattern decorates the lower half, large grooves separate the top and lower halves, and curves and angles along the top give this paintgun a more high end appearance.  This, combined with a variety of fade anodizing gives the marker a clean, high end look.

Since its introduction, the Sentinel has undergone a number of design changes, two of which are found at the top front of the receiver.  While the ball detents have seen some minor changes, their basic operation has not changed.  They are a spring backed ball bearing with a cap screw holding them in place.   Early models used a hex head screw in the center of a tapered washer.  The washer holds down the spring which backs the ball bearing.  Later models feature a screw with a wide knurled head which does not need a washer, or tools to be removed for cleaning. 

Action Markers placed one detent on each side of the breech, with the idea that dual nubbins are less likely to induce a spin on the ball causing a hook shot.  The receiver’s vertical feed tube has also undergone a design change that is not so obvious.  Early models featured a tube that was held in place with an industrial metal adhesive.  Newer models have a threaded feed neck, using the same thread dimensions as a WDP Angel.  This means that aftermarket feed necks whether high rise, low rise, or clamping designs are an easy upgrade.

The Sentinel’s bolt is of a central bore design, and machined from a low friction plastic.  O-rings on either side of the gas port help gas efficiency by minimizing air loss around the sides of the bolt.  A captured ball bearing inside the bolt locks the gun’s link pin in place.  A knurled stainless steel pin slides into the top of the bolt, through a slot in the top of the receiver to link the bolt to the hammer.  Pulling the pin and bolt takes all of about two seconds, to provide complete access to the upper receiver and barrel for a pull through squeegee or swab.  Dropping it back into place takes a few seconds longer.  The alignment of the pin to the hammer in the bottom of the receiver can be made by feel.  A flare on the back of the bolt allows the Sentinel to be cocked either by pulling on the rear of the bolt, or the link pin on the top, which ever a player prefers.

While the rear of the receiver has a very short sight rail, its proximity to the link pin limits the number of sights that will be able to fit.  Players considering a red dot sight would do best to check its fit on the Sentinel before purchasing.

The grip frame of the Sentinel TS is also billet machined, giving it a more solid and professional feel than the molded plastic or die cast grip frames found on so many blowback markers.  The trigger group components are held in place by press pins.  The two finger trigger is a straight blade style with a generous width, again billet machined.  A row of lightening holes add to the triggers high end looks.  The trigger is surrounded by a full trigger guard that allows more than ample room for gloved trigger fingers.  Mounted on the grip is a set of Hogue wraparound rubberized grips, a standard in the shooting industry.

The bottom of the Sentinel receiver has a raised strip running its entire length.  This strip locks into a channel in the grip frame ensuring proper lateral alignment, and relieving the grip frame screws from side to side stresses.  Tight tolerances on this fit allow for tight tolerances between the sear and hammer.

While the Sentinel TS is available with a variety of gas configurations, the model reviewed featured a drop forward munted ASA hosed to the gun’s vertical ASA connection.  The drop forward is of a very simple, utilitarian design compared to the looks of the rest of the paintgun.  It is angled well to minimize the chance of liquid CO2 feeding into the Sentinel.  

Unfortunately, the vertical ASA connection is held in place with a central screw that will not act as a pin depressor for most CO2 tanks.  This means that for players who like the compact feel and anti-liquid properties of a vertical CO2 tank, they will need to get a tank with an on/off valve rather than a standard pin valve.  Vertical inline regulators and gas through fore grips will fit just fine.  The pin depressor in the drop forward mounted ASA is a stainless steel insert, sure to give a long operational life.

The stock barrel is of quite nice quality.  It is twelve inches in length and features three rows of straight line porting holes along its last third.  Its internal finish is well honed to provide a smooth surface.  At the rear are WGP Autococker compatible threads meaning that the Sentinel is ready to accept a wide variety of existing aftermarket barrels.

On the field, the Sentinel performed admirably.  The close fit of the trigger group components, combined with the shape of the trigger gives it a surprisingly nice trigger mechanical trigger pull.  Field testing was done primarily with a Centerflag fixed output compressed air system, and the Sentinel had no recocking problems or ball breakage issues when fed with an agitating loader.  Switching the barrel with a Titianium Paintball Longbow barrel brought about an increase in velocity, likely due to increased gas efficiency with a better paint to barrel fit.

Players who want the design and maintenance simplicity of a blowback semiauto, but wanting more than just another mass marketed low end product would do well to consider the Sentinel.  It’s machining quality and overall feel place it at the upper end of the paintguns in its class.

Copyright © 1992-2019 Corinthian Media Services.

WARPIG's webmasters can be reached through our feedback form.  All articles and images are copyrighted and may not be redistributed without the written permission of their original creators and Corinthian Media Services. The WARPIG paintball page is a collection of information and pointers to sources from around the internet and other locations. As such, Corinthian Media Services makes no claims to the trustworthiness or reliability of said information. The information contained in, and referenced by WARPIG, should not be used as a substitute for safety information from trained professionals in the paintball industry.