A choke is to a shotgun, like a nozzle is to a water hose.
The nozzle of a water hose controls the spray dispersion of many droplets of water. A shotgun choke controls the dispersion of the pellets (called BB's or shot) that are fired from each shot shell.
Choke: The choke is located at the muzzle end of the barrel (the end farthest from the shooter when firing.) Depending on the choke system, it is approximately the last 1" to 3" of a bore. The amount of the choke's constriction determines the diameter of the shot dispersion at a given distance.
The most common choke constrictions are "Full", "Modified" and "Improved Cylinder."
A Full (tight) constriction controls the fired pellets to a narrow column for the longer distance. The Modified is a medium, all-purpose setting, between Full and Improved Cylinder. The Improved Cylinder is a more open constriction that allows the pellets to spread sooner, and in a wider circle.
Fixed Choke: The term "fixed choke barrel" means the choke constriction is pre-machined into the barrel at the factory; no choke adjustments can be made. Before interchangeable choke tube systems became popular, most barrels were fixed choke types. Fixed choke barrels are still offered on guns made for specific shooting purposes; their barrels will be stamped with their specific choke constriction.
Interchangeable Choke Tubes: The majority of today's shotguns feature an interchangeable choke tube system. Instead of fixing the choke in the barrel, each choke tube is internally machined to a specific choke dimension. This convenience allows the shooter to perhaps use the "full" tube for waterfowl in the morning, and simply change the choke tube (instead of the gun or barrel) for different game that afternoon. The terms "Accu-Choke™" or "Accu-Mag™" are stamped onto Mossberg® barrels to identify the choke tube system of each barrel.
The short Accu-Choke™ tubes in the foreground represent the style used in standard Mossberg® 12 and 20-gauge barrels. The larger Accu-Mag™ tubes are used in 12-gauge Mossberg® models with over-bored Ulti-Mag® barrels. All tubes displayed here are flush-fitting (fits flush with the end of the muzzle when properly installed,) except for the longest (turkey) tube shown. It is described as an "extended" tube, because the wider portion of it extends beyond the muzzle when properly installed.
The amount of the constriction and the length of the constriction are the two important factors for maintaining consistent performance.
Accu-Choke™ Tube Installed in the Muzzle of the Barrel: To remove the choke tube, loosen it with the choke wrench, turning it counterclockwise. When loose, remove completely with fingers. To install the tube, carefully thread it clockwise by hand, then tighten the tube with a choke wrench until it is snug.
Choke tube tightness should be checked periodically and tubes should be removed for cleaning on a regular basis. All removable choke tubes have very fine machined threading and should be handled carefully. Never fire the gun without a choke tube installed. Before attempting to adjust or change any choke tube, be sure to follow all safety warnings found in the firearm's owner's manual.
There are many BB or shot sizes. Depending on the load, they can range from very small #9's, having around 1,000 pellets in each shell, which are popular for target practice, to large #2's that are often used for waterfowl, with less than 100 pellets per shell. There are even larger loads, such as buckshot, that may only have nine large pellets, or a "slug," which is a shell containing a single large projectile. If fired at a sheet of paper, the shot load will produce as many holes as there were BB's. The round-shaped area of holes that the BB's produce is called a pattern.
Understanding and controlling the shot pattern is important to obtain good, solid hits. For example: A skeet shooter's clay targets are flown relatively close, and cross quickly in front of the shooter. In this case, an open choke, producing a wide pattern, is preferred. While at the trap range, the targets are flying straight-away from the shooter at a greater distance. For this type of shooting, a tighter choke constriction and pattern is preferred to keep the shot closer together for a longer time. Skeet and trap shooting are excellent practice exercises, replicating many of the upland bird and waterfowl flight patterns.
Choosing the right choke tube is like choosing the right golf club. Each tube is stamped with the type of pattern it will produce, but like the numbers on a golf club, choke tube designations are only a guide. A choke tube stamped "Full" will produce a pattern tighter than a "Modified" tube; and the "Mod" produces a pattern tighter than an "IC" or "Improved Cylinder." However, the actual pattern size will vary depending on distance, shot load, size of shot, ammo brand, standard load or magnum. As in any sport, practice and experience are your best instructors.
ACCU-CHOKE™ TUBES: The Accu-Choke™ tube system is used on Mossberg® 500®, 505™, 535™, 930™ and Maverick® 88™ shotgun barrels. These tubes handle lead, steel and other non-toxic loads and are stamped with one of three pattern designations: Full, Modified, Improved Cylinder. Special Accu-Choke™ tubes include XXFull Turkey and Skeet.
Accu-Choke™ and Accu-Mag™ choke tubes are not interchangeable.
ACCU-MAG™ CHOKE TUBES: Mossberg® 12-gauge 835®, 935™ and Maverick® 91™ model Accu-Mag™ choke tubes are substantially larger in overall length and diameter than the 12-gauge Accu-Choke™ tubes. Although both models are 12- gauge, 935™ and 835® 12-gauge barrels are overbored to 10-gauge dimensions.
Each choke tube is stamped with a pattern designation, and each will handle lead, steel and other non-toxic loads except for the specialized lead only "Extra-Full Turkey Tubes." Lead, steel and other shot materials do not compress equally and will not react the same when forced through the constricted "choke" area of a barrel. Therefore, expect patterns to differ between shot type, size and even ammunition brand. A shotgun should be pattern tested to know which ammo and choke tube combination performs best in each particular barrel.
Please remember: No one can call a shot back - shotgun pellets can travel 500 yards.
Pattern test in a safe location. Hang up a large piece of paper (approx. 40" x 40") with an "X" marked in the middle to aim at. Pace off the approximate distance you expect your target will be from you (35 yards is a good starting point.) Use the same ammo you expect to hunt with and fire one round. On the target, write your distance, brand, shot size of ammo and other pertinent information - such as wind/weather conditions, because you won't remember later. Using the same ammo, hang a new target paper, install a different choke tube and fire another round, again writing all of your notes on the paper target. In addition to your pattern results, you might also notice you're shooting a little to the left, right, up or down; adjust your sights or point of aim to compensate. Move forward or back by 10 yards and repeat your tests. Performing this type of test allows you to see, compare and understand the performance of your gun. Perform pattern tests with different ammo and choke tubes to completely fine-tune your shotgun.
The only way to really know what kind of a pattern you're getting from each tube and ammo is to pattern test.
CHOKE & LOAD USAGE GUIDEGAMEGAUGE/BOREDISTANCECHOKESHOT SIZEquailwoodcock12 & 2012 & 2015-30 yds.30+ ydssk,ic,modic/mod#7-1/2,8,9#7-1/2,8dove12 & 201220-30 yds30+ ydsic/modic/mod#7-1/2,8,9#7-1/2,8pheasantgrouse12 & 201220-30 yds30+ ydsic/modmod/full#5,6,7-1/2turkey12 & 201215-30 yds30+ ydsx-full(turkey)#4,5,6rabbit12, 20, 41012 & 2015-30 yds30+ ydsic/modic/mod#4,5,6,7-1/2#4,5,6squirrel12, 20,41012 & 2015-30 yds30+ ydsic/mod/fullic/mod/full#4,5,6,7-1/2#4,5,6large duckmallard,pintail12 & 201215-30yds30+ ydsic/modic/mod/full#1,2,3,4#bb,1,2,3small duckteal,bufflehead12 & 2012 & 2020-30 yds30+ ydsic/modmod/full#3,4,6#3,4large geesegiant canada121220-30 yds30+ ydsic/modmod/full/xfull#t,bbb,bb,1#t,bbb,bbmed. geesesnow,les.can.121220-3-yds30+ ydsic/modmod/full#bbb,bb,1#bbb,bb
Important Notes: Choke constrictions - SK: Skeet; IC: Improved Cylinder; Mod: Modified; XFull: Extra Full. The above chart is only a guide. Choke and shot size selection will vary depending on ammunition, target distance and hunting conditions.
For additional details on the many types of shotgun ammunition and recommended uses, please visit one of the ammunition manufacturer's websites or request one of their catalogs.