Choke tube markings are a series of lines, notches, letters, or numbers that help identify the size of a choke tube. The letters IS are usually written on the outside walls of the choke tube, and it can be confusing if you haven’t seen it before.
IS stands for IMPROVED SKEET. It designates the choke tube constriction size and in this case IS is between a Skeet and Improved Cylinder choke with regards to tightness. It measures 0.7175” in diameter in fixed 12 gauges.
Improved Skeet chokes are used for sporting clays and dove hunting and they help provide open patterns at distances between 20 and 35 yards. If you see “IS” or “ISKT” written on a choke tube, you can be sure it’s tighter than a Cylinder choke.
What does IS mean on a choke tube?
Choke tube letters designate what diameter a choke tube is and IS is included in these designations. IS stands for Improved Skeet Choke and is the third most open choke other than those marked as Cylinder and Skeet.
Some chokes can be labeled as ISKT and this means improved skeet as well. This designation is brand specific and isn’t related to the standard naming scheme. Improved Skeet will be listed as IS, Improved Skeet, or ISKT. IS chokes should not be confused with cylinder or Skeet choke tubes.
What is the diameter of Improved skeet chokes?
Improved Skeet diameters differ based on shotgun brand and choke system. Below is a chart showing the diameter of IS chokes by brand.
| Type | IS Diameter (inch) |
| Beretta/Benelli Mobil | 0.716 |
| Benelli Crio | 0.717 |
| Beretta Optima Plus | 0.722 |
| Benelli Super Sport | 0.717 |
| Beretta Optima | 0.722 |
| Browning Invector | 0.717 |
| Invector Plus | 0.730 |
| Remington | 0.717 |
More Choke Tube Markings
There are over 30 different choke tube markings used for choke identification. Below are the most common markings. Please click the links below to see what each choke tube marking means.
What are IS choke tubes used for?
IS choke tubes pattern wider at the closer ranges. They are ideal for shots on dove and upland game out to 35 yards. They work best with smaller steel and lead shot on fast flying birds that are hard to hit.
Improved Skeet chokes aren’t a popular choke size outside of the sporting clay ranges and usually aren’t included when you purchase a new shotgun. However, the performance of skeet chokes between 20 and 35 yards is worth the investment.
Are IS choke tubes open chokes?
Improved Skeet choke tubes are tighter than Skeet, which is essentially two sizes greater than the bore diameter itself. They are considered an open choke tube and they are designed for close shots. 35 yards is usually the max distance with small lead shot on doves with these chokes.
Improved Skeet chokes excel with lead shot, especially smaller shot in #6 though #8 range. They also can be used with TSS shot which delivers devastating downrange patterns for waterfowl and turkeys.
Bottom Line: IS Means Improved Skeet Choke
IS stands for Improved Skeet. It will be written on the side of the choke tube. Improved Skeet chokes perform in between that of a Skeet Choke and an Improved Cylinder choke.
Improved Skeet chokes are great for dove, quail, and other upland game as the open pattern is more forgiving for fast moving birds. It’s also the preferred choke for competition shooting and sporting clay events.
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Related
- Complete Guide to Identifying Choke Tube Sizes
- Choke Tube Diameter and Constriction Table
- What do the numbers mean on a choke tube?
- Ultimate Guide to Shotgun Pellet Sizes
- What does 3 lines on a choke tube mean?
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