Technical Notes

IMM Open® Compensator Maintenance

Updated Feb 8, 2011

Important Warranty Information

The IMM Open® configured with a combination of conventional compensator ports; chambered barrel ports and hybrid barrel holes represents an advance in firearms technology which delivers an exceptionally fast and flat shooting system.

High performance racing machines frequently have specific maintenance and fuel requirements, and the Infinity IMM Open is no exception. These requirements are specific to those versions of the IMM open which contain hybrid holes and/or chambered ports cut directly into the barrel in addition to traditional compensator ports.

IMM Open handguns which utilize hybrid barrel cuts and/or chambers cut directly into the barrel in addition to a traditional compensator obtain superior performance through the use of a tuned high performance gas system.

If you allow excessive deposits to build up in the compensator chamber ports, or use non-recommended ammunition or ammunition components, it is possible that the altered gas dynamics will allow bullets to touch the compensator baffles upon exit. The Infinity Firearms warranty does not cover damage caused to the firearm by such improper maintenance and usage. Any use of heat or chemical means to clean compensator ports also invalidates your warranty.

Compensator Maintenance – Ports

It is important that the compensator ports be kept free of buildup since excessive accumulation deposits in the ports, or use of incorrectly loaded ammunition, can interfere with the gas dynamics of the handgun and result in the bullet hitting the compensator port. Such buildup is inevitable if you are using bullets with an exposed lead base. For that reason, we strongly recommend that bullets with an exposed lead base not be used in any Infinity compensator equipped firearm. This is good advice for any compensated firearm, but is especially important for IMM Open Users.


Build-up should be mechanically removed from the compensator, taking care not to damage the ports or the exterior finish of the gun. Any use of heat or chemical means to clean the compensator can damage the gun and void your warranty.

Compensator with extensive buildup visible through an integral barrel port

Ammunition Selection

The use of even a small quantity of incorrect ammunition in your IMM Open® can cause permanent damage to the gun.


The only powder we recommend for use with our IMM Open® firearms with hybrid holes or ports in the barrels is VV 3N38. There are no known substitutes at this time. Refer to the VihtaVuori website for loading information. If you are using an older Infinity compensated firearm without hybrid holes or integral barrel ports which pre-dates the IMM series, or an IMM Open which does not have any hybrid holes or ports in the barrel, the “3N38 powder only” restriction does not apply.


Bullets for all Infinity compensated firearms should not have an exposed lead base. Some popular brands, in our order of recommendation, are:


  • Sierra
  • Hornady XTP
  • Montana Gold JHP
  • Montana Gold CMJ

Not all of the bullets made by these firms meet the “no exposed lead at the base” requirement. In general, hollow point ammunition will be covered at the base as the jacket material is typically swaged from the rear of such bullets, whereas FMJ and TCFMJ ammunition usually has the jacket swaged on from the front, leaving an exposed lead base.


IMM Configurations

The IMM Open competition firearm comes in a variety of configurations which vary in performance and maintenance requirements. If you prefer a handgun which does not have these additional maintenance requirements, you may wish to consider an IMM Open without the additional hybrid holes (i.e., a conventional compensator configuration).

Highest performance guns are at the top of this list
Barrel/Compensator Configuration Powder
3 Hybrid Barrel Holes + 4 Chambered Barrel Ports +
Compensator (Tribrid Barrel)
3N38 ONLY!
6 Hybrid Holes + Compensator 3N38 ONLY!
3 Chambered Barrel Ports + Compensator 3N38 Preferred*
4 Hybrid Barrel Holes + Compensator 3N38 Preferred*
3 Hybrid Barrel Holes + Compensator 3N38 Preferred*
2 Hybrid Barrel Holes + Compensator 3N38 Preferred*
Compensator Only (no barrel ports) Conventional 38 Super Powders
* – IMM Open Tribrid ribbed barrels with fewer than six ports (in the barrel rib) from the muzzle end may also use a slightly faster burning powder such as IMR 7625 or VV N350 or a slightly slower burning powder such as VV N105 or N110 without risking high case pressures (to make major power factor) that will degrade extraction of the case from the chamber. In all cases the best choice for a compensated type pistol is to use the slowest burning powder possible to make major. The slower burning powder will require more grains of powder to make major and subsequently generate more gas to increase the compensator efficiency.