Pump-action shotgun IZH-78 "MR-155" - one of the most popular smooth-bore guns among hunters and athletes in Russia. Its reliability and simplicity of design do not eliminate the need for regular maintenance. Disassembly of MP-155 required for cleaning after shooting, replacing parts or troubleshooting. However, incorrect actions can lead to mechanical failure or even injury.

In this article you will find detailed instructions for complete and partial disassembly, a list of necessary tools, as well as common mistakeswhich should be avoided. We will figure out how to remove the forend, separate the barrel from the box, remove the bolt group and disassemble the firing mechanism (trigger) without the risk of damaging the parts. For clarity, we present unique disassembly diagrams indicating the “weak” points of the structure where problems most often arise.

If this is your first time taking apart MP-155, we recommend that you first read the official manual from the manufacturer (Izhevsk Mechanical Plant). However, even experienced owners will find useful tips here - for example, how to do without specialized tools or how to check the wear of critical parts.

Preparing for Disassembly: Tools and Safety Precautions

Before you begin disassembling, make sure that the gun discharged. Even if you are sure there are no rounds in the magazine, visually check the chamber and magazine. Incomplete discharge - one of the main causes of accidents when servicing weapons.

To work you will need:

  • 🔧 Flat screwdriver (3-4 mm) - for the screws of the forearm and swivels.
  • 🔧 Phillips screwdriver (PH2) - for some modifications of the MP-155.
  • 🔧 A soft metal punch (copper, aluminum) - so as not to damage the thread.
  • 🔧 Tweezers - for removing small parts (springs, cotter pins).
  • 🔧 Clean rags and a brush - to remove dirt and grease.
  • 🔧 Lubricant for weapons (for example, Ballistol or RP-7).
  • 🔧 Camera or smartphone - to record the stages of disassembly.

Work on a flat surface covered with a soft cloth to avoid scratching the stock and metal parts. If you are disassembling a gun for the first time, take photos of each stage - this will help put it back together without errors. Do not use WD-40 or other harsh solvents as they may damage plastic and rubber parts.

⚠️ Attention: Do not disassemble the gun in direct sunlight or at low temperatures. Plastic parts (such as the handguard) may become brittle and crack under stress.
📊 How often do you clean your gun?
After every shooting
Once a season
Only if problems arise
Never cleaned

Partial disassembly of the MP-155: removal of the forend and barrel

Partial disassembly is required for cleaning the barrel, lubricating the guides or replacing the forend. It does not affect the trigger mechanism and bolt group, so it is less risky for beginners.

Sequence of actions:

  1. Make sure the gun is unloaded and the safety is in the "" position.S» (safe).
  2. Unscrew the two screws securing the forend (located under the barrel, closer to the muzzle). In some modifications, the screws may be hidden by plugs - pry them off with a flat-head screwdriver.
  3. Slide the forend forward and remove it from the barrel. If the forend gets stuck, do not use excessive force - drop a few drops of lubricant into the attachment points and wait 5-10 minutes.
  4. Pull the bolt frame back as far as it will go and secure it in this position (for example, using a stopper or a screwdriver).
  5. Press the barrel lock (located on the right, at the base of the receiver) and pull the barrel forward, separating it from the receiver.

After removing the barrel you will have access to gas system and shutter guide. Clean them from carbon deposits using a brush and a rag soaked in solvent. Pay special attention gas piston — its contamination can lead to delays during recharging.

☑️ Preparation for partial disassembly

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Complete disassembly: bolt group and trigger

Complete disassembly MP-155 required for deep cleaning, replacing springs or repairing the trigger mechanism. This process is more labor-intensive and requires accuracy.

Instructions for removing the bolt group:

  1. Remove the barrel and handguard (as described in the previous section).
  2. Move the bolt carrier to its rearmost position and remove it from the grooves of the receiver.
  3. Disassemble the bolt carrier:
    • Remove mainspring (it is located at the back of the frame).
    • Remove drummer and shutter, pulling them forward.
    • Disconnect extractor (it is secured with a small pin).
  • To disassemble the trigger:
    • Take out trigger (it is fixed with a cotter pin).
    • Remove whispered and its spring.
    • Remove fuse (be careful not to lose small details!).

    When disassembling the trigger don't put in too much effort — many parts are fixed with thin cotter pins that are easy to break. If the cotter pin does not budge, use a drift and light blows with a hammer.

    Detail Typical problems Recommendations
    Mainspring Loss of elasticity, corrosion Replace when weakened (service life ~5000 shots)
    Extractor Worn teeth, broken spring Clean after each shooting, lubricate with graphite lubricant
    Gas piston Soot contamination, corrosion Clean with solvent, check for leaks
    sear Chips, wear of the working surface Replace if delays occur when firing
    ⚠️ Attention: When assembling the trigger, make sure that whispered interacts correctly with trigger. Incorrect assembly can lead to spontaneous shots!
    What to do if you lose your extractor spring?

    If the extractor spring is lost or broken, do not use the gun until it is replaced! Without it, the extractor will not reliably hold the cartridge case, which will lead to delays. A temporary solution may be to install a spring from another model (for example, from IZH-27), but this will reduce reliability. It is better to order an original part from the manufacturer or a specialized store.

    Cleaning and lubrication after disassembly

    After disassembly, all metal parts must be cleaned of carbon deposits, dirt and old grease. Use:

    • 🧹 Solvent (for example, Karcher or Gasoline "Galosha") - to remove carbon deposits from the barrel and gas system.
    • 🧹 Copper brush - for cleaning the bore.
    • 🧹 Toothbrush — for cleaning hard-to-reach places (for example, grooves of the bolt frame).
    • 🧹 Lint-free rags - for final wiping.

    Pay special attention to:

    • 🔹 Bore — clean with a brush with solvent, then wipe with a dry cloth until the moisture is completely removed.
    • 🔹 Gas piston — remove carbon deposits with a wooden stick, do not use metal tools!
    • 🔹 Bolt group - lubricate the guides with a thin layer of grease (Ballistol or Litol-24).
    • 🔹 USM — apply lubricant to the rubbing surfaces of the sear and trigger.

    Do not overdo it with lubricant - its excess will lead to the accumulation of dirt. Enough thin uniform layer. After lubrication, dry fire the bolt group several times to distribute the lubricant.

    💡

    To clean the barrel after shooting shot, use felt pads soaked in solvent. They are better at removing plastic residue from shell casings than regular rags.

    Common mistakes during disassembly and how to avoid them

    Even experienced owners MP-155 Sometimes they make mistakes that lead to breakdowns. Here are the most common:

    1. Excessive force when unscrewing screws - especially true for handguard screws. They often “stick” due to rust, and an attempt to unscrew them by force leads to the thread breaking.
      ⚠️ Solution: Before unscrewing, apply penetrating lubricant to the threads (WD-40 or Liquid Wrench) and wait 15–20 minutes.
    2. Loss of small parts — springs, cotter pins, and clamps are easily lost when disassembling the trigger.
      ⚠️ Solution: Work on a large, light-colored surface (such as a piece of paper) and use a magnetic mat to collect the metal parts.
    3. Incorrect bolt assembly - if the firing pin or extractor is installed crookedly, the gun will misfire.
      ⚠️ Solution: Refer to photographs taken prior to disassembly or the official diagram.
    4. Using inappropriate tools - for example, pliers instead of tweezers for cotter pins.
      ⚠️ Solution: Buy a specialized kit for disassembling weapons or use available tools with caution (for example, a toothpick instead of a drift).

    If after assembly the gun does not work correctly (delays, misfires, tight bolt movement), don't shoot! Disassemble it again and check that all parts are installed correctly.

    💡

    The most common cause of malfunctions after disassembly is incorrect installation of the mainspring. If it is skewed or compressed too much, the gun will misfire or fire spontaneously.

    When is professional repair required?

    Not all faults MP-155 you can fix it yourself. Contact a gunsmith if:

    • 🔧 The trunk has swellings or cracks - this is dangerous for the shooter!
    • 🔧 Bolt carrier jams in the rearmost position.
    • 🔧 When shooting, they appear longitudinal cracks on liners - This is a sign of chamber wear.
    • 🔧 USM works unstable (self-release, delays when cocking the hammer).
    • 🔧 Gas system not sealed (gases burst into the shooter’s face).

    You will also need professional help if you have lost critical parts (for example, mainspring or drummer) or you cannot reassemble the gun after disassembling it. In Moscow and large cities there are certified weapons workshops where you can order diagnostics and repairs.

    Repair cost MP-155 depends on the complexity of the work:

    • 💰 Replacement of the mainspring - from 800 to 1500 rubles.
    • 💰 Cleaning and adjustment of USM - from 1500 to 2500 rubles.
    • 💰 Replacement of the barrel - from 5000 rubles (excluding the cost of the part).

    Video tutorials and additional resources

    For clarity, we recommend watching the video showdown MP-155 from experienced gunsmiths. Here are some verified sources:

    • 🎥 Channel "Weapon Master" on YouTube - detailed analysis with comments.
    • 🎥 Forum "Okhotniki.ru" — topics with photo reports on repairs.
    • 🎥 Official website of the Izhevsk Mechanical Plant - diagrams and manuals.

    If you prefer printed materials, pay attention to the books:

    • 📖 “Repair and maintenance of smooth-bore weapons” (Author: A.B. Zhuk).
    • 📖 “Izhevsk guns: design and operation” (Author: V.N. Rybakov).

    Don't forget that DIY weapon repair requires not only technical skills, but also knowledge of laws. In Russia, any modifications to a gun (for example, shortening the barrel) must be approved by the Russian Guard.

    FAQ: Frequently asked questions about disassembling the MP-155

    Is it possible to disassemble the MP-155 without special tools?

    Yes, but with caution. For example, instead of a punch, you can use dull nail, and instead of tweezers - magnet for removing small parts. However, for the forend screws, it is still better to use a screwdriver of the appropriate size so as not to strip the threads.

    How often should the gun be disassembled for cleaning?

    Depends on intensity of use:

    • 🔹 After each shooting - cleaning the barrel and gas system.
    • 🔹 Once every 3-6 months - partial disassembly (removing the forearm and barrel).
    • 🔹 Once every 1-2 years - complete disassembly with cleaning the trigger.

    If the gun is stored in a damp place, disassemble it more often to prevent corrosion.

    What should I do if, after assembly, the shutter does not lock in the rear position?

    The reason is usually incorrect installation of the shutter stop or wear of its spring. Disassemble the bolt group again and check:

    • 🔹 Is it installed correctly? bolt spring.
    • 🔹 Is there any play in barrel lock.
    • 🔹Aren't they bent? shutter stop.

    If parts are worn out, they need to be replaced.

    Can WD-40 be used to lubricate MP-155?

    WD-40 is only suitable for decarbonization (removing rust and carbon deposits), but not for lubrication. After treating with WD-40, be sure to remove any remaining residue and apply a specialized gun lubricant (for example, Ballistol or FP-10). WD-40 dries out and does not protect metal from corrosion.

    Where to buy spare parts for MP-155?

    Original spare parts can be ordered:

    • 🛒 On the website Izhevsk Mechanical Plant.
    • 🛒 In the stores “Armory Dvor”, “Sniper”, “Hunter”.
    • 🛒 On forums (for example, Guns.ru — used parts are often sold there).

    Please check before purchasing modification of your gun (The MP-155 comes in a variety of barrel lengths and stock types).