Tips for Rimfire Success:
Troubleshooting Rimfire Problems

Most people shoot a lifetime and never have a problem with their rimfire rifles or handguns. However, some problems may turn up and, fortunately, many can be diagnosed and corrected by the shooter. We hope this guide makes the job easier for you in the unlikely event you have problems. This is for function problems. If you need to troubleshoot accuracy problems, head over to the "Accuracy Testing" article in this web site.

IMPORTANT SAFETY NOTICE!
Before doing any mechanical analysis, cleaning, or repair of a firearm, verify that it and any magazines are unloaded. Often full diagnosis of feeding problems means manually running cartridges through the firearm and watching for hang-ups. You must not do this with live ammo. Use action proving dummies for this work. Brownell's (www.brownells.com; 800-741-0015), a purveyor of excellent gunsmithing supplies, stocks these at a reasonable price. They are available in 22 Short, 22 Long Rifle, and 22 RF Magnum, and are distinctively colored to prevent their being mistaken for live rounds.

Misfires
With modern ammunition, most misfires indicate a problem with the firearm, not the ammo. There are a number of gun-related factors that can lead to misfires.

Spring tension: The first item to consider is the firing pin spring or hammer spring. Some springs can weaken with age. Most spring problems come from alterations or improper replacement of the springs. The spring must develop a certain level of force to reliably ignite a cartridge. Some people will reduce the force of the springs to obtain a lighter trigger pull and, in the process, induce misfires. In rimfire firearms, it is vitally important that ignition springs be left at factory strength. When a misfire occurs, the first question to ask is, "Have I, or someone else, weakened the springs? " If so, the best path is to install a new, factory-approved spring. If a very old firearm that once fired normally begins to misfire, suspect an age-weakened spring.

Another spring issue can often be traced to maintenance. Even though the spring is up to spec, it can produce a weak strike if it is covered in stiff grease. This usually affects coil springs. Springs are often confined in the bolt body or a hole in the frame. In a confined space, grease or congealed oil can reduce the speed of the spring and parts driven by it. If your gun fires normally in warm weather but misfires in cold weather, then grease is the prime suspect. Coil springs and their channels should be thoroughly flushed with a spray solvent such as Outers® Crud Cutter™. Once the spring and its surrounding parts are clean, either leave them dry, or apply a light coat of a non-gumming oil.

Headspace: Simply put, headspace is any free space between a fully-seated cartridge and the bolt face when the bolt is completely closed. Some headspace is required to allow the firearm to work when residue starts to build. However, excessive headspace means the firing pin must reach farther to reach the cartridge and may not maintain enough force over this distance to reliably ignite a cartridge.

Excessive headspace is usually a wear-related problem. After tens of thousands of rounds are fired, the constant impact on the bolt can wear the surfaces that control headspace. In revolvers, the recoil of the cylinder pounds the tube that holds the cylinder in proper position. The result is the same-the firing pin ends up too far from the cartridge rim.

Headspace problems are seldom correctable by the user. It requires attention from the factory or a factory-authorized service station. In bolt-, lever-, and pump-action rifles, proper correction of headspace may require replacing of the bolt or locking mechanisms.

Excessive headspace can cause much more serious problems than misfires. Easily 95 percent of rimfire case head ruptures are the result of too much headspace. If headspace becomes excessive, the thin rim tries to stretch under pressure and can fail, releasing hot gas and metal fragments. Often, rimfire guns suffering from this affliction will produce thickened rims before one lets go. If you see rims that are significantly thicker after firing, STOP! Do not use the firearm until the problem is corrected. Excessive headspace is a MUST FIX NOW condition. If it can't be corrected, retire the gun.

Firing pin issues: With normal, clean springs and proper headspace, a misshaped or mispositioned firing pin strike can cause a misfire. There is a "sweet spot" on a rimfire cartridge head within which the firing pin must strike. A mispositioned firing pin usually requires professional assistance. In some firearms, it may require a new bolt to properly correct.

The shape of a firing pin can affect ignition. One that is too wide spreads its force over a broader area and may cause a misfire. One that is too sharp can cut into the cartridge rim and release gas. Some soft pins can wear or compress with use, making them too short. Some firing pins are user replaceable; other require professional services.

Special Issues with Semi-automatic Firearms
Semi-auto fireams may cease to cycle properly. Most of these problems are caused by a build-up of residue. Usually a good cleaning and degreasing will restore these to proper function. Headspace is rarely an issue as rimfire semi-autos are seldom of locked-breech design. Here are areas to inspect for residue:

• All areas in which the bolt or slide must travel. Residue here can slow the action's cycle time.
• The back of the barrel and the face of the bolt. Build-up here can prevent the bolt from fully closing, and cause problems similar to excessive headspace in locked-breech guns.
• The carrier or lifting mechanism in rifles with tubular magazines.
• The box magazine. Most are built so they can be disassembled for cleaning.

Too much oil anywhere in a semi-auto will slow cycling. Use oils sparingly, don't let oil build up, and use dry lubricants if you plan to use the firearm in very cold weather.

In addition to oils and greases, the residue from cartridge firing can contribute to the build-up. Blind focus groups of expert rimfire shooters identified CCI® rimfire ammunition as the clean-burning champ. We agree. One guy called it "gun care you shoot ".

With semi-autos, the ammunition can also affect functioning. The energy to cycle the action comes from the cartridge, not your muscle power. Rimfire ammunition is loaded to different power levels depending on the intended use.

Light loads, like reduced-power CBs or shotshells, are not designed to cycle semi-auto firearms. They are loaded light for a reason; in the case of shotshells, to minimize spin effects on pellet patterning in rifled barrels. Don't expect them to function your semi-auto.

Match and standard velocity 22 LR ammo is loaded to the velocities desired by target shooters. This is normally transonic, 1120 ft/sec, or subsonic. In some sporting semi-autos, this velocity may not provide the impulse needed to cycle a firearms designed for high-speed (1230+ ft/sec) ammunition. In these cases, you may have to try different types and makes of ammunition. If a firearm is to be used only for target shooting but was built for hi-speed ammo, a "softer" spring can restore function with standard velocity ammo. However, you must replace the original spring when shooting hi-speed ammo or if you sell the firearm.

Many semi-auto firearms, regardless of class, may show finicky ammo preferences when new that go away after the gun is "broken in" through normal use. There are a lot of moving parts that have to react with freshly machined surfaces. Regular firing burnishes these parts and they require less energy to move after break-in. Usually, 100 to 300 rounds will be sufficient for break in. Don't make decisions about ammo until the gun is fully broken in.

Feeding Problems

Even with proper maintenance, correct ammunition, and good springs, a cartridge may occasionally fail to feed. This is interaction between the cartridge and the surfaces that control its path from magazine to chamber. That includes the magazine, carriers or lifters in tubular-magazine models, the bolt face, feed ramp and chamber. The first part to check is the magazine. Are the feed lips damaged or asymmetrical? Is the magazine dirty? If yours is a box magazine, does the top cartridge sit with the bullet nose too high or low to enter the chamber smoothly? You either need to clean the magazine or replace it. It is true that some magazines can be manipulated to improve feeding, but it is a tiresome trial-and-error chore that could make feeding worse.

Some rimfire guns have feed ramps to guide the bullet nose. If the magazine is holding the cartridge properly and the cartridge "stubs" on the ramp, light polishing of the ramp can ease the bullet's travel up the ramp. Don't be too aggressive; if you remove too much, it's hard to put it back. Other rimfire guns have no feed ramp, relying instead on the magazine lips or feed rails to center the cartridge in line with the axis of the chamber.

Gun Quality Issues
Let's face it; there are a number of guns out there that shouldn't be fired with any ammo. It may be due to wear or abuse, but cheaply-made firearms can be dangerous when new. Some cheap foreign guns or small-shop domestic makes may not have been built to accepted industry specs. We have seen new 22 caliber revolvers whose critical barrel-cylinder gaps were 80 percent over the maximum permissible gap allowed by US industry standards! These revolvers area accidents looking for a place to happen.

• Learn what good firearm quality is, and stick with those makes that adhere to quality manufacturing processes.
• Be realistic when considering shooting an old heirloom. It may have family value, but could be worn to the point of being hazardous.
• Use a feeler gauge to measure maximum barrel-cylinder gaps in revolvers. The allowable maximum gap is only 0.012 inch, about the thickness of a business card!
• Never guess about the condition of any firearm. If you're unsure, get professional help.