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Posted by ron
on 1/29/2008, 11:33 pm
68.42.239.235
After reading some of the older posts on this forum, I realize so other people may of had the same problem I had.
Six months ago, when I first got my Gatling firing, about 40% of the rounds didnt fire. I went to alarger spring, .038, and reground the firing pins. I overtightened the head space and broke the small gear on the crank shaft. Nothing worked. I tore it down a dozen times, checking, springs,firing pins, headspace.
I had been using Remington ammo, which is a quality product, ive used it in .22 rifles as a kid.
I switched to CCI ammo and the problem disappeared. Out of every 200 round drum magazine, at least 195 will fire.
On the shells that didnt fire, I examined the pin marks under an optical comparator. The strikes were good, yet the rounds were unfired.
Long story short, I found that my bolts were slightly loose in the carrier block. The powerful extractor springs caused the bolt to lift up when chambering, this made the firing pin strike .035 from the outer edge of the casing. I took 2 spent casings, 1 Remington, the other CCI. I ground them longwise to expose a cross section. Inside of the rim is an explosive charge. On the CCI shell, the groove is deeper toward the OD of the brass than is the Remington, but ony by about .010. Enought to make a difference.
I`m not saying anything negative about Remington ammo, this problem may be specific to my own gun.
The following info is taken off the CCI website.
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.
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