The Gunsmith Is On The Case!
Many times a Gunsmith will have to be smarter than Sherlock Holmes to find the cause of a malfunction. The ability to inspect a fired case and determine what happened when it fired or attempted to fire can be a great help in solving the mystery. Let’s look at how many clues the brass can give up to the savvy Gunsmith.
Reloading problems are always center stage when the customer says “It works fine with factory loads!” Start with getting as much info from the customer as possible. Ask the customer to describe the malfunction in detail. Was it a failure to load, feed, fire, extract or eject? Does it happen on the first, second or third round? Is it always, frequent or sometimes? Did it ever work or has this just started? Have any recent changes or repairs been made to the gun? Do you have any of the ammo you can leave for analysis and testing? Was this a load you found in a reloading manual or other reliable source? Have you reloaded ammunition before?
Look at the ammo for any abnormal signs like bulges, dents or primers that are not fully seated. If it looks normal measure case length and bullet diameter (It is hard to tell the difference between a 270 and a 7mm without a micrometer!). If you have a case micrometer measure the headspace of the ammo and compare with a go headspace gauge or factory ammo. While good ammo is very consistent it has a maximum and minimum size just like your chamber so remember the largest ammo should not be larger than the go gauge.
If the ammo looks correct you can try it in the gun for ease of chambering. Now I hope I don’t have to tell you about safety and loading firearms in the shop! Do this at the test range and use personal protection or remove the firing mechanism like taking the firing pin out of the bolt or just unscrewing the cocking piece on a bolt action. Actually with the firing pin and spring removed most bolt actions allow you to “feel” the action closing a lot better. For an even better feel you might want to also remove the ejector plunger if it has one like a Remington 700.
If you feel resistance when closing the bolt and the case dimensions measure good for headspace then look carefully at the bullet seating depth and make sure the throat is long enough to accommodate the bullet. Color the bullet with layout ink, magic marker or smoke and look for impressions left on the bullet from the rifling. The barrel might need throating if it was just rechambered or it might be solved by seating the bullet deeper or changing to a different style bullet.
If the loaded cartridge chambers without interference and the loading data looks correct then it is time to test fire. If there is any doubt as to the safety of the firearm or the ammunition then you must play it safe and fire the gun with a lanyard. An old tire makes a good rest if you place the butt of the stock on the inside edge and tie the forearm down with a piece of rope to the opposite side. This will secure the gun so it can’t flip off the tire but allows it to recoil against a surface that will give way enough to prevent damage. Placing the tire and gun on the other side of a berm or solid object and using a long cord will keep you safe.
After firing inspect the fired case for any abnormalities like splits, bulges or odd impressions on the case. At full chamber pressure the brass case will push brass into any old pits or tool marks and cause extraction problems. These might show up as a freckled surface on the fired case. It might also show up as damage to the rim of the case when the extractor has to pull harder than normal to free the case from the chamber.
Push a new bullet into the neck of the fired case and check for clearance. If the fired case mouth is tight on the bullet the case neck might be too tight. This might be from a tight neck chamber or brass that has flowed forward into the neck area and thickened the walls of the neck. This could result in pressure variations from shot to shot and even lead to pressures in the danger zone. Measure the diameter of neck on the loaded ammo and compare with fired cases and factory ammo if available. Many custom chambers will require case necks to be reduced in diameter to match chamber dimensions. Experienced benchrest competitors understand these loading techniques but the guy that just bought his rifle at the gun show might need some help!
Chamber pressure above normal limits will usually show on the fired case as well. This can be tricky and should never be used as a reliable indication of a normal load but the signs of high pressure should not be ignored. Primers that have “flattened” or lost their rounded edge, brass that has started to flow into extractor or ejector recesses or just sticky brass in a gun that extracts factory loaded ammo without problems can all indicate higher than normal pressure.
Even if the chamber pressure is within normal limits some guns can still have ammo problems. Probably the M1 Garand is the most famous for having problems with gas port pressure but it can affect other gas operated guns as well. These mechanisms are not powered by the pressure at the chamber by rather the pressure behind the bullet when it passes the gas port. This “port pressure” can be much higher with slower burning powders even when muzzle velocity is lower. This higher port pressure can slam the working parts to the rear damaging operating rod, bolt and even the receiver to the point of failure. Make sure the load is an accepted load for the type of firearm that will be firing the ammo.
Even where the ammo falls on the ground in relation to the gun can give information about the functioning. Brass ejected forward of the gun usually indicates a light load and brass ejected rearward can indicate the action operating with more force than necessary. Even brass ejected with no pattern can indicate something changing from shot to shot.
Whatever the cause of the problem the brass can many times give up some good clues and help you solve the riddle. Go slow, look at everything and above all, “Do Good Work”, it’s the only kind that matters!