Testing Firearms Safely
Only a truly foolish person would test fire anything from the shoulder if there any indication that this firearm has a problem that might result in a catastrophic failure (BLOW-UP!). Only after a through inspection that reveals no damage to critical areas of the gun and an exhaustive inspection of the ammunition is it time to test fire. This inspection should pay special attention to the high pressure areas of the gun and be done in sunlight or strong artificial light. The receiver, bolt, chamber area barrel and stock should show no sign of impending failure such as cracks, bulges or stretching. If you stop to consider the normal working pressure and failure pressure in a modern firearm it makes it clear why these precautions are necessary.
Many times the firing history of a particular firearm will alert you to a possible problem. If the customer brings it to you because it blew the head off the case last time it fired then you know something wasn’t right. Maybe it was the wrong ammo, or maybe a reload with insufficient headspace, or maybe it has been rechambered to another cartridge or just bad brass or any of another dozen causes but if it happened last time it is up to you to find out why so it won’t happen again. Listen carefully and ask questions to make sure you gather as much info as possible from the owner.
The ammo is always suspect in any blow-up. Ask if it was reloaded ammo. If it was reloaded then by whom and what was the load? Was the gun fired before the blow-up? Did that round sound normal and was there an impact from it? Has this happened before? Do you have any ammo from the same batch? If the fired case is available for inspection look closely for signs of high pressure such as brass flow in the unsupported areas of the bolt head like the ejector or extractor. Look at any fired brass from the same batch of ammo for signs of high pressure as well. Primers flattened on the edge might indicate that this load was too hot for this particular gun. If the entire head is blown off make sure the ammo was not resized too much leaving excessive headspace when it was chambered. This test can be done using a case micrometer or comparing the reloaded cartridge with a known factory round. If it is a wildcat and no ammo exist for comparison remove the firing mechanism for safety and load a round into the chamber with a shim over the bolt head. If the bolt will close with a .010 inch shim between bolt and cartridge head the gun should not be fired. Carefully pull the bullet and weigh the powder and bullet to make sure it wasn’t a hand loading mistake. Inspect the powder charge and compare with a known sample to make sure powder didn’t get dumped out of the wrong canister. When you are finished inspecting ammo you can move on to the firearm.
Even if you are sure the ammo caused the problem the firearm will still need a detail inspection to make sure it was not damaged by the faulty ammunition. Test headspace in the usual way with the correct headspace gauges. Make sure the chamber has not been damaged so the hardened steel headspace gauges can rest upon the correct surface in the chamber. Looking closely at the outside of the barrel will usually show if there are any bulges. Many times the bulge will be slight but by looking down the barrel when the gun is shouldered the reflections of light along the outside of the barrel will show an abnormality that might otherwise go undetected. After the barrel is cleaned a tightly fitted patch saturated with oil will allow you to feel if there an area of less resistance when you push it through the bore that might indicate an enlarged area.
If there is any doubt about the caliber or the firearm is not marked you may want to do a chamber cast. It can be done with lead but Brownells sells cerrosafe that is 10 times easier to use and safer than lead due to the working temp being less than 200 degrees compared to 600 degrees for the lead. Follow the instructions for the best results but it really isn’t much more than you plug the bore ahead of the throat with steel wool and pour the molten cerrosafe till the chamber is full. Tap it out after it hardens and you have a perfect reproduction of the chamber and throat. It should be a little larger than the ammo if you are comparing the two side by side. Remember the ammo has to go inside the chamber. This is also a good way to look at the throat length and concentricity. The rifling should start evenly around the bullet and the casting will show this. This is incredibly important for accuracy. Save the casting and show the owner if you discover anything wrong like a damaged throat. The cerrosafe is reusable for years.
The receiver has to withstand the pressure of firing and must be inspected with a critical eye for any sign of failure. Be especially careful when looking for cracks or damage in the load bearing area between the barrel threads and the surface that the bolt lugs rest upon. If the bolt is a rear locking type this means virtually the entire receiver. If the firearm is of a case hardened manufacture look closely at these areas for signs that the bolt lugs are setting back into the receiver. This is seen on Mauser bolt actions that have been have the bolts lapped for better contact. The lapping cuts away the hard skin and exposes the low carbon steel to the high pressure of the bolt lugs during firing. It might also be a problem on a receiver that was burned in a fire. The fire annealed the steel and the receiver was later polished and reblued with the new owner thinking he got a great deal.
Having a perfect receiver doesn’t help much if the bolt is damaged. After it is cleaned look it over carefully with a strong light. I found that if you don’t have anything else you can wet the clean area with a high lighter pen and wipe with a dry cloth. Then go in the closet and find that black light from the party at your house in the 70’s. You might want to repeat the test a few times to make sure it isn’t just a tool mark but if any doubt exist consider it bad and destroy it or send it too the factory for replacement. Of course if it is a 1898 Mauser that might be a problem too. All those B-17s didn’t leave much of a factory but luckily they were made in enough numbers to have a lot of parts left over! Never leave a bolt with possible damage in the parts bin. It would be a recipe for disaster!
Only after the ammo and firearm have been completely inspected are you ready to test fire. This is a test firing to expose what went wrong when the gun-ammo combination failed. Test firing a firearm that jams is called function firing and has no expected risk of danger or shrapnel. Our goal is to fire the gun without exposing the tester to harm and then inspect the fired case and firearm for any damage or dimensional changes that indicate a problem.
While you could build a fixture to hold the firearm it can be done safely with nothing more than an old tire and some rope. Place a pad of some type like an old towel under the front and place the butt inside the tire so it will have something firm to take the recoil. Next use a soft rope and tie down the front to the tire. If you are using a chronograph or target it would be positioned it front of the muzzle at this time. After making sure the firing and target area is safe tie a loop in a small cord looping it through the trigger and extend it back to a safe area. Test by dry firing and make sure it snaps. Make sure you have eye and ear protection and everybody is viewing from a safe place. Finally load and place some type of cover over the gun like a piece of old carpet. Move carefully to the safe area without tripping on the cord and shout “fire in the hole” (optional) before pulling the cord.
After firing begin the inspection process anew looking at the fired case and the firearm for any signs of failure. Hopefully you will find all is fine and firearm can then be function fired or accuracy tested.
While this might seem like a lot of trouble it really is not much effort and doesn’t take much time to do safely. Even if you never have one come apart it is still better to be safe.