To Gauge or not to Gauge? Liability is the question.
We talk to hundreds of gunsmith’s each month. It surprises me how often these “professionals” decide not to use a headspace gauge when they are available to them. They say, “No, that’s OK I will just use brass.”
The reason that we are still using brass cases in firearms after more than a century is that so far brass provides a cheap and reliable mechanism for safely sealing the breach during the firing of the round. Brass is surprisingly forgiving and acts a bit like an inflatable gasket when pressures rise. The properties of brass have saved many an experimenter who did not understand the problems of headspace and pressure.
I will be the first to admit, that on some rare occasions you may not have a choice with regard to gauges. Obviously, if the gauge is not available and delivery time for one from a reamer maker or a rental agency is too long then you may be forced to move forward. Using brass or ammo as the gauge to set headspace is expedient, not ideal. Nobody likes a client to be angry about delays, so we push ahead with an expedient method of headspacing…
Before you decide to send me a nasty-gram and defend the practice as acceptable, let’s talk about it for a bit. The primary reason for discussion is that brass can and does vary widely in manufacturing tolerances. This is all allowed and planned for in the SAAMI specifications the industry utilizes for both firearms and ammunition production.
There are instances where the practice is not really a danger or a liability. However, that does not mean that it’s a good idea all the time. Starting with a list of the times it might be safe and reasonable to do so.
- Rimmed cases
- Low Pressure cases
- Wildcat designs
With rimmed cases your pretty safe for two reasons. First, most are what we consider low pressure or are often straight walled so pressure drops dramatically for ever increment the bullet moves down the barrel. Second, single shots and lever guns that normally accept these cartridges will function fine with a small amount of excess headspace.
If we are talking about revolvers then using brass for headspace is something to be cautious about. It can certainly be done; however, I would check the rim thickness of my cases against the SAAMI specs for the cartridge at hand. If you have a minimum spec piece of brass and you set the gun to minimum headspace with it, then it will not be long before the client complains that the gun jams up and the cylinder will not turn.
If your client is a reloader or shoots commercial reloads the problem might be intermittent. Why is that? Because his brass is probably mixed from lots and makers so there is no aparent rhyme or reason as to when the problem appears.
When we talk about low pressure cartridges we are referring to cartridges that operate under 40,000 PSI in rifles. Black Powder cartridges are good examples of this type of cartridge. The most popular of all is probably the 30-30 Winchester. Why is headspace less important with these cases? Because they will generally work safely with a large amount of excess headspace, simply because the brass is strong enough to deal with the low pressures generated. So your liability is minimal.
In the example of the 30-30 you can actually have so much headspace in a 94 Winchester that the cartridge will sometimes misfire and yet you will never have a case head separation. That is because this cartridge when loaded to factory levels cannot overcome the strength of the brass to produce a catastrophic failure.
When you jump up in pressure though, as with the 375 Winchester compared to a 38-55 you will see that catastrophic failure is a real concern. Why? Because there is much more pressure in the 375. So using brass to headspace a midrange cartridge (40,000 PSI to 47,000 PSI) is a more delicate decision. Again you would want to be sure about the rim thickness of your sample brass vs. the SAAMI specifications for that cartridge.
With wildcat designs of your own making, headspace is totally up to you the maker. That is not to say it’s not important. You should set a standard for any design you come up with. The reason for doing this is so that you can show that you work to specific dimensions if something were to go wrong. Plus it makes it much easier for you to diagnose problems if you know exactly what the dimensions are supposed to be.
If we are talking about an existing wildcat, then you should use the correct headspace gauge for that cartridge. If you fly by the seat of your pants you have no way of proving the gun was correct when it left your shop. Which brings up an important point, you should always test fire and retain at least one piece of brass for that gun. It makes your files a little fatter but it’s worth it when you need to diagnose a problem when a gun comes back or you have to show that things have changed since you last saw the gun.
One way to handle the fired cases is to simply put them in a bag with the invoice number or serial number of the gun and file them on an annual basis with your other records. A box for each year with nothing but your exemplar brass does not take up much room and is easy to locate when you need it. It’s habits like these that can save you time and money when working out a problem. Many times the client has changed the gun or damaged it in some way, or taken it to another gunsmith and these fired cases are a record of how the gun left your shop.
Of course if you’re a hobby gunsmith you can keep exemplar brass just to diagnose any problems that may arise. And record keeping for you is probably no burden at all.
Look for part II next week.