If you search around the website we have discussed things like Case and Cartridge Gages, milligram scales, pressure transducers, and micrometers. All of these are tools used to measure specific dimensions of a both cartridge components, and loaded cartridges. Some of the methods are destructive, meaning the process used to test the component results in it’s destruction, and example of this is simply firing a cartridge in a test gun. More often this measurements can be taken without the destruction of the sample.
This write up is going to cover some of the basic tools used to check quality in ammunition. Where there has been a write up previously done that goes into more detail, we will reference that write up. This is a follow up to an email I received asking about what equipment and tools are used in the evaluation of ammunition.
Micrometers and Calipers
Undoubtedly the most used tool on the bench is a good Digital Caliper. Many of your critical measurements can be made using a basic 0-6in Dial or Digital Caliper that you would be several handicapped by not having a good pair on your bench. They are quick to use, and provide all the basic measurements you can ask for quickly at a small sacrifice of accuracy.
While many old timers use a dial caliper, there is a bit of a learning curve, for someone who grew up in a digital world. With that said the digital calipers can give one a false sense of accuracy, with it reading out to .0005″, really calipers, even the expensive ones are +/-.002″ at best.
Where precision is an absolute must, a quality Micrometer is a must have. These can be accurate out to the .0001″, if you do your part. Again they come in analog and digital varieties. They are not as useful as a pair of calipers, you’ll most often use them to check bullet shank diameters. Occasionally you might use them to check the diameter of button in your sizing die. Don’t get me wrong, they are far more useful for all sorts of precision measuring but they usually take the back seat to my calipers.
There is an analog micrometer I do use a lot. It is a called a tubing micrometer and it has a ball end. This allows the accurate measurement of the neck thickness. If I take the measurement in three or four locations I can assess how even the neck is. A neck that is thicker on one side then the other may not be holding the bullet concentric to the bore, which may result in a flier.
It is not a bad idea to have a couple standards to keep handy on your bench to check you Calipers and Micrometers with. Also, treat and store them like the precision tools that they are. I once accidentally dropped my pair of calipers and bent over one of the edges used to measure I.D’s. It was an expensive mistake.
Gages
There is one basic gage that everyone should have. That is the cartridge gage. Dropping a round into a proper cartridge gage will quickly tell you if that cartridge will chamber in a live firearm. In a pinch, a firearm can be used, but you should removed the bolt, barrel, or otherwise render the firearm inoperable before you attempt to check it. In a production environment, this just isn’t feasible and a gage should be used.
I detail the design of a Cartridge Gage in this write up. This is specific to cartridges that head space off the case mouth. However the concept is the same for all cartridges. These gages can be purchase from a variety of manufacturers but my favorites are from Sheridan Engineering.
For production, they make multi-hole gages, where you can check 20, 50 or even 100 hundred at once.
These larger gang type gages are often made from aluminum as oppose to steel or stainless steel. The reason being is weight and operator comfort. As such they can be more easily damaged by dirt or debris.
While the cartridge gage is more popular, there is also a case gauge, which is used to check the quality of brass as it comes off the press before it is placed on a loading machine. Most loading machines have a limited ability to resize a case, thus is is important the brass comes in below SAAMI Max cartridge. Cartridge gages can be used as a case gage, which is why you don’t typically see case gages for sale. I have an example case gage design detailed here.
It is important to note that in a production environment, a gage can be created for just about any metric you want to measure. A simple gage can be created with a pair of calipers set to the max cartridge overall length, and used to sort brass that needs to be trimmed. Alternatively you can purchase a gage with cutouts that have multiple COAL’s as shown below.
I have also seen gages made to check the case head, making sure the depth and angles for the extractor groove was cut correctly. If you are in the firearms industry for long, you will hear about head space gages, which check the distance between a close bolt to a specified dimension in the chamber. For the most part it is up to the manufacturer and quality department to figure out what gages are needed for their checks.
Comparator Rings
There’s a few names for these, but they are all the same. They are a type of gage, that attach to the calipers. The ring has a specified diameter such as .264, which in theory will match up to the same diameter (called a Datum) on the bullet or on the shoulder of the cartridge.
The most famous examples I am aware of is the ones produced by Hornady.
The problem with the cheap aluminum comparators is they are not perfectly matched to your ogive. This requires a bit of a separate write up, with CAD examples to show how different ogives require slightly different comparators to get a precise measurement, but just know you’ll spend a lot of money and time to get something better then what Hornady has to offer.
Measuring base to ogive, as shown in the image is a better way to determine the distance off the lands as it is more precise. Often extra jacket material get’s forced up into the meplate (nose) of the bullet which creates a ragged and uneven tip. Measuring base to tip, will pick up this variation and you will chase your tail trying to get ever bullet seat exactly the same. Measuring to the ogive shows you where the bullet will begin to contact the lands (Assuming the ring gage diameter is equal to bore diameter) and due to the way the bullet was formed there is far less variation.
Even bullets which have a plastic tip, or have an open base and a closed meplate will exhibit some variation in the tip of the bullet, and you are usually better off trying to measure from the ogive datum rather then the meplate.
Another use is measuring base to shoulder. This measurement is something that is specifically called out in SAAMI Max Cartridge and Min Chamber drawings. It determines how the cartridge will set in the chamber. This dimension is also known as the headspace dimension. It can be useful to know how this dimension changes on a fired case, verses a case that you just resized. A cartridge gage checks to make sure this dimension doesn’t exceed the maximum, while a properly sized comparator gage ring will tell you exactly what this dimension is.
Scales
There are a variety of scales on the market, and someone could conceivably spend anywhere from $30 to well over $5000 on a miligram scale. Certainly a great deal of work has been done with a single beam scale and these scales are remarkably accurate, though slow to use.
Digital scales have become the standard for sometime, they are quick to use, and if made correctly they are robust. We employed many of the RCBS Rangemaster Digital scales to check nearly every weight when doing Quality Control. However the scales accuracy became an issue when we began to implement Statistical Process Control.
Given most scales under $300 only read accurately to +/- .1gr the data generated was more properly classified as categorical rather then continuous. For some of the work we did we found upgrading to a scale that was accurate to +/-.01gr was more appropriate. This came with a notable jump in price. The A&D FX 120i, starts at nearly $750, but is available with a card that allows for integration with a PC. This makes it easy to measure hundreds of components as it negates the need for manual entry into Excel.
Given the price tag, these scales were reserved for Quality Control, or the Ballistics Lab where precision was given preference over robustness.
Chronographs
There really used to be only one type of chronograph, and that was the optical chronograph. This simple velocity measuring device is triggered when a bullet passes over it’s first screen, which consists of an optical sensor, and sometimes a light. A second screen placed at a set distance from the first is subsequently triggered turning off the devices internal counter. The time passed between turn on and turn off is divided over the known distance in order to calculate speed.
We have seen a few new devices come out over the last few years that are somewhat unique. Most notably the Lab Radar, which uses a Doppler Radar to take velocity measurements at several preset intervals down range. Depending on the bullet’s cross sectional area, the radar can read a bullet out to around 100 yards. This makes it possible for the hobby shooter to calculate a 100 yard Ballistic Coefficient, without the need for multiple optical chronographs.
This technology is a scaled down version of what commercial labs and militaries have been using for some time. The larger units cost north of $100k and will track small caliber projectiles out to around 1000 yards, sometimes further. Medium and Large bore calibers can be track for miles using the same system, and I have even seen it where multiple projectiles, including a load of buckshot and the wad was track with these advanced systems. You are not getting any of that with the $560 dollar unit though, also you won’t go sterile if you walk in front of it.
While the entry level reloader is probable not going to spring for a chronograph or a Labradar, it is an extremely useful tool. A chronograph, a target, and the spent brass, will tell you about 90% of what you need to know when it comes to your load’s performance. The rest of the information is nice to know but you will spent a lot of money to get it.
Horizontal Comparator
We are beginning to leave the realm of what a hobbiest will have and what production facilities will have. The first item that I think is of great value is the Horizontal Comparator.
These units are basically glorified shadow boxes. A light shines on the object and the shadow is magnified 10x or 20x and projected to a screen. Once focused extremely accurate measurements can be taken. Often times a transparent sheet is place on the screen to compare complex features, like the ogive of a bullet, to make sure the bullet is being formed correctly in the die.
I have section cases, and taken a series of measurements to model the internal dimensions and compared the construction of one manufacture’s case to another, using a comparator like the one shown above. Sectioning a bullet and placing it on a comparator can give the interested party a close up look of the construction, including things like jacket thickness, jacket taper, or even partitions.
As with most tools, there are numerous uses for a comparator such as this, however they tend to be slow to use. In the cases where a transparency is used, time can be saved. It is still slow and not suitable for mass inspections. However there are machines that do this, and can handle rates up to 300ppm.
Force Testing
One important spec that is often overlooked is neck tension. This is the tension that holds the bullet in place. Many people believe that the crimp will always stop the bullet from moving. This often not the case, and if fact the force needed to overcome the crimp is less then the force of the case neck squeezing the bullet.
We usually are most concerned about cartridges failing when the bullet is pulled from the case. This happens when the cartridge is slammed into the chamber. The inertia of the bullet often causes the cartridge overall length to grow. However sometimes the failure can be in compression, where the bullet compresses into the case. This is true when bullets are stacked in a tubular magazine.
One of the more tricky standards to test for and check, as each firearm has a different recoil impulse, or in the case of Semi Auto’s, a different bolt speed on cambering. There is a lot of testing to be done, and we would try and take the neck tension down to the point of failure. Sometimes we needed to have a neck tension of well over 100lbs, other times neck tensions of only 50lbs were acceptable.
Mark 10 makes force testers that work well for this. You will need to design your own fixture,to pull the bullet from the case, but a standard shell holder will hold the case. For the most part, neck tensions will not exceed 400lbs, however we did see neck tensions exceed 500lbs and max out our 500lb load cells when testing straight wall magnum cartridges such as 454 Casual, or 357 Magnum.
Depending on the work you will be doing, it is likely advisable that you look at using a 750lb test fixture.
We spent well over $10k on a test fixture, load cell, and software that would do over 1500lbs, but we wanted to look at engraving force. The force needed to press a bullet into the lands and grooves of the rifling.
Pressure Testing Equipment
When most people think of quality testing for ammunition, they are thinking of measuring the Pressure and Velocity. Velocity we covered, but pressure, is another thing completely. So much so, that I did another write up addressing this specifically. You can read that here.
While this can be done using strain gages, there is no corresponding SAAMI or CIP standard. Following a standard is important especially if the ammunition with be for sale in a CIP Market, or if you are seeking liability protection from SAAMI. (SAAMI only provides liability protection if their standards are followed, and the company is a SAAMI member).
Copper or lead crusher standards which were, employed prior to the advent of piezoelectric pressure transducers, are obsolete. It has been at least two decades since a new cartridge had Copper Unit’s of Pressure published. The last I had heard, only one or two companies were making the copper slugs used for the tests. There are some cartridges which only have the CUP listed in the SAAMI spec. I believe CIP has updated all their specs to accommodate piezo testing.
Similar to the CIP standards the NATO standards are another options for companies looking to test NATO standardized ammunition. Unless you are looking at military contracts it is difficult to justify spending the money on the equipment only to be able to test for a few cartridges.
As mentioned in the write up, the investment for testing pressure can be under $10,000 to well over $100,000. It depend’s on the standard you plan on testing to, and how many different calibers you plan on testing for.
Concluding Thoughts
We have covered most if not all the basic tools, and most of the advance tools used to conduct quality control testing in ammunition. We have not talked about some of the tools used to assess primer quality, which have their own specialized fixtures. There are other tools that are sometimes employee to take specific measurements, for example there is a fixture that is used to measure and correct bullet run out. However we did not use that as it is impractical to check bullet run out on mass, much less correct it. If it gage’s it is determined to be good.
Quality Control can often mean different things to different companies and so the specialized tools to measure specific metrics vary considerably from company to company. Hopefully we have established a baseline for interested parties to seek out the tools they need to set up their own quality controls. The sky’s the limit here, but let me know what I missed and maybe I can do a follow up article.