If you are not familiar with SAAMI/CIP Min Chamber and Max Cartridge Prints, please read the article found here.
After reviewing the SAAMI/CIP prints for a cartridge, an astute student might ask what the value is to the commercial loader, or handloader that does not intent to manufacture their own brass or chamber rifles? After all there is a lot of information presented but it is not always obvious to how this information can be readily utilized. One of the first things that may be done is to take your intended load and see how it fits within a SAAMI/CIP chamber. Using programs such as SolidWorks, Google SketchUp, AutoCAD, or other 3D modeling software you may model the bullet and chamber to see if there will be any issues.
To give an example of how this works we’ll work through a hypothetical.
There is a potential customer, Terry, who loves everything 30 Carbine. He lives, breathes, and sleeps with his 30 Carbine M1 rifles collection and is constantly wanting to do more with them. His latest request is a handload that will reliably take down hogs, for use in his 30 Carbine rifle. He’s promised to purchase 1,000 rounds of ammunition in order to have a single lot and he’s asked that the bullets have a higher Ballistic Coefficient (BC) value then typical round nose 30 Carbine bullets found in most off the shelf loads.
You agree to provide him with top quality ammunition and set out to figure out what bullet is going to work in his 30 Carbine. There are thousands of possible choices, everything from 100gr all the way up to 230 grain, made in all sorts of shape and sizes. Before purchasing 1,000 bullets you want to make sure that the bullet will fit and feed in a 30 Carbine chamber.
The first step is to look up the SAAMI Min Chamber and Max Cartridge print. This can be found here, or you can reference the picture below.
Once we have the print we can use that to model the Min Chamber using the minimum dimensions listed on the print. We use the minimum chamber dimensions to simulate a worse case scenario. A min chamber will allow a max cartridge to chamber reliability with the tightest fit. A min chamber also creates the highest pressures, which is why they are used in test barrels. In reality, Terry’s old war pony’s have somewhere between a min or a max chamber. By modeling a min chamber we ensure the ammunition will work in all his M1 Carbines, not just the worn out ones.
The Ballistic Assistant is proficient in SolidWorks, so that is the software that will be used to model this.
When modeling off the SAAMI or CIP prints there are a few things to keep in mind. Make sure you start with the Basic Dimensions. Then fill in with the remaining dimensions. Add the reference Dimensions last, if the model is sketched correctly then the reference dimensions should match up exactly to the ones listed on the print. In order to created a 3D solid the model needs to be closed and the revolve feature used.
Once the chamber is modeled you will need to model the bullets you intend to use. This can be tricky, you can reach out to bullet manufacturers and explain the you are a commercial loader and would like to evaluate the use of their bullet in a load. They may provide some basic specs that will allow you to model the bullet, or you may be able to purchase a sample of bullets and take some fairly basic measurements to model the bullet. We will model two types of bullets to see if they will work in a 30 Carbine Chamber.
Both of the bullets models are intended for different applications. The first bullet, with a spitzer ogive is of similar weight and style to bullets loaded in 300 AAC Blackout. These bullets may also be used in 308 Win or 30-06 Sprg Cartridges as lightweight loads and are typically suitable for taking game up to white tail deer.
The second bullet sports an tangent ogive that is more typically seen in pistol cartridges and more closely mirrors ogives that are typically found with 30 Carbine Ball and soft point ammunition. The bullet is a bit heavy for 7.62 or 7.3 caliber pistols, but in theory it sports a profile that would work in those pistols.
It should be noted that in both cases the bullets are a bit longer than typical as they are solid copper, this was done due to the ease of modeling, and I wanted to keep both bullets of similar weight ~110gr. The shape of the bullet is the most important when generating and evaluating the chamber fit. A material does not need and details like the cavity, or radi do not need to be included unless there is some potential for them to have bearing on the use of the bullet.
Once the chamber and bullets have been modeled it is time to assemble them as they would be assembled when a loaded cartridge is chambered. In Solidworks this is pretty straight forward and is show below.
Once the components are mated the bullet can be dragged along the axis. Solid Works has a handy collision detection feature that will stop the bullet as soon as it connects with the bore diameter.
We are able to say that this bullet will be usable in a 30 Carbine and still fall within the SAAMI 1.625 to 1.680 which is the Min-Max for cartridge length. Based on the model and the bullet provided the best target COL is 1.641in. This will place the case mouth in the middle of the cannelure. Additionally we can say the theoretical Distance off lands (DOL) is 0.035in.
We know that this bullet will work, but it’s not a particularly high B.C. bullet that Terry was asking for. So let’s take a look at the other bullet.
The spitzer point bullet has too long of an ogive to fit within the SAAMI Max Cartridge. We want to accommodate Terry’s request to have a higher B.C. bullet then what is typically found within 30 Carbine Ball ammunition but we are unable to load ammunition that falls within SAAMI specs and have a higher B.C. bullet. We could load this ammunition, but it is highly likely that the loaded rounds will not fit within a standard M1 Carbine Magazine. However they may be fed singly fed one at a time into a chamber. Terry is likely not going to be happy with turning his prized M1 Carbines into single shot rifles, no matter how high the B.C. value of the bullet is.
Going through this exercise takes about a hour or two of work, but utilizes the SAAMI technical drawings to demonstrate what is or isn’t possible to do with a cartridge. It also provides a visual to the customer to communicate what the potential issues may be. It has one last benefit.
Bullet Chamber Fit Drawings are extremely useful tools in communicating to the operator of the loading equipment what the Target COL needs to be. This drawing can capture other useful information such as the stock numbers for the brass, bullet, powder and charge weight, as well as notes as to how to set up the machine. This type of information is valuable if Terry comes back and asks for another 1,000 rounds. The work that was done is now captured on paper and ditigatally to ensure that he gets as close to the same load as you first provided.
The majority of this work is done utilizing SAAMI or CIP Max Cartridge and Min Chamber prints. It would be near impossible to do otherwise. In addition there needs to be some ability to either get specs from a bullet manufacturer on their bullet, or an ability to take a sample bullet and measure some fairly basic dimensions in order to generate a meaningful model.
We will detail further uses of SAAMI/CIP Max Cartridge and Min Chamber Prints in future write ups, but these gives an introduction into how this information is valuable to the handloader, or aspiring internal ballistician.
If this is something that you feel may be of benefit to your company, The Ballistic Assistant offers this as a service. Please email jayandrew338@gmail.com for details.