Forming B&M Cases
Forming Cases for the B&M calibres is a relatively straight forward process. Winchester Short Magnum (WSM) cases are used for the .458, .474 and .50 Super Short calibres and the .458 and .50 Semi-Auto calibres. It is simply a matter of cutting the case to the approximate length (a little longer), running it through the appropriate full length sizing die to form the neck (either by increasing or reducing the case diameter, depending on the calibre) and then trimming the case to the exact length and chamfering. If making the B&M Semi-Auto calibres, use the largest calibre WSM parent case available to you (where possible, the .325 WSM) as this will require the brass to stretch less. Annealing may be advisable to ensure that the necks don't become brittle from the working hardening they suffer due to the necking up process. See below.
Forming cases for the other B&M calibres is a similar process, except that the longer Remington Ultra Magnum (RUM) cases are required as the parent case. RUM cases will need to be necked down, rather than up, as the B&M shoulder and neck are formed below the standard RUM shoulder. Again, the cases will need to be cut to approximate length, run through the full length size die and then trimmed to exact length and chamfered. In the case of the .50 calibre B&M cartridges, no necking up or down will occur as the cartridge is essentially a straight-walled case.
Empty cases should be tested for fit in the rifle's chamber. Then make a dummy cartridge, with the projectile you intend to use, but no primer or powder, and test it in the chamber also. Provided that the dummy cartridge loads and extracts from the chamber easily, no further action is required. Should there be difficulty in loading or extracting the dummy cartridge, it may be an indication that some neck turning may be required (assuming that you have checked that the projectile is not contacting the lands). For cases that are necked down, some thickening of the neck wall will generally occur as the brass needs to go somewhere. This may sometimes be required only to the base of the neck where it joined the shoulder, or the entire neck may require it. This can be easily achieved with a neck turning tool by hand. While it is a somewhat tedious process, it will only be required once. Most times, B&M brass formed from RUM cases will not require any neck turning.
The B&M website shown on the Links page has infomation and pictures also.
Fireforming
Fireforming is the process of forming a converted case to fit the chamber that it is to be used in. It is achieved by firing the newly formed case in the chamber. It is not always a necessary task. When necking cases down, the dies should form the case well enough to make fireforming unnecessary. However, when necking up, or especially where an increase to the shoulder height or angle is required, it may be necessary.
While it can be achieved in a few ways, the most reliable is to load a light to moderate load in the newly formed case and then fire it in your rifle. Do not use maximum loads for fireforming. Maximum loads may well produce excessive pressures, and may lead to difficult extractions from the chamber and ruined cases. Especially where the case capacity of the un-fireformed case is less than the capacity of a fully formed case, this risk exists. Be safe and use a light to moderate load. If you have cheap projectiles, this is a good time to use them up and do some practice with your rifle at the same time. Once a case has been fireformed, it can be used with full power loads.
Annealing
Cases that have been necked up or down (and those that have been fired numerous times) may suffer some work hardening of the neck and shoulder, which could decrease case life. Annealing is a process of heating the case neck and shoulder to soften it, preventing premature case failure.
The intent is to heat only the case neck and shoulder to around 480 degrees C (900 deg F). The case body and especially the head, must not be heated, as they are designed to be hard and not flow with the pressure of firing. A propane torch or similar should be used to heat the neck until it is just starting to glow red. Don't heat the neck until it is bright red or you will overheat the brass the likely the case body also. Performing the process in a darkened room helps you to see when the brass starts to change colour.
While there are a few different techniques that can be used to anneal brass, the following is the simplest method:
First deprime the cases if they have been fired, and if they are dirty, clean the necks so you can see the brass change color as its crystalline structure is changed by the heating.
Next, fill a shallow tray (such as a metal baking tray) with 15 – 20mm of clean water. Stand the empty case in the water with the neck up. Use the propane torch to heat the neck only until it just starts to glow red. Don't heat the shoulder specifically, as the heat will spread to it from the neck anyway. When the red start to show, tip the case over into the water to cool the case. Note that the only function the water performs is to keep the case head and body cool to prevent them being heat affected, as they need to remain hard. Quenching merely cools the case before the heat can spread to the lower areas of the case.
Be aware that if you have multiple cases set up in the tray, space them apart so that you don't accidentally knock over the ones that you haven't annealed yet. You're bound to knock over more trying to stand the fallen cases up again.
After you have annealed the brass the neck and shoulder develop the characteristic darker colour. This is normal. This is often seen in military brass and also with new Lapua brass. Many brass manufacturers polish their cases after the necks are annealed at the factory, which is why the darker colour is not evident.
Once you've completed the batch of cases shake the water from the cases and dry them with a cloth. To prevent water marks, you can put the cases into a shallow tray (standing them up is best, but can be tricky) and put them in the oven at no more than 50 degrees C for a short time to dry them internally. Alternatively, you can put them out in the sun if it's a warm day.
Another method you can use for annealing is to put the case into a case holder that can either be attached to a cordless drill or that can be spun by hand. Spinning the case will ensure even heat distribution across the neck. Spin the case only at low speed and when the colour change occurs, stop the spinning and quench the case. Note that with this method the case body is more vulnerable to overheating as it doesn't have the cooling effect of the water, so you need to be vigilant as to when the colour change starts. Make sure that you rest both hands against something during the process to keep them steady, so that the flame tip only comes in contact with the case neck.
Take care not to introduce the drill to the water, to prevent electrocution or damaging the drill. This is why a cordless drill is recommended.
Cases should be annealed after 5 to 10 firings, depending on how hard you're working the brass. This will depend on how hot your loads are and the degree to which the neck expands and is resized. A match chamber and correctly sized neck sizer die will work the case less than a loose chamber and full length resizing. If you apply a heavy crimp, consider annealing more often, perhaps after 3 firings. Cracks at the case mouth or neck are a good indicator that your cases would benefit from annealing.
Note that nickel plated cases are unsuited to annealing. Heating the case will soften the brass but not the nickel. Because nickel bonds to the brass at a molecular level, the relatively hard nickel will start to crack, and this failure will continue into the brass.
Disclaimer
Reloading ammunition and shooting firearms can be dangerous if performed incorrectly or without due care. While Meplat Firearm Services provides advice on certain aspects of reloading based on accepted safe practices, it does not provide complete information related to the reloading process. Persons who reload ammunition should ensure that they seek further information from other sources to that which is presented on this site and adhere to accepted, safe practices. Meplat Firearm Services cannot control the reloading practices of any person who may utilise information found on this site. As such, it accepts no liability for any event related to reloaded ammunition or shooting that may occur from reference to this site.