I have covered some general issues as well as some specific issues relating to semi-automatics and revolvers. In this article, I’ll be looking at some different types of projectiles, and their related crimping considerations.
Crimping Considerations for Projectiles
When I discussed projectiles, I identified some basic variations on projectile types, but omitted considerations related to crimping. There are lots of projectile manufacturers and lots of projectiles out there, and pretty much every one of them is slightly different. Some projectiles, generally those specifically designed for handguns that use rimmed cases, come with a crimping groove or cannelure. However, not all projectiles designed for rimmed case calibers will have these crimping grooves.
Figure 1 shows a .44 magnum projectile with a crimping groove. i.e. this is a projectile suitable for a firearm using a rimmed case.
Figure 2 shows a .45 ACP projectile which does not have a crimping groove. i.e. this is a projectile suitable for a firearm using a rimless case.
Where Should The Crimp Be Placed?
To begin with, I have previously discussed Overall Ammunition Length (OAL). This is defined in reloading tables for each caliber, and is the measure of the length of the round from the base to the end of the projectile. Figure 3 shows the method measuring OAL with a micrometer.
Exceeding the maximum OAL may cause feed issues with semi-autos or stop the cylinder of a revolver from rotating. When setting the seating depth, which in turn defines where the crimp will be placed, never exceed the maximum OAL specified for that caliber.
In general, if a projectile has a seating groove, this is where the crimp should go. Figure 4 shows a two .38/.357 projectiles with seating grooves and two .38/.357 projectiles without seating grooves. These projectiles are designed to take a roll crimp in the location indicated.
Figure 5 shows three 9 MM projectiles which have no crimp grooves. These projectiles are designed to take a taper crimp in the location indicated.
If a projectile does not have a crimp groove, the crimp can be placed anywhere along the last land on the projectile, provided the OAL is not exceeded.
A case gauge is good way of ensuring that the OAL is not exceeded. Figure 6 shows a number of case gauges and how the OAL can be checked using them. These case gauges also replicate the breach of the appropriate firearm, and are thus a good way to confirm the amount of crimp has removed the bell and not distorted the case to the extent that it won’t feed into the breach.
How Much Crimp Should Be Used?
The “correct” amount of crimp is somewhat difficult to specify, but generally just enough to do the job is what you are looking for! It is far easier to specify what constitutes too little or too much crimp. Between the extremes (somewhere) will be the correct amount of crimp for your application. This is often a matter of trial and error with your specific projectile type.
Too little crimp. The absolute minimum crimp will remove the belling from the case and lay the case mouth flat against the projectile. If the crimp is too light, during firing the projectile may leave the case before all the powder has been burnt. Un-burnt powder, on or in, the firearm is one sign that the crimp needs to be tightened up.
Too much crimp. Any deformation of the case, particularly around the case mouth, is a sign that the crimp may be too aggressive. Cases generally fail by splitting at the case mouth due to repetitive expansion (belling and firing) and compression (crimping). Another sure sign of too much crimp, and hence excessive case pressures, is failure (splitting) of the case along the side as opposed to the mouth. This failure mode will occur occasionally, but if you are seeing lots of cases splitting along the side before they split at the mouth, and the powder charge is correct, you probably have too much crimp.
Next Article
I have had a number of questions relating to setting the depth of reloading dies. Due to the variety of reloading presses and reloading dies, this is a difficult topic to address in any detail. However, in my next article I will attempt to provide some general tips on the issue.
