Reloading Basics - Pressure signs
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- Last updated: 18/01/2019
Once you have put together your first batch of ammunition, having followed all the safety instructions, the next step will be a visit to the range to fire them. You might be both excited and a bit apprehensive, as you are about to fire ammunition that you have put together yourself for the first time. If you have stayed within the guidelines published with the loading data, there is little need to be concerned but when it comes to testing your reloads there are a number of things to watch out for. Unfortunately, it is beyond the reach of us shooters to be able to carry out pressure tests on ammunition, as it is a very complex and technical process, requiring very specialist equipment and knowledge. We therefore have to rely on the simple checks that we can do. If you do have access to a chronograph, it is a good idea to check the velocity of your ammunition, to ensure that it is performing in line with the published velocity.
The pressure generated when you fire a round of ammunition, which drives the bullet up and out of the barrel, needs to be within the safe limits for your particular firearm. The guidelines contained within the loading data are specifically intended to keep your loads within the limits, but you still need to keep an eye open for both excessively high, and unacceptably low, pressure signs. While excessively high pressure can be disastrous, very low pressure can also bring its own dangers.
The most obvious risk when chamber pressure is excessively high, is that you can literally blow the gun up and this in turn can cause serious injury to the shooters and anyone else stood nearby. This is extremely unlikely, due to both the safety margins employed by gun and powder manufacturers and the fact that many calibres cannot fit sufficient powder in the case to do this level of damage; it is however possible to use the wrong powder, so care should always be taken to ensure that you’re using the right powder for the load on question. There is still however the risk that high pressures will damage the gun and cause problems.
If there is insufficient powder in the case, then the bullet can often fail to acquire the energy required to exit the barrel and will get stuck part way along it. I know of at least one case of a shooter ending up with more than one bullet stuck in the barrel, having failed to notice that nothing was exiting the barrel or reaching the target!
The gun was damaged and required rebarreling at some considerable cost. When a bullet enters a barrel that already contains a stuck bullet, there is likely to be a considerable amount of blow-back, which can be dangerous to the shooter.
The most easily spotted indicators of pressure problems are the amount of felt recoil when the rounds are fired and the accompanying sound. If you have already fired factory ammunition through your gun, you will know what it normally feels and sounds like.
If you don’t feel any significant recoil, and/or you hear more of a ‘phut’ than a bang, then you are probably using too little powder. Be sure to check your barrel is clear and look for a hole in your target. Another indicator of loads that are too light is the appearance of a lot of soot on the outside of the ejected cases. This happens because on firing there is not sufficient pressure to fully expand the case in the chamber and seal the gap between the outside of the case and the walls of the chamber. Continued use of rounds with this problem will make it harder and harder to chamber rounds as the soot builds up in the chamber.
If felt recoil is heavier than normal, accompanied by the barrel jumping and a louder report, then you may have a problem with excessive chamber pressure. You should then examine the spent cases for further indications of high pressure, including the following:
Flattened primers this is an easy one to spot, with the exposed surface of the primer completely flat with no curved edges. In more extreme cases, the primer can ‘flow’ into the firing pin hole, giving the appearance of a crater-like dent in the primer.
Pierced primers: with even higher pressure, you may experience the primer bursting through where the firing pin has struck it. A hole all the way through the primer into the case will be clearly visible where the firing pin struck.
Blown primers: when this occurs, the primer falls out when case is ejected, because the brass has been stretched so much by the excessive pressure that it no longer grips the primer. Ejector groove marks: With high pressures, the brass of the case will be pushed against the ejector with sufficient force for it to leave an indentation on the case head. You may also see an impression of the bolt face on the head of the case. Extraction problems: if high pressure has stretched the case beyond the limit of its elasticity, it will have expanded to the size of the chamber and not shrunk back again after firing. When you try to extract the case, you will feel increased resistance and, in extreme cases, can tear the head off the case trying to free it. Cracked cases: Split necks are not generally indicators of high pressure, but cracks or holes blown in the side of a new case, back from the rim, may be a sign of high pressure.
Although this is not an exhaustive list, and also taking into account that the above symptoms may not always be signs of high pressure, if you watch out for these signs you should be able to ensure your loads are safe to use. It is of course also important to ensure that the gun you are using is in good condition, with a clean chamber and bore, and that the ammunition is the correct calibre for the gun. Shooting is a generally safe sport, as is reloading, provided it is done correctly, and, if in doubt, you should always seek advice from a more experienced participant.
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