Written on: 19/06/2012 by Nec_V20 (9 reviews written)
As Scotty used to say to Captain Kirk, “Ye canna change the laws of physics”.
The problem with alloy pellets being inaccurate is not because of their supersonic velocity, but rather that after about 10 yards or less they enter what is called the “transonic region”.
To be truly supersonic an object has to move at 1339 ft/s (Mach 1.2) at sea level, to be truly subsonic the object will move at 803 ft/s (Mach 0.72) or below.
When I say “truly supersonic” I mean the velocity where ALL of the airflow around the pellet is supersonic (Mach 1.2).
When a pellet leaves the air rifle at truly supersonic velocity it will very quickly – due to drag – decelerate and enter the transonic region and this is where the fun starts.
At transonic speed the drag on the object increases dramatically, but it gets worse; the centre of pressure (CP) of the pellet will move forward and this will cause an erratic and sudden CP shift and (temporary) decrease of dynamic stability.
What this means is that you can basically forget the accuracy of any air rifle pellet leaving the muzzle of an air rifle at truly supersonic velocity beyond the range of 5 – 10 yards. When the pellet decelerates into the transonic region it will go “cuckoo for coco puffs”.
Any company claiming any kind of accuracy for their pellets leaving the barrel of an air rifle at truly supersonic or very high transonic (Mach 1.0+ or greater than 1116 ft/s) beyond 10 yards maximum are – how can I put this politely? – lying.
The catastrophic effect of velocities in the transonic region obviously decline as the pellet decelerates towards the subsonic region where the pellet will stabilise, but by that time the damage will have been done to the accuracy. They can be ignored for pellets that leave the muzzle in the range of velocities between Mach 0.72 and 0.8 or so – truly subsonic to just entering into the transonic – or 804 – 893 ft/s.
What makes me really angry however is recommending alloy pellets for springers.
In a springer the piston depends on the pellet offering enough resistance to the blast of air so that the crown of the piston is cushioned on a layer of air in the cylinder before it makes contact with the cylinder itself.
With the very light alloy pellets this is not assured which will result what is known as “piston slam”, and if, on top of this, the alloy pellet fits loosely into the barrel of a magnum power springer air rifle then you can basically measure the lifespan of the piston crown in tens of pellets and not tins of pellets.
I also have concerns with regard to using alloy pellets in choked air rifle barrels. The choke has a beneficial effect on the accuracy of lead pellets because they are malleable and the choke homogenises the pellets to assure that the pellets out of the same tin will leave the barrel the same shape every time.
When pellets are produced there are tolerances which will be deemed acceptable for the diameter of the head of the pellet. The choke has no tolerance whatsoever and the pellet will come out of the barrel at EXACTLY the diameter of the choke. Also pellets, the head of which may not engage the rifling of the barrel properly as it moves up it will be forced to leave the barrel straight by the choke.
Anyone who has looked at a lead pellet they have fired at a soup can will see how deformed the pellet has become. Fire an alloy pellet at that same soup can then it is almost like you could put the pellet back into the rifle and fire it again as far as the deformity of the head is concerned.
This makes me suspicious with regard to the effect of firing alloy pellets through a choked air rifle barrel and the damage to that choke which will accrue over time thus making the rifle intrinsically less accurate.
Another thing that drives me absolutely NUTS is the penetration claim for alloy pellets with regard to hunting.
Now to put “driving me NUTS” into perspective is the age old marketdroid claim of “New and Improved”. Look, if something is “new” then it is something which has not been there before, and if something is improved then it is something which has been around before and it has been enhanced. There is no way that something can be new AND improved at the same time.
With regard to hunting, penetration is a good thing right? I mean if the pellet bounces off the target then it pretty much defeats the point of shooting the pellet off in the first place.
But hunting is not just about the pellet penetrating the target, but also delivering traumatic damage to the quarry. Lead pellets do this by penetrating the target, deforming and through this deformation causing a large wound channel destroying a lot of tissue as it enters the quarry’s body and if it stays in the quarry’s body then it will have transferred all of the energy of that pellet to the target causing even more trauma – so called “stopping power”.
Of course alloy pellets have a higher penetrating power than lead pellets – the bloody things are armour piercing – however they will not deform (thus less tissue damage once it has penetrated) and for the kind of quarry one can typically hunt with an air rifle, it will exit out of the other side (thus not transferring the energy of the pellet to the animal).
Therefore I would suggest that the danger of just wounding the more highly penetrated animal (and thus leaving it to suffer) instead of killing it outright at the instant of impact is a lot higher with alloy pellets.
I can thus not in any way shape or form (puns intended) recommend alloy pellets for hunting.
I started this post with a Star Trek quote, but my favourite Star Trek joke has to be:
Question: What did Mr. Spock find in the toilet of the USS Enterprise?
Answer: The Captain’s log.