Our aim, is to try to guide the enthusiast who is reading these few lines towards a choice - hopefully correct - for a practical and possibly appropriate use of the chokes, when it comes to ammunition containing environmental friendly shots (steel, tungsten and copper).
Before we get into this issue, it's worth mentioning a couple of things:
cartridges equipped with shots other than lead ones are loaded with a greater quantity of powder (to obtain higher speeds) and shells featuring a large volume (in order to withstand the greater charge i.e. weight density caused by the lower specific weight of green shots), made from high density materials.
The two aforesaid factors, namely a greater quantity of propellant along with extremely rigid shells combined with shots with high hardness, contribute to increase the pressure inside the barrel; this implies greater stress precisely at the choke bore. Therefore, it is clear that dedicated choke tubes are advisable.
The increased speed of such cartridges boasting materials harder and less dense than lead (except for tungsten) is necessary to compensate for the rapid loss of velocity of the charge; for the same purpose it is recommended to use different numbers of shot compared to our normal habits (practical example: if we use lead shots No. 5 when hunting ducks, we should opt for steel shots No. 3).
Out of pure curiosity we performed a penetration test on packed reams of paper.
We refined our focus on two ammunition with equal velocity V0 (420 m/s) (lead No. 5 shots and steel No. 3 shots). As a matter of fact, the penetration observed when shooting at a distance of 30 metres was almost identical, however with the substantial difference that compared to steel, the holes in the lead were more marked and irregular due to the evident deformation of the latter upon impact.
A further difference consists in the higher number of sheets stuck together due to the tearing of the paper when the lead shot penetrates it.
This test, although empirical, highlights the greater transfer of energy from the lead shots, what can be remarked just observing them; those in lead showed deformations due to friction between them that occurs inside the barrel bore and when hitting the target while those in steel were almost intact.
Now, let's move on to choosing the most suitable choke tube for this type of ammunition. From the trials we carried out with steel shots No. 3 cartridges, it emerges that by using 42CrMo4 steel chokes the best distribution and concentration oucomes are obtained with the Extended or Ported + 20 mm models, provided a maximum MOD *** (5/10) constricion size.
Conversely by using titanium chokes we have achieved excellent results always with the Extended or Ported + 20 mm models up to maximum IMP MOD ** (7/10) constricion size, hence with a higher degree.
For all our chokes marked "Steel Shot", which can therefore be used with alternative ammunition, we also recommend those not exceeding 35 grams of total load with shots boasting a maximum diameter of 4 mm as regards the 12-gauge and 3.25 mm regardin the 20- one.