The Big HAM Slugs Test. Part Two. Muzzle Energy And Consistency For Slugs
In the first part of the Big HAM Slugs Test, we looked at changes in BC. This time, we’re looking at variations in Muzzle Energy and consistency for slugs.
What’s that photograph above? It’s a slug that failed to fire during our testing. We’ll talk about it more below…
The Slugs We Tested
For this test, we shot 13 different .22 caliber slugs, plus a “control” pellet for comparison. This pellet was the 25.39 Grain JSB Jumbo Monster Redesigned.
Here’s a list of the slugs, together with their specified weights. They run from the 20.3 Grain Daystate Howlers to 30 Grain H&N Slugs HP.
We know very well that the manufacturer’s specified weights for slugs and pellets are subject to some variation – as you can see by reading any HAM pellet or slug test review.
However, we did not sort the ammo for this test. It was fired “straight from the tin” to replicate the consistency for slugs that an average user would encounter.
We also made the Muzzle Energy and Ballistic Coefficient calculations based on the manufacturers’ specs.
We fired 10 shots for each type of .22 caliber slug – and the pellet – then averaged the results for our calculations.
First let’s look at the Muzzle Energies we achieved from these projectiles – all fired from the same KalibrGun Cricket 2 Tactical, of course.
Interestingly, we see that the highest Muzzle Energy – 46.0 Ft/Lbs – was achieved using the JSB Jumbo Monster Pellets and not any of the heavier slugs, as we might have expected.
Why is that?
Our guess is that the significant bearing surface from the parallel body of the slug causes major frictional resistance to the slugs as they travel down the barrel. In comparison, the bearing surfaces of a traditional diabolo pellet – the head and skirt – are very small and thus generate less friction.
Overcoming barrel friction requires energy. That results in less energy retained in the slug as it exits the barrel.
Retained Kinetic Energy At 30 Yards
Once the projectiles have exited the barrel, however, the much-vaunted higher Ballistic Coefficients of slugs means that they loose velocity at a slower rate as they travel down range.
Hence we would expect to see the Monsters lead in Muzzle Energy to decline the further out we shoot.
Already at 30 Yards downrange, we see that the energy lead of the Jumbo Monsters has vanished. The 38.3 Ft/Lbs retained kinetic energy of the pellets is already overtaken by seven of the slugs, with the 25.5 Grain ZAN slugs being the highest at 39.3 Ft/Lbs.
Retained Kinetic Energy At 50 Yards
By 50 Yards, we see that the 33.8 Ft/Lbs energy of the Monsters has been overtaken by ten slugs. Now the H&N 25 Grainers have the highest kinetic energy at 36.9 Ft/Lbs.
The other slugs are closing-up, too, except for the H&N 30 Grainers. What’s happening here? We’ll get to that soon…
So clearly the higher Ballistic Coefficients of the slugs is making a significant difference already even at 50 Yards, which is a relatively short distance to shoot slugs.
FPS Consistency For Slugs – Muzzle Velocity
Now let’s look at the consistency of Muzzle Velocity for the projectiles in this test. For this we calculated the Extreme Spread for the 10 shots made for every type of projectile. That is, the difference between the fastest and slowest in the string.
The lowest Extreme Spread was delivered by the 23 Grain H&N Slugs HP. There was just 3 FPS difference between the slowest and fastest slugs in the 10-shot string. That’s extremely impressive!
As you can see from the chart above, most of the slugs tested had an Extreme Spread in Muzzle Velocity of between about 5 and 10 FPS. (In fact, the average was 9 FPS).
By comparison, the Extreme Spread for the Monsters was 13 FPS.
The two outliers in this test were clearly the FX Hybrid Slugs and the 30 Grain .218 Caliber H&N Slugs HP.
There was clearly something untoward happening with those 30 Grain slugs, as we indicated earlier!
FPS Consistency For Slugs At 30 Yards
Out at 30 Yards, the 23 Grain H&Ns were still the most consistent. However the average Extreme Spread for all except the FX Hybrid Slugs and the 30 Grainers was up slightly to 11 FPS.
We know from extensive HAM testing that the Extreme Spread of every type of slug or pellet increases rapidly beyond that range. That’s why we we calculate HAM Ballistic Coefficient values at 30 Yards.
Beyond that point the Extreme Spread can become so large that an average FPS calculation can produce some very dubious figures.
FPS Consistency For Slugs At 50 Yards
Guess what! The average Extreme Spread for all except the FX and 30 Grain slugs was now up to 28 FPS. It had increased to 45 FPS for the Monsters, too. I rest my case, your honor…
At 50 Yards, it was the 21 Grain H&N Slugs HP that showed the lowest Extreme Spread at just 14 FPS. That’s completely outstanding!
Overall, as we can see, the consistency of the slugs tested by HAM – when measured by their Extreme Spread of FPS – was generally very good.
So What About The H&N 30 Grain Slugs?
At first the HAM Testers were confused about what was happening with the 30 Grain H&N Slugs HP. But slowly we figured it out…
It became clear that – just like heavier pellets – heavier slugs tend to be not only longer but have a larger diameter. For example, the comprehensive HAM test review found that JSB Jumbo Monsters Redesigned have an average head diameter of 5.56 mm.
A small sampling of 30 Grain H&N Slugs showed the body diameters all to be 5.56 mm or greater when tested using a PelletGage. Not only that, but the bearing surface of the slugs is so much greater that tiny variations of diameter were having HUGE variations on the Muzzle Velocity.
That meant changing frictional losses so significant that we saw Muzzle Velocities varying by no less than 159 FPS in the test string!
To confirm our suspicions, we then loaded a 34 Grain, nominal .218 Inch body diameter 34 Grain H&N slug into the Cricket 2 Tactical. The result was a jam that required the gun to be dismantled to clear. End of testing.
The combination of diameter, bearing surface length and weight of that 34 Grain slug was just too much for the available power of the gun. It refused to completely enter the barrel, let alone exit from it!
Here’s another photograph of the slug concerned. The rifling marks are immediately clear, as you can see, together with the point at which the slug had failed to enter the barrel.
So there you have it…
Part Two of our Big HAM Slugs Test proves that consistency for slugs – when measured as Extreme Spread of FPS in a string – is generally extremely good.
Muzzle Energy for the slugs may start-off being lower than that for a heavy pellet. However the improved Ballistic Coefficients associated with slugs really does mean that they deliver more energy to the target downrange.
Typically we find that heavier pellets will provide higher Muzzle Energies when shot using a PCP air rifle. This was not the case, however, in this slugs test.
While the tested slugs varied in weight by 48% (20.3 to 30 Grains nominal weight), the Muzzle Energies varied only by 24% (35.3 to 43.7 Ft/Lbs). Not only that but the heaviest slug fired produced – on average – by far the lowest Muzzle Energy.
We certainly didn’t anticipate this result!
Furthermore you may find that some heavy slugs may be incompatible with your air rifle’s barrel, as we’ve found out. Again, that was a big learning for us!
Again, thanks to Matt Coulter for all his help in producing this test review.
Part three is here.