Both Barrels: busting the steel myths

In the latest edition of his Both Barrels column, Bill Harriman takes on the belief that steel shot cannot be fired from a barrel choked greater than half without damaging your gun…

Can steel shot be fired from a barrel that is choked greater than half?

When it comes to steel shot (which is actually soft iron), there is a wealth of misinformation out there, with precious little empirically derived data.

One piece of perceived wisdom that is routinely trotted out is that standard steel shot should not be fired from a barrel that is choked greater than half. No reason is ever given for this advice and as far as I am aware there are no results from any testing that sustains it.

It is true that the international proof authority (CIP) do provide guidance on choke use for high performance steel cartridges; ie. high performance steel cartridges should not be used through tighter than half choke. The CIP are silent on the matter of choke for standard steel cartridges, yet many in the sector are adamant that the ‘half choke rule’ applies here, too.

As an arch-sceptic, I am no longer prepared to believe in articles of faith and will only believe something if I have seen it with my own eyes. To that end, I resolved to fire some steel shot cartridges through a barrel that was choked more than half.

Let's put the theory to the test

The gun I decided to use was a 12 bore Basque boxlock non-ejector, made in the 1980s.

These are its vital statistics.

  • Bore diameter at proof 18.5mm (.728)
  • Actual bore diameter .726 (14 inches from the breech)
  • Wall thickness .042 (14 inches from the breech)
  • Choke constriction .040

While there is no standard measure for designating choke, forty thou (thousandths of an inch) constriction is generally accepted as being full choke.

The cartridges I used in my test were Eley VIP Steel loaded with 32g no. 5 pellets in Pro Eco Wads.

I fired a box (25) and then cleaned the gun using a bore solvent, finishing off with a white cotton patch. I then looked at the muzzle very carefully with a 10X loupe to see if there was any evidence of damage, e.g. scoring marks. 

As I couldn’t see any, I stuck my finger into the muzzle and rotated it to see if I could detect any roughness (your fingertips are very sensitive and will readily detect any change in texture). 

I had a final look with a digital microscope set to its highest magnification. I was expecting to see evidence of scoring, but my examination did not reveal any damage. I also checked for any bulging around the area of the choke cone, by both the fingertip test and by squinting along the barrel when held up to the light. Again, no sign of any damage whatsoever.

I repeated the process, cleaning and checking after every box of 25. 

I gave up after I had wound 200 cartridges through the gun as there was absolutely no sign of any damage. I checked the internal dimensions with a micrometer gauge, but they remained unchanged; so did the wall thickness.

The verdict

Now, I know that a single swallow doesn’t make the summer, and this was only one gun with a mere 200 cartridges, but I would have expected any damage to occur early on in the test sequence. I intend to fire more steel cartridges and repeat my testing regime. I shall also do the same with another make of full choke gun with a different barrel profile.

The seeds of doubt have been sown in my mind about the advice of no steel shot through half choke or greater. Having bolted this particular fox, I intend to hunt it hard.

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