Possible effects to guns

Is my gun safe to use steel shot? Most firearms manufactured since World War Two are quite safe to use with today's steel shot if they are lightly choked (modified or lower). Half of them have interchangeable choke tubes so the hunter has no problem; he just shoots a quarter choke more open than he used to with lead. Those with fixed chokes will just throw tighter patterns. Some fixed chokes tighter than modified may develop a minor pressure ring at the start of the choke-forcing cone that will not alter the performance of the gun. The likelihood of ring bulging can be easily remedied by having a gunsmith open the chokes which is a minimal cost service, or by fitting a quality steel compatible interchangeable choke tube system. If you are unsure about the suitability of your shotgun to use steel shot, consult a qualified gunsmith.

Cut away showing internals of a typical lead shot shell
Familiarise yourself with a typical lead shot shot shell 

The possible effects to guns arising from use of steel shot are the following:

  • Creation of a pressure ring (ring bulge) in the barrel of the firearm.
  • Excessive stress to the chamber of the gun caused by selection of a shot shell that develops higher pressures than the gun can or should accommodate.
  • Barrel wear or scouring if steel shot comes into direct contact with the barrel.

Discussing each in turn:

Ring bulging

This is a ring deformation of the barrel caused by the outwards pressure of the shot charge as it passes through any choking system before leaving the barrel. A build up of oil or any other obstruction in the gun barrel can also cause ring bulging. Ring bulging can occur when using either lead or steel shot. A ring bulge does not pose a safety risk to the user, it will not continue to increase in size, nor will it shorten the useable life of the firearm or influence shot patterns and performance. In the case of steel shot, the factors which, on their own or in combination, contribute to the possibility of a ring bulge occurring are as follows:

  • The degree of choke constriction and, more particularly, the rate at which the constriction is applied.
  • The choice of shot shell – the higher the initial chamber pressure, the higher the risk.
  • The robustness of the firearm – the strength of the steel forming the barrels themselves.

Advice received from the American agency CONSEP, who played an important role in the non-toxic shot implementation in their country, is that ring bulging has not been a significant issue over the twenty or so years since steel shot was introduced. There have been occurrences, usually in full choked barrels, either as integral chokes or screw-in chokes. Where these have been known to occur, the actual deformation was in the range of three to five one-thousandths of an inch (0.003 to 0.005 inch), which is barely discernible to the naked eye. In the early days for some screw-in chokes, the threading expanded and chokes were difficult to remove, however, today, manufacturers have overcome this problem through redesign.

English and European manufactured firearms may not be as robust as their American counterparts, particularly older, lightweight game guns with tight chokes. The effect of steel shot on the barrels of a selection of 10 English and European manufactured firearms was undertaken by the Royal Military College of Sciences in the UK in 1996. The types of firearms used included a Browning U/O, Beretta U/O, Miroku U/O, Purdy SxS, Holland and Holland SxS. All guns used were full choke models, some with integral chokes and some with screw in chokes.

After over 9000 standard steel shot cartridges had been fired through the ten different guns, no measurable damage had occurred to any of the guns. The standard cartridges used recorded muzzle velocities in the range of 377 m/s to 392m/s with shot weights between 24 and 32 grams. These were regarded as being fairly light for game loads. Three of the guns were then tested with cartridges loaded to produce much higher muzzle velocities (438m/s, 28 gram) and in each case deformation of the chokes resulted after only 50 cartridges, to about the same extent as reported from CONSEP.

These tests therefore confirm that:

  • It is possible to produce steel shot cartridges that will not damage the barrels of typical lightweight firearms with full chokes.
  • High velocity cartridges loaded with steel shot may deform full chokes in firearms of English and European origin.

Australian importers are tending to import shot shells which are classified as high velocity in Europe, which is why hunters are being advised to avoid shooting steel shot through full chokes. Fortunately, because steel shot patterns much more tightly than lead shot, full chokes are unnecessary.

Chamber pressures

If a cartridge manufacturer wishes to increase the muzzle velocity of a shot charge to improve its down range effectiveness, it is done at the expense of increased chamber pressure. This is a potential risk area for hunters when selecting steel shot loads for the first time, particularly if their firearm is not in good condition, or if a cartridge is selected which develops chamber pressures above the design limits of the firearm.

The HAC has produced a separate fact sheet – "Steel Shot – Standards, Pressures and Proofing", which explains in detail the European and American standards for cartridge manufacture. Australian ammunition importers source all their steel shot stock from one or both of these areas.

This fact sheet is essential reading for hunters intending to use steel shot in an older firearm, particularly those of European or English origin.

Barrel wearing or scouring

When steel shot was first used in conventional lead shot wads, barrel scouring was an issue. Wads used for lead shot allowed the steel pellets to come into contact with the barrel wall and, because steel is harder than lead, the barrel could be eroded. Today, after twenty years of refining steel shot shell design, this problem has been overcome because all of the shot is now completely encased in the plastic wad, preventing it from coming into contact with the wall of the barrel. Also, the wad in a steel shot shell is much tougher than its lead shot counterpart – it is made from shock absorbent and highly impact resistant plastic.

Read the Shotgunning Education Manual for more details.