Steel shot standards, pressures and proofing
Australian hunters use a wide range of shotguns and shotshells for waterfowl hunting, usually equipment originating from European or American manufacturers.
In the past most hunters have probably given little consideration to the issue of shotgun proofing and shotshell chamber pressures when purchasing new guns and ammunition. However, the use of steel shot has raised some new questions about shotshell compatibility for use with existing firearms, particularly those of European origin.
This fact sheet reproduces material from British and American sources to provide guidance to hunters purchasing steel shot for the first time. It is necessary to understand the issues from both the British (or European) perspective as well the American perspective.
Twelve European countries are members of the International Proof Commission (CIP) who form a regulatory body for firearms and ammunition. The decisions made by CIP are legally binding on all governments of member countries. No such regulatory body exists in Australia. In America their Sporting Arms and Ammunition Manufacturer's Institute (SAAMI) acts as their recognised standards provider.
The Victorian Hunting Advisory Committee (HAC) wrote to Australian product manufacturers and suppliers seeking advice about how their products compared to the CIP standards, in particular those products which they were intending to market in Victoria.
In response, information was obtained from the USA industry and SAAMI sources to provide the paper which is reproduced in full below, under the heading "The American Perspective". "The European perspective", has been prepared with a collection of extracts from published papers to a British Association for Shooting and Conservation (BASC) seminar held on non-toxic shot, at the Royal Military College of Science, Birmingham, in May 1996.
The European perspective
The CIP has been working since 1914 for the standardisation of proof of firearms. This also involves standardisation of methods used to measure the pressure of ammunition, chamber and bore sizes, as well as setting the maximum cartridge service pressures and dimensions.
A CIP Working Group was set up to study the effects of steel in existing British and European shotguns and to provide limits of performance that, if complied with, would ensure a safe level of performance.
In 1992, after several years of study, the Working Group presented its findings which define levels of performance for what was defined as Standard Steel Shot Cartridges which could be used in any 12 gauge shotgun that had been nitro-proofed. A higher level of performance had been set for steel shot to be used in shotguns designed for steel shot and which have been Steel Shot proofed (see Diagram 1).
In deciding on the limits for Standard Steel Shot cartridges, CIP had to take into account the worst case condition of barrel strength and choke profile of existing shotguns, without the requirement for reproof, and with shotguns of different age, make and construction. Not only were limits set for pressure, velocity, momentum and shot size, to take into account the worst condition of barrel strength and section, but also the steepest angle of choke and also the possibility of full choke in one of the barrels.
SAAMI's limits, by comparison, are set for modern shotguns of robust construction, or specifically designed for steel shot, and with the generally understood view that steel shot is not fired through fully choked barrels.
The American perspective
The following is an over-view of Sporting Arms and Ammunition Manufacturer's Institute (SAAMI) guidelines concerning the manufacture and use of steel shot ammunition in firearms in the United States. Where possible, the SAAMI guidelines are compared to those of the Commission Internationalle Permanente (CIP).
This summary will start with basic information such as the make-up and purpose of SAAMI and CIP. Next, there will be discussion of steel shot versus lead shot and the performance parameters of both SAAMI and CIP. Specific issues such as proof requirements, shot size, velocity, etc. are covered. In closing, the state of the art in steel shot use and performance in the United States will be reviewed.
Throughout this report, both metric and US units of measurement will be discussed. Where relevant, both units of measurement will be shown. To ensure comparable analysis, following are the conversion factors (including relevant decimal places) that were used throughout this report.
1 Bar = 14.504 psi 1mm = 0.039 inch 1 m/s = 3.28 f/s 1 g = 15.432 grains
SAAMI was founded in 1926 at the request of the United States government to ensure safety in the use of firearms through standardisation of ammunition and firearm parameters. SAAMI consist of member companies representing United States ammunition, propellant, and firearms manufacturers. SAAMI is an accredited standards developer for the American National Standards Institute (ANSI).
For the United States, SAAMI establishes standards for firearm and ammunition dimensions, testing, definitive proof loads, and ammunition performance specifications. Compliance to the standards and, in the case of gun manufacturers, proof testing is conducted by the individual member companies that belong to SAAMI. Winchester is a member of SAAMI.
CIP is an international association of proof houses. The proof houses are government entities as the members of CIP are individual countries. Like SAAMI, CIP has established standards in dimensions, performance, and proof requirements. Unlike SAAMI, the proof house in each member country interprets the CIP requirements and performs all the required testing. Individual companies cannot be members of CIP.
The United States is not a member of CIP, as standards here are based on SAAMI. SAAMI and CIP have been co-operatively working together to establish universal international standards. However, at this timethere are numerous differences between SAAMI and CIP. These range from conversion and rounding factors between metric and US units, different pressure measuring systems – notably for centre fire products, to different standards of compatibility between ammunition and firearms. This latter difference is particularly noticeable in steel shot firearm proofing and use requirements. This document will focus on safety and proofing methods only. Dimensional and ammunition performance will not be compared, unless directly relevant to the point in hand.
In SAAMI, the safety/compatibility of a firearm and ammunition is controlled through chamber pressure. For 12 gauge 2-3/4" and 3" ammunition, SAAMI established 11,500 psi (793 bar) as the maximum test pressure of an ammunition sample of 10 shots fired at time of loading. NOTE: this value is for all shot shell products manufactured for 12 gauge 2-3/4" and 3" ammunition; lead shot – all shot sizes, buck shot – all shot sizes, slugs – all types, AND steel shot – all shot sizes. This makes sense in that the same firearm may be used with all these product types (see Diagram 1).
SAAMI established definitive proof pressure level by statistical calculation based on the pressure limit per above to ensure the minimum average proof pressure exceeds the maximum average working pressure of the cartridge. These pressures substantially exceed those developed by normal service loads and are designed to stress firearms components which contain the cartridge in order to ensure safety in the recommended use of the firearm during its service life.
For 12 gauge 2-3/4" and 3" ammunition, the SAAMI definitive proof load pressure is 19,000 psi (1,310 bar) minimum average and 20,500 psi (1,413 bar) maximum average. This range of definitive proof pressure applies for every gun, independent of action type (over/under, side x side, pump, semi-auto, single shot) or intended use (including steel shot and lead shot).
As an over-view, SAAMI looks at the safety/compatibility of gun and ammunition as a factor of stress to the firearm through the cartridge pressure. The cartridge pressure is established at the time it is loaded and is controlled to a specified level.
The gun is proofed at a significantly higher level. The gun does not know if lead shot, steel shot, buck shot, or a slug is being fired. The gun sees metal stress as applied by the internal pressure of the cartridge.
CIP varies from SAAMI in its approach to gun proofing, notably singling out steel shot loads.
CIP not only considers chamber pressure but also places restrictions on shot velocity, shot size, momentum (shot weight x velocity) and choke restriction. The following are opinions from a SAAMI/United States perspective on these extra CIP requirements.
Standard steel/high performance steel ammunition and proof chamber pressure
CIP sets two levels of chamber pressure for steel shot classification and proof: Standard Steel Shot and High Performance Steel Shot. The Standard Steel Shot has a maximum average pressure of 740 bar (10,733 psi). This maximum average is below the limit for all 12 gauge shells (11,500 psi) in the United States – lead and steel. The proof level for Standard Steel Shot, 1,200 bar (17,405 psi) is also below the proof level of all 12 gauge guns (lead and steel) in the United States.
The High Performance Steel Shot has a maximum average pressure of 1,050 bar (15,229 psi). This maximum average is significantly higher than all 12 gauge shells in the United States – lead and steel, even including the new 3-1/2" loads. The proof level for High Performance Steel Shot, 1,370 bar (19,870 psi), actually falls right in the middle of the United States proof load specification (19,000 to 20,500 psi). Note that from a SAAMI standpoint, this CIP High Performance proof level is low for the actual working pressure of the service loads (see Diagram 1).
CIP sets a maximum velocity for each of the steel shot levels; 400 m/s (1,312 f/s) for Standard Steel Shot, and 430 m/s (1,410 f/s) for High Performance Steel Shot. SAAMI has not limits on velocity. Since chamber pressure is established at time of loading, for ANY shot weight load, the stress on the chamber applied by the cartridge is established and controlled. In studies conducted over the last 25 years, it has been found that stress to the choke and choke tubes will generally increase with velocity. However, the amount of stress is actually controlled by the complete cartridge system, most importantly the steel shot wad design. From a SAAMI/United States perspective, velocity is independent of chamber stress as long as the pressure is controlled properly, and damage to choke tubes cannot be controlled by velocity alone since wad design is the significant controlling parameter.
CIP sets limits on maximum shot size. SAAMI has no limits on shot size. The reasons are identical to those discussed under Maximum Velocity above. Note it is very common in the United States to use shot sizes larger than CIP maximum. Again, from a SAAMI/United States perspective, the concern with shot size relates to potential choke damage and this is controlled through wad design.
Maximum momentum (shot weight multiplied by velocity)
CIP sets limits on maximum momentum. SAAMI has no limits on momentum. SAAMI has no explanation why momentum would be limited but suspects it is another attempt to control choke deformations as with velocity and shot size limits.
Maximum choke restriction
CIP sets a maximum choke constriction of 0.5mm (0.0195 inch) for High Performance Steel only. This
This correlates roughly to a modified choke in United States terminology. SAAMI has no restriction on choke size used for steel shot. It is common knowledge, and recommended by firearm manufacturers, that there is no reason to fire steel shot in a choke tighter than modified. This is for two reasons: there is no performance (pattern) improvement with steel shot in tighter than modified chokes; and the ighter choke will result in more strain to the choke. As previously mentioned, with proper wad design choke strain is controlled. Under worse case condition of load design, gun metal strength, choke constriction, and usage (number of shots fired) there is the possibility of the choke constriction being deformed after extensive firing. This will normally result in the inside diameter of the choke opening up a slight amount, possibly also showing a visible bulge on the barrel exterior. Note that this has no impact on safety or even gun performance with steel shot, but could open up patterns slightly with lead shot fired in the same gun (no safety issue).
To summarise, there is a significant difference in the approach taken by SAAMI and CIP in respect to steel shot performance and firearm proofing methods. SAAMI sets limits based on chamber pressure of the cartridge, independent of the type of shot charge being fired.
CIP has established two different pressure levels for steel shot. The first, Standard Steel Shot, is lower in maximum pressure than all SAAMI products, including lead shot. The second, called High Performance Steel Shot, actually has service pressure far in excess of SAAMI 12 gauge 2-3/4 inch and 3 inch service loads. Interestingly though, the CIP proof level for these products is much less severe (lower) than SAAMI would set for a similar service pressure.
In practice, all SAAMI 12 gauge 2-3/4 inch and 3 inch cartridges have service pressures that fall inbetween the two grades for steel shot established by CIP.
CIP has established multiple other criteria that from a SAAMI viewpoint have no impact on gun safety as defined as stress to the action. A best guess is that these ancillary criteria were established in an effort to control choke deformation. Choke deformation is not a safety issue and, unfortunately, the parameters controlled by CIP will not guarantee there is no choke damage. The significant system parameter that controls choke deformation is wad design.
Steel shot cartridges have advanced significantly in design and performance over the past 25 years. Items of concern early in the steel shot era included barrel and choke damage and poorer performance than standard lead loads. We have learned that steel shot must be approached as a total components system.
Currently manufactured American steel shot cartridges are closer than ever to lead shot performance and are safe in any firearm manufactured to SAAMI criteria.
The following diagram has been prepared by the HAC from the information provided above to assist in interpreting chamber pressures and proof pressures applying under the SAAMI standards and the CIP regulations.
Diagram 1: Chamber Pressure and Proof Limits for SAAMI Standards and CIP Regulations
Australia does not have proofing houses where we can pressure test our guns (as in Europe), nor do we have a standards association like the American Institute (SAAMI). We are therefore, by default, under the influence of both, when we buy and use imported European and American manufactured products. There are no relevant controls on what is brought into and sold on the Australian market. All American 12 gauge 2¾" & 3" shot shells are manufactured to a set upper limit for chamber pressure, and all their guns are built to accommodate these pressures with a wide safety margin. We are advised that steel loads in America are manufactured to the same maximum pressure limits as their current lead counterparts.
In Europe, their regulatory body (CIP) has developed two standards for steel shot shells, called Standard loads and High Performance loads. Like America, these standards include limits for chamber pressure, but also include velocity, momentum and shot size. CIP believe these regulatory standards are necessary to ensure the steel shot marketed in CIP countries is matched to the range of firearms they make and use in Europe.
SAAMI suggest the last three of these CIP standards appear to be controls to limit the chance of choke swelling in thin-wall barrelled and tightly choked guns. The American manufacturers believe these additional controls still may not eliminate the possibility of choke swelling - in their opinion, it is the design of the wad that is the most significant controlling parameter.
So, from a user safety perspective, it would seem we should apply the same precautionary rules for selecting steel shot cartridges as we should when selecting lead shot cartridges. That is, we should be using a gun which is safe for the chamber pressure generated, irrespective of the shot type in the load.
In addition though, ballisticians around the world do agree there is an increased risk of choke swelling in tightly choked guns and recommend hunters should consider having these chokes opened a little in existing guns when using steel shot, or consider the installation of interchangeable choke tube systems.
European gun manufacturers and retailers are often including "proofed for steel" in their advertising for new guns. We can take this to mean that the barrels and choke tubes have been constructed to ensure choke swelling does not occur, and that higher chamber pressures can be safely used from the CIP's High Performance group. It does not mean that an existing gun, without this proof stamp, is inherently unsafe to use steel loads which generate lower chamber pressures, comparable to existing lead shot loads. If in doubt about your gun – see a competent gunsmith.
It has to be acknowledged that this is a less than perfect arrangement for the Australian hunter. But we can take some reassurance from the practical experience of steel shot use in Australia. After nearly a decade of non-toxic shot use in South Australia and the Northern Territory and several years of use in Victoria, no user safety or gun damage incidences have been reported from its use.
If you are in any doubt over your shotgun's ability to use non-toxic alternatives (especially steel), consult a qualified gunsmith or your firearm's manufacturer.
Read the Shotgunning Education Manual for more details.