Hoening Big Bore Slug LLC has been on a quest to improve ammunition for the 45-410. The idea is to improve performance of these guns by use of better ammunition. After considerable testing and design of ammunition it is apparent the gun design needs improvement. Ammunition that works well in one gun does not work well in another because of chamber design and mechanical tolerances. After all there is no real design other than it uses 45LC and .410 bore shotshell. There is much room for variation and the manufacturers use it liberally. Both types of basic ammunition have similar "standard" pressure limits which makes for a good pairing. The calibers are fairly close but not close enough for ready made accuracy (typically) when using both in the same firearm. The greater problem is the difference in shell case diameter, shell case length, and barrel throating. These three items may be rated by significance differently depending on the particular combination of ammunition and firearm.
The approach used by HBBS LLC to improving performance in the 45-410 is simply increase power and accuracy when using slugs. Increasing power is perhaps the easiest to accomplish by virtue of the crude methods that may be employed, simply increase the powder charge or in a more refined approach change the powder selection, charge and characteristics. The three significant problems mentioned above now have greater importance and one may clearly be more significant than another depending on the particular manufacturers chambering. For instance, for safety reasons excessive clearance at the base of the shell may prohibit a more powerful load that is generally associated with higher pressure. Power can be achieved without the increased peak pressure but this limits the selection of powders available to achieve the goal. With a limited selection of powders suitable for the desired outcome, shell capacity now becomes important and the shell case length and diameter now have increased significance. A case length that has the required powder capacity may be long enough to limit the slug selection and seating depth that maintain the required over all length and that length may be limited by throating or other transition to the barrel bore.
Improving accuracy has another set of problems stemming from the three most significant problems. The most obvious may be the long jump to the barrel for the 45LC slugs leaving their shorter cartridge and becoming unstable before engaging the barrel with the resulting deformed slug, an example of shell case length importance. The common forcing cone used for shot cartridges causes similar problems with the longer 410 slug becoming unstable in the cone area before engaging the rifling and the 410 slug is grossly undersized anyway, another serious problem affecting accuracy. A suitable throat may help this situation but a throat suitable for .410 bore slugs will not work for .45 LC slugs and vice versa. Shell case diameter (or more correctly in this instance, slug diameter) importance is shown here.
There are general factors independent of shell length and diameter or throating varying from one manufacturer to another that affect ammunition performance. Bore size and depth of rifling grooves will affect slug fit and performance. Muzzle finish or crown will affect performance and consistency. HBBS LLC has been working on slug load performance but keep in mind what is good for shooting slugs may not be good for shooting shot shells. To keep the versatility of the 45-410 intact this has to be dealt with. In some instances it may be of interest to forfeit the use of shot shells and this would solve some of the accuracy problems with the 45-410.
The conclusion from research to date indicates the quest for improved 45-410 ammunition is best left for the custom loader to load for a particular firearm to overcome its particular deficiencies. Finding a universal load that significantly improves power and accuracy in the many different manufacturers 45-410 chamberings is much more difficult than loading for a specific application. Modified brass hulls or better yet custom brass hulls, custom slugs, and suitable powder charge can help accuracy and power to varying degrees, the goal HBBS LLC set out to accomplish. Use of standard materials can improve power or accuracy to some extent in some instances and not in others depending on the variables present. Probably the most significant improvement for ammunition will be a custom brass hull (that can be fireformed if needed to fit "sloppy" chambers) for the 45-410 chamberings. It is also clear that a custom 45-410 chamber with suitable tolerances will greatly lessen many problems and with a custom brass hull it would eliminate the problems associated with using slugs. 45LC could still be used but with a decrease in accuracy from the level of the custom brass loads and of course less power. Shot shells could be used but with the same problems associated with the rifled barrels in common use now. A straight rifled tube accessory may help this.
An alternative to a custom barrel and chambering and the approach used by HBBS LLC for practical testing is modification of existing chamber and barrel. Some things can be improved by machining where possible. Some designs being overly large or having excess clearance can not be helped. The custom modified barrel with custom ammo goes a long way toward improving accuracy and power, especially for a slug only gun. HBBS LLC has developed custom .45 slugs, and worked on modifying brass shells for use in 45-410. Work continues on this project and it is expected that custom loading components will result from this research.
The above summarizes what I received from Ed Hoening of Hoening Big Bore Slug LLC about the work on the 45-410 project. Ed's many observations and comments included: Barrel selection and basic platform, in this instance the TC platform, fitting to frame, headspace, barrel to cartridge base clearance, barrel sites or optics, brass selection and/or plastic hull, neck clearance for custom 45 slug, barrel throating of absence of throat, starting powder charge and unexpected results, use of safe loading practices, recognizing and troubleshooting case warning signs, annealing, barrel crowning, and overall opinion of 45-410 performance, typically settle for what it is or go completely custom. JH