Background

Like the name implies, the Hispano cannon was developed by the French company Hispano-Suiza. It was based on the earlier Swiss Oerlikon FF S weapons, which the company manufactured under license in France as HS.7 and HS.9. In the late 1930s, engineer Marc Birkigt designed a new and much improved version with a revised action, much faster rate of fire, and somewhat higher muzzle velocity. The result was the Type 404, or HS.404, which was widely considered the best aircraft cannon of its kind. Great Britain acquired a license to build the HS.404, which was first used in a British fighter as the Hispano Mk.I with the Westland Whirlwind in 1940. British engineers developed a belt-feeding mechanism and the new design was adopted by the RAF and FAA in 1941 in a slightly modified form as the Hispano Mk.II. Four cannons replaced the eight Browning .303 machine guns in the Hawker Hurricane Mk. IIc and in Supermarine Spitfire Mk. Vc, and became standard armament in late-war British fighters such as the Hawker Typhoon/Tempest family and late marks of the Spitfire. Although earlier Spitfires equipped with Type C wing could accommodate four cannon, most of them carried only two because of technical difficulties such as inadequate gun-heating capacity for the outboard cannon leading to the gun freezing at high altitudes.
Martin Waligorski and Wikipedia

Contents

Master has released two all metal improvement sets depicting the uncovered early type cannons on the Typhoon Mk.Ib. The barrels feature two different types of recoil spring: flat and round. Each release is double bagged with the outer bag being press sealed. The various components are separetly stored in clear plastic pouches. Uncovered cannons barrels seem to feature a fair bit in photographs of the Typhoon being serviced. This release contains just the cannon barrels and the recoil spring.

Am-24-014 Hawker Typhoon Mk.IB early type cannons with uncovered barrels with flat springs. This release contains twelve turned metal parts and instructions

AM-24-015 Hawker Typhoon Mk.IB early type cannons with uncovered barrels with round recoil springs. This release has twelve turned metal parts and four springs as well as instructions.

The quality of the parts for both releases is quite stunning and will certainly add to the look of the finished model. They are simple to put together thanks to the excellent instructions and the fit is very good. They will need a dab of cyanoacrylate glue to attach the parts together and to glue in place in the kit.
The instructions are simple black line drawings and provide not just information about constructing these beauties they also illustrate how to adapt the kit parts to accommodate the Master cannon barrels

Conclusions

Uncovered cannons barrels seem to feature a fair bit in photographs of the Typhoon being serviced. So if you are thinking of going in the direction of using your Airfix 1/24 scale Typhoon in a diorama, then these releases from Master are well worth considering. The quality and fit is excellent and the separate round springs with AM-24-015 and the turned flat springs of AM-24-014 certainly add an air of reality.