06/02/2024 | Hints from the experts

Dear reloaders,

It is possible to use “classic” fast burning powders to achieve reduced loads and subsonic loads for long guns. However, the fact that only 30 - 50% of the possible load volume is typically used results in certain disadvantages. The low filling level means the development of the shot is affected by the position of the powder inside the case. What’s more, a double loading is also possible.

RS14 is free from these disadvantages. Its low bulk density and low energy content mean the filling level is always above 50%. Even a load with a 100% filling level (normally) remains below the permitted Pmax. Reload Swiss has carried out intensive testing on RS14 in many different calibres, enabling us to provide the following recommendations.
 

RS recommendations

• Shorter barrels are more suitable for long guns when using reduced loads and subsonic loads. RS14 is a fast-burning powder. A brief impulse is followed by a long travel distance with resistance, which can have a detrimental impact on the extreme spread of the muzzle velocity (V0).
• QuickLoad and GRT are unable to simulate such processes precisely. As a result, actual velocity is usually lower than the simulated value.
• When making subsonic loads, it is always advisable to start with the load in the supersonic range. The load can then be continuously reduced until the subsonic range is reached. This prevents squib loads, when the projectile does not exit the barrel.
• Projectiles with lower resistance in the barrel are advisable for subsonic loads.
• Heavy projectiles with reduced V0 require a faster twist rate if they are to be stable in flight.
• Normal (not Magnum) primers are advisable.
• Although loads with a filling level of around 50 - 100% are possible, the best V0 extreme spread is (normally) achieved when the filling level is approximately 70 - 90%.
• Compressed loads are not advisable.
• If a sound suppressor is to be used, the load should be developed with it.

 

Shooting .308 Win. subsonic

One typical application for RS14 is in a .308 Win. subsonic load with heavy projectiles. V0 must be in the subsonic range (less than 343 m/s in dry air at 20°C). The speed of sound in air and the V0 of the projectile vary depending on the temperature (and V0 always has a spread). Consequently, V0 must be lower, ideally between 300 m/s and a maximum of 330 m/s.

A C.I.P. test barrel measuring 600 mm in length with a 1:12" twist is unsuitable for projectiles that are over approx. 190 gr. These projectiles are unstable in flight, often flying diagonally after only a five-metre distance from the muzzle. These loads were therefore shot in a special test barrel. The barrel measured just 450 mm. Projectiles up to 240 gr could be stabilised satisfactorily with a twist of 1:8".

Excellent results were achieved with 200 gr Lapua subsonic projectiles. The shooting configuration is set out in the table below:

Calibre	.308 Winchester
Load	RS14 10.5 gr
Filling level	78%
Test barrel	Barrel length 450 mm, twist rate 1:8"
Case	Lapua
Projectile	Lapua Subsonic B416 200 gr
Primer	S&B LR
Cartridge length	66.6 mm
Shots per group	10

The guide section of the projectile features several grooves designed to reduce resistance in the barrel. The cartridge length was kept short to reduce the loading volume. The first part of the test examined the results produced by different powder positions (SD = standard deviation):
 

21 °C		Position of the powder in the case
		Against the primer	Horizontal	Against the projectile
V5 mean value	m/s	315	320	325
V5 SD	m/s	3.7	2.0	1.9
V5 min.	m/s	309	317	322
V5 max.	m/s	322	323	329
Pmax mean value	bar	1651	1924	1996
Pmax SD	bar	87	44	12

When using this configuration, the position of the powder has little influence on the results. The differences would be much bigger when using a “classic” powder filled to a low level. This configuration was also tested at different temperatures and the results are very consistent:
 

Powder horizontally oriented		Temperature shooting test
		-30	21	50
V5 mean value	m/s	316	320	324
V5 SD	m/s	4.0	2.0	3.9
V5 min.	m/s	309	317	318
V5 max.	m/s	322	323	331
Pmax mean value	bar	1832	1924	1969
Pmax SD	bar	36	44	82

 

Summary

• It is very easy to adjust a load when using RS14. In contrast to usual practice, it is advisable to start with a higher load and work down to a lower load in order to prevent squibs.
• Excellent V0 extreme spreads can be achieved, although these are highly dependent on the projectile and gun.
• Due to very low bulk density, it is practically impossible to exceed the gun pressure limit, which makes RS14 very safe to work with.
• The position of the powder and external temperatures have little influence on RS14 loads.

Jan Krcmar
February 2024