Impact Shift with a Suppressed Kalashnikov Action M62 Assault Rifle
The Suppressor Project experiments about suppressor effect on accuracy and Shift of group center with suppressors and empty suppressors jackets of different weights and a flash hider was tested with a 7.62 x 39 Kalashnikov action Sako/ Valmet M62, fitted with a PSO-1 sniper scope. Test was carried out 15.9.1992 at the 90 meters test range of Finnish Army Arsenal 1 (or Army Depot 1), shooting from sandbag rest with regular Finnish Army ammo. Manufacturer and ammunition lot was VPT 78. 5 round groups were fired with each combination by shooter T. Romppanen.
90 m average 5 shot machine rest group diameters were without
suppressor 83 mm and with suppressors 74.8 mm, so tested five different suppressors
produced combined 10 per cent tighter average groups. Best groups were shot with TX8,
resulting to 52 mm average group diameter, or 37 per cent improvement in accuracy from
Impact shift test was shot to demonstrate the effect of mass attached to rifle barrel. It was suspected, that suppressors contributed to accuracy and shifted point of impact primarily by slowing down and suppressing barrel vibrations by their own mass, and not necessarily by affecting the flight of the bullet (excluding wipe type suppressors not tested). It was found, that any extra masses attached to muzzle, including regular flash hider and empty tubes made for this test, produced shift of impact. The amount of shift was roughly proportional to the mass and centre of gravity of the muzzle device. Results are shown in a neighbouring picture.
With the modified Kalashnikov clone, the Valmet M62 assault rifle, barrel vibrations clearly dominate accuracy and impact shift. In all Kalashnikovs, the barrel tends to strongly vibrate diagonally in up and right to down and left plane. The vibration is triggered mainly by the short two lug bolt suddenly clacking from loose to it's right position under chamber pressure. This causes strong bending vibrations in the barrel. The muzzle is allready moving diagonally, as the bullet emerges it. So, any mass attached to muzzle, including flash hider or suppressor, affects the phase and amplitude of muzzle vibrations, thus giving the bullet a usually reduced orthogonal velocity component.
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