View Full Version : Different Loads For Silenced Weapons

May 29, 2008, 08:25 PM
I was watching a few videos on silencers and I know it makes sense that when they were shooting the Mini 14 with subsonic ammo it did not have enough return gas to auto cycle. I guess my confusion lies in all the other rifles out there (Mp5, M-4, etc.) that still have enough return gas to auto cycle. I only assume that larger rifles require more gas to cycle on their own. I hope some of that made sense lol. Thanks :confused:

May 31, 2008, 11:05 AM
Still confused lol

May 31, 2008, 03:58 PM
Submachine guns (MP5, Sten, Sterling) use a variation of the same blow-back principle; the inertia of the bolt at rest is overcome by the back pressure created by firing the cartridge and moves rearward, extracting and ejecting the empty case on the way and chambering the next round on the return trip, powered by the recoil spring. No gas or gas system is involved. Any sub- or supersonic load that can overcome the bolt inertia (and recoil spring pressure) will function the action. For gas-operated systems (M16, M4, AK47, AK74) functioning is dependent on the pressure of the gas at the gas port being high enough to push the operating rod or piston back with enough force to push the bolt back, unlock the action and extract and eject the fired case. The next round is chambered by the energy stored in the operating spring that was compressed when the bolt was pushed back. For automatic functioning to occur with subsonic ammo, it has to produce the same pressure as supersonic ammo, which is not easily done. The Russians solved the problem by using a high-pressure chamber in the suppressor that creates enough back pressure to cycle the action. They also use a 180-gr. bullet in their subsonic 7.62x39mm ammo which helps maintain gas pressure in the barrel, being heavier and more difficult to move than the normal 125-gr. bullet. The heavier bullet gives better terminal performance, too. They fielded a 9.3x39mm round and a suppressed sniper rifle that was designed from the ground up for that purpose alone. You could also go with a slower-burning powder that would reach the required pressure just as the bullet was passing the gas port, but that would really involve some finagling. I was recently on hand for some suppressed M4 and bolt-action .308 WCF firing, and even with supersonic ammunition, muzzle blast was on par with a .22 Magnum rifle.

June 1, 2008, 11:15 AM
by shortening the gas rod or put a weaker spring in.

June 1, 2008, 11:16 AM
it's that simple

June 1, 2008, 11:58 AM
I use regular loads in my MP5-SD. However, using subsonic will eliminate the noise.

June 1, 2008, 12:17 PM
by shortening the gas rod or put a weaker spring in

Which firearm platform are you refering to?

June 2, 2008, 09:08 PM
I was referring to the Mini 14 in this video when using subsonic loads he had to cycle himself.