Look at it this way, if the minimum safe load you can shoot a bullet for your caliber exceeds 1100 fps the supressor may not be as quiet as you might think. Suppressors work great with subsonic rounds of 1100 fps or less. Unfortunately the 1:9 twist rate will stabilize the lighter bullets which have velocities much higher than the 1100 rounds, so you might still hear a sonic crack with a supressor. The heavier bullet might eliminate the sonic crack but the twist on your rifle may not be able to stabilize the bullet to provide you with the accuracy you would like to have. It is a hit and miss and you won't know until you try different loads. Below is a listing of the twist rates and bullet range that they can stabilize :

Due to the constant diameter inside the barrel and the fact that most bullets are manufactured with the same components, the best way to determine the proper twist rate is based on the weight of the bullet (measured in grains). The higher the weight, the longer the bullet, and the faster the twist rate.

Twist rate Spoken pronunciation Written notation Bullet weight stabilization
One revolution every 7 inches "One in Seven" 1/7 55-85 grains
One revolution every 8 inches "One in Eight" 1/8 50-80 grains
One revolution every 9 inches "One in Nine" 1/9 45-75 grains

 

Thanks for the good information.

 

You're talking a .223-I have'nt seen anyone selling subsonic ammo or even reloading-a waste of time for this caliber(just buy a .22 and suppress it)........That being said-I run a suppressor on a 12.5",reason-don't have to wear ear protection-can converse with others while shooting-flash suppression-sound of where it's coming from is distorted.

 

Thanks for the input. Some more food for thought. But now a follow up question: Does velocity determine a specific twist rate required?

 

Velocity is just one of several factors that can affect a bullets stability. If I shoot a bullet at 1500 fps and then shoot a like bullet at 3000 fps from the same barrel, the 3000 fps bullet will spin at twice the rate as the 1500 fps bullet. Conversely if I shoot a bullet at 3k fps from a barrel with half as much twist as the bullet traveling at 1500 fps, both bullets will have the same rate of spin.

http://kwk.us/twist.html

Here is an easy to use online twist rate calculator.

It will let you change parameters like bullet length, velocity and diameter to see the optimal twist rate would be for those parameters.

 

Weight of the bullet AND length have more to do with twist rate than velocity.A perfect example is the 1/7 AR-only reason to have is to stabilize 856 round...totally un needed but like those stupid M4 barrels-people want them,so companies make them.A .224 Valk NEEDS a 1/7 barrel to stabilize those long,heavy for caliber bullets.

 

• look up the green hill formula. use a variance of 120 instead of 150. get the right length of bullet for your twist using this formula with a variance of 120 and it will shoot holes in holes at any distance. a neighbor had a 25/06 that didnt shoot for crap. i did the math and told him the bullet length to use when he reloaded. he took my advice and 12 years later he is still dropping bad critter way way out their. still reminds me of how good my advice was. not advice, just good science.

 

I have ar-15's with 1-7 and 1-9 twists. The 1-7 twist is best with 62 grain and up. The 55 and 62 gain bullets work fine in 1-9 with no tumbling or baffle strikes.

If a silencer reduces noise by 30 decibels with subsonic ammo, then it will do the same with standard ammo. The standard ammo is much louder to begin with, so it will also be much louder than subsonic when suppressed. To appreciate how well (or not) a silencer works on an ar-15 with supersonic ammo, stand between them while they are shot. You will notice that the suppressed rifle is much less noisy than the one without the muffler, no matter what ammo is used, provided they are using the same ammo.

I think a 70 grain bullet loaded to 1050 fps in an ar-15 or a bolt gun is far superior to a 40 grain 22lr at 1060 fps or a 60 grain bullet at 700 fps in power and penetration. I've come to expect groups twice as big when shooting subsonic ammo in a rifle made for supersonic ammo.

 

I have ar-15's with 1-7 and 1-9 twists. The 1-7 twist is best with 62 grain and up. The 55 and 62 gain bullets work fine in 1-9 with no tumbling or baffle strikes.

If a silencer reduces noise by 30 decibels with subsonic ammo, then it will do the same with standard ammo. The standard ammo is much louder to begin with, so it will also be much louder than subsonic when suppressed. To appreciate how well (or not) a silencer works on an ar-15 with supersonic ammo, stand between them while they are shot. You will notice that the suppressed rifle is much less noisy than the one without the muffler, no matter what ammo is used, provided they are using the same ammo.

I think a 70 grain bullet loaded to 1050 fps in an ar-15 or a bolt gun is far superior to a 40 grain 22lr at 1060 fps or a 60 grain bullet at 700 fps in power and penetration. I've come to expect groups twice as big when shooting subsonic ammo in a rifle made for supersonic ammo.

In a bolt gun,you're right.....It won't cycle a normally sprung/buffered AR...bolt guns are superior for suppression,but it seems the younguns want everything to cycle an AR,guess a bolt is too difficult...The one I run on a 12.5 gives 135db,which is "hearing safe",but I'm more concerned about flash suppression.

 

I've loaded the Speer 70 grain soft points with about 4 grains of H110 to get 1050 fps. Sounds okay, but I don't like an AR-15 that does not cycle. So I use them in a Mossberg bolt gun.

I have an old worn out 10.5" upper that I might experiment with. A gas port 2" downstream of the chamber might give enough pressure to cycle the bolt if I cut down the spring and empty out the buffer tube.

 

I've loaded the Speer 70 grain soft points with about 4 grains of H110 to get 1050 fps. Sounds okay, but I don't like an AR-15 that does not cycle. So I use them in a Mossberg bolt gun.

I have an old worn out 10.5" upper that I might experiment with. A gas port 2" downstream of the chamber might give enough pressure to cycle the bolt if I cut down the spring and empty out the buffer tube.

Just dedicate upper to subs---lightweight carrier 75$/20% reduced spring/3.0z buffer.....16" and 10.5" both cycle flawless with this setup...In a bolt,try Trail Boss,my Savage is "hollywood"quiet with TB.

 

Thanks. Sounds better than drilling a new gas port.

 

70 grains at 1050 fps only gives you 171 foot pounds of energy. That's less than a CCI Stinger.

 

Yeah, not powerful at all. But far less noisy than the Stinger. Any 22lr moving more than 1150 fps is going to make a loud whip cracking sound that is impossible to eliminate. I think the 70 grain subsonic 223 is going to be more accurate than the Stinger also. Of course it will have a rainbow trajectory; 18" high at 100 yards with a 200 yard zero.