Gunsmithing How to slow a bullet down in a bolt gun?

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okiehuntnfish

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Dec 15, 2009
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#1
I would like to know if it is possible to slow a subsonic bullet down going through a bolt gun so there will be no "crack".

I have two guns and one silencer I share with each. I am shooting sub-sonic rounds. (I have tried 4 different brands of sub-sonics all with the same results)

-1st gun POF 308 with 2-position gas plug for normal (N) or suppressed (S) operating modes.
-2nd gun Rem 700 with the threaded AAC barrel.

Both guns shooting subsonics through the same silencer. The Rem 700 has a sonic crack. The POF has the same sonic crack until I put the gas plug on suppressed. Then it is REALLY quiet with no subsonic crack.

Is there something that can be done to the bolt gun that will release some of the pressure and slow down the bullit so there will be no sonic crack?
 
#3
Re: How to slow a bullet down in a bolt gun?

It is the expanding POWDER gas that is supersonic...not the bullet. Experimenting with different powders may help. Perhaps one that has passed its peak pressure while in the bore may decrease the noise.
 
#5
Re: How to slow a bullet down in a bolt gun?

Many different things can have an effect on muzzle velocity and just because a bullet is sub-sonic in one platform/rifle, doesn't mean that it will perform identically in another. Even a seemingly slight variation in MV or in the atmospheric/enviornmental conditions could have an impact.

Try running a chrono on the loads you are using to determine what MV you are getting out of each rifle, both shooting suppressed and not. You may be surprised at the results.

Depending on your results, move up to a heavier bullet (if your barrel can adequately stabilize a heavier bullet and not cause problems) or change out your powder.

It would be helpful to know what specific ammo (or the specs of your reloads) you are using running.
 
#6
Re: How to slow a bullet down in a bolt gun?

As pointed out you really need to chrony the ammo before going further. I'm guessing you're buying after market subsonic ammo which is right on the edge as opposed to rolling your own. Here's a handy calculator Speed Of Sound that will give you the speed of sound based on your temperature. If your chrony'ed velocity is under the ft/s value, you shouldn't have a sonic crack, over it and you will. There are other more sophisticated sos calculators on the web.

I'm guessing the reason you get subsonic performance on the POF is the gas port is dumping enough pressure before the bullet uncorks to keep the projo subsonic. Best bet is roll your subsonic, at least for the Rem. Sierra has recommended loads, just call.
 
#7
Re: How to slow a bullet down in a bolt gun?

first off, as stated in above posts...CRONO !

stop shooting indoors.

when you jock up and go smack something out of doors, i garUNtee you the boolit hitting the target will make more noise than the report right after the trigger yank......regardless of first round pop
 
#8
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BOLTRIPPER</div><div class="ubbcode-body">..When you jock up and go smack something out of doors, i garUNtee you the boolit hitting the target will make more noise than the report right after the trigger yank......regardless of first round pop </div></div>

My quiet loads all have that caveat, soft bullet stop, like the body of a pest.
 
#9
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">
Understand the speed of sound is not constant. Its directly related to the air density at a given elevation.
</div></div>

Not to be too technical, but the speed of sound is primarily dependent on air temperature (which directly affects air density).

Here is a good explanation of the physics details:

http://www.sengpielaudio.com/calculator-speedsound.htm
 
#10
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: johnsopa</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">
Understand the speed of sound is not constant. Its directly related to the air density at a given elevation.
</div></div>

Not to be too technical, but the speed of sound is primarily dependent on air temperature (which directly affects air density).

Here is a good explanation of the physics details:

http://www.sengpielaudio.com/calculator-speedsound.htm </div></div>

I've read through this and although math is something I firmly believe in, I'm not quite understanding this.

In order for the sound generated from your vocal chords to rattle against my ear drums some medium has to be present right?

Be it normal earth atmosphere, water, or even baby oil if we want to get kinky.

That being said since as long as I can remember it's well understood that sound travels through water at a higher velocity than it does our atmosphere. As we increase in altitude the air becomes progressively thinner until we enter the vacuum of space. Never been there but I'm told its a pretty quiet place.

Looking from that perspective if I'm on the moon and it's 400*f outside is sound really going to travel at the same velocity as it does at the bottom of the ocean next to a volcanic vent spewing out 400*F seawater?

I mean if pressure really means nothing. (as described in the context of the link you provided) I realize this is an extreme example, but I'm still not buying that if I chronograph a bullet on top of Mt. Everest on a toasty -20*f afternoon and hear a supersonic crack that same report is going the same speed as a -20*F day here in S. Dakota.

I've shot subsonic loads indoors at the OTC in COS, CO that occasionally snapped that under virtually identical conditions (temperature wise) don't crack when at Camp Perry.

In this case the only thing different is the air density. CO is substantially drier and higher in elevation than all of Ohio where it's a muggy, dense miserable biche in August.

Again, I love the math, but practical experience just isn't allowing me to get my head around this.

C.
 
#11
Re: How to slow a bullet down in a bolt gun?

Chad's right. It is far more the density of the medium that dictates the speed of sound over the temperature. For an ideal gas such as air, the temperature has a lot to do with the density.

However, the same temp day at sea level vs. Mt Everest you will find the speed of sound to be higher on the beach. Cold, clear, winter days tend to be higher pressure and therefore higher density than warm summer days in the same location. Developing a subsonic load in July in Montana could really screw a "tactical silence" operation during the winter in Texas.

ETA: The speed of sound in water is far higher than that of air, even if they're at the same temperature. This is why unless you have a LOT of underwater experience it always sounds like the jetski across the harbor is about to treat you like a manatee. After some time underwater diving in a river I've come to recognize when something is really close and where it's coming from, but my brain is programmed and used to listening for differences in sound through air, not through water. It took a while to learn how to handle it in water.

Likewise, the speed of sound in barrel steel is something along the lines of 6km/s (~20,000fps) so the bullet moves at a subsonic speed through that barrel, but the shock waves from the primer going off move at the speed of sound through the medium (barrel steel) and this is one of the ideas involved with optimal transit theory.
 
#12
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">Chad's right. It is far more the density of the medium that dictates the speed of sound over the temperature. For an ideal gas such as air, the temperature has a lot to do with the density.

<span style="font-style: italic"><span style="font-weight: bold">However, the same temp day at sea level vs. Mt Everest you will find the speed of sound to be higher on the beach. Cold, clear, winter days tend to be higher pressure and therefore higher density than warm summer days in the same location. Developing a subsonic load in July in Montana could really screw a "tactical silence" operation during the winter in Texas.</span></span>

ETA: The speed of sound in water is far higher than that of air, even if they're at the same temperature. This is why unless you have a LOT of underwater experience it always sounds like the jetski across the harbor is about to treat you like a manatee. After some time underwater diving in a river I've come to recognize when something is really close and where it's coming from, but my brain is programmed and used to listening for differences in sound through air, not through water. It took a while to learn how to handle it in water.

Likewise, the speed of sound in barrel steel is something along the lines of 6km/s (~20,000fps) so the bullet moves at a subsonic speed through that barrel, but the shock waves from the primer going off move at the speed of sound through the medium (barrel steel) and this is one of the ideas involved with optimal transit theory. </div></div>

<span style="font-style: italic">
I've shot subsonic loads indoors at the OTC in COS, CO that occasionally snapped that under virtually identical conditions (temperature wise) don't crack when at Camp Perry.</span>

I said this right right?
 
#13
Re: How to slow a bullet down in a bolt gun?

It's been said, but to the point, it is the speed of the gas causing the problem, you should be able to solve the problem, with hand loads. Go to a faster powder. Also have you shot the offending weapon over a chrono, as it may not be sub-sonic at all. For all practical purposes if your shooting at 1050 fps, you're subsonic (projectile not gas). Have you tried shooting your can wet?
 
#14
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">Chad's right. It is far more the density of the medium that dictates the speed of sound over the temperature. For an ideal gas such as air, the temperature has a lot to do with the density.

<span style="font-style: italic"><span style="font-weight: bold">However, the same temp day at sea level vs. Mt Everest you will find the speed of sound to be higher on the beach. Cold, clear, winter days tend to be higher pressure and therefore higher density than warm summer days in the same location. Developing a subsonic load in July in Montana could really screw a "tactical silence" operation during the winter in Texas.</span></span>

ETA: The speed of sound in water is far higher than that of air, even if they're at the same temperature. This is why unless you have a LOT of underwater experience it always sounds like the jetski across the harbor is about to treat you like a manatee. After some time underwater diving in a river I've come to recognize when something is really close and where it's coming from, but my brain is programmed and used to listening for differences in sound through air, not through water. It took a while to learn how to handle it in water.

Likewise, the speed of sound in barrel steel is something along the lines of 6km/s (~20,000fps) so the bullet moves at a subsonic speed through that barrel, but the shock waves from the primer going off move at the speed of sound through the medium (barrel steel) and this is one of the ideas involved with optimal transit theory. </div></div>

<span style="font-style: italic">
I've shot subsonic loads indoors at the OTC in COS, CO that occasionally snapped that under virtually identical conditions (temperature wise) don't crack when at Camp Perry.</span>

I said this right right? </div></div>

Yep, I'm not sure what you're getting at though? Perhaps I was unclear with what I was going after above, but let me try again.

The stuff cracked in CO because even though the muzzle velocity was the same, the local atmospheric conditions dictated a lower speed of sound, so the bullets were supersonic in CO as opposed to OH. The change in atmosphere was not the temperature effect but rather the local pressure due to altitude change.

Going from sea level to 2000' ASL in 2 different shooting positions near me gives me lower local pressures in just 2000' of altitude change at any time of the year compared to any other time of the year at the sea level shooting area. Altitude change has more effect than the temp change.
 
#15
Re: How to slow a bullet down in a bolt gun?

Let's talk actual data
speed of sound at sea lever 15C MPS 340.3 or 1116fps
at 5000 feet 5.1C MPS 334.4 OR 1097 fps
at 10,000 feet -4.8C MPS 328.4 or 1077fps
If you are shooting at or below 1050FPS, you'll be sub-sonic in all but the very highest of peaks in the US. And as you'll be almost alone up there, who'll hear it anyway?
 
#16
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: paw print</div><div class="ubbcode-body">Let's talk actual data
speed of sound at sea lever 15C MPS 340.3 or 1116fps
at 5000 feet 5.1C MPS 334.4 OR 1097 fps
at 10,000 feet -4.8C MPS 328.4 or 1077fps
If you are shooting at or below 1050FPS, you'll be sub-sonic in all but the very highest of peaks in the US. And as you'll be almost alone up there, who'll hear it anyway? </div></div>

"Critical Mach Number" is an important thing to keep in mind. The actual "Speed over ground" of the bullet is secondardy to the CMN value over a particular bullet and it is entirely shape dependent.
 
#17
Re: How to slow a bullet down in a bolt gun?

Part of the problem here is that there are several different things going on.

As far as your example of sound in space, you need to consider both the speed of sound(which is practically independent of pressure) and acoustic impedance( which is proportional to density). This means that as density goes to zero, the distance that a sound travels, before its amplitude decays to almost nothing, also goes to zero (it actually is an exponential decay in amplitude as a function of distance).
 
#18
Re: How to slow a bullet down in a bolt gun?

What bullet are you shooting? Let's not speculate. I hope it isn't one of those special tear drop bullets Navy Crane developed?
 
#19
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: paw print</div><div class="ubbcode-body">What bullet are you shooting? Let's not speculate. I hope it isn't one of those special tear drop bullets Navy Crane developed? </div></div>

Doesn't matter what bullet you shoot: Round nose, flat point, spire point flat base, OTM, Amax, OTM backwards in the case, or a specially designed subsonic flight optimized flight projectile.

CMN is extremely important for quiet flight of ALL of them. Simply stating a speed to shoot all bullets at doesn't solve the problem every time.
 
#20
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: paw print</div><div class="ubbcode-body">What bullet are you shooting? Let's not speculate. I hope it isn't one of those special tear drop bullets Navy Crane developed? </div></div>

Doesn't matter what bullet you shoot: Round nose, flat point, spire point flat base, OTM, Amax, OTM backwards in the case, or a specially designed subsonic flight optimized flight projectile.

CMN is extremely important for quiet flight of ALL of them. Simply stating a speed to shoot all bullets at doesn't solve the problem every time. </div></div>


My understanding is that when the CMN is reached/exceeded you will get a shock wave, which is noisy, but that you don't get a sonic boom unless the object itself is traveling faster than the speed of sound, causing the shock waves from different points in the objects trajectory to arrive at the same point simultaneously.

So you are saying that there can be significant differences in how loud two subsonic bullets sound, depending on their CMN, or do I misunderstand you?
 
#21
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JustForFun</div><div class="ubbcode-body">


So you are saying that there can be significant differences in how loud two subsonic bullets sound, depending on their CMN, or do I misunderstand you? </div></div>

Yep, that's exactly what I'm saying.
 
#22
Re: How to slow a bullet down in a bolt gun?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: okiehuntnfish</div><div class="ubbcode-body">I would like to know if it is possible to slow a subsonic bullet down going through a bolt gun so there will be no "crack".

I have two guns and one silencer I share with each. I am shooting sub-sonic rounds. (I have tried 4 different brands of sub-sonics all with the same results)

-1st gun POF 308 with 2-position gas plug for normal (N) or suppressed (S) operating modes.
-2nd gun Rem 700 with the threaded AAC barrel.

Both guns shooting subsonics through the same silencer. The Rem 700 has a sonic crack. The POF has the same sonic crack until I put the gas plug on suppressed. Then it is REALLY quiet with no subsonic crack.

Is there something that can be done to the bolt gun that will release some of the pressure and slow down the bullit so there will be no sonic crack? </div></div>
Someone has gotten way off the subject at hand, in fact has gone sonic, but based on your post, your bullets are not the problem, same load, two different guns, one can, one is loud one is not, common sense should tell even those that think they are super-smart, it is the rifle, not the projectile shape or size, nor the can, causing the problem. The "loud" rifle shoots that load faster than the "quiet" rifle. It is true large caliber bullets make more noise going at same speed through the air than a smaller bullet at same speed etc., less gas to push around, this has nothing to do with your problem, because when you fire those rounds from one rifle with the same can it's quiet. The loud gun is allowing the bullet to go super sonic. Try a faster powder, or wt reduction in you load, should work.
 
#23
Re: How to slow a bullet down in a bolt gun?

your bullet is exiting too fast out of one gun. shoot over a chrony and figure out how much you need to slow it down.

Cold dry air is more dense than warm humid air btw folks. Yeah when speed of sound is important, air temp is a factor..
 
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