Building a quiet SBR and a cartridge to make it worthwhile.
Posted: Tue Jul 26, 2016 11:36 am
Building a quiet shooting SBR or pistol, is a whole lot more than screwing a suppressor on a short barrel and grabbing a box of subsonic ammo off the shelf. In fact that will lead to a big disappointment.
There have been a lot of threads over the years looking for the quietest suppressor and quietest powder. These threads number in the hundreds it seems and are only outnumbered by the number of posts that say my gun is loud. Well that's not completely true. (The top asked questions are probably, Why won't it cycle and Why are my case mouths dented).
Let's start right off with, if you want a quiet SBR, do not load with 1680. It's loud, it's dirty and basically just disappointing to work with. Save it for heavy supers, or use it if you are just learning to reload until you have some experience and can deal with the possible side effects of faster powders.
The next thing to be aware of is that the quietest loads, can be the most dangerous and unpredictable to work with. They require fast powders at low case fill rates and many times reach the same firing pressures as many supers. Double charging a load is certainly possible . The pay off is a reasonably hearing safe load that can be fired indoors without ear protection.
Suppressor choice, or build style come into play. Mono cores like Gemtech's purpose built 300 can, tend to have a pretty good first round pop. This can negate all the work you put into your build and handloads if used in an emergency situation, no ears inside.
Finally all of this is a waste of time if the whole system is unreliable. If you can not do at least two successive mag dumps and have the bolt lock back on empty each time, then you are no where near having a reliable setup.
Let's start with the basics.
There are way too many variables for the "quietest subsonic load". The basics won't change, but if you are doing a purpose built rifle, it can be very quiet and reliable.
First, what is counter intuitive is to leave the gas port as small as possible, or run an adjustable block. This will reduce port noise. No sense making it quiet at the muzzle just to have it louder at the other end. There is no reason to have a pistol length port over .100" and plenty of reasons to have it less.
Barrel length also makes a noticeable difference. I have had the chance to run 7-8.5" in 1/2" increments and noise increases noticeably at each length. Shorter is louder.
Bullet choice will also be an issue. A longer bearing surface can help create back pressure and choice of material can play a role. A good example would be the Lehigh 174 grain bullet. I tried very hard to develop a load for it that met other requirements I had. Basically I chose to run Accurate #9. I had no problems getting full function using Sierra 175 and 168 Matchkings, but I had trouble with reliable cycling and locking back if the 174 Lehigh stayed subsonic. I cured it by moving to the 194. The problem was the brass, it behaves more like lead when it comes to creating pressure.
Powder choice as pointed out earlier is critical. The two powders I have ran that are the quietest and still have full function are Accurate #9 and Vihtavuori N105. N105 is slightly quieter, but needs a heavier bullet than #9.
I take a certain amount of criticism using #9. Generally being told it's not safe in low charges, you'll have high ES blah, blah, blah..... there is some truth to that and there is a great pic of a barrel and bolt carrier that gets posted a lot on the forum to drive that point home. That's my work, it was a loading error. Cost me a bolt, barrel and upper.
The other truth is that for the most part I am using data straight out of Hornady #9 for reference. The fact that the barrel is 8-9 inches shorter means that I just don't get the velocity printed. This is a big plus when loading for an SBR. You can use low end super data and have a functioning sub sonic load in an SBR.
All that said be very careful and attentive when using fast powders. All the noise it saves you, comes out in one shot when things go wrong.
Velocity matters.
There is a huge difference in muzzle pressure and pop above and below 1000 fps. There is also a difference because of the burn rates of powders. It's not always true that faster powder is quieter, experimentation is required.
What about the rifle?
There are just as many variations here, as in your load. But the main things are buffer spring and weight, carrier weight. I won't even discuss gas port size except to repeat what I said before. Smaller is better, bigger is noisier and there is never a need, that I have found to be over .100" and plenty of reasons to stay under. An adjustable gas block makes shooting supers in your dedicated sub gun much more enjoyable.
I am a fan of the JP captured set up because you can adjust both weight and spring tension. The quietest operating rifle will be the one that takes the least amount of gas to make it go. It will also be cleaner running and therefore more reliable for longer shooting strings.
I have had the chance to run a Gemtech 300BLK, a couple of Thunderbeasts 9" and 7" and a I think it was a Sandstorm?. The Gemtech was the loudest and created the least back pressure. This meant that it was the least helpful for the specific application. The most reliable, quietest on first(most important)round and subsequent shots were the Thunderbeasts. My choice would be an Ultra 7.
I am sure there are other things I have forgotten or do not know and this is meant as a general guideline or thought process to getting quiet. As always it's not the only way and hopefully others will chime in.
My purpose built SBR and dedicated load.
8" Excaliber 1/5 barrel with .097" gas port
JP silent capture w/steel weight and black spring.
LMT enhanced F/A bcg
Thunder Beast 7"
194 Lehigh
8.2 grns #9
1010 fps.
There have been a lot of threads over the years looking for the quietest suppressor and quietest powder. These threads number in the hundreds it seems and are only outnumbered by the number of posts that say my gun is loud. Well that's not completely true. (The top asked questions are probably, Why won't it cycle and Why are my case mouths dented).
Let's start right off with, if you want a quiet SBR, do not load with 1680. It's loud, it's dirty and basically just disappointing to work with. Save it for heavy supers, or use it if you are just learning to reload until you have some experience and can deal with the possible side effects of faster powders.
The next thing to be aware of is that the quietest loads, can be the most dangerous and unpredictable to work with. They require fast powders at low case fill rates and many times reach the same firing pressures as many supers. Double charging a load is certainly possible . The pay off is a reasonably hearing safe load that can be fired indoors without ear protection.
Suppressor choice, or build style come into play. Mono cores like Gemtech's purpose built 300 can, tend to have a pretty good first round pop. This can negate all the work you put into your build and handloads if used in an emergency situation, no ears inside.
Finally all of this is a waste of time if the whole system is unreliable. If you can not do at least two successive mag dumps and have the bolt lock back on empty each time, then you are no where near having a reliable setup.
Let's start with the basics.
There are way too many variables for the "quietest subsonic load". The basics won't change, but if you are doing a purpose built rifle, it can be very quiet and reliable.
First, what is counter intuitive is to leave the gas port as small as possible, or run an adjustable block. This will reduce port noise. No sense making it quiet at the muzzle just to have it louder at the other end. There is no reason to have a pistol length port over .100" and plenty of reasons to have it less.
Barrel length also makes a noticeable difference. I have had the chance to run 7-8.5" in 1/2" increments and noise increases noticeably at each length. Shorter is louder.
Bullet choice will also be an issue. A longer bearing surface can help create back pressure and choice of material can play a role. A good example would be the Lehigh 174 grain bullet. I tried very hard to develop a load for it that met other requirements I had. Basically I chose to run Accurate #9. I had no problems getting full function using Sierra 175 and 168 Matchkings, but I had trouble with reliable cycling and locking back if the 174 Lehigh stayed subsonic. I cured it by moving to the 194. The problem was the brass, it behaves more like lead when it comes to creating pressure.
Powder choice as pointed out earlier is critical. The two powders I have ran that are the quietest and still have full function are Accurate #9 and Vihtavuori N105. N105 is slightly quieter, but needs a heavier bullet than #9.
I take a certain amount of criticism using #9. Generally being told it's not safe in low charges, you'll have high ES blah, blah, blah..... there is some truth to that and there is a great pic of a barrel and bolt carrier that gets posted a lot on the forum to drive that point home. That's my work, it was a loading error. Cost me a bolt, barrel and upper.
The other truth is that for the most part I am using data straight out of Hornady #9 for reference. The fact that the barrel is 8-9 inches shorter means that I just don't get the velocity printed. This is a big plus when loading for an SBR. You can use low end super data and have a functioning sub sonic load in an SBR.
All that said be very careful and attentive when using fast powders. All the noise it saves you, comes out in one shot when things go wrong.
Velocity matters.
There is a huge difference in muzzle pressure and pop above and below 1000 fps. There is also a difference because of the burn rates of powders. It's not always true that faster powder is quieter, experimentation is required.
What about the rifle?
There are just as many variations here, as in your load. But the main things are buffer spring and weight, carrier weight. I won't even discuss gas port size except to repeat what I said before. Smaller is better, bigger is noisier and there is never a need, that I have found to be over .100" and plenty of reasons to stay under. An adjustable gas block makes shooting supers in your dedicated sub gun much more enjoyable.
I am a fan of the JP captured set up because you can adjust both weight and spring tension. The quietest operating rifle will be the one that takes the least amount of gas to make it go. It will also be cleaner running and therefore more reliable for longer shooting strings.
I have had the chance to run a Gemtech 300BLK, a couple of Thunderbeasts 9" and 7" and a I think it was a Sandstorm?. The Gemtech was the loudest and created the least back pressure. This meant that it was the least helpful for the specific application. The most reliable, quietest on first(most important)round and subsequent shots were the Thunderbeasts. My choice would be an Ultra 7.
I am sure there are other things I have forgotten or do not know and this is meant as a general guideline or thought process to getting quiet. As always it's not the only way and hopefully others will chime in.
My purpose built SBR and dedicated load.
8" Excaliber 1/5 barrel with .097" gas port
JP silent capture w/steel weight and black spring.
LMT enhanced F/A bcg
Thunder Beast 7"
194 Lehigh
8.2 grns #9
1010 fps.