Building a quiet SBR and a cartridge to make it worthwhile.

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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dellet
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Building a quiet SBR and a cartridge to make it worthwhile.

Post by dellet » 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 :oops:. 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.
300 Blackout, not just for sub-sonics.

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QuietMike
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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by QuietMike » Tue Jul 26, 2016 12:17 pm

Great post.

Thanks for the info.

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certifiable
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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by certifiable » Tue Jul 26, 2016 1:13 pm

Excellent post dellet!
Thank you for taking the time to help enlighten the masses
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If we falter and lose our freedoms, it will be because we destroyed ourselves."

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bangbangping
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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by bangbangping » Tue Jul 26, 2016 1:28 pm

dellet wrote:The problem was the brass, it behaves more like lead when it comes to creating pressure.
Excellent post, dellet.

I wonder how much of a difference there would be, similar to what you noted in bullet construction, with the different bore treatments. Seems like chrome might produce a little more pressure than, say, melonite. Don't know if it would be enough to matter.

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dellet
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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by dellet » Tue Jul 26, 2016 2:15 pm

bangbangping wrote:
dellet wrote:The problem was the brass, it behaves more like lead when it comes to creating pressure.
Excellent post, dellet.

I wonder how much of a difference there would be, similar to what you noted in bullet construction, with the different bore treatments. Seems like chrome might produce a little more pressure than, say, melonite. Don't know if it would be enough to matter.
Just like everything else, it depends.

The tighter, smoother surface should win out for a better seal, less pressure leaking by the bullet and more consistent grooving pressed into the bullet.

But there is one huge dirty little secret in the world of machining tolerances and quality control.

The raw materials and the machinery used to produce the finished product have less to do with final quality, than the person producing it. A barrel made using the best materials and machines, will be less accurate, for a longer period of time, than a barrel made from the worst materials on the worst machine by a more competent machinist.

A lot of the budget barrels out there are made from blanks mass produced overseas and contoured here. The part that matters the most, the bore, is where all the savings come from.
300 Blackout, not just for sub-sonics.

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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by rebel » Tue Jul 26, 2016 9:09 pm

I know this is about "the entire system", suppressor, rifle and load, but I'd like to add it wasn't to many years ago here that a lot of smart guys were telling folks that drilling your gas port out solved all problems from case dents to bunions on your feet or yellowing teeth :shock:

I think Robert got it right, and dellet has found again, the optimum port size for running 4 ways. Good news for those that are worried about an AGB on their rifle and not being on the right setting when needed - BTW, there is a setting where everything runs - that's where my SBR gets turned to after shooting.

Shooting a tuned AR is just sweet. Adding an AGB to a big gas port actually opens your options to use powders for a quieter load.
One other observation - most folks when buying a rifle or a suppressor go for the cheaper option. Why not curb the impulse to buy it now, save a bit more and by something better? I have never regretted buying quality, I have regretted buying crap knowing I could have had quality. All the "bargain" ARs are of the shelf at my shop, the higher quality mid priced ones are still on display.
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orbitup
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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by orbitup » Tue Jul 26, 2016 9:35 pm

This should be a sticky!

Kind of surprised to see you are using a F/A BCG. Can you go into why you chose that?

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dellet
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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by dellet » Tue Jul 26, 2016 11:55 pm

orbitup wrote:This should be a sticky!

Kind of surprised to see you are using a F/A BCG. Can you go into why you chose that?
I guess because I tried it and it worked. :P

AAC originally ran the heavier carriers and the more I have played with this cartridge and platform the more I appreciate the thought and planning that Robert did in making it work. He had to make some compromises for universal sales to the public, but many of the things a lot of people questioned five or six years ago make more sense all the time.

One of the things that a heavier carrier does is move slower. This can be good and bad. When the bolt travels backward extracting and ejecting, you don't want weight slamming into the buffer tube. Moving forward the weight will help stripping the next round and chambering. More mass will push harder. So as long as I can keep the buffer from bottoming out, the weight moving forward is a plus. Remember we are pushing cartridges that weigh twice weight the bolt and buffer are designed to push.

The LMT enhanced bcg is worth the extra cost. More so if you run hot loads, but I have found zero issues running subs. There are two major differences one in the bolt and the other in the carrier.

The enhancement on the bolt is the face and extractor. Here's a pic for comparison.
Image
Dual springs on the extractor and the bolt face fully supports the brass. More holding power and no more bent bases from brass flowing into the half moon of a normal extractor.

The carrier has an eccentric shape in the cam path. This slows the unlocking of the bolt. For supers again this makes extraction process easier on brass. It stays in the chamber longer, so it has time to shrink back closer to pre-firing size.

For subs one thing I noticed, but can not prove, is that I felt my sub loads may burn slightly cleaner because the powder is held at a higher pressure longer. The other plus is that the delayed opening time drops blow back from the gas system.

Here's a pic of the modified path
Image

I had questions if this bolt would help or hinder the reliability of this build, for a better understanding of that here is the thread:
viewtopic.php?f=128&t=96365

A lot of thought went into the assembly of this rifle. It has paid off very nicely.
300 Blackout, not just for sub-sonics.

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certifiable
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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by certifiable » Wed Jul 27, 2016 12:12 am

orbitup wrote:This should be a sticky!
I think the cartridge and the shooting community as a whole would be better served by a sticky titled something along the lines of...
300BLK: dispelling the myths, misconceptions and pushing the limits

Where links could be compiled leading to other threads such as the sub challenge, makers project as well as this thread

Lay it out like the "Pet Loads" thread so it wouldn't end up another thread containing a bunch of crap posts
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If we falter and lose our freedoms, it will be because we destroyed ourselves."

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John A.
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Re: Building a quiet SBR and a cartridge to make it worthwhile.

Post by John A. » Wed Jul 27, 2016 1:50 am

I do appreciate topics such as this. Rarely do you see such insight.

And I agree with essentially every point that was made. Buying a silencer and throwing it on the gun and grabbing a box of "subsonic" ammo alone is not very likely to net the "quietest" combo out there.

As a guy who has studied, designed and built several silencers for myself over the last decade, I have always focused more on the baffle design than anything else. Some baffles work better for some things than others.

But despite the 300 being marketed as a good (niche) "suppressed" carbine round, I was honestly a little let down by it at first. It's not that it "can't" be a good suppressed round, but it is taking me a lot more than I expected to get it to a point where I personally consider it "good".

On to the blackout, it is seriously plagued by first round pop. Regardless of baffle type and suppressor manufacturer. You can look at just about any youtube video that you want of suppressed blackouts, and while it's a little hard to "hear" the pop in many videos, after you are experienced with and familiar with suppressed shooting, you can usually pick out frp anyway and you surely hear it in person.

The 300 being a "low pressure" round (speaking in terms of typical rifle pressures), seems to do better with baffles that disrupt the flow of gas and entire volumes of books could be written on that topic alone.

On silencertalk, most people will chalk up FRP to nothing more than a large expansion chamber. I'm here to tell you that while that may be true some of the times, even with an unusually small/short expansion chamber, the blackout still exhibits first round pop. And a lot of it if comparing to 9mm or especially 22lr. Though on topic to the OP, in all fairness, subsonic 9mm often has less than 4 grains of fast burning powder. 1680 subs are around 10.2-11.0 grains. That's a huge difference in charges.

And that's where I think the powder choice and burn rate comes into play with suppressed shooting moreso than most people realize or perhaps especially where the blackout is concerned.

I have applied to make a dedicated blackout suppressor that will be loosely based on the old Delisle. It will be a hybrid integral and reflex suppressor. And I have a baffle design in mind to try that I came up with about 7 years ago that I think will both disrupt and slow the release of the "low pressure" gas.

Or at least that's the plan right now.

But I sure would appreciate any specific low charge suppressed recipes that you've worked up that would function in a semi with an 8.5" 1:8 barrel. So, if you don't mind and if it isn't too much of a bother, I sure would appreciate to hear from you in a PM or email so I could tap into your tests and knowledge.
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