View Full Version : What is a optimum barrel length (as short as possible) to use with silencer?
I am in a process of build a new AR to use with the suppressor, would like to know which barrel length I should pick and why, thanks..
10.5"
Why? because you want the shortest possible barrel
Thanks, and is that length works 'optimum' with suppressor? I like it to be as reliable as possible cause I think there is some others factor that involve while using w/the can, just dont know the technicality of it....
doriwoogie
01-27-12, 13:58
In 5.56? I've got a 10.5" Noveske Switchblock with an AAC M4-2000 that works very well (for me, low speed civilian).
If you are considering .300 blk, AAC and Noveske (and others too) make them in even shorter lengths to run suppressed.
In 5.56? I've got a 10.5" Noveske Switchblock with an AAC M4-2000 that works very well (for me, low speed civilian).
I wouldn't go any less than 10.5" as mentioned here already. Anything less and you will increase the chances of a baffle strike.
If you are considering .300 blk, AAC and Noveske (and others too) make them in even shorter lengths to run suppressed.
This is what I ended up doing and now I have a 9" upper in 300 Blackout that I'm quite happy with.
I wouldn't go any less than 10.5" as mentioned here already. Anything less and you will increase the chances of a baffle strike.
This is what I ended up doing and now I have a 9" upper in 300 Blackout that I'm quite happy with.
Why do you think there is a bigger chance for a baffle strike on a shorter 5.56 barrel compared to a 300BLK?
Why do you think there is a bigger chance for a baffle strike on a shorter 5.56 barrel compared to a 300BLK?
The bullet might not stabilize, but that depends on the bullet length/weight.
Why do you think there is a bigger chance for a baffle strike on a shorter 5.56 barrel compared to a 300BLK?
There are lots of factors but the likelihood of a 5.56 round not stabilizing properly is much higher. The 300 Blackout round was developed specifically with this in mind and the bullets stabilize in much shorter barrels.
The 300 Blackout round was developed specifically with this in mind and the bullets stabilize in much shorter barrels.
This is one of those statements I keep seeing but haven't been able to find any hard data on. Do you have something? Some kind of reference for this that shows the instability of a 5.56 round out of say... an 8" barrel as compared to the 300 out of the same length barrel?
This is one of those statements I keep seeing but haven't been able to find any hard data on. Do you have something? Some kind of reference for this that shows the instability of a 5.56 round out of say... an 8" barrel as compared to the 300 out of the same length barrel?
If you will find a suppressor manufacturer that warranty their 5.56 can on an 8" barrel, let me know.
If you will find a suppressor manufacturer that warranty their 5.56 can on an 8" barrel, let me know.
But that's not what you said.
There are lots of factors but the likelihood of a 5.56 round not stabilizing properly is much higher. The 300 Blackout round was developed specifically with this in mind and the bullets stabilize in much shorter barrels.
I would like to know what you base this on. I have heard for years that the reason the 5.56 silencers AREN'T advisable on <10.5" barrels is due to "instability" but I have yet to see any data on it. I'm wondering if you're just repeating what you heard or if you have some data or information that backs it up.
I too would like real facts to back this up... I'm not sold on the notion that increased velocity = increased stability.
Eurodriver
01-30-12, 07:39
I would like to know what you base this on. I have heard for years that the reason the 5.56 silencers AREN'T advisable on <10.5" barrels is due to "instability" but I have yet to see any data on it. I'm wondering if you're just repeating what you heard or if you have some data or information that backs it up.
Rob,
I have no "hard data". The following is from my own experiences with stupid friends that just had to have short barreled (pistol) AR15s.
I've found when you get below 8", and this is solely my speculation, that the velocity being so slow, coupled with the 17,000 PSI pressure "blast" at the muzzle, is enough to deflect the round and cause instability initially. We were not keyholing and still got decent accuracy out of the 8" but out of the 6.5" we had some problems.
On the 6.5" barrel we could see strikes on the muzzle brake and accuracy at 10 yards was almost non existent. This was with an Olympic Arms upper. I'm sure the 1:9 twist did not help any.
However, when we removed the muzzle brake all those issues went away. The accuracy came back and there was no keyholing. I really do suspect that the initial blast of pressure at the muzzle causes some issues especially because the round is traveling about 1000 FPS slower than it is out of a 20" barrel.
I would like to see a chart of barrel pressures in 300BLK because they do not have this problem and the lack of blast at the muzzle on short barrels is obviously less. I do not necessarily think that it is the short barrel itself that causes instability but rather the barrel pressure. I think the round wobbles a bit as it exits the muzzle but the twist stabilizes it after a few inches, otherwise there is no way we could get the accuracy we were getting at 25 yards.
A great test to run would be some super short barrels with varying twist rates with both super and subsonic ammo. I bet with subsonic ammo on a 6.5" barrel and 1:7 twist there would be no issues leading me to believe that the blast of the 5.56mm on short barrels is what causes stability issues, not the slow velocity or short barrel itself.
http://i42.tinypic.com/dokysi.jpg
A great test to run would be some super short barrels with varying twist rates with both super and subsonic ammo.
That's a good point. We load .308 ammo for our Bolt guns that stabilizes just fine. Velocity is about 1050 fps compared to 2515 for full powered ammo.
This is one of those statements I keep seeing but haven't been able to find any hard data on. Do you have something? Some kind of reference for this that shows the instability of a 5.56 round out of say... an 8" barrel as compared to the 300 out of the same length barrel?
the shorter barrel warranty on a 300BLK setup versus 5.56 doesn't have anything to do with stability, it has to do with baffle erosion from unburnt powder.
300 BLK works very well in SBRs and VSBRs because of its small/fast burning powder charge.
If you will find a suppressor manufacturer that warranty their 5.56 can on an 8" barrel, let me know.
AAC will warranty the 762-SDN-6 and SR7 down to 7.5" on a 5.56..
The larger bore gives you more can life (spread out the abrasive abuse).
And as for stability, you can probably find the right [wrong] combo- a very short 5.56 barrel in a slower twist shooting a longer bullet... That'll screw up your day.
the shorter barrel warranty on a 300BLK setup versus 5.56 doesn't have anything to do with stability, it has to do with baffle erosion from unburnt powder.
This is essentially what I was wondering/getting at, without any concern for 300, in the original question.
"Michelin won't warranty my tires if I go 200 MPH on a dirt road. Ergo it is unsafe to ever go 200 MPH!"
Everyone ASSUMES the issue is unstable rounds, mostly because that's what someone else that didn't know told them and it was easier to believe it than question it, but nobody ever seems to produce evidence of same.
I've seen umpteen reports of endcap and baffle strikes on cans mounted on barrels under the mythological 10.5", but all too often they are shit barrels from shit makers anyway, so it's hard to say that it was the fact that it was 7.5" that caused the strike and not the fact that it's an Oly arms with an 88* shoulder instead of 90.
Eurodriver
01-30-12, 11:38
Everyone ASSUMES the issue is unstable rounds, mostly because that's what someone else that didn't know told them and it was easier to believe it than question it, but nobody ever seems to produce evidence of same.
Who, aside from Jer, assumes that? I thought it was pretty well known, all over this forum, that baffle erosion on short barrels in 5.56mm weapons was the reason.
Who, aside from Jer, assumes that? I thought it was pretty well known, all over this forum, that baffle erosion on short barrels in 5.56mm weapons was the reason.
The world does not begin and end with m4c.
the shorter barrel warranty on a 300BLK setup versus 5.56 doesn't have anything to do with stability, it has to do with baffle erosion from unburnt powder.
300 BLK works very well in SBRs and VSBRs because of its small/fast burning powder charge.
Email reply to me from Jon Hollister of AAC.
thank you for the email and your interest in our silencers.
We do not have a barrel length written into our warranty. In the past, when we were asked about 5.56mm and 7.62x51mm. By way of example, 5.56mm was designed and is still loaded today for a 20” barrel. Meaning that to get a complete powder burn inside the barrel, you need a 20” barrel. If you shoot 5.56mm in a 16” barrel, you get powder burning outside the barrel, 14.5” even more, 12.5” even more and so on. We recommended that people not go below 10” with 5.56mm due to the amount of unburnt powder hitting the blast baffle, the amount of pressure and the amount of muzzle flash that the silencer is having to contain, all of which cause accelerated erosion in the silencers.
When it comes to 300 Blackout, we designed 300 Blackout around shorter barrels. There is still enough powder burn to be used in longer barrels, but it was optimized for shorter barrels. Meaning that you do not have the massive muzzle blasts in shorter barrels, with huge amounts of burning powder outside the barrel. This also means that the muzzle flash and excessive pressures, as well as accelerated wear are not present. So can you use the 762SDN6 with an 8” Noveske barrel? No problem.
The use of a muzzle brake does give muzzle blast an additional surface or two to hit prior to the blast baffle, which will theoretically partially protect the baffles in any given barrel length. Obviously the longer the barrel and lower the pressure, the less wear as well.
Our warrant covers Materials and Workmanship. We do not warranty against wear associated with normal usage.
We do have a provision in our warranty that says that if there is an issue with the silencer, that is not covered by Materials and Workmanship and was not Criminally Stupid and it cannot be repaired, we will offer the customer a replacement at half price. Try that at a Car dealership. Put 500,000 miles on a Volvo, tow it into the dealership and asked for your half price replacement. J
You will have to get a new serial number per a BATFE ruling a few years ago, meaning a new $200 tax paid.
Thanks,
John Hollister | Sales Manager
Advanced Armament Corp.
I have heard for years that the reason the 5.56 silencers AREN'T advisable on <10.5" barrels is due to "instability" but I have yet to see any data on it. I'm wondering if you're just repeating what you heard or if you have some data or information that backs it up.
There are various formulas to calculate bullet stability based on factors like bullet length, barrel twist, and velocity. A calculator based on such a formula can be found here (http://www.jbmballistics.com/ballistics/calculators/calculators.shtml) at the bottom of the page.
I plugged in various data that I was able to find around the web to try to simulate M193 out of a short barrel:
Muzzle velocity of 2700fps (estimated MV of M193 from a 10" barrel, from here (http://counterstrikefox.freeservers.com/mv.htm))
Bullet length of .750" (a SWAG based on the Sierra 55gr FMJBT, found here (http://www.jbmballistics.com/ballistics/lengths/lengths.shtml#Sierra))
Bullet diameter of .224"
Barrel twist of 1 turn in 7"
Default temperature and pressure.
This resulted in a stability value of 3.6, which is well above what they say is required (1.3 to 2.0). Even at 1000fps it still gives me ~2.6. This seems to indicate that this bullet+twist combo is going to be stable even down to subsonic speeds. That sounds odd to me, but a quick sanity check of the calculator with the 77gr Matchking (.994" length) at 2500fps out of a 1/9" gives 1.324. That's at the bottom end of their "acceptable" result which seems to match others' practical experiences of "some 1/9 guns will stabilize 77s, some won't."
Now clearly this is a theoretical model so we can't automatically go around saying that 5.56 bullets are stable at subsonic speeds. The short-barrel/subsonic test that Eurodriver proposes would tell us for sure.
I too would like real facts to back this up... I'm not sold on the notion that increased velocity = increased stability.
Well, increased velocity = increased stability as far as bullet rotational velocity (and therefore stability) is proportional to velocity. Out of the same 1/7" twist, a bullet going 3000fps is going to be spinning faster than a bullet going 2000fps. Of course, this only matters if the additional rotational speed takes the bullet from unstable flight to stable flight. If it's already stable at 2000fps then who cares?
A great test to run would be some super short barrels with varying twist rates with both super and subsonic ammo. I bet with subsonic ammo on a 6.5" barrel and 1:7 twist there would be no issues leading me to believe that the blast of the 5.56mm on short barrels is what causes stability issues, not the slow velocity or short barrel itself.
Agreed, that would be a great test. Also, if you can't pry a 300 BLK pressure chart out of Silvers, I might be able to dig up my old copy of Quickload and simulate it. Again it would be based on a theoretical calculation, but it'd at least give us a ballpark value to compare against the 5.56 data that you have.
Magic_Salad0892
01-31-12, 03:42
I too would like real facts to back this up... I'm not sold on the notion that increased velocity = increased stability.
I have a theory that there is a ''velocity cap'' on 5.56mm, where more velocity may make the bullet LESS stable.
Proof:
BCM 1:8 18'' SPR had slightly worse accuracy, but slightly better velocity.
BCM 1:7 18'' SPR had slightly better accuracy, but slightly worse velocity. \
I belive there was a 200fps -/+ difference in velocity.
I believe Robb Jensen (I think) may be able to confirm that, as it was results he posted( where he reviewed BCM SPRs or something like that, IIRC) that inspired me.
I haven't tried to replicate it though.
Just a theory. And it isn't the first time I've heard of it.
I have a theory that there is a ''velocity cap'' on 5.56mm, where more velocity may make the bullet LESS stable.
Think of a bullet as a top, but with one extra force acting on it. When it first leaves the barrel, it will wobble slightly; this is called precession, or torque-induced wobble. Torque comes from the expanding propellants, which is the first force affecting stability. Soon after the bullet leaves the barrel, the first source of torque (the propellant gases) goes away. Now the bullet, like a top, will want to stabilize around its rotational axis and stay that way. This is the bullet's moment of inertia, or its resistance to rotational change. The faster the bullet is turning, the stronger it resists changes to its rotation. Gravity and friction (air resistance) will eventually overcome the bullet's moment of inertia and again produce torque-induced wobble until the end of the bullet's flight.
I geeked out on you so that I could say no, technically speaking there is no "velocity cap" on a cartridge or caliber, but there is one on the bullet itself. Bullets made of heavier, stronger materials of concentric shape and distribution can be spun faster in flight than bullets of lighter, weaker materials or ones with physical imperfections. The faster you can spin it, the greater its moment of inertia and the more it resists deviating from its rotational axis (less drift and somewhat less drop). Weights and sizes being equal, you can shoot a solid Barnes bullet much faster and with a much tighter twist than you can a pulled SS109. What you might be seeing Salad are differences in the barrel vs effects of velocity on the bullets.
How much faster or tighter I don’t know. I remember a phone call with Noveske where they described testing twist rates down to ridiculous twists at varying velocities, and they reported few to no stability problems with modern bullets. They did get a few of the lighter ones to disintegrate on leaving the barrel at high velocities, though. :D
Reader's digest version: better-made bullets can be pushed and turned faster than lesser bullets, which means they will resist destabilizing forces for more of their flight duration. Construction matters more than speed. Barring differences between individual barrels, anyway.
-B
I have a theory that there is a ''velocity cap'' on 5.56mm, where more velocity may make the bullet LESS stable.
Proof:
BCM 1:8 18'' SPR had slightly worse accuracy, but slightly better velocity.
BCM 1:7 18'' SPR had slightly better accuracy, but slightly worse velocity. \
Proof? That does not mean anything except those barrel and ammo combos had different precision. One barrel can give different velocity than another depending on variations in (mostly but not exclusively) how the chamber was cut. Thus different harmonics and different accuracy nodes.
Also, there is no such thing as being "too stable". The worst that can happen to a bullet spinning too fast is it comes apart.
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