Suppressors and Stability

[BulletFactory]

Maybe Im overthinking this, what are your thoughts.

I'm going to be shooting an Accurate molds 31-215 E3, which is the 300 BLK powder-coated round + gas check. This will be using Accurate 1680, but I'm not sure about how much powder yet. Subs and supers. I'm using a 9" BCM barrel, and through a can.

My worries are on whether the bullet is going to be stable enough between the time it leaves the bore, and the 8" down the suppressor. Obviously Im worried about a baffle strike.

So, is this much ado about nothing?

And how much powder should I be using? I'm asking because this looks like its going to compress the powder quite a bit.

[runfiverun]

shoot it without the suppressor first and see what the paper tells you.
a square clean hole is a boolit spinning properly, oval shaped ones mean trouble.

[BulletFactory]

Ok, but maybe I'll also make a cardboard baffle stack to test with. If it takes them out, I doubt it would hurt anything.

[runfiverun]

you could also do a 10-25-35-50 yd paper test and shoot through all of them at the same time.
doing one from card board just past the muzzle [with a hole in it for the gas and boolit to pass through] would also show your lube spin-off.

[BulletFactory]

I'll be powder coating these.

[dudel]

Ok, but maybe I'll also make a cardboard baffle stack to test with. If it takes them out, I doubt it would hurt anything.

Now you're overthinking it!

Do what 5river suggested. A clean hole means it stabilized, a non round hole indicates keyholing or instability.

Make sure you have good fill and no voids. You want very uniform Boolits. A good boolit may perform fine; but one with a void could go unstable.

Personally, I don't use lead in my suppressors (well other than 22LR, and I try to use the plated rounds). It's shooting the unplated 22LR that got me to see the lead accumulation I the suppressor. Is your a sealed suppressor; or can you take it apart for cleaning?

[BulletFactory]

Sealed. I can't justify the cost of jacketed rounds after loading so many cast boolits.

[Cap'n Morgan]

Don't try cardboard baffles! They're guaranteed to disintegrate completely. A baffle strike due to a loose and therefore drooping suppressor could spell trouble, but a baffle strike from a wobbling boolit is no big deal - any contact between boolit and suppressor due to wobbling will be completely random, and clearly manifest itself on the target.

[BulletFactory]

I thought contact between the bullet and the baffle meant the end of the suppressor. Not sure what it does to the barrel threads, muzzle, or receiver.

[popper]

Don't use a suppressor so not my problem. That said, army testing of stability of 223 used cardboard (at an angle) to cause instability, far enough away to avoid the muzzle blast. They then checked stability (targets) at many distanced down range to verify gyro action. Hard to set up on a public range but doable. Holding a paper target in front of 40SW to check lube pattern doesn't work. FYI.

[guywitha3006]

Personally I would worry about the gas check coming off. When i shoot cast through my .30 cal can, I only shoot unchecked boolits (also powdercoated) through my sealed 762SD, if it shoots straight out of the barrel you should be fine, of the two suppressors I have (.22 and .30 cal) both have larger then barrel bore holes. I hope that makes sense.

[Digital Dan]

Bullets are either stable or not when they exit the muzzle. The journey thru the can will make no difference in that regard. Good advice offered previously, shoot it without the can, see what happens.

[BulletFactory]

Well, I still have to collect all the parts. I'll be using a BCM barrel, and BCG, so Im starting from a good place. Im about half way through the build now.

[runfiverun]

paper gets trashed cardboard with a hole for the blast and boolit doesn't.
if done right you can count the lands and grooves in the barrel, which BTW is also an indication of the lube needing more fling off at the muzzle.
it could be caused by one of the lubes additives [paratack, or lanolin] or that the waxes used are stopping their flow too soon and you need to change the percentages or modify them.


okay,,, well I got that off track.
using the powder coat is a good idea in a can that can't be easily cleaned.
but I would get my ducks in a row before screwing it on.

[BulletFactory]

Thats why I'm here my friend.

[milsurpcollector1970]

Normally 300 blk barrels intended for shooting subs using a faster twist such as 1-7 or 1-8 to stabilize a a 200 gr+ boolit.
Do you have a fast twist? I would shoot for about 1000fps

[BulletFactory]

1:7 on a 9" BCM barrel. 215gr round, checked and powder coated, prolly 220. I'll have to weigh one, guess I forgot or forgot to weigh it to start with.

[TimGS]

Never tried the Accurate 215 bullet you are using, but I use an A.C.E 230, basically the same as. http://noebulletmolds.com/NV/product_info.php?cPath=30_333&products_id=2360&osCsid=jchdgua4o4u9jnkaoa8lulfs15

In my 8" 1-8 barrel sbr it is perfectly stable down to under 900 fps using lilgun.

I prefer lilgun to 1680, it is cleaner for me.

The 1680 load that worked best for me was 10.4 gr ~1000fps.

But always shoot a new load without the can first to insure stability.

With my mix i get ~223gr, after powder coating they average 225gr.

[NoZombies]

That bullet will be stable in that twist at about any reasonable speed.

No need to overthink this.

Test for accuracy with and without the check, if it's more accurate with, then so-be-it, if it makes no difference, no need in incurring the extra expense for subsonic rounds. Checks can also come off in the can. I've had it happen, but there was no damage to the can (Inconell baffle stack on that one). I wouldn't like the idea of them piling up in the baffles though.

There is a big difference between a baffle strike, and a baffle kiss. A strike can be catastrophic, and usually the result of a very bad threading job, bad mounting of the can, or something else putting the bore of the can off axis with the bore of the barrel. A baffle kiss, like you would see from an unstable bullet would likely hardly even be noticed except for the erratic groups and key holing it would cause downrange. A kiss will also usually reward you with an almost cartoonish "zip-zip-zip" sound as the bullet tumbles towards the target. It's usually easy to hear because the suppressor has removed so much pf the muzzle blast.

[BulletFactory]

Wow, thanks. :)

[Digital Dan]

On the topic of bullet stability it appears there may be some misunderstanding about the topic and I offer the following for whatever it may be worth.

The need for inducing gyroscopic stability stems from the imbalance of center of gravity (CG) and center of aerodynamic pressure (CP) in conical projectiles. In round balls they are one and the same location, but as length increases the CG remains constant while CP moves forward. In short, longer bullets require more spin to supply sufficient angular momentum for stability. Velocity is only pertinent for a given length in context of the degree of moment generated between the two points. Velocity has significant influence on that issue as it presents different levels of drag. In typical circumstances as drag increases so to does the moment. The graph below represents a comparison between drag and velocity, with the former represented as Cd, or coefficient of drag. Cd is a fundamental component of BC calculus.

173232

The point I wish to make is that if a bullet is stable at Mach 1.5 it is also stable at Mach .80. As the speed of sound is variable subject to temperature I'll let you twiddle the fine numbers if you wish, don't get lost in a mathematical fog. You will notice from the graph that as represented that the drag increases sharply as one approaches the speed of sound, peaks and then drops with some rapidity. Not shown on the graph is the CD numbers found up around Mach 4. The slope continues its downward journey and in this realm drag is actually quite low, as is the necessity for fast twist.

Couple of points on this and I'm on my way. Most cast bullets dwell in the high drag regime or what is known as the transonic range of velocity. Roughly Mach .80 to 1.3 in general terms. I'm NOT talking about bullet velocity so much as I am the velocity of air in the flow field. At subsonic velocity air is not compressible. The form of the bullet weighs heavily upon flow field velocity as air seeks to null compression factors by accelerating about the bullet. In short, the bullet might be cruising at 1050 fps but the air velocity around the ogive/meplate may be considerably higher. That means increased drag and a higher requirement for angular momentum. Bullets with more pointed or elliptical nose forms suffer far less from this. Now you know why marginal stability in long range guns leads to bullet upset/tumbling at long range when the bullet falls to lower velocity, and likewise, why this can be fudged to small degree with higher muzzle velocity. Higher velocity equates to higher angular momentum to a very small degree. Twist rate is the more influential metric in the equation.

Some time back a fella at a respected barrel shop told me a few things that were wrong. 1) cast bullets with a suppressor was not practical. 2) 1:12 twist would not stabilize a 180 gr bullet at subsonic velocity. He was quite wrong about that. Do your homework before diving into the deep end of the pool. There are many programs available on the 'net which will allow proper calculation on these fine points. http://www.jbmballistics.com/

http://img.photobucket.com/albums/v298/muddler/Guns/Sneezer/Ducks_zpscqr0rx5a.jpg (http://smg.photobucket.com/user/muddler/media/Guns/Sneezer/Ducks_zpscqr0rx5a.jpg.html)

http://img.photobucket.com/albums/v298/muddler/Guns/Sneezer/LG2_zpshq59nb9c.jpg (http://smg.photobucket.com/user/muddler/media/Guns/Sneezer/LG2_zpshq59nb9c.jpg.html)

[popper]

transonic range of velocity. Roughly Mach .80 to 1.3
Thanks Dan, point I have tried to make for a while - and it gets worse for some of the standard ogives we use.Like .5-1.5.