Subsonic rifle bullet shape

[TRX]

I've been looking at .300 Whisper stuff lately. The cartridge was originally intended for subsonic use, though a lot of people load it supersonic.

The idea is for a big bullet going just below supersonic, able to carry a lot of energy downrange at modest velocity. SSK's web site has some figures on it.

The popular bullets are all typical boat tail spire points. I know most bullets have looked like that for a long time, and they definitely work, but... they're contrary to what I've learned about airflow. The typical bullet has the center of pressure (where the shock wave attaches at supersonic speed) pretty close to the center of gravity, or even behind the CG. So we spin the heck out of them to stabilize them while they fly through the air backwards, for all practical purposes. When the bullet drops subsonic, the center of pressure moves even farther back, making the problem worse. Which seems to be borne out by how bullets behave downrange, and net.lore that loading bullets backwards in the Whisper sometimes works better than sending them out point first.

An aerodynamically stabilized bullet ought to have the center of pressure behind the center of gravity - that is, like a teardrop or weathervane. Then it would maintain stability as it drops through the transonic area.

I'm guessing most bullets are tail-heavy is so that they'll be more likely to tumble once they hit meat, and therefore cause more damage. Because I'll be darned if I can see any reason for spire point bullets otherwise...

[felix]

You need to include the rest of the story: twist. ... felix

[Greg5278]

Alot of the real Subsonic loads use the boat tail projectiles loaded backwards. They are a truncated cone shape with a tear drop tail. I would try some that way before I had a mold cut.
Does anybody make a boat tail mold in the caliber you need?
Greg

[2Tite]

Precision Shooting, 1992......produced an annual. There was an article printed in the magazine and the annual that year.........There's a copy here somewhere that I can"t find right now. Anyhow there was an article on aerodynamic bullet design and how velocity affected the ideal design characteristics. Basically, at lower velocity, such as subsonic rifle rounds, the design of the Eley 22 lr bullet can't be improved upon. I've suspected that's why bullets such as the 311291, 457125 etc shoot as well as they do. As velocity increase the need for the more pointed bullet becomes apparent. I'll try to find the article and PM some specifics about title, author etc. It is interesting reading. I'm sorry but I can't place it right now.

[TRX]

Best as I can figure, a good subsonic bullet shape would be a round nose and a boat tail, to move the center of pressure back behind the center of gravity.

Of course, I'm more interested in punching holes in targets; hunting isn't my thing.

Once I figure out how to run my CNC machine I might try making some bullets. Not practical to CNC mass quantities of them, but I could put some lead wire in the collet and turn enough of any given shape to see how they perform before investing in a custom mold.

[longbow]

You might find this of interest:

http://members.shaw.ca/cronhelm/SubsonicBullet.html

Doesn't help with a mould but there might be something useful there.

Longbow

[lwknight]

Longbow , That was a good read.
Thanks,

[Artful]

http://img291.imageshack.us/img291/6055/qakulaakasubsonicperfec.gif

qakula aka subsonic perfect bullet shape cira 1880

[lwknight]

Thats also a very fuel efficient submarine design. Coincidence?

[Artful]

Nope - it's mother nature at work - you know the newer sub's skipjack on was redesigned around a fish, right? look up Albacore hull named after a tuna
http://cheddarbay.com/0000special/diner/charlie_tuna.jpg - right charlie

Laws of fluid dynamic's work for air as well - don't need to change the shape until you get up to transsonic velocities. I posted a table of cast bullets at different speeds and it's very interesting to see if the Ballistic Coefficent goes up or down with the speed change.

http://castboolits.gunloads.com/showthread.php?t=94638

[TRX]

That "perfect" shape is pretty much what the first production bolt-action rifle used - the Dreyse "needle gun". It used a teardrop shaped bullet in a paper sabot to give the rifling something to grab onto. It also used something close to "caseless" ammunition - the cartridge case was consumed when the powder burned, so there was no case to eject.

The "needle" part came about because the firing pin couldn't get a good strike on the primer if it was sitting on a pile of powder, so they moved the primer up to the back of the bullet, to use the bullet as an anvil to back up the primer.

[TRX]

Lots of interesting stuff at the shaw.ca site. Thanks for the link. Looks like he's already had the same questions I did, except he's a lot better at expounding on them.

That Lapua bullet is interesting. It appears the combination of grease grooves and boat tail remove enough metal to move the center of gravity forward. The "cigar box" bullets are closer to what I was thinking of. Hmm...

[lwknight]

I have never read it as fact but my theory of a super sonic bullet was that the tail had no affect since it is in a void. I realized this while studying the developement of super sonic aircraft. The had to make a full live tail section because flaps would not work.

If that be true , then would it not be a better bullet if the tail was suited for subsonic speeds for both applications.

[Good Cheer]

A design factor worth noting...
see the red arrow below.
http://i791.photobucket.com/albums/yy192/SNARGLEFLERK/zzznosespike.jpg
Sometimes boolits fly flatter than the BC tables and programs say they should. In '91 this one blew my mind.
http://i791.photobucket.com/albums/yy192/SNARGLEFLERK/375296.jpg
Finally figured out that I was launching at the right speed for the flat point to function just right, as does the aerodynamic spike on a SLBM. In other words, the spreading shock cone coming off the flat point gave a profile resulting in lesser resistance to travel. After it slows down a might bit the benefit is lost. Anyway, that's the only explanation I could come up with. Kinda filed it away in the back of my mind for future use and never pursued it. But, it taught me that punching paper at distance was a whole lot different from BC tables.

[home in oz]

The ballistics article was interesting reading.

[rhbrink]

Somewhere a while back I was reading about a guy that was shooting cast boolits at silhouette and having a hard time of it at 500 meters. So had the bright idea to hollow point his boolits and then insert a piece of nail into the hollow point. Maybe something like the picture that Good Cheer posted. Anyway worked so well the he modified his mold to cast with a nail in the end of the boolit. Don't remember what he was shooting or how fast but is kind of interesting.

[Larry Gibson]

Good Cheer

But, it taught me that punching paper at distance was a whole lot different from BC tables.


What you did not consider was the aerodynamic spike was part of the "projectile". It altered the airflow profile and thus altered the BC of the total SLBM. Basically the BC of the SLBM was thus higher at the super sonic speeds than the SLBM without the spike. That's why it flew better, just like a bullet with a higher BC. The rules are pretty consistent. We just have to understand how they are applied. Under equal conditions and velocities a bullet with a lower BC is not going to shoot flatter than a bullet with the higher BC.

Larry Gibson

[Artful]

I have never read it as fact but my theory of a super sonic bullet was that the tail had no affect since it is in a void. I realized this while studying the developement of super sonic aircraft. The had to make a full live tail section because flaps would not work.

If that be true , then would it not be a better bullet if the tail was suited for subsonic speeds for both applications.

close

http://www.foxnews.com/photoessay/photoessay_7570_images/0701091140_M_shockwave_f18.jpg

http://www.physicscentral.com/explore/action/images/shockwaves-img8.jpg

http://history.nasa.gov/SP-4219/4219-065.jpg

http://images.encyclopedia.com/utility/image.aspx?id=479233&imagetype=Manual&ohig=90&owid=90&height=112&width=112

[x101airborne]

I may not be a very smart man....... but i know when im in WAY over my head.

[finishman2000]

i played with 300 whisper for awhile. couldn't get it work 100% in the ar so sold it all off.
i used jacketed only and used 220-240 match bullets. the strangest test was with mil surplus ap heads as sub levels. i was testing rounds in the basement and shooting into 3/4" melamine pieces about 18" stacked deep. the ap rounds went right through the block. still can't explain it.

you may want to take a look at a new round made by aac (the supressor company). it had a industry spec to it which allow it to be available commercially and will do everything the whisper does. i can't remember what it is called now but will post back when it comes to me.

[Artful]

you may want to take a look at a new round made by aac (the supressor company). it had a industry spec to it which allow it to be available commercially and will do everything the whisper does. i can't remember what it is called now but will post back when it comes to me.


http://300aacblackout.com/


CARTRIDGE
http://300aacblackout.com/images/300BLK-556Pic2.jpg

DESIGN OBJECTIVES
• Create a reliable compact 30-cal solution for the AR platform
• Utilize existing inventory magazines while retaining their full capacity
• Create the optimal platform for sound and flash suppressed fire
• Create compatible supersonic ammo that matches 7.62x39 ballistics
• Provide the ability to penetrate barriers with high-mass projectiles
• Provide all capabilities in a lightweight, durable, low recoiling package

REASONS 7.62x39 wAS NOT CONSIDERED
Extreme cartridge taper
• Reduces reliability of feeding in AR Magazines
• Reduces Magazine capacity
• Cartridge taper induces considerably higher bolt thrust-
exacerbating the AR Bolt's weaknesses
• Requires a larger Bolt Face which reduces Bolt Locking Lug strength-
exacerbating the AR Bolt's weaknesses
Limited projectile selection
• 0.311" diameter not a common option in most modern bullets

MUZZLE ENERGY COMPARISON
http://300aacblackout.com/images/300-chart2.png

HANDLOADING INFORMATION

If you load your own ammo, pay special attention to all of the normal safety practices. Recommended powder for most supersonic loads is Hodgdon H110.

For subsonic, there are special requirements and nearly all published loads are non-optimal for the 300 BLK upper. Many existing loads were developed for Thompson Center® single-shot pistols, or for ARs by people not aware of the magazine limitations. These loads pay no attention to automatic rifle function and should not be used. Look for a load which results in a cyclic rate of 700 rpm or more. AA1680 is recommended because its bulk density matches the case capacity and it will generate enough gas pressure to cycle the weapon.

Suggested subsonic load:

• R-P 300 AAC BLACKOUT brass
• Remington 7.5 primers
• 11.2 grains of AA 1680 powder
• Case length is 1.368 +0.000 -0.020
• Sierra 220 MK loaded to 2.089 OAL (this length is optimal for reliable feeding from USGI magazines)
• Chamber pressure 21,100 psi.

Existing AR magazines have a rib which normally contacts the 5.56mm case-neck. With 300 BLK ammo, the contact is on the bullet. Because the bullet is a larger diameter, the rib will push the cartridges out of alignment, and can lead to binding potentially resulting in Failures to Feed. For this reason, it is important to load ammunition so that the contact point with the magazine rib is on the bullet ogive in an area of about 0.250 inch diameter. Here are some suggested OAL for popular bullets:

• Hornady 110 V-Max, OAL: 2.000
• 110 TSX, 2.015 OAL
• Sierra 155 Palma, 2.150 OAL
• Sierra 220, 2.089 OAL
• Lapua B416 200 grain, 1.960 OAL
• Hornady 150 FMJ-BT 3037, 2.065 OAL
• Nosler Ballistic Tip 125 grain, OAL: 2.085
• Remington AccuTip 125 grain, OAL: 2.085
• Hornady 130 SP #3020, OAL: 2.010
• Sierra H2120 125 ProHunter, OAL: 1.950
• Speer TNT 125 1986, OAL: 2.010

http://www.youtube.com/watch?v=HbYLyfFf9u8

[missionary5155]

Good morning
Me I would be inclined to get a 220 grain RN FB and pop whatever needed popping. I have shot those at subsonic at I would say with a 1-10 twist barrel (308 7 grains Unique) they seem good enough at 100 yards 2.5 " . Maybe you would miss a gopher head half the time but I do not see a real need to pop gopher with a 220 grain.

[Artful]

i played with 300 whisper for awhile. couldn't get it work 100% in the ar so sold it all off.
i used jacketed only and used 220-240 match bullets. the strangest test was with mil surplus ap heads as sub levels. i was testing rounds in the basement and shooting into 3/4" melamine pieces about 18" stacked deep. the ap rounds went right through the block. still can't explain it.


Were these the M2 .30'06 black tip AP's?
http://www.inetres.com/gp/military/infantry/rifle/30-06/30_M2_AP.gif

[finishman2000]

yup, i had 2k laying around.

[fecmech]

I posted a table of cast bullets at different speeds and it's very interesting to see if the Ballistic Coefficent goes up or down with the speed change.

http://castboolits.gunloads.com/showthread.php?t=94638

They most certainly do. Here is a list of handgun and some handgun rifle bullets in the supersonic, transonic and subsonic ranges with the changes in BC. If you select "Show all handgun" you can scroll through the list.
http://www.sierrabullets.com/index.cfm?section=bullets&page=bc&bullettype=1

[Artful]

yup, i had 2k laying around.

Yep, that .30'06 M2 AP is quite the penetrator, tested that ammo again 7.62x51 nato penetrator on steel - it went thru plate armor that the 308 wouldn't. Part of the Magic is the jacket is very thick and doesn't change shape much but has the right angle to "thread the needle"

[Canuck Bob]

As an airplane homebuilder the teardrop shape is common for streamline tubing and such. The best dimensions have been worked out for subsonic applications for a long while. It should be possible to clip the long rear tip without adverse problems and reduce the length of the bullet. A ratio of 3.5 to 4 of length versus width is regarded the best at light plane speeds.

Also an angle of greater than 9 degrees on flat reducing surfaces will cause flow seperation on inlets and afterbodies. I'll try and track down some links.

Bullet application seems to require shape adjustment to supply a strong area for driving bands. Paper patchers could send a very low drag subsonic slug downrange with no grooves or rifling, interesting!

http://ecomodder.com/forum/showthread.php/flow-separation-tiger-woods-meets-cinderella-5-seconds-2104-2.html

http://www.gassavers.org/showthread.php?t=1134

http://qm-aerospace.blogspot.com/

[x101airborne]

My swat team uses AP-2 rounds as a control for testing metal penetration / overpenetration (especially on vehicles). if anyone would like to sell any of these projectiles, please let me know by PM. Thanks.

[82nd airborne]

101, try hi tech ammo.

[308 caster]

After 2 years of trial and error I now have a 308 cast that will expand and frag upon impact at subsonic speed. If anyone is interested..

[Artful]

Of course we are you tease.

[35remington]

I must say.....that AAC "BLK" propaganda under rates the competitive rounds in order to make their proprietary round look a lot better. There is little actual real difference. The short Russian can do 2400 fps....so no superiority ballistically for the AAC stuff. I wasn't aware the competitive rounds were much of a strain on the AR action, mostly because they're designed not to be.

[Artful]

So how do you explain all the broken bolt heads when the 7.62x39 was first set up to be used in the AR platform?
-And I agree ballistically the 7.62x39 is ahead of the BLK but the 30-30 is also the BLK/whisper is just a barrel change for any AR platform no other parts need changed (unless you count the gas tube)
- I'd take a 788 in 30-30 ahead of an AK for a suppressor platform for hunting any day.

[35remington]

Ain't talking about broken bolt heads all that much, really. The 6.8 SPC are already proven there, and no advantage exists for the BLK in various iterations.

Just commenting on the propaganda angle.

Further, if I'm not mistaken, quite a few AR clones are chambered in the 7.62 X 39......still.

If there's a problem, then somebody's missing something obvious and selling them anyway. Haven't heard a groundswell of complaints from the 7.62 owners. Apparently any "problems" have been addressed to date.

I suspect any issues have been due to case head size differences rather than taper.

I've never been a great believer in the "case cling" theory of a straighter case given that the head of a brass case will stretch and yield, thinning at the web due to pressure, straight or not, headspace or no. In these instances bolt face thrust is equal. Brass doesn't have magical holding properties and resists stretching and reduces backthrust just because it's straight.

Think about yield stretch of brass and get back to me on that one.

[Artful]

I was going to go 7.62x39 AR-15 (after using a friend Colt) - couple of things stopped me - one searching the WWW found at that time a number of issues with broken lugs on 7.62x39 bolt heads - Surplus ammo had primers hard enough some where having issue with consistant ignition, Shortage of large capacity magazines able to feed reliably in AR platform.

Remington's advantage with the black is those who already own a 223 AR can do a caliber conversion quite easily - heck just a second upper and swap the bolt carrier over and your in business - same mags etc.

So it does have advantages for AR platform users, And if your cases are oily or wet I can see more bolt thrust happening with a more tapered case. Does it matter to me - not much all the guns I use 7.62x39 in have strength a plenty from SKS, or AK to converted Mauser bolt gun.

[rsilvers]

I must say.....that AAC "BLK" propaganda under rates the competitive rounds in order to make their proprietary round look a lot better.

I did those charts and did not under-rate the other rounds. For 6.8 I took it right off Hornady's website.

[rsilvers]

Ain't talking about broken bolt heads all that much, really. The 6.8 SPC are already proven there, and no advantage exists for the BLK in various iterations.

300 AAC BLACKOUT has several advantages over 6.8 SPC.

1. Cheaper brass and ammo.
2. Uses normal AR mags with 30 round capacity.
3. Uses normal bolt face.
4. Less blast/flash.
5. Works for subsonic.

[rsilvers]

Further, if I'm not mistaken, quite a few AR clones are chambered in the 7.62 X 39......still.

If there's a problem, then somebody's missing something obvious and selling them anyway. Haven't heard a groundswell of complaints from the 7.62 owners. Apparently any "problems" have been addressed to date.

7.62x39 does not work in ARs very well. You only get about 5 rounds in a normal magazine before feeding problems. The bolts lasted me about 200 rounds each when I tried it. They are not addressable - the mag well in an AR is straight, so you can never put a curved mag in it. And then there are the primer problems.

[frkelly74]

I confess I have not read all the entries on this topic. But I have tried loading the 147 gr FMJ bullet backward once and found them easy to get to group. I was trying to fire form some brass to a 30 rem Chamber and those were the cheapest 30 cal bullets I had. I loaded them backwards because of the tube magazine. I was really surprised that they were at all accurate.

[L1A1Rocker]

After 2 years of trial and error I now have a 308 cast that will expand and frag upon impact at subsonic speed. If anyone is interested..

Pics please.

[35remington]

Another perspective on the competition:

http://demigodllc.com/~zak/firearms/6.8SPC/faq.php

Puts some of the other claims into question.

[leadman]

I don't shoot ARs, but do shoot the 223 and 300 Whisper in a Contender carbine. The whisper is loaded with 125gr Nosler ballistic tips to just under 2,100 fps, the 206gr cast boolits are loaded to 1,100 fps approx.
I normally shoot 55gr Hornady bulk bullets in the 223 at approx 3,300 fps.
If I had to use these cartridges with these loads in a combat type situation I think my first choice would be the 223 if ranges could be beyond 200 yards.
The Whisper even super-sonic just has too much drop for any shots to be placed quickly. I have shot the 206gr cast past 200 yards and the drop is drastic. I need to change the scope on the Whisper and practice.
I'm not sure if the OPs idea on bullet shape would help on longer ranges. I guess if he gets some bullets to play with it would be interesting to see the results.
One issue with the small 300 Whisper case would be were to put the powder needed with a long tapered bullet like that. Maybe go to a case like the 30TCU?

[barrabruce]

I'd like to see these expanding/fragmenting cast projectiles too!

or how it is done.
All I can do is get nose bending and tubling or slight flattening of the tip.

Be handi for the light boned varmit critters if I could get my low velocity load to behave like high speed grenades.

I might try my 170 fp lee backwards to see if it can shoot.

Drop at 325 yrds is around 62 moa.
Barra

[rsilvers]

Another perspective on the competition:

http://demigodllc.com/~zak/firearms/6.8SPC/faq.php

Puts some of the other claims into question.

6.8 SPC cannot make those numbers within SAAMI pressure limits. Hornady is not underloading their ammo and I quoted Hornady's own data. Hornady was the fastest ammo which I am sure is within SAAMI specs. So to say I am under-reporting 6.8's performance is just not true.