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 Subsonic .30's & .338's
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TxTickPkr
Advanced Member

USA
1637 Posts

Posted - Jul 23 2012 :  16:30:09  Show Profile  Send TxTickPkr an AOL message  Send TxTickPkr a Yahoo! Message Send TxTickPkr a Private Message  Reply with Quote
So much has been made of the 300 Wisper/Blackout. I have wondered why not just use the haviest for calibre projectile at a reduced load to achieve sub-sonic velocity? I have heard that cowboy shooters, useing large cases and light target loads, have experienced "Wave Detonation Phenomenon" as the powder lays along the length of a horizontal cartrige and is all ignited at once by the primer. Has this ever been proven in a lab? I would think that inert packing would keep the powder where it belongs, but have always suspected these incidents were doublecharges since the powders used could fit into the cartrige.Inquireing minds want to know before droping a hammer on this one.
Just because you think they are all out to get you doesn't meen they really aren't.
Those that relenquish liberty for security deserve and shall have neither.

Those who relinquish liberty for security deserve and shall have neither.

Fred_C_Dobbs
Advanced Member



678 Posts

Posted - Jul 23 2012 :  18:15:23  Show Profile Send Fred_C_Dobbs a Private Message  Reply with Quote
There is a phenomenon called "Secondary Explosion Effect" (SEE), which seems to involve too little case fill of a fast powder, but that's strictly a "theory." No one is able to reproduce it at will under controlled conditions. That's one of the chief reasons A1680 is the most often recommended powder in the 300blk. With heavier bullets, it takes very close to 100% case fill to get to 1000 or 1050 fps.

The inert filler is a workable solution, too.

I'll bet ya a hundred and five thousand dollars you go to sleep before I do.
-- Dobbsie

Edited by - Fred_C_Dobbs on Jul 23 2012 18:17:23
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TxTickPkr
Advanced Member

USA
1637 Posts

Posted - Jul 23 2012 :  23:29:58  Show Profile  Send TxTickPkr an AOL message  Send TxTickPkr a Yahoo! Message Send TxTickPkr a Private Message  Reply with Quote
Fred C Dobbs, I can never get enough of that original character, the antagonist in all of us though few admit, only a thin veneer mask him. I have been researching the reports of SEE and have loaded 300 wisper. That was an impressive round, but I am as reluctant to dedicate a complete rifle as I am to drop the hammer on a packed load given the extreme reports of SEE. As I read the reports, the problem seems to be the powder exposing too much surface area to initial detonation. I guess it's time to machine a fixture. Wanted to avoid that if anyone had real data. Guard your polk Dobbsie and don't go grabin Ghila Monsters under rocks.

Those who relinquish liberty for security deserve and shall have neither.
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Fred_C_Dobbs
Advanced Member



678 Posts

Posted - Jul 24 2012 :  15:53:33  Show Profile Send Fred_C_Dobbs a Private Message  Reply with Quote
It amazes me how many people never pick up on the avatar or the handle. Guess people just don't watch B&W classics any more.

There's a whole lots of competing theories on SEE, and it could be they all are right, at least partly. Gasoline engines experience pre-ignition for a lot of different reasons but the end result is that the fuel explodes violently rather than burning in an (somewhat) orderly fashion. Every phenomenon (I can think of) that produces 'pinging' in a gas motor has an equivalent in firearms cartridges. Plus the cartridge has some possible causes motors don't because its fuel is solid, not gaseous. And some people are convinced that SEE's cause is nothing more than double-charging.

In any case, it does seem to be the Internet panic topic du jour, but I think it's a tempest in a teacup. Check in with the guys at www.300blktalk.com, which was spun off from www.silencertalk.com. There's probably a larger aggregation of 300Blk experience there than anywhere else on the Internet, and they'll straight up tell you you're more likely to have a meteorite fall onto your house that you are to have an SEE, particularly if you're forewarned of its existence and exert a little common sense toward avoiding low case fills.

I've balked at building a 300Blk, but not for SEE concerns. I don't think there are any suitable bullets for it. If I were going to build a .30-cal AR15 and did not intend it to be dedicated subsonic, I'd go with the .30BR, a wildcat of the 6mmBR that already has an outstanding target competition pedigree.

However, if you're going dedicated subsonic, if you have any "real-world" use for it, IMHO you've got to limit yourself to bullets that demonstrate reliable mushrooming at such low velocities. You don't get that in the heavier jacketed bullets (like the 220-gr SMK) and have to get down to 170-180 grainers before they'll perform as needed subsonic.

Except that a 180-gr bullet @1050 fps gives you an IPSC/USPSA/SASS power factor of 189, and John Moses Browning's bespoke load for the Colt 1911 (231-gr @825 fps) is a power factor of 190. So why bother?

I thought maybe cast boolits were the answer, because soft lead bullets got no problem with low speed mushrooming. Mountain Molds has a really slick online bullet mold configurator that gives estimated dimensions based on your design parameters. The 300Blk's standard 1:8 twist would have no problem stabilizing the heaviest .30 their web interface can accomodate -- 330-gr -- but then I started experimenting with those bullet lenghts and weights in QuickLoad.

If I used a shank seating depth to produce the recommended OAL (2.240"), QuickLoad calculates there's too little case capacity for A1680 to produce 1050 fps at a safe pressure from my theoretical 14" barrel. When I backed the bullet weight down to 300-gr, it was on a razor's edge for both pressure and case capacity, and when I got down to 290-gr, it gave me about 10% breathing room in both case capacity and Pmax. Since this data was all theoretical, I figured the 280-gr probably was optimal because this is a very blunt-nosed bullet, and might require some OAL jiggery to feed reliably. And on the pointy end, the target probably can't tell the difference between 280-gr and 290.

280-gr @1050 fps gives a PF of 294, which is a substantial step up from 190, but that's all there is and all there likely ever will be. And I still question whether that's enough an improvement over a .45 ACP to make a 300Blk worthwhile, especially since it also means I'd have to take up bullet casting. Which was not the conclusion I wanted to arrive at because my largest caliber suppressor is a .30, and if I have to go for any of the larger dedicated subsonic AR calibers, I'm immediately in the hole a grand before I start with the rifle because of the cost of a new can and tax stamp.

I briefly looked at the .338 Spectre, but there isn't near as much diversity of available .338 bullets as for .308. The heaviest jacketed .338 bullet is about 300-gr, not that much better than the 280-gr cast boollit in the 300Blk. Since anything larger than .30 means I gotta get a new suppressor anyway, I decided in for a penny, in for a pound, so I might as well look into the big bores. Between the .450 Bushy, the .50 Beowulf and the .458 SOCOM, the SOCOM seems to have the best selection of suitable bullets. And frankly my standards are far less stringent because just how much mushrooming does a .45 caliber bullet need anyway? There are jacketed bullets in .458 all the way up to 600 grains, which comes to a PF of 630, which stomps a mudhole in the .45 ACP.

So unless something changes my mind (which always is a possibility), my next AR will be a .458 SOCOM, which unfortunately means I also have to save up for a new suppressor.

I'll bet ya a hundred and five thousand dollars you go to sleep before I do.
-- Dobbsie
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Mike70560
Senior Member



USA
309 Posts

Posted - Jul 24 2012 :  21:53:10  Show Profile  Visit Mike70560's Homepage Send Mike70560 a Private Message  Reply with Quote
Fred,

I shoot a 300 Whisper built on Stiller action loaded with 240 Grain SMK and a AWC suppressor. It is a fun setup for armadillos and turtles around the pond.

That being said do you shoot cast lead bullets through a suppressor? My experience is limited with suppressors but it seems as though I read not to shoot cast bullets through a can. Is this true or is there no issue with cast bullets and a can?

Thanks,

Mike
New Iberia, LA
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Fred_C_Dobbs
Advanced Member



678 Posts

Posted - Jul 24 2012 :  22:03:43  Show Profile Send Fred_C_Dobbs a Private Message  Reply with Quote
Mike, I have not but have been told that is a distinct possibility. And they do make take-apart suppressors (normal for RFs but unusual for CFs) specifically for the use with cast boolits.

If you've shot the SMKs subsonic, what are your terminal effects experiences with them?

OT, but have you tried loading them backwards? In theory they are supposed to be easier to stabilize that way, and a blunt meplat is supposed to produce better SSS terminal effects.

I'll bet ya a hundred and five thousand dollars you go to sleep before I do.
-- Dobbsie
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Mike70560
Senior Member



USA
309 Posts

Posted - Jul 24 2012 :  22:25:46  Show Profile  Visit Mike70560's Homepage Send Mike70560 a Private Message  Reply with Quote
Terminals have only been on turtles and armadillos. The SMKs just pencil through when they are subsonic.

Accuracy wise I am about 1 MOA at 100 yards. All vertical stringing. Windage is less than 1/2 minute. Small changes in velocity make a big difference in accuracy. I will try some RL 7.

Never loaded them backwards. I do like a big flat nose bullet in my big bores.

Mike
New Iberia, LA
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Fred_C_Dobbs
Advanced Member



678 Posts

Posted - Jul 25 2012 :  19:00:36  Show Profile Send Fred_C_Dobbs a Private Message  Reply with Quote
I know of specific instances where guys have shot SSS .308s from 1:10s that were too heavy to stabilize frontwards but did perfectly fine bass-ackwards. Your 240-gr SMK also probably will have better terminal performance when shot backwards, too, especially if the base isn't copper clad. There's a thread somewhere over at the Sniper's Hide where the guy compared the terminal effects of SSS VLD Bergers frontwards versus bass-ackwards. The damage was much more extensive when they were fired bass-ackwards, which would seem to be in keeping with the purpose of Woodleigh's "hydrostatic" bullets.

I'll bet ya a hundred and five thousand dollars you go to sleep before I do.
-- Dobbsie
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Mike70560
Senior Member



USA
309 Posts

Posted - Jul 27 2012 :  06:59:57  Show Profile  Visit Mike70560's Homepage Send Mike70560 a Private Message  Reply with Quote
Fred,

If you like shooting bullets backwards, this is your bullet.

http://site.cuttingedgebullets.com/raptor


Mike
New Iberia, LA
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hwy40
Advanced Member



USA
544 Posts

Posted - Jul 27 2012 :  09:59:08  Show Profile Send hwy40 a Private Message  Reply with Quote
I loaded boat tails backwards in sub sonic 7.62x39 loads. I used Trailboss powder and made some great stray dog loads. With the bullet seated backwards it seemed to do more damage than standard loads going 1300 fps faster.

If it ain't broke, fix it 'till it is.
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