5.56 vs 5.45 vs 300 blk in a 8 inch sbr

[brycewise]

I would like to build a new upper for a sbr it would have a 8 inch barrel.Which of these 3 rounds would offer the best performance inside of 100 yards from an 8 inch barrel? Which would be the most pleasant to shoot and have the least concussion? I am mostly curious how the 5.45 stacks up to the 5.56.

I have read that the tumbling and yawing effectiveness is a 50/50 split in terms of terminal ballistics with half of the data supporting it and half of the data disproving it. I also know it was called the "poison bullet" by the mujahedeen because wounds caused by the 5.45 frequently required amputation.
The name poison bullet sounds pretty intimidating but If it caused a lot of amputations then im pretty sure that the person who was shot by it lived.

[civiliansheepdog]

.300>5.45 or 5.56
The BLK was deigned to be suppressed from a short barrel. Both the 5.56 and 5.45 are heavily dependant on velocity for best performance. The 5.45 is better out if shorter barrels than 5.56 because of tumbling instead of fragmentation( when talking FMJ) however when considering an 8 inch barrel, I think there are really only 2 choices. Blackout or 6.8 SPC. And .300 is the better of those two. My question would be why your SBR has to be 8 inches? Why not 10 or 12? An 11" BCM 5.56 upper would be a great option.

[civiliansheepdog]

300 wins even more when considering concussion with its subsonic loads.

[wahoo95]

I wouldn't compare the subsonic 300blk ammo to supersonic 5.56 or 5.45. The subs are cool but supersonic 300blk is about optimal from an 8" barrel unlike the others which need more barrel length to develop the necessary velocity to be effective.

Inside 100yds I feel the supersonic 300blk is an excellent choice with or without a suppressor.

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[strambo]

Yes, for terminal effectiveness out to 100yds the supersonic .300BLK wins. Subsonic it is kinda like a .45 ACP with really poor (terminally) performing bullets. In 5.56 the TSX line will expand down to 2300 or 1900-ish fps depending on the particular load and an 8" barrel will drive them well above 2300.

I'd go 300BLK supersonic with an 8" barrel and a can if I could afford it.

[HCrum87hc]

Count me in on the 300blk train. It was made to be shot out of short barrels and loves to be suppressed.

[domestique]

35901


300BLK with the right load is effective out to 320-360 yards (9 inch barrel).... also less flash and concussion than a 8" 5.56. I personally wouldn't go less than 11.5" for a 5.56 SBR.

An example of the 70gr. TSX: 2,400 FPS out of a 8" 5.56 would yield effective expansion to 200-230 yards. A 11.5" barrel would yield 2,600 fps and reliable expansion to 300 yards...... this is even assuming you can get the 70gr. bullet moving that fast. I was optimistic in my numbers for the 5.56 load as the graphs represent the 62 gr. M855 round.

ETA:

From another thread:

-1800fps for the 70gr TSX
-1900fps for the 55,62 gr TSX
-The "non 5.56" 50gr bullet (handloading component) is also 1900fps
-The 5.56 loading by Black Hills using the 50gr Barnes has an expansion threshold of 2300fps, as it is a tougher design meant for use at close ranges against windshields, etc.
-300 BLK 110gr Blacktip has an expansion threshold of 1300fps. The blue-tip 110gr .308" dia TSX bullet has an expansion velocity of nearly 500fps higher, as it is meant for other cartridges, if you will.

Hope this helps. If anything it proves that you need to know the EXACT bullet beign discussed, and "transposing" expansion velocities doesn't work with the Barnes. It's very very VERY caliber/loading specific.



5.56 barrel lengths with 62gr. M855 "green tip"

www.sadefensejournal.com/wp/?p=1093

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[Auto-X Fil]

As the others have said: 5.56 from an 8" MAY have acceptable terminal ballistics at close range, if you're really picky about bullet selection. It will still have crazy muzzle blast (I've shot a 9" a bit, and it SUCKS), and you can't put a suppressor on it (nobody I know of makes a can rated for 5.56 on an 8" barrel).

With 300BLK, you get decent velocity and great terminal performance with less muzzle blast, and you can run a suppressor (many are rated down to 8").

I agree with the last poster: 11.5" is a good lower limit for a 5.56 SBR. 10.5" is really pushing it. If you want an 8" gun, go 300BLK.

[domestique]

The Silencerco Saker 556/K is rated to a 7" barrel...... not that I would recommend that setup over a 300blk SBR.

[civiliansheepdog]

If running a can, .300. If not, it's hard to be the 90 gr. Gold Dot in 6.8 bc of its affordability combined with its terminal performance.

[brycewise]

.300>5.45 or 5.56
The BLK was deigned to be suppressed from a short barrel. Both the 5.56 and 5.45 are heavily dependant on velocity for best performance. The 5.45 is better out if shorter barrels than 5.56 because of tumbling instead of fragmentation( when talking FMJ) however when considering an 8 inch barrel, I think there are really only 2 choices. Blackout or 6.8 SPC. And .300 is the better of those two. My question would be why your SBR has to be 8 inches? Why not 10 or 12? An 11" BCM 5.56 upper would be a great option.

It doesn't have to be 8 inches this seems to be a popular 300 blk length. having said that, if im going to have a short barrel rifle then I want it want to be short. if it was going to be 11 or 12 inches I would just skip the hassle and get a 16 inch barrel.

[brycewise]

.300>5.45 or 5.56
The BLK was deigned to be suppressed from a short barrel. Both the 5.56 and 5.45 are heavily dependant on velocity for best performance. The 5.45 is better out if shorter barrels than 5.56 because of tumbling instead of fragmentation( when talking FMJ) however when considering an 8 inch barrel, I think there are really only 2 choices. Blackout or 6.8 SPC. And .300 is the better of those two. My question would be why your SBR has to be 8 inches? Why not 10 or 12? An 11" BCM 5.56 upper would be a great option.
Does anyone have any links to "hard" evidence that the tumbling actually is effective in terminal ballistics? I have read that organic tissue is to elastic for a round tumbling to have a significant immediate impact.