Ballistic-only advantages to sticking with 5.56?

[Swatdude1]

So if you didn't have a multi-purpose carbine and your choices were the KAC SR-15 and the SR-30, identical in every way except caliber, which would you choose?

I could start a tangent and say "neither", KAC is overpriced and doesn't offer anything magical over any other solid mil-spec platform other than name, but I will stay to the topic and ask: What range do you intend to use the weapon at?

[Tacti-square]

I could start a tangent and say "neither", KAC is overpriced and doesn't offer anything magical over any other solid mil-spec platform other than name, but I will stay to the topic and ask: What range do you intend to use the weapon at?

I only used them as an example because I'm interested in their E3 bolt and URX 4 rail system. Just because they're overpriced doesn't nullify their innovation.

As far as range, standard engagement distances. 50 to 400 yards, maybe 500

[Swatdude1]

I won't discredit the E3 bolt, but Barrett, LWRC, LMT and others have offered enhanced bolts with some of these features like re-inforced lugs and dual extractor springs.

https://www.m4carbine.net/showthread.php?t=3379

I am partial to TTSX bullets so if I were going with 300 blk I would choose the 300blk Remington loading of the 110 TTSX. Doc did some testing here:

http://m4carbine.net/showthread.php?t=126288

The problem with 300 blk will always be a sacrifice in muzzle velocity. The 110 TTSX round was tested at roughly 2250 fps MV. You will start to see some pretty substantial bullet drop after about 250 yards with most of the 300blk loadings. Also, their effective range if depending yaw, fragmentation or expansion will be significantly reduced. Doc noted excellent yaw characteristics with the 300 blk 115 UMC round. Doc would have to comment on at what velocity this bullet stops exhibiting the excellent yaw. TTSX bullets have been know to expand reliably down to about 1700 fps in the 110gr loads. Using a ballistics calculator that puts the effective range for the 110 TTSX at about 200 yards. Doing my best apples to apples I can compare this to the 62 gr .22 TTSX bullet at 3000 fps MV. If we assume the same velocity expansion threshold of 1700 fps, this occurs at approx. 460 yards for the 62 gr 5.56 bullet. Curiously enough, both bullets have BC's of .295 so the bullet drops at 400 yards for 110 (2250fps) and 62 grain (3000 fps) TTSX are -56.3 and -25.7 respectively.

I would welcome Doc's comments on the topic but it is my opinion the .300 blk begins to loose its terminal advantage over the better 5.56 loadings after about 250 yards.

[Tacti-square]

I won't discredit the E3 bolt, but Barrett, LWRC, LMT and others have offered enhanced bolts with some of these features like re-inforced lugs and dual extractor springs.

Yes, but as far as I knew KAC is the only company of those listed which offers identical 5.56 and .300 BLK systems.

[BufordTJustice]

Yes, but as far as I knew KAC is the only company of those listed which offers identical 5.56 and .300 BLK systems.

KAC was the first to invent those improvements to the bolt, as they were a result of input from Gene Stoner himself while he worked at KAC before he died. It may not be everybody's cup o tea, but everybody else is basically just a copy of those KAC/Stoner innovations in the E3 bolt and barrel extension.

Just sayin.

Tacti, I would select the SR15 in 5.56x45mm 10 times out of 10 for most uses......with the SR25 ECC (w/ 16" barrel) being probably the best .308 AR-10 pattern rifle out there right now. It has a 16" barrel with 5R rifling, precision CL-ing, rifle-length gas system, longer AR10 buffer (std AR15 carbine length and room for a longer action spring). Haven't been able to shoot one yet, but LAV was thoroughly impressed when he shot it.

[Tacti-square]

Tacti, I would select the SR15 in 5.56x45mm 10 times out of 10 for most uses.

Thanks for the input, do you mean over the SR-30?

[bzdog]

TTSX bullets have been know to expand reliably down to about 1700 fps in the 110gr loads. [...] If we assume the same velocity expansion threshold of 1700 fps, =

Not a huge difference, but my understanding is the 300 BLK version is supposed to expand reliably down to about 1300fps. Supposedly it was tuned specifically for 300 BLK.

-john

http://www.outdoorlife.com/blogs/gun...0-aac-blackout

[BufordTJustice]

Thanks for the input, do you mean over the SR-30?

Sorry. Roger that, over the SR30.

I had just spent 8 hours running around in the rain when I posted that. Brain fade.

My comments about the SR25 ECC do stand though.

[DocGKR]

Here is what I would want:

1. Good quality 16" barrel 1/7 twist 5.56 mm AR15
2. Good quality 16" barrel 1/8 twist 7.62 mm KAC or LaRue
3. Good quality 16" barrel 6.8 mm upper for AR15 if option 2 not utilized.

[Swatdude1]

Here is what I would want:

1. Good quality 16" barrel 1/7 twist 5.56 mm AR15
2. Good quality 16" barrel 1/8 twist 7.62 mm KAC or LaRue
3. Good quality 16" barrel 6.8 mm upper for AR15 if option 2 not utilized.

So no .300 blk on your list?