I have had this question and cannot find anywhere to ask it . I know you folks really "know your stuff" This is just a question about the .300 blk round and close quarters combat .

I seem to have read where our troops are having some trouble with the short barrel .556 rifles they are using in close quarters . The idea is that the short barrel reduces the velocity to where the .556 doesn't have the "Knock Down" power it would have at longer ranges or if the barrel was longer . And in some cases the .556 round was passing thru the bad guy only leaving a small .22 cal hole . Some of the enemy have had to be hit several times to stop them ...

Here's my question .. Wouldn't the 300 blk with its 30 cal 220 grain projectile do more damage and if it is used in the "suppressed" mode approx 1100 FPS it should mushroom and fragment more often than just going right thru them ..

This is just something I have been thinking about and didn't know who to ask .. You people know your stuff an I think can give me a reasonable answer to this . Maybe our toops should be armed with some 300 Blk for the house to house work the have to do ..

Once again Thank You for looking at my questions . I have been studying .223 and .300Blk balistics and allthou I want a 300 blk now I don't see a lot of difference between the 69 grain .556 and the 125 grain 300 blk as far as term. energy goes but the 220 grain 300 blackout looks like it could be really useful in a couple of ways also our troops would only need 1 weapon for scilenced work or full power work ..

Sorry this is so long . Thanks Again , Don J.

Switching to 300AAC subsonic will not provide any fragmentation in soft targets. Considering that 7.62 bullets typically need about 2800fps to fully fragment, and most 300AAC subsonics reach 1000-1100fps for only the first 100 yards, all you will do is punch a hole. You've actually made the problem you are trying to avoid worse. If you want more weight and fragmentation in a subsonic package, then a suppressed H&K UMP or similar style 45ACP platform is your best bet.

As for 5.56 rounds in short barrels, the 5.56 SOST rounds were designed to address these concerns. They retain the barrier penetration of M855, but also have an open tip (not really hollow point) with a lead core. This allows for great expansion of the copper and full fragmentation of the lead core at velocity that can be achieved out of short barrels. Use these in combination with 11.5-12.5" uppers for indoor CQB, and 13.5-14.5" uppers for 100-200 yard skirmish. For longer range than that, you should be using M855 out of 14.5" or longer M4's.

Thank You for your reply . Some things you told me about I haden't ever heard of . Looking at ballistics on several types of ammo yesterday on the internet. (used Wikipedia) I saw where .223 ammo with 69 grain "HPBT?" has a energy # of 1330 and the .300 Blk 125G bullet has a 1360 energy #.. I have been thinking the .300 Blk idea was totally cool but now with those numbers am wondering what the advantage is .

I had read about the problems with .556 ammo in Short Barreled Rifles because of the loss in velocity and people saying the bullet won't do as much damage it won't tumble at that lower velocity. And some of our military were still being shot back at after hitting the enemy.

So now my thoughts were the bigger 220 grain round from the .300 blk would do more damage sorta like the difference in the 9mm and .45 cal pistol rounds??

I still think the .300 blk idea is cool and "sorta" want one but now I wonder what the advantage is . With full power ammo the energy difference is very little like 3o foot pounds . And the subsonic loads allthou being 220 grains may not be any better than the 69 grain .556 round ?? I never plan on going with a scilenced rifle anyhow allthou it would be totally cool.

I understand that you can use just one weapon for scilenced and full power work with only changing the ammo so we won't need the H&k 9mm and the M16 or m4 weapon for our troops but other than that is there any other benifits to having the 300 blk over a .556 ??

Sorry this is so long and probabally sems like a dumb question to you . If there is a resource you can suggest for me to go to with this question let me know . I don't like bugging you allthou you'r the best source of info I know and found you when I had a couple of questions before buying my Spikes mid length 16 inch upper which seems to be the best you can get and at GREAT prices . The 1 in 7 twist is a plus I found out about after buying it along with a bunch of other components that excede the other "supplier" products.

Any reason to buy a .300 blk or should I just stay with this spikes tactical and "Explore" all it has to offer .. Thanks again and as usual I'm sorry about being so long winded.. Don J.

Kinetic Energy (1/2 x Mass x Velocity Squared) is similar to E=Mc2. When you were researching the different ammo types, did you happen to look at what the test setup was? By this I mean what barrel length, powder charge, muzzle velocity, impact velocity, etc.

And subsonic ammo does not fragment, unless the bullet is designed to do so at lower velocities. Doing this would make the bullets no good for supersonic use, and hence why nobody makes such fragile bullets. So let us compare a couple different loads/calibers. To simplify, we will calculate if impact occurred at the point of measurement (unless you have time to learn momentum, resistance, lateral forces, etc to calculate what the velocity would be at a given distance down range).

A 69gr 5.56 subsonic (1000fps @ 50ft from 14.5" barrel) would put into a target at 50ft.
1/2 (.5) x 69gr (.00447 Kg) x 1000fps (304.8 meters) x 1000fps (304.8 meters) = 207.63 J = 153.14 Ft/Lbs

A 62gr 5.56 supersonic (2975fps @ 50ft from 16" barrel) would put into a target at 50ft.
1/2 (.5) x 62gr (.0040 Kg) x 2975fps (906.78 meters) x 2975fps (906.78 meters) = 1644.5 J = 1212.92 Ft/Lbs

A 220gr 300AAC subsonic (985fps @ 50ft from 10.5" barrel) would put into a target at 50ft.
1/2 (.5) x 220gr (.01425 Kg) x 985fps (300.2 meters) x 985fps (300.2 meters) = 642.1 J = 473.59 Ft/Lbs

A 125gr 300AAC supersonic (2200fps @ 50ft from 16" barrel) would put into a target at 50ft.
1/2 (.5) x 125gr (.0081 Kg) x 2200fps (670.56 meters) x 2200fps (670.56 meters) = 1821.08 J = 1343.16 Ft/Lbs

You see that the energy changes are dramatic between subsonic and supersonic. You can also see why you don't consider subsonic to have much stopping power. Yes, what you've read in regards to subsonic being stronger and supersonic being similar is correct. But subsonic does have substantially less energy put into the target in either caliber. In fact, a 45ACP 230gr from a 5" barrel will put 500 Ft/Lbs into a person from 20ft. But this doesn't "knock down" anything either. Reason being is that a person that is braced or tense can actually push a car. So why would anyone think a small bullet at a fraction of the weight of a car is going to make a person fall down?

Now here is a M855 round from a 11.5" barrel @ 50ft. Let's see if this is better than a 220gr subsonic 300AAC.
1/2 (.5) x 62gr (.0040 Kg) x 2770fps (844.3 meters) x 2770fps (844.3 meters) = 1425.68 J = 1051.53 Ft/Lbs

So, would you rather hit someone with 474ft/lbs of energy or 1052ft/lbs of energy? This is why the troops won't get 300AAC SBR's shooting subsonic rounds for CQB. Since 300AAC subsonic is about the same energy as a 45ACP, this is why I said it would be easier to just give them H&K UMP's for CQB if you want fragmentation (because 45ACP HP can mushroom at those speeds, while 300AAC and 5.56 cannot fragment).

While 300AAC is a far more effective subsonic ammo for SBR's over subsonic 5.56, it isn't more effective than what the troops are currently fielding with 5.56 NATO rounds. In fact, if you used M193 instead of M855 you can increase the distance you can still maintain fragmentation velocity (2700fps) all the way out to 240ft (80yd). So if you want an indoor/outdoor SBR that can do the most damage (energy, cavity & fragmentation) to soft targets in a battlefield, the 0-75yd range of an 11.5" SBR using 55gr M193 is your best bet. If you must have steel core penetration & fragmentation, then M855 drops your range to 150ft (50yd). Unfortunately, with a 10.3/10.5" barrel neither M193 or M855 will fragment at any range. It is just below the threshold at 50ft on M193 and just below at 25ft on M855.

I hope this gives a fuller explanation for you.

Dear JaxChris, Thank You Very much for your time and the explaination about how the torque number is arrived at. I have written down this formula but understand how sometimes it is "Tweaked" like car dealers do .
This changed a lot of the opinions on the .300 blk that I had . Thanks for taking the time to explain your answer to me. I have new opinions about the 300 Blk but still need clairification on a couple of things .

I can see where it is real close between the .556 and 300 AAC in the full power version only about 14 fps .. and I see where the suppressed version or subsonic version is pretty useless as far as stopping power goes.

Now then just to play the devils advocate and also to answer a couple of questions that I and probabally other do want to know about. The AAc300 seems sorta useless if you just go by the numbers but then I think about the 1 gun for multi puropose <sp? use .

The AAC 300blk has close enough full power Numbers to use instead of a .556 round . So ... If you were using this rifle inside in the suppressed mode like the 9 mm H&K at close quarters you'd be sorta OK . I learned from your answer that there is not a bullet made that expands or fragments like the 9mm or .45 cal. Now I'd think a bullet could be made that would work in the AAC300 to have the same stopping power as the 9mm in the H&K ... So then lets just say your done inside with the CQB and and scilenced work you go outside just to find someone shooting at you from 75 yards away . With the H&K 9 mm you might be in trouble but with the 300blk you could just change mags to the full power ammo and be back in buisness . This is just one of the reasons I have read about for the 300 blk .

Please don't get the wrong Idea . I totally respect the information you have given me and am soooo grateful for it . This is just a senario I have read about for the 300 blk. The idea is that our military personel would need only 1 weapon and the other thing is tha I have read where the H&K is somewhat trouble prone and parts are expensive.

Thanks so much for putting up with me . I have learned a LOT from you and really appreciate it . Thinking now I will put my spikes tactical rifle as first amd only for when the zombies arrive . I want to load some of the SOST rounds you have told me about.

OK this is too long again I just got home from work and am a little"punchy" now ... Time to sleep now I hope this make some sense to you as I was tired when typed it out .. Thanks so much again .. Don J.

What barrel length will your CQB rifle be? If you throw away the fragmentation requirement, then you can make do with 300AAC. Even the 125gr 300AAC @ 2200fps in a 16" barrel won't fragment more than 2-3%. Kinetic energy dumped into target is important, and more important than fragmentation.

Also, if full time suppression is a requirement you would greatly increase cost to convert and introduce a lot more heat to the front of the weapon. There is a reason why fully suppressed weapons are not used in heavy fire scenarios and suited more for short engagement (home defense, spec ops, SWAT, etc). The additional heat can cause a drop in accuracy over time during a prolonged engagement, make the weapon too hot to safely hang/sling, and prematurely wear existing components that were not upgraded/improved during the conversion process (increasing the maintenance costs).

There are a number of factors the military has to contend with when coming to a compromise on a service weapon. A short barrel carbine will never be the end all be all for our front line troops. You don't want the enemy to have an effective range advantage. And the military is adverse to introducing any new cartridges to the field, which is evident by the rejection of 6.8SPC during the trials for a 5.56 replacement (which ended with the introduction of the SOST round). With 300AAC being a magazine compatible round to 5.56, the convenience is looked at as possible high stress failures from confusion. You wouldn't want your entry team unable to share ammo with their patrol team in a fire fight. And if someone grabbed the wrong mag back at camp, they will only look to make sure there is brass before they load -- not really pay attention to the size of the bullet in the casing. This could lead to a failure to load the 300AAC into a 5.56 chamber or a weapon-ruining kaboom from a 5.56 tumbling in a 300AAC bore and destroying the suppressor.

Also, I have only been talking about the H&K UMP45. A 9mm subgun would be less effective because you would end up with 147gr bullets to make them subsonic, while 230gr 45ACP is already subsonic.

In the end, the military is going to stick with what they are used to for as long as they can. It is what they do with the budget they have. Ramping up and retooling for 300AAC at LCAAP would also be cost prohibitive.

Thanks for all of the info . I feel like a kindergardener talking with a college professor . I understand most...er "some" of what youv'e explained to me. In the end it doesn't affect me as I hope to never be put in any situation where this technical info will be that important to me .

This is all very interesting to me . I need to read a lot more ... A LOT More.. Before I can come close to talking with you about some of this stuff. I'm just glad there are people like you working on the products for our military and the public. Each time I have read about some good part or part/weapon treatment and then looked into this Spikes equipment I have found that Spikes has allready been using it in their products. The Bolt and bolt carrier and the barrel are 2 items that pop into my mind right away.

I will just continue to enjoy the quality equipment you are produceing and maybe not try to figure out so much what makes it tick so well . It's like when I go to the Dr. often I don't understand what's the reason why he/she does something but the short answer is .. It's because he has had 10's of years of schooling and experience on top of that ..

Thaks again for trying to explain the questions I have . I know it can be frustrating dealing with an amateur you are very good at doing so . A patient and kind person. I will continue to enjoy your products and spread the word about the quality I have experienced.. Thanks Again , Don J.

Don't ever feel like you can't ask us a question. We want everyone to be as educated as possible with their firearms.

Thank You , You are very Kind ... Don J.

JaxChris knows his stuff. I've learned a lot about the AR from him. As far as the UMP goes, I've got a form 1 out on one now. It's a completely badass gun. However, like Chris said, you're not going to really use it past 50 yards, but for clearing rooms and stuff, I don't think you can beat it.