View Full Version : 7.5" AR ballistics
parishioner
10-17-09, 20:07
I was just at Gander Mtn. looking for a an American flag but they don't carry any so as I was leaving I picked up an issue of SWAT. There was an article about the Troy M7A1 upper in 5.56 which has a 7.5" barrel. One of the tests they did with it was set up a dummy 50 yards away with a Safariland Level III vest. They loaded 4 rounds of 75gr Tap or BH, I cant quite remember, and fired it into the vest. The article said the bullets went through the trauma plate, the body armor and the dummy. I don't know how good the Safariland body armor is but this seemed a little strange.
The reason I thought it was stange is because I have read on this site that some people only expect their SBR to perform well at about 25 yards and that was with a 10.5" barrel.
I really don't know much about this topic so I could be completely off base.
Is the 7.5" barrel that effective?
jman4427--I think you may have some misconceptions/misinformation.
First, are you sure the "VEST" was not IIIa soft armor, as level III armor is generally in the form of a hard plate of approx 10x12".
If the armor was IIIa, then a pointy rifle projectile fired around 2000 fps should easily completely penetrate through the vest. If the armor is indeed level III hard armor, then there is NO possibility of a 75 gr OTM round penetrating through the armor, even when fired from a 20" barrel, let alone a 7.5" one...
parishioner
10-17-09, 20:27
jman4427--I think you may have some misconceptions/misinformation.
First, are you sure the "VEST" was not IIIa soft armor, as level III armor is generally in the form of a hard plate of approx 10x12".
If the armor was IIIa, then a pointy rifle projectile fired around 2000 fps should easily completely penetrate through the vest. If the armor is indeed level III hard armor, then there is NO possibility of a 75 gr OTM round penetrating through the armor, even when fired from a 20" barrel, let alone a 7.5" one...
I am quite sure all the article said was a Safariland Level III armor. I dont recall the "a". It continued to mention penetrating a trauma plate, body armor, and dummy. I dont know if that means level III or IIIa.
Somewhat off-topic, but there has been a rash of people lately asking about the "best" load for 7.5" barrels. I just don't see why people hamstring themselves with ultra-short SBRs like that. They may be fun toys, but it seems like there's no way to get decent bullet performance out of something that short - not to mention a tremendous fireball.
Somewhat off-topic, but there has been a rash of people lately asking about the "best" load for 7.5" barrels. I just don't see why people hamstring themselves with ultra-short SBRs like that. They may be fun toys, but it seems like there's no way to get decent bullet performance out of something that short - not to mention a tremendous fireball.
Agreed... But there is probably a very small niche where a 7.5" AR would work well. I imagine maneuverability in tight spaces would be the biggest asset of a 7.5" gun and not ballistic performance. That being said, if you have a 7.5" you had better know the limits of your weapon/ammo.
Spooky
Level IIIa vests can have a "trauma" plate over the soft armor to help with edged weapons; level III armor IS the "trauma" plate. Again, I believe there is something erroneous regarding the parameters of the initial question.
Those who have a need to run a nominal 8" barrel AR15 for real world tasks will find 6.8mm FAR more effective than 5.56mm in these ultra SBR's...
Old_Painless
10-18-09, 08:57
Agreed... But there is probably a very small niche where a 7.5" AR would work well. I imagine maneuverability in tight spaces would be the biggest asset of a 7.5" gun and not ballistic performance.
If you receive proper professional training, you will find there is little to no "maneuverability" issue with an M4 of normal length.
There is little reason for a 7.5 inch barrel in an AR.
Level IIIa vests can have a "trauma" plate over the soft armor to help with edged weapons; level III armor IS the "trauma" plate. Again, I believe there is something erroneous regarding the parameters of the initial question.
Those who have a need to run a nominal 8" barrel AR15 for real world tasks will find 6.8mm FAR more effective than 5.56mm in these ultra SBR's...
Doctor Roberts: Are there any published results of terminal performance for ultra SBRs or gelatin shots at reduced velocity that would mimic the CQB performance of these things?
There are USG test reports available to select LE and military organizations, but I am unaware of any valid open source test results at this time.
parishioner
10-18-09, 16:37
Ok. This is what the magazine says word for word.
DEFEATING BODY ARMOR
Some may be asking, "How far out can you defeat body armor with a 7.5" barrel?" Lets find out. I took a Safariland Level III vest an wrapped my bad guy in it. Then I stepped back to the 50 yard line and fired four quick holes through the vest using Hornady 5.56mm 75-gr. BTHP/WC T2. Not a single round was stopped by the vest. It pierced the trauma plate, the body armor, the dummy, and then just kept going.
It continued
Back out at the 50 yard line, I set up a plywood silhouette, taped up a paper target, and zeroed a Trijicon Acog onto the M7A1. I then refaced the target and put three shots into a half-inch group without even breaking a sweat. I defy anyone to tell me that they can't take down a bank robber or an errant gunman wrapped in body armor with an M7A1. Also note that the holes in the target are perfectly round. The reason I mention this is that I have had conversations with manufacturers who have said to me, "A 7.5" AR actually sends bullets downrange with an unstable wobble after only a few feet." NOT!
So does this sound accurate or not?
Is that type of ammo law enforcement only?
Looks like a typo. I wouldn't go as far as saying the dude doesn't know what he's talking about, but it might be a typo.
Google safariland III vest
Correction is: safariland IIIA vest
VooDoo6Actual
10-18-09, 17:59
nevermind...
parishioner
10-18-09, 19:29
I tried to do some research on the T2 bullet that is utilized in the TAP 5.56mm cartridge. What I found was that it offers about 180fps more muzzle velocity than the standard .223 version which equates to an additional 50-75yards worth of fragmentation range.
This could explain the good performance out of such a short barrel. Then again I am in ignoramus when it comes to this. Can anyone confirm this?
I read that article. I don't think the author knows that there is a difference between III and IIIA. Other than that, I'm going to bite my tongue with regard to any further commentary on the article or the author, except to say that ending a point with "NOT!" is pretty telling. :rolleyes:
I read that article. I don't think the author knows that there is a difference between III and IIIA. Other than that, I'm going to bite my tongue with regard to any further commentary on the article or the author, except to say that ending a point with "NOT!" is pretty telling. :rolleyes:
Yeah... They let anyone write articles for that magazine!;)
I tried to do some research on the T2 bullet that is utilized in the TAP 5.56mm cartridge. What I found was that it offers about 180fps more muzzle velocity than the standard .223 version which equates to an additional 50-75yards worth of fragmentation range.
This could explain the good performance out of such a short barrel. Then again I am in ignoramus when it comes to this. Can anyone confirm this?
5.56 TAP is indeed loaded to higher velocity and is more desirable for that reason over standard .223 TAP.
Like DocGKR said - it wouldn't make a difference against a IIIa plate.
There are USG test reports available to select LE and military organizations, but I am unaware of any valid open source test results at this time.
Could you give a brief summary of what there is that works best (if any) without violating any confidentiality agreement? Or maybe a rough summary?
For ultra SBR use, consider sticking with barrier blind projectiles vice fragmenting ones. Also, for very short barrel weapons, a faster twist rate may be necessary to ensure an appropriate rotational velocity to maximize the terminal performance of some types of projectiles...
Kahlendrrari
10-30-09, 07:28
IIRC in an article i read about Noveskes, that John routinely takes his 7.5" barrel out to 100 yds. i have a friend with an AR set up with a 7.5" (5.56) and we have not had any problem hitting the target at 100 yds., now what remains to be seen is if it would penetrate a vest at 100yds. as neither him or i wish to put up the money to get a vest, then fill it with holes, i guess we will never find out. i know at extended ranges (past 200yds.) that the projo velocity is marginally slower than the same one from a longer barrel.
Where did this idea come from that a 7.5" barrel would be any less accurate than a 16" barrel of the same quality?
and in a real "what the F---" moment, how did this idea of penetrating a soft armor vest become any kind of barometer for terminal performance?
Solid question rob_s.
I don't buy the argument in the 'magazine. 3 rounds in a half-inch group at 50yds "without breaking a sweat". Yeah right. I personally have ...shall we say supervised...the instruction of many "normal" shooters and you'd be amazed how many couldn't crack 4moa. 1/2" at 50yds = 1 MOA.
Less than 1/10 people even got close to 4moa - as in, reliable -- on demand 4moa, consistently. This is prone, supported with a rifle sling. If he did it from a bench, I would understand the accuracy statement, but not that conflicts with this statement: "I defy anyone to tell me that they can't take down a bank robber or an errant gunman wrapped in body armor with an M7A1."
You definitely will not be able to use a nice bench with a rest on it and bags in that situation.
Moreover, many normal home defense AR15 owners who also like to blast would be served just fine with a 16". 18" gives you better velocity but for urban use I would use a 16". 7.5" is a movie or toy upper, IMO.
Godallmighty
12-23-09, 09:27
I think it's an "unfair" comparison that people tend to compare a 7.5” barrel to a full length rifle or a carbine length barrel. They are not intended to be used for the same type of distance or environment... It's like comparing a Ferarri to a Fiat, cuz they both are italian!
a 7.5” barrel (or a 10.5) should be comparable to a SMG! Meaning a 7.5” AR... compare it to a 9mm SMG... that would be more equal and more realistic! (and they would be in the same size) If you want a rifle or carbine with accuracy and range, go by rifle or carbine. You want a 5.56 SMG... 7.5”, 10.5" or the "Commando" 11,5" are relatively OK!
If you intend to engage targets at 300m+... 7.5” is useless... but for targets around the 50m rage it works ok, and the 11.5" can without problems reach out to 300m at will, if you are not a total "nube" behind your rifle!
So, can I ask:
Does an 7.5" AR beats a 9 mm SMG, in:
- penetration against Level IIIa vests (I assume yes)
- permanent cavity damage (?)
We know by DrGKR the recommendations for 9 mm ammo, do the same choices sitll hold true at the slightly higher velocities (longer barrels) of a SMG?
What are the best ammo choices for an 7.5" AR?
Is there a (marked, slight, or?) difference between a 10.5" AR and a 7.5" AR regarding terminal ballistics and fragmentation range?
To my very ignorant point of view, an AR barrel is better sized at 11.5"+, those 4" don't seem like too much in size unless concealment is a requirement.
Godallmighty
12-23-09, 12:14
I’m not an expert, just a user so i dont know the numbers. I have 3 rifles, LMT Patrol Rifle (carbine) , Elisco 11,5” and some cross breed 7.5”. (Work Executive Protection) ) 90% of the time I carry the Elisco, but when “fancy” I carry my x-breed!
I wouldn’t consider my 7.5" to be able to take out targets beyond 50m, and using Norma 55g lead tip they would not be able to penetrate a class III BA... but luckily most bad guys don’t carry BA! On a soft target you could probably F***F*** the exit wound when using the Norma Ammo! (It's intended for deer hunt, and has excellent expansion capabilities!)
Outside of penetrating soft armor, and operating under the assumption that the round isn't going to expand, conventional wisdom appears to be that you'd be better off putting a 9mm hole in someone than a 5.5mm hole.
Is this hunting ammo you're using in the 7.5" 5.56 guns expanding/mushroominig/fragmenting in soft tissue at close range?
Godallmighty
12-23-09, 12:30
correct! the DoD issued 5.56 has to high velocity on close range, it was never designed for CQD!
Using a std issued military round on close range is ineffective! It has a too high velocity to deliver any punch into target!
A hunting round on the other hand has a lower velocity, and is designed to be used on shorter range!
geminidglocker
12-23-09, 12:30
So the Author got paid buy Hornady and Troy. This is nothing new. Don't beleive everthing you read. Either that or the trauma plate was made of wood. Disregard the article. 99% of SWAT magazines readership is mall ninjas anyhow.
Outside of penetrating soft armor, and operating under the assumption that the round isn't going to expand, conventional wisdom appears to be that you'd be better off putting a 9mm hole in someone than a 5.5mm hole.
Is this hunting ammo you're using in the 7.5" 5.56 guns expanding/mushroominig/fragmenting in soft tissue at close range?
Seems to me that the ONLY reason for owning a 7.5 AR is for penetrating soft body rmor. It would not seem to be good at anything else!!
Now I gotta know what mag and who wrote this article. I have mostly stopped reading gun rags anymore, because of the tripe that the writers were spouting.
If i had to make a SWAG on the author I'd have to say that it sounds alot like Charlie Cutshaw... the uber accessorizor. :D
Necro bump.
I am planning on building an 8.5 inch upper. This is just a range "toy" but I'm still interested in "ballistics". Everyone always says how poor ballistics with 7.5 barrels are but I've never actually seen any data or gel testing or whatever. In my search I found this thread...
http://www.silencertalk.com/forum/viewtopic.php?f=56&t=42484&p=469368&hilit=Hornady#p469368
... now I don't know how scientific milk jugs are but that's the closest thing to any actually testing I've ever seen.
I got issued a M4 at work so I no longer have to carry my personal AR which is why I'm building this VSBR but I am still interested in finding a possible good defensive load for it just in case ya know. I have a buddy that goes coyote hunting a lot and I'd like to take one out with my VSBR.
So I bumped this thread to see if Doc, or anyone else, has any updated ammo recommendations or can link to any test data where a VSBR platform has been tested.
If you receive proper professional training, you will find there is little to no "maneuverability" issue with an M4 of normal length.
There is little reason for a 7.5 inch barrel in an AR.
Once the gun is out of the backpack you smuggled it into the third world in... ;)
Check the comments in post #18 of this thread...
Thanks Doc I missed that post. Would the Black Hills load with the Barnes bullet be considered barrier blind?
Check the second paragraph: http://m4carbine.net/showthread.php?t=19881
i know at extended ranges (past 200yds.) that the projo velocity is marginally slower than the same one from a longer barrel.
False. At 210 yards, Hornady 5.56 TAP fired from a 7.5" barrel is going to have a retained velocity that is more than 600 fps less than the same load fired from a 20" barrel.
http://www.box.net/shared/static/5nl1vp26h6.jpg
...
NightFighter
12-30-10, 18:48
does it drastically change the usefulness and performance if a 7.5" sbr uses 7.62 x 39 ammo? from the little i have been able to read and understand it seems that 7.62 x 39 ammo is a better performer than 5.56 ammo at short distances < 200yds. now i may be completely wrong, but i figured if anyone could set me straight it would be the people on this forum. thanks for reading and replying to this post.
from the little i have been able to read and understand it seems that 7.62 x 39 ammo is a better performer than 5.56 ammo at short distances < 200yds. now i may be completely wrong, but i figured if anyone could set me straight it would be the people on this forum
You are wrong.
http://www.box.net/shared/static/0k13tf0rcu.jpg
courtesy of DocGKR
correct! the DoD issued 5.56 has to high velocity on close range, it was never designed for CQD!
Using a std issued military round on close range is ineffective! It has a too high velocity to deliver any punch into target!
A hunting round on the other hand has a lower velocity, and is designed to be used on shorter range!
Respectfully sir, your grasp of this subject matter is incorrect.
The military 5.56 ball ammo, generally speaking, works better the faster it goes.
Hunting bullets do not work better because they are going slower, it is because of the design of the bullet.
NightFighter
12-31-10, 07:13
You are wrong.
ok, from my interpertation of the image. the 77 gr 5.56 and 6.8 round do the most damage? if my understanding is correct. thanks for the clarification.
variablebinary
01-13-11, 00:01
Let's not forget the SCAR PDW, and HK416 PDW.
There is a market among military and LEO for super short 5.56 weapons. I don't think there is anything to gain by going so short, personally.
Logistically, it does make sense to use a common weapon platform and ammo for PDW's, instead of an PS90, KAC PDW and HK MP7. These guns and the associated ammo are very expensive, and don't have a support pipeline in place, in the same way an HK416 PDW would.
Then again, does a 5.56 PDW make more sense than an MK18, Colt Commando, HK416 D10RS or CQC SCAR? I say no.
http://3.bp.blogspot.com/_VMdraHwAbeg/TPZMNcwjFOI/AAAAAAAAD8g/5WFvsUISlOw/s1600/fn-scar-pdw.jpg
http://cdn5.thefirearmsblog.com/blog/wp-content/uploads/2009/09/hk416c_01-tfb.jpg
Badly wishing KAC would release their PWD on a lower with XCR/ACR/Bushmaster ambi features... that could be a game-changer in police work, if it works as advertised.
-B
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