Page 1 of 4 123 ... LastLast
Results 1 to 10 of 40

Thread: 7.5" AR ballistics

  1. #1
    Join Date
    Aug 2008
    Posts
    1,571
    Feedback Score
    3 (100%)

    7.5" AR ballistics

    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?

  2. #2
    Join Date
    Jul 2006
    Location
    Palo Alto, CA
    Posts
    3,347
    Feedback Score
    0
    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...

  3. #3
    Join Date
    Aug 2008
    Posts
    1,571
    Feedback Score
    3 (100%)
    Quote Originally Posted by DocGKR View Post
    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.

  4. #4
    Join Date
    Jan 2009
    Posts
    169
    Feedback Score
    0
    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.

  5. #5
    Join Date
    Dec 2006
    Posts
    1,043
    Feedback Score
    0
    Quote Originally Posted by Zhukov View Post
    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

  6. #6
    Join Date
    Jul 2006
    Location
    Palo Alto, CA
    Posts
    3,347
    Feedback Score
    0
    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...

  7. #7
    Join Date
    Oct 2009
    Location
    Texas
    Posts
    32
    Feedback Score
    0
    Quote Originally Posted by Spooky130 View Post
    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.

  8. #8
    Join Date
    Jan 2009
    Posts
    169
    Feedback Score
    0
    Quote Originally Posted by DocGKR View Post
    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?

  9. #9
    Join Date
    Jul 2006
    Location
    Palo Alto, CA
    Posts
    3,347
    Feedback Score
    0
    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.
    Last edited by DocGKR; 10-18-09 at 13:31.

  10. #10
    Join Date
    Aug 2008
    Posts
    1,571
    Feedback Score
    3 (100%)
    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?
    Last edited by parishioner; 10-18-09 at 16:41.

Page 1 of 4 123 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •