M113 armour

[geronimo]

I'd like to know the type of projectile that can be stopped by M113'A1/A2s aluminium armour. 7.62mm AP? Or even less? Same for the AIFV (XM765) please. I didn't find much on the www, the info on most websites is pretty general. Here's something more detailled and quite interesting, that however doesn't answer my question:

 

"Historically, the superiority of weldable aluminum armor for protection against high explosive shell fragments was recognized about 60 years ago but it was not in use until the year 1960 when the first quantity of aluminum-armored vehicles appeared. This was the M113 and was constructed from the aluminium-4.5% magnesium alloy 5083; this vehicle was in production for the next 25 years.

 

Although the resistance of this alloy to 0.3 inch armor-piercing (AP) attack is slightly less than that of steel, it is slightly better than steel for 14.5mm diameter AP and the vehicle is lighter than an equally protected steel version. Additional weight savings are gained from the use of aluminum because of the greater rigidity of the thicker, but lighter, plate -- nine times stiffer than steel -- with the consequent saving on stiffening structure."

 

Source: http://www.key-to-metals.com/Article90.htm

[jwduquette1]

Verses .30-caliber M2 AP:

The V50 limit velocity for 54mm of aluminum armor plate (alloy 5083 or 5456) @ 0-degree obliquity is 2880-fps.

The V50 limit velocity for 42mm of aluminum armor plate (alloy 5083 or 5456) @ 30-degree obliquity is 2880-fps.

 

I don’t know the armor thickness on the M113 for certain. This is one Internet source for plate thickness: http://afvdb.50megs.com/usa/m113.html

 

If the above internet site information is correct, than:

 

Upper Front 1.5” @ 45-degrees would be immune at all ranges to .30-cal M2 AP

 

Lower Front is indicated as 1.5” @ 30-deg. It would be immune to .30-cal M2 AP at ranges beyond about 125 to 150 yards.

 

The upper sides of 1.75” @ 0-degrees have a V50 = 2585-fps vs. .30-cal M2. It would be immune to .30-cal M2 AP at ranges beyond about 100 to 125 yards.

 

The lower sides of 1.25” @ 0-degrees has a V50 = 2100-fps vs. .30-cal M2. It would be immune to .30-cal M2 AP at ranges beyond about 300 to 325 yards.

 

Off-angle shots would likely result in lowering the immunity ranges.

[Paul Lakowski]

RMO JANES July 2003 article [pp 42] reports 48mm of Aluminum 5083 alloy is needed to resist a 7.62mm x 51 AP shot at normal impact at pointblank range.

[geronimo]

Thank you gents!

[jwduquette1]

I recently came across a paper on Titanium Armor. One of the bench mark comparison tests was with aluminum alloy armor – (However the article said it was 5883 series aluminum armor?).

 

V50 for 1.875” of 5883 @ 0-degrees (~47.62mm) was indicated as 2700-fps.

 

Dunno if the 5883 was a mistype or not. They may have meant 5083 as I can’t seem to find other references to a 5883 series aluminum armor.

 

Of course 7039 series was ballistically better than 5083 series. It's weight per unit area was also lower than steel armor for the same level of protection against 0.30 caliber M2 AP. No idea if 7039 series was employed on latter versions of the M113 or not.

[mcantu]

IIRC, the M113A2 is protected from 14.5mm AP at the front and 7.62 AP for the sides...

[Paul Lakowski]

IIRC, the M113A2 is protected from 14.5mm AP at the front and 7.62 AP for the sides...

353656[/snapback]

 

I would think this requires considerable applique armor to achieve that level of protection . If we go by RMO figures 7.62mm AP should be able to penetrate at pointblank range along the side armor unless the angle is too severe. Frontal armor should be resistant to 7.62mm AP, since its about the same thickness but with a 30-45° angle. Its possible that if a 14.5mm API shell hits the section where the engine is, it might not get through into the interior of the APC, but can a APC function with 14.5mm API shells embedded in the engine?

[mcantu]

Paul,

 

Have you ever looked into the effect that distance has on a rounds penetration? I often see people stating that a hit at point blank range is the most difficult to protect agaisnt but I do not believe that that is true.

 

If you look at the US Army's FM for Urban Ops, it stated that both the 5.56 and 7.62 rounds penetrate more at longer distances. The 5.56 achieves optimum penetration at 200m and the 7.62 at 600m.

 

http://www.globalsecurity.org/military/lib...3-06-11/toc.htm

 

At closer ranges, a round hasnt had a chance to stabalise yet. The 5.56 can have about 10 degrees of yaw soon after leaving the barrel. At around 150m, is gets down to around 2 degrees. It is the combination of stablity and velocity (which has to be low enough to not over stress the projectile) that lead to greater penetration at further distances

 

Whats your opinion?

[Doug97]

Paul,

 

Have you ever looked into the effect that distance has on a rounds penetration?  I often see people stating that a hit at point blank range is the most difficult to protect agaisnt but I do not believe that that is true.

 

If you look at the US Army's FM for Urban Ops, it stated that both the 5.56 and 7.62 rounds penetrate more at longer distances.  The 5.56 achieves optimum penetration at 200m and the 7.62 at 600m.

 

http://www.globalsecurity.org/military/lib...3-06-11/toc.htm

 

At closer ranges, a round hasnt had a chance to stabalise yet.  The 5.56 can have about 10 degrees of yaw soon after leaving the barrel.  At around 150m, is gets down to around 2 degrees.  It is the combination of stablity and velocity (which has to be low enough to not over stress the projectile) that lead to greater penetration at further distances

 

Whats your opinion?

353980[/snapback]

Are you talking about AP or standard ball? Why does a bullet have so much yaw when it leaves the barrel, and what is it that makes it stabilise? Does the disintegration of the round have anything to do with poor AP performance at very close range?

Edited August 6, 2006 by Doug97

[mcantu]

I just rechecked my source and I was wrong about the amount of yaw on leaving the barrel. Its 4 degrees, not 10.

 

That is exactly why pentration is poor at close ranges. The high velocity causes the round to break-up. After the round has slowed a little, it is able to remain together and penetrate deeper

 

 

Edited August 7, 2006 by mcantu

[Paul Lakowski]

Paul,

 

Have you ever looked into the effect that distance has on a rounds penetration?  I often see people stating that a hit at point blank range is the most difficult to protect agaisnt but I do not believe that that is true.

 

If you look at the US Army's FM for Urban Ops, it stated that both the 5.56 and 7.62 rounds penetrate more at longer distances.  The 5.56 achieves optimum penetration at 200m and the 7.62 at 600m.

 

http://www.globalsecurity.org/military/lib...3-06-11/toc.htm

 

At closer ranges, a round hasnt had a chance to stabalise yet.  The 5.56 can have about 10 degrees of yaw soon after leaving the barrel.  At around 150m, is gets down to around 2 degrees.  It is the combination of stablity and velocity (which has to be low enough to not over stress the projectile) that lead to greater penetration at further distances

 

Whats your opinion?

353980[/snapback]

 

Most weapons testing is done an 5-15m distance and yaw rounds results are just discarded.

[mcantu]

Most weapons testing is done an 5-15m distance and yaw rounds results are just discarded.

354109[/snapback]

 

 

I was thinking more about how rounds seem to penetrate better at longer ranges. In the US Army manual I linked to it states that the optimum pentration ranges for the 5.56, 7.62 and 12.7 are 200m, 600m and 800m respectively.

 

One example given is that the 7.62x51 ball round will penetrate 18" of pine board at 100m and 41" at 200m.

 

http://www.globalsecurity.org/military/lib...3-06-11/ch7.htm

[jwduquette1]

I was thinking more about how rounds seem to penetrate better at longer ranges.  In the US Army manual I linked to it states that the optimum pentration ranges for the 5.56, 7.62 and 12.7 are 200m, 600m and 800m respectively.

 

One example given is that the 7.62x51 ball round will penetrate 18" of pine board at 100m and 41" at 200m.

 

http://www.globalsecurity.org/military/lib...3-06-11/ch7.htm

354930[/snapback]

 

From what I have seen from studying reports and papers on the subject, I wouldn’t expect huge contrasts in limit velocity for armor piercing bullets against metallic targets with low yaw angles –equal to or less than say 5-degrees of yaw. Bumps of no more than about (+)5% to (+)8% in limit velocity -- give or take -- depending upon target configuration and bullet. I mean AP bullet calibers in the realm of 7.62mm to 20mm vs. hard targets such as aluminum or steel armor.

 

Table 7-6 of the FM being refered to shows 0.50-caliber “ball” piercing 1-inch of armor steel at 35-meters. This seems pretty impressive for ball ammunition. 0.50-caliber M2 AP into RHA @ 0-degrees and 2900-fps is only about 30mm – penetration is somewhat less into HHA.

 

7.62mm Ball going thru 3/8 of mild steel at 25meters also looks higher than what I typically see for this round. See Table 7-5. Also hard to believe this represents a shot with a great deal of yaw. 0.30-cal M2 AP will do about 0.6" of RHA at a striking velocity of 2710-fps.

 

On the other hand, softer cored ball ammunition may be a different story – particularly for extremely long penetration paths into soft targets -- ala 5.56mm and 7.62mm ball ammunition penetrating into thick timber, soil, ballistic-gelatin, etc. Bullets penetrating into softer materials will tumble and the penetration path can be arching or extremely curved, particularly for oblique attack angles or if the bullet is yawed before entering the target. In the case of 7.62mm Ball, Table 7-3 is in essence saying that at 25meters the limit velocity of 13” of Pine Board is about 2720-fps. Conversely at 200m the limit velocity for the same bullet is only 2275-fps for slightly over three times the thickness of wood. This suggests a fairly huge influence of yaw on ball ammunition penetration into soft materials.

Edited August 12, 2006 by jwduquette1

[jwduquette1]

The other aspect of soft cored jacketed bullets which is likely influencing the somewhat counter intuitive penetration characteristics shown in Chapter-7 of FM 3-06.11 is the tendency for these bullets to shed their jackets during penetration of wood or sand, etc. The soft core can subsequently mushroom or fragment – depending upon impact velocity. It would appear that the higher the velocity the greater the tendency for mushrooming and fragmenting of soft core projectiles.

 

While looking over test data for penetration of a variety of bullets into confined dry sand, those projectiles that remained intact invariably penetrated far deeper into the sand. For example 0.45ACP (FMJ) impacting at about 1/3 the velocity were penetrating over twice as much sand as 7.62mm (FMJ). The 7.62mm FMJ bullets were mushrooming and breaking apart at impact velocities of about 2200 to 2300-fps. Penetration paths for the 7.62mm bullets were also extremely erratic.

 

A more extensive set of trial data included 9mm FMJ into confined dry sand. What was rather fascinating was the very minor effect of velocity on average penetration depth into sand. For the 158 grain bullet there is only about a 2-inch contrast in average penetration between 500-fps and the peek penetration at about 1250-fps. There’s also a fairly evident threshold velocity after which projectiles begin mushrooming or fragmenting. After the threshold velocity is reached, penetration depth began dropping off rather dramatically.

 

The following figure represents the condensed data from the 9mm FMJ trials. The dash lines represent average penetration depths as a function of impact velocity.

 

Edited August 12, 2006 by jwduquette1