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Protection ballistic limit, BL (P). |
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|  MIL-A-12560H (MR)
w/INT. AMENDMENT 4
APPENDIX A
A.2.6 Protection ballistic limit, BL (P).
A.2.6.1 Caliber .30 M2 AP caliber .50 M2 AP, 20 mm M602 APIT penetration tests. The BL (P)
shall consist of an equal number of fair impact complete and partial penetration velocities
attained by the up-and-down firing method. All BL (P)'s shall be computed using the highest
partial penetration velocities and the lowest complete penetration velocities. Firing shall continue
until either a 4 round BL (P) having a maximum velocity spread of 90 ft/sec has been attained,
whichever comes first in the normal sequence of firing. If both occur simultaneously, the 6 round
BL (P) shall be reported.
A.2.6.1.1 Difference between the high partial penetration velocity and the low complete
penetration. In the event that the zone of mixed results (difference between the high partial
penetration velocity and the low complete penetration velocity, the PP (P) velocity being higher
than the low CP (P) velocity) exceeds 90 ft/sec, the firing data shall be compared with the
specification minimum ballistic requirements. If the lowest complete penetration velocity is
equal to or above the minimum specified ballistic limit velocity for the plate thickness, the
ballistic limit shall be computed on the basis of 4 or 6 rounds using the smallest possible velocity
spread. If the lowest complete penetration velocity is below the minimum allowable ballistic
limit velocity then testing shall continue until a ten round ballistic limit has been attained using
the smallest possible velocity spread.
A.2.6.2 57 mm M70 AP and larger caliber projectiles. For the purpose of this specification, the
protection ballistic limit is the average of four fair protection criteria impact velocities
comprising the first two lowest velocities in the firing order resulting in complete penetrations
and the first two highest velocities in the firing order resulting in partial penetrations which meet
the condition that the velocity spread for the 4 rounds shall not exceed 100 ft/sec.
A.2.6.3 Reduction of large velocity gap in borderline cases. If the ballistic limit which has been
determined is within 10 ft/sec from the minimum allowable ballistic limit and a gap exists
which is greater than 25 ft/sec, then another round, or rounds, shall be fired to reduce the gap to
25 ft/sec or less. The ballistic limit shall then be recomputed using the criteria of paragraphs
A.2.6.1 or A.2.6.2 as applicable. The recomputed BL (P) shall be reported as the BL (P) of the
plate. In borderline cases a reduction of the gap between the high partial penetration velocity and
the low complete velocity shall result in a better evaluation of the BL (P).
A.3 REQUIREMENTS
A.3.1 Resistance to penetration. The minimum acceptable ballistic limits shall be in accordance
with the values shown in tables X through XVII.
A.3.1.1 Class 3 armor plate. For class 3 armor plate, upper ballistic limit (maximum) values shall
be as specified in the applicable footnotes of tables X through XVII.
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