Boat Tail vs Flat Based Bullets: Post Your Comments

[STLSNIPER]

7.62x39 Wolf ammo is a Boat Tail bullet. Brown-Silver Bears are a Flat Based bullet. Shooting both of these types from my Romanian AK I have found the Bears are a little more accurate than the Wolfs at 60 yards using a bench rest. Please post some replies with your results.

[50 cal]

Boat tail ammo's primary function is accuracy at extended ranges. It keeps the turbulence to a minimum.
Flat base projectiles are primarily for hunting and keeping the bullet weight intact and dumping the energy into the target. Flat base bullets won't have the inherent accuracy of boat tail designs.

[Yoda-Dad]

because every weapon is an individule , accuracy is where you find it .

the 762x39 is unique in that , being a .30cal moderate power/velocity carbine , its more dependant on bullet type for downrange velocity/energy than other cartridges . moderate power carbines can use every extra fps/ft.lb. available .

while the differences in B.C. with the 3 bullet types used in 762x39 ammo are fairly meaningless out too 150M , they begin to show up at only 200M and by 300M can mean a lot .

given nominal velocity (2311fps) at standard conditions , the range to penetrate a 3.17mm steel sheet (about 500ft.lbs. needed) for 'US67' LeadCore bullets (Win , Rem , Fed) is about 280/290M
for LeadCore M67 bullets , about 325M
for LeadCore M43 types , 400/425M
the Hornady V-Max would extend that range out to 450/470M
the Sierra 155grn OTM at 2100fpsMV would extend it out to nearly 520M

search back over my old posts ...

[Yoda-Dad]

understanding exactly what B.C. is can be quite mindboogling . since the 'industry uniform method' based on the commonly misunderstood G1 table can not plot a realistic trajectory for common 7.62x39 bullets without some mathmatic backflips .

this is the KRUPP bullet , the firing of which G1 is based on ...

http://steyrscout.shecora.com/krupp.gif

as you can plainly see , it is not similar AT ALL to modern bullets . the drag profile cant match any of the bullets we normally use . the BACKFLIPS SierraBullets came up with was to CHANGE the B.C.# at velocity intervals . it works ok , untill you use a common ballistics calculator (using the G1 profile) that can not change the B.C.# at the velocity intervals . this gives a calculated trajectory that gains velocity/energy with range and is flatter than what it really is ...

SierraBullets came up with this G1 'system' because the military G functions didnt work well with THEIR bullets and the plethorea of other G-models and #s/scales of different values , causing confusion .

take a common 762x39M43 Wolf or Chinese'PS' FMJ-BT bullet @2300fps . its B.C.
in G1=about .300 to .305 . to get a close trajectory requires you CHANGE the B.C.# at 2500fps , 2000fps , 1500fps ... , ... the #s will be different for different bullets because we're not following the drag profile for a G1 shape bullet but , each individual bullet , which must be calculated/tested individualy and assigned an approprate , average , G1 # for THAT velocity range .

in G5=.196 this is the correct function for a 762x39 M43 bullet . it closly matches the shape of the G5 test bullet . once you find its B.C.# @muzzel velocity , it drags according to the G5 profile .

in G7=.156 even G7 can calculate a reasonably close trajectory as the M43 bullet is at least similar to it ...

just from memory,
G5 is based on a bullet with a ~6.1 (calibre)Tanget radius ogive with a modest boat tail .
G6 is based on a bullet with a ~6.1 (calibre) tangent radius ogive and a FLAT BASE (762x39 M67).
G7 is based on a Secant ogive bullet with a lowdrag boat tail (762x51 M80 FMJ-BT)
G8 is based on a Secant ogive flatbase test bullet of similar shape to the 30-06 M1 bullet .

[ August 21, 2004, 21:29: Message edited by: Yoda-Dad ]

[Dave S]

When money or reputation is on the line @ 300yds or below..........FLAT BASE.

400yds and above..........BOAT TAIL.

Don't believe me? Ask me.....I'd be glad to tell you again. Or ask the Bergers.