B&T Ammo Labs Fragmentation Experiment #7:
"Multiple Round, High Velocity 5.56mm 61.7 grain Tracer (M856) performance in bare gel."
Tatjana von E. and Derek W. F.
This experiment was designed as an excuse to shoot more M856 tracer under the guise of scientific experimentation for terminal performance of the round in 10% calibrated ballistic gelatin.
Note that some discrepancies in weight of tracer rounds exists. While FM 23-14 lists 63.7 grains as the weight of the bullet IMI, the manufacturer of the L-110 tracer bullet, lists it as 61.7 grains. We believe the latter figure to be more accurate.
It is probably redundant to say that the outstanding support of the AR15.com community makes this experiment possible. Nevertheless, the outstanding support of the AR15.com community makes this experiment possible. Special thanks to
Eric the Ammoman who's quick delivery and excellent service meant that we have had far too many tracers for far too long. (Please slow down delivery in future to help alleviate this problem).
Also, as always, thanks to AR15.com member "Hi-Vel" for the gel molds.
If we forgot you please let us know.
Specifics and Conditions:
Ammo: 5.56, 61.7 grain Copper Alloy Jacketed tracer (L-110) rounds with cannelure. (M856).
Rifle: Pre-ban 16" Colt M4 1:7 upper on a Bushmaster lower.
Temp: 85 F
Humidity: 60%
Altitude: 215 ASL
The target was a FBI spec block (20x20x50cm) of 10% ballistic gel (9 parts water, 1 part gelatin by weight). Vyse ballistic gel was prepared according to FBI ballistic gel testing protocols. Additionally, gel temperature was not permitted to exceed 37 degrees C at any time during preparation.
Following preparation, gel was stored at ~4 degrees C and permitted to cure for 72 hours before testing. Gel was tested within 15 minutes after removal of blocks from refrigeration. Gel blocks were calibrated with a .177 caliber BB immediately before testing. (Optimum = 8.5cm @ 590 fps). Our results (8.55cm) were well within accepted calibration standards for ballistic testing without penetration measurement adjustment.
Procedure:
Velocity tests on the rounds were conducted using a Oehler Research 35P chronograph 15 feet from the muzzle.
After some alignment shots, targets (bare gel blocks) were placed 16 feet from the muzzle and each subjected to a single round. Velocity of the projectile was again measured at 15 feet, 1 foot before the gelatin block.
Multiple blocks were shot. We are now out of gel and have to buy a bunch more. This bothers Dr. Tatjana because gel is made from Horsies.
The blocks were examined, photographed and then dissected into slices. Slices were photographed to measure and record wound profile size. Fragments were then extracted and their penetration depth measured and recorded. Fragments were organized according to penetration depth and photographed to record fragment distribution throughout the wound cavity.
The ammunition was quite consistent in gel- but not the way you might think. Probably as a result of the length of the round, all shots exhibited a significant course deviation mid-gel and just after yaw, before exiting the side of the gel block at around 12-13"
Results notes/Observations:
Velocity of the displayed gel shot was 2954 fps.
Fragmentation of the rounds was nearly absent.
Total penetration (before exit from the block) averaged 12.5" and would probably exceed 13.5" if not for bullet exit.
Neck length (as defined by distance before a significant degree rotation of the round) was generally around 5.75-6".
The largest recovered fragments typically appear to be the bullet's base and rear jacket structures and core.
Recovered materials included 0.2gr of ash and 50.6gr of jacket/core. Given the lack of fragments it seems clear that upwards of 10gr of bullet weight is tracer element.
Wound cavity size at its extreme was a dramatic 6.3" at inch 7. This is probably the result of the unusual length of the round.
Recovered Weight:
50.8 gr
Fragmentation:
N/A
Neck:
5.75"