Technology

Commercial manufacturers promote bullet traps as an economical technology for lead management of small arms ranges. USAEC assessed the feasibility of utilizing commercially available bullet traps on Army ranges. The assessment culminated in USAEC publishing a feasibility study and user's guide in 1996. Both documents were based solely on manufacturer's performance claims and observations of the traps installed on indoor ranges. At that time, use of the traps on outdoor ranges was limited and no data was available on their performance.

Approach

To determine the effectiveness of the commercial traps on outdoor ranges, USAEC completed an accelerated field demonstration of three of the most popular designs of commercially available traps (granular rubber, steel decelerator, and rubber block type bullet traps). The Environmental Security Technology Certification Program (ESTCP) also funded testing of Shock-Absorbing Concrete (SACON) as bullet trapping material on small arms ranges. These traps were tested using standard M16 M855 rounds (no tracer rounds were used). Generally, none of the traps completely met the manufacturer's performance claims.

Results

Some of the bullet traps provided a means of effectively capturing and containing lead on small arms ranges. However, most available bullet traps do not contain or control 100% of the lead captured by the trap. During the testing and demonstration process, significant problems were noted with airborne releases of lead dust, the potential for storm water transport, and the flammability of bullet trap materials.

During testing of the deceleration trap, 5000 rounds were fired at the trap. Firing was concentrated within a 12-inch diameter area near the deceleration chamber opening. This was believed to provide for optimum containment ability of the trap. A dust cloud was present at the trap entrance during firing. The mass of 5000 M855 bullets is approximately 20,088 grams. A total of 16,059 grams of material was contained within the deceleration chamber and ventilation unit of the trap. The optimum containment scenario firing resulted in 80% containment of the bullet debris with the majority of debris emissions being dust. Elevated airborne lead levels were measured at the deceleration chamber ventilation exhaust port, the sides of the trap entrance, and 12.5 meters in front of the firing line. As a result of the less than desired lead containment, USAEC halted any further live fire testing of the deceleration trap.

A rubber trap used on an outdoor range may be damaged significantly during its life on the range. Range impact areas are generally maintained in a grassed-over condition to minimize erosion and range run-off. During hot, dry weather, the grass dries out and fires become a potential problem. Range fires can be caused by a number of mechanisms including tracer rounds, muzzle flash, and lightning. Rubber bullet traps on the range are susceptible to consumption by the range fire. Burning rubber complicates fighting range fires by creating a hot, smoky fire that produces complex hydrocarbons containing carcinogens. Rubber fires produce a thick, black smoke visible for miles and can generate nuisance complaints from neighbors and inquiries from the regulatory community.

With the exception of SACON, none of the bullet traps exhibited the ability to inhibit the leaching of lead corrosion products. Most bullet traps require hazardous waste classification and disposal at the end of their useful life. SACON debris when analyzed for leachable lead content was consistently non-hazardous (less than 5-ppm TCLP lead). Debris samples taken from rubber traps have consistently failed the TCLP criterion for a characteristic hazardous waste. The hazardous classification results in more expensive handling and disposal requirements for the range debris generated from the use of traps using rubber as the friction media.

Costs

Bullet traps, when used in a backstop-type application, compares directly with the traditional soil berm. Estimated costs associated with installation, maintenance, and disposal or remediation for a 20-lane, 25 meter range application are presented below for the bullet traps and the conventional berm.

Bullet Trap Technology Cost
Technology	Start-Up	Annual Operation and Maintenance	Annual Environmental Activity Costs	Disposal
Deceleration	$316,270	No estimate	No estimate	$340,500
Granular rubber	$229,035	$18,224	$2,505	$50,050
Block rubber	$132,895	$30,664	$4,440	$30,123
SACON	$33,331	$74,471	$3,900	$17,664
Conventional berm	$58,920	$2,600	$480	$1,176,000

Using the estimated costs above, an Annual Net Equivalent Value (ANEV) can be calculated to make direct comparisons. The following table presents ANEV's for the bullet traps and berms with respect to an assumed risk of lead migration. On ranges that exhibit a low risk for lead transport the soil berm provides the lowest cost method of capturing rounds. However, as the risk of lead transport from the range increases (lead transport risk should be determined prior to implementing any form of corrective action) the use of bullet traps becomes economically feasible when compared to the prospect of periodically removing the lead from the soil.

Annual Net Equivalent Value Comparison
Technology	ANEV Cost
	Low Risk	Medium Risk	High Risk
Conventional berm	$14,237a	$68,525b	$406,266c
SACON	$82,201
Deceleration	No estimate
Block rubber	$48,309
Granular rubber	$47,707
a Based upon a 50-year berm life. b Based upon a 15-year berm life. c Based upon a 5-year berm life.

Conclusion

Bullet traps are an expensive last resort solution for keeping outdoor small arms ranges environmentally compliant. Prior to selecting a bullet trap, other alternatives should be investigated such as establishing vegetative cover and redesigned berms to reduce erosion, or the addition of soil stabilizing additives to reduce lead leaching. New methods of stabilizing the lead on the range and mitigating physical lead transport in storm water runoff are being developed and may provide more cost effective means of reducing lead transport risk and bioavailability.

If an installation determines that a bullet trap is the only option to control the migration of lead contaminants on a range, then further investigation must be conducted to ensure the bullet trap will contain the lead. Even if a trap stops the bullet, lead can leach or wash out of the trap into the environment. In order to benefit the range, the trap's performance must continue long after the initial bullet impact. Questions to consider before the application of bullet traps on an "outdoor" range include:

• Will the trap contain all bullet debris within the trap?

• Will the metal wash or leach out of the trap over a period of time?

• How will wastes generated by the trap be handled?
  • All material from a trap will not be recyclable.

• What are the maintenance requirements?
  • This includes hazardous material handling and safety requirements. Training and proper personnel protection equipment will be needed. Bullet traps will require maintenance.

• How will the bullet trap impact the use of the range?
  • Bullet traps are designed to accept a certain range or type of ammunition. If the range mission changes, the bullet trap may not be suitable for the new ammunition. Significant damage and environmental impact can be created if the trap is not properly designed for the ammunition being used on the range.

• How will exposure to outdoor environment effect the trap?
  • Today's commercial traps were originally designed for indoor use. Currently they are being marketed for outdoor use with little or no consideration for the effects that climate, precipitation, temperature change, or weather have on the trap's durability, maintenance, or capability to contain lead.