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canebrake 12-05-2010 07:08 AM

Steel Target Maintenance
 
Steel Target Maintenance

Editor's Note: Today's timely maintenance information comes to The Shooting Wire from MGM Targets. Mike Gibson offers some thoughts on how to make your steel targets last longer and perform better.

Someplace back in time, maybe 50 years ago, U.S. Steel developed a product affectionately known as T-1, designated by the ASTM (American Society for Testing Materials) as A-514. Sometime after that, shooters decided it was a great steel to use for targets. It did a great job then, but there are better products out there now. The catch is, virtually all of them are heat hardened steels, so there are some complications related to repairing them.

The easiest and best way to repair damage to steel targets is to purchase steel that isn't easily damaged. Pretty basic, but frequently overlooked while trying to save a relatively inconsequential amount of money. That's why we at MGM Targets use the 500 Brinell hardness steel (with the exception of our .22 targets) on everything we sell. AR500 plate can range in hardness from 460-530. At MGM we only accept steel rated 495 or higher.

(If your organization has old steel, like most do, we hope the information that follows will help you make better repairs until you can replace the old stuff. If you have any questions, please feel free to call us at 888-767-7371. We'll be glad to help in any way we can.)

One of the most misunderstood, or overlooked factors impacting target life is heat. Virtually all target steel in use today is "quenched and tempered", meaning that at the time it is rolled (at the mill) it is heat treated. The chemical content of the steel certainly plays a big role in target life, but any heat applied after the mill heat treatment will adversely affect the life of your targets. This stuff isn't mild steel, so you can't treat it as such.

There are some manufacturing processes that affect hardened steel during fabrication. The first thing that comes to mind is the cutting process. The hardened steel cuts nicely with an oxy-acetylene torch, but the heat that is put into it when the torch travels at 30-40 inches per minute is significant. At MGM we cut all of our steel with a laser. The heat affected zone is about .0005" or about the thickness of two sheets of paper and basically only at the extreme edge of the target. You'll never notice it under pistol fire, but it can be seen to an extent when you begin to hit the edges with high power rifle rounds.

If you have to repair cracks, our recommendation is to use the edge of a grinder to grind the crack out, all the way to the bottom. You may need to grind some from both sides, rather than all from one side. If you don't remove the cracked material, and just weld over a crack, the life you'll get out of the repair will probably be half (or less) than if you do it right. It is unreasonable to think that your repair will never crack again. You have a heat treated hardened area, coupled to a chemically hard but soft area (softened by the heat you introduced into it), coupled to a soft weld area. "Ductility" is the technical word describing the rates with which metals flex or bend. The ductility of the three areas of your repair is all different. You WILL get another crack there. The only question is, when? If you are the person who did the welding, don't take it personally. Without the technology, welding facilities, (and expense) of NASA, everyone should expect a new crack at some point in the future. Like death and taxes, it's inevitable.

When you weld on any heat treated material, use multiple small, hot beads, rather than a large one. The object is to limit the amount of heat you put into the steel as much as possible. Let the first weld get cold enough to touch before you make the second pass, or before you make a pass on the other side. This will minimize what is technically called the "heat affected zone", and consequently minimize the amount of temper that is removed from the parent material. Heat on mild steel has very little effect but it is critical when you are working with heat hardened steel.

If someone delinquently or intentionally shoots a hole in one of your targets and you have to fill the area, you've got two real problems. First, all of the area surrounding the weld repair (or plug) will be softened because of the welding heat. Second, your welding filler material will be the same hardness as mild steel. The trouble with this is you have a spot of 135 Brinell hardness on your target. This is going to significantly crater the first time it sustains a direct hit from a .38 Super, or something similar. Your welding supply store may be able to suggest a much harder filler metal than the traditional E-7018 or E70S-6 wire, but it's never going to be as hard as it was before the repair.

you half the replacement cost of the targets, or more, especially if you have to pay freight there and back. Additionally, they usually need to know specifically what type of steel you have and what you want done to it. They might be able to recommend a generic treatment, but it is a safe bet they aren't going to guarantee anything without knowing the specific chemical composition of the material. If you are the original purchaser of the material, you can probably find that out from your supplier. If the purchaser has moved on and you can't locate the source of the steel you may be out of luck.

If you want to really lengthen the life of your steel target make sure you turn your target as soon as it gets a curve in it. Hard steel will go convex (bulge toward the shooter) soft steel will go concave (bulge away from the shooter). Turning your target will double the life expectancy of a steel target. TURN YOUR STEEL.

We don't have all the answers, but we'll be glad to help you to the best of our ability. Just give us a call at 888-767-7371.

--Mike Gibson

Gibson is president of MGM Targets of Caldwell, Idaho (MGM Targets | Home Page)

russ 12-05-2010 09:45 AM

Good info Cane.

canebrake 02-25-2011 11:22 PM

** bump **


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