Saga of the MP40 and the baffle box

Saga of the MP40 and the baffle box

Stopping steel and lead in its tracks

By Dennis Adler

The Umarex MP40 is not only accurate but pretty powerful, even at 25 feet on full auto. And I have a blown to bits baffle box to prove it.

My recent exploration of the MP40 weathered model’s accuracy proved to be quite exceptional. After Thursdays article, I went back and shot several more magazines to test quick reloads (I have one spare magazine) and firing with the gun shouldered and my support arm through the sling (as pictured) my groups from 25 feet kept getting tighter. This is one very accurate CO2 air rifle on full auto, especially shooting in short bursts. I average six to 10 shots by feathering the trigger, i.e. just enough pull to fire the gun but not an extended trigger press, on and off in under a second. You can hear it and feel it in the bolt’s recoil so less than a second and you’ve got it. Some of you have already tried this using the shoulder strap to really stabilize the MP40 from the shoulder and are getting the same kind of accuracy, so I haven’t done anything exceptional. What I did do, however, is blow the entire center out of my baffle box! I usually get about 10 gun tests done before I have to make a new baffle box. I shot this one to piece in two days with the MP40.

After four full magazines with the MP40 I blew out the entire center of the outer box, a big enough hole to put my hand into. This not only blew through the outer box but all the way through the first inner box!

Baffle box theory

I’ve thrown the term baffle box around a few times before but never explained what it is. There is more than one way to make a baffle box, and my system is simply what I developed by recycling boxes and cardboard around the house. This basically costs nothing but your time. You can also buy ready made ones, but you will wear them out as well and since cardboard is cheap and so are cardboard boxes you can make one rather inexpensively. Some people just stuff a box with old newspapers and shoot into it. That works with BB guns and some lower velocity pellet pistols, but I like to build a baffle box that stops them dead in their tracks. I shoot both outside and indoors (basement) at anywhere from 21 feet to 10 meters, a little further sometimes when I’m outdoors, but I like to trap all my rounds, even outside. My baffle box design varies in overall dimensions but usually measures 11 x 14 inches and 10 inches in depth. That sounds small, and it is, but I have been shooting for 40 years and I rarely hit outside of a 4-inch radius even with cartridge firing handguns from 25 yards. A good size for most shooters should be a 20x20x20 square box; that gives you a good margin with airguns at 21 feet to 10 meters. The depth isn’t as important so long at it is at least 10 inches, if you build the baffles correctly. My baffle box will stop a 4.5mm pellet from the Sig Sauer MCX at 10 meters.

A simple baffle box requires two boxes, one a little smaller to fit inside the larger box. The idea is to fill the first box with paper or other energy absorbing material and place it at the front of the box. It will be the first area to begin slowing the BB or pellet once it passes through the target and the outer surface of the larger box.

The inside of the baffle box, constructed properly, will outlast the outside for a long time. Usually when I’ve punched a lot of holes through the front of the box, I’ll patch in a new front board to keep from making an entirely new box. The MP40 kind of used up a lot of gun tests all at once! So here is how to make my kind of baffle box.

Shipping boxes are your best friend

Cardboard is like metal, it comes in all gauges (thicknesses) and qualities. Cardboard from China is junk (no pun intended) and won’t stop your finger let alone a BB or pellet. You need good shipping box cardboard (the Uline catalog has great choices in heavy duty cardboard boxes 20x20x12) but you probably get shipments from one vendor or another that use good quality cardboard, so pick one that is a size you are comfortable with and make your own baffle box.

Heavy paper can be stuffed into the first box. Newspaper will work as well.

Here you can see all the various elements of a good baffle box that can stop a .177 caliber BB or 4.5mm lead pellet at velocities up to around 460 fps. What you are looking at is a top down view of an 11x14x10 inch shipping box with a smaller box packed with paper as a first buffer. Behind that the V formed heavy cardboard presents a surface that will begin absorbing energy as the BB or pellet passes through. This cardboard needs to be the strength of a FedEx or UPS shipping box, something sturdy that will stop the projectile dead in its tracks. The added paper at the back of the box is to assure the V shape of the cardboard remains intact. When the box is taped closed it will be turned on end, the right side as you are looking into it will become the top of the baffle box.

It is how you build the baffles inside the box that make it effective at stopping BBs and pellets at up to 460 fps. As the photos illustrate the heavy cardboard that is bent into a V shape is in layers and the BB has to pass through each, slowing it down as it goes. I have yet to have a BB or pellet make it to the fourth baffle; most stop at the second, higher velocity rounds still won’t get past the third baffle.

All taped closed and ready to go, this 11×14 inch box is the right size for my shooting accuracy at 21 feet to 10 meters. Your shots should stay within a 4-inch circumference of the center. Targets can be hung in front of the box (smaller ones taped to it), and the box can be on top of whatever platform you are using for shooting. I have mine set up in the basement on top of a tall shipping box that measures 46 inches in height, which places the baffle box right at average chest (center mass) height.

Looking at the side of the baffle box the outlines of the interior show how the combined elements and layers absorb the energy of the BB as it strikes the center of the target and passes into the baffle box.

In the disassembled baffle box photos you can see there is a smaller front box filled with paper (or heavy plastic) which takes the initial hit as the BB passes though the target and the cardboard box. By the time the BB hits the first baffle it is already slowing down. BBs seldom get past the second baffle.

Here I am illustrating how wrapping my hand through the shoulder strap helps further stabilize the MP40. This is especially helpful firing on full auto.

With the used baffle box cut open and looking into it, you can’t see how much wear it absorbed from the MP40…

…but when you look at front of the inner box it is shot clean through with all of the BBs passing out the other side and into the first and second cardboard baffles.

Looking into the box you can see where BBs penetrated the first cardboard baffle. These also went through the second baffle but only 1 shot out of more than 200 went into the third baffle and none reached the fourth. Each baffle is folded cardboard so there are actually eight layers. And keep in mind, the outer box and inner box were already shot completely through.

The fourth cardboard baffle, which is two folded surfaces, shows zero impact from any projectiles fired into this baffle box with the MP40 and a few other BB and pellet guns before this test. I always blow out the center of the baffle box but never this soon; time to rebuild it.

This is a very inexpensive and simple way to shoot indoors and out that prevents BBs or pellets from getting past the target. Not at all baffling, just shoot straight and hit the bullseye.

Next week, we will begin a series on target shooting and dedicated target pistols starting with an old friend.