Hoots Note: Finally fixed all the broken image links for a 2nd time
Hoot's Cheap Carrier Weight System
A while back I read This Thread
discussing the merits of greater bolt carrier weight or a heavier buffer. One of the items mentioned in the thread was the Tubbs CWS Carrier Weight System. Some of the thread participants had experience with it, while others had experience with heavier buffers. The physics behind the merits struck home with me, though the price of the CWS, along with the hassle it created when trying to open the action made me ponder if there was a better way of simply and affordably implementing such a system. Here is a quote from the David Tubb web site:
The addition of weight to the carrier slows its rearward start upon action cycling. Technically, it increases the "moment of inertia," but that simply means that the rifle will stay "locked" a little longer. This additional time reduces the influence of pressures on the cartridge case and also softens rearward carrier movement. The result is better brass life, fewer "pressure problems," and greater flexibility in velocities attainable using all bullets -- especially the heavier bullets used in High Power Rifle competition. There is also noticeably less rifle movement during firing and longer parts life from a softer recoil pulse. The rifle stays on target better, effectively giving the shooter more time to focus on shooting a higher score.
Given the fact that with the 450b, we were pushing bullets that weigh somewhere between 4 and 5 times the weight of a 5.56 projectile, it seemed that increasing the inertial resistance of the bolt carrier might benefit our group highly. Having shot about 70 rounds through my 450b of differing velocities and weights, I felt I had an understanding of the energy released during the process and the behavior that it led to with the 450 Bushmaster rifle. There was room for improvement enough to make the effort to come up with an alternate way to implement a bolt carrier weight increase, without having that weight stick out the back of the carrier and to make it easily with junk
around the shop.
Here is an installment of Hoot's Junk Science
Tubbs uses a steel sleeve that accepts either an additional steel or tungsten insert. While Tungsten is about the perfect material for a weight, due to its properties, it is both awfully expensive and miserable to machine. If someone has access to some 5/8" diameter by 2" long Tungsten rods that don't cost as much as two boxes of 450b ammo, I might have used that instead. Next best available material is our good friend Lead. Anyone who shoots has some or for a small amount of effort at the range, can get some. The berm behind out rifle targets at my club probably has tons of it. Ditto on the pistol range. You can see all kinds of spent bullets lying in the gullies carved behind each target position.
So what are our parameters?
The inside diameter of my AR-15 bolt carriers is .625 inches, so my guess is that is the spec for it.. The distance from flush at the rear of the bolt to where the rod has to stop so as not to obstruct the standard hammer is 2 inches. So, we need to come up with a lead rod 5/8x2 inches and a means to make it stay where we put it. In case you're curious, that length and diameter rod using lead should be about 4 ounces. My rod has stayed where I glued it for  EDIT: Over 2000 rounds now! Where it will be 500 or 5000 rounds from now, I can not say. I can say that so far, the JB weld has not cracked, or shown any intention of moving. It is resisting the various chemicals I use to clean and lubricate. If it does start to creep, I'll have to come up with a Plan B. For the moment, Plan A is holding nicely.
This is geared towards ease of manufacture and implementation, with minimum inconvenience to remove it if I have a better idea and of course cheap to make.
I have loved lead since a child due to its ease of melting and molding. Fond memories of racing off to the local tackle store, saved allowances in my pocket, to get my bank sinker mold and cast iron ladle are as fresh as yesterday. My trap line
from one service station to the next toting coffee cans of wheel weights in my backpack. Evenings at the kitchen stove watch that gleaming, alluring, magical liquid... Aaah! Oops, Hoot's drifting a little...
Anyway, here are the things to have ready:
A sheet of 220 grit wet-or-dry sandpaper.
A 4x8 inch piece of plywood, sheet metal, plastic sheet, whatever. Needs to be thick enough to be stiff.
JB Weld 2-part epoxy
Something to mix it in
A flux brush and some cotton tipped swabs
4-5 ounces of lead
A heat source to melt the lead
A metal cup or ladle to melt it in. If you cast bullets use your melting pot
Strong solvent. Read, not eco-friendly. If it has methylene chloride in it, buy more and squirrel it away while you still can.
Rotary tool (Dremel) with cutoff disks
Good table vise. The beefier, the better
Punch or rod to drive the slug out
A 5/8 (.625) inch diameter mold. in scrounging around my shop / junk repository / man-cave, caliper in hand, I came upon a piece of common EMT conduit that was exactly .625 ID. This will be our cheap mold of choice. If you have some aluminum block stock around, drills and a press, you could make a nice mold. For a run of just one, that's a lot of work though. Just to keep your effort later to a minimum, measure the inside of the rear of your carrier to make sure it's not some weird diameter. If it is, you may have to try several pieces of conduit to get the closest match.
Cut off a piece of the conduit 4-5 inches long and remove any burrs from the ends.
Clean it inside and out using some good solvent and thoroughly dry.
Clamp one end in a vise, squashing it flat.
I kept cranking the vise until, when I blew in it, no air passed through. If your vise doesn't have enough oomph to smash the conduit, pound the end flat with a hammer first, then clamp it tightly in the vise in an upright position to finish the squash.
Using whatever method you have at hand, melt some lead scrap in some form of crucible. I used a small stainless steel measuring cup (don't tell my wife), skimming off the crud. Ooh, the memories crept back....
Preheat the conduit a little with the torch, melt the lead and pour enough in stopping just short of the top the pipe.
When it is cool, clamp it sideways in the vise and with a rotary tool (dremel) and some cutoff wheels, cut a slit down the side of the conduit. I can't stress this enough. Go slow, making a lot of passes from one end to the other along the line, evenly removing a little at a time.
and here's an end view of the cut:
When the slit is almost through to the lead, you will hear / feel a pop as it splits open. The lead exerts a small amount of outward force upon the conduit that causes this. If you look closely, you can see the split at the bottom of the slit line. If you were less than consistent with the cut depth and it doesn't split all the way, you can touch up those spot(s) with the dremel and it will open up. Now, measure about 2 1/4 inches from the end and cut the conduit off of the crushed end.
Remember stopping just short of the top when you poured? There was a reason for that. Tap that end of the mold on a hard surface a couple of times to dislodge the lead slug. It should slide down to the end of the mold, just like an inertial bullet puller works. Open the vise wider than the .625 slug, but able to catch the lips of the mold. Stand the mold up on the vise jaws and using a punch and hammer drive the slug out of the mold.
Face it off using your choice of abrasive device. That can be a file, grinding wheel, sand paper on a hard surface or a belt sander and reduce the length to no more than 2 inches. A little short is OK, just not longer.
I finished mine up by rotating each end it against a piece of Scotchbrite pad in the flat of my hand.
Here we're going to pause a moment and talk about adhesives. Any glue job relies heavily upon surface preparation. For epoxy, it is best to have both surfaces thoroughly degreased, free of crumbs, roughed and dry. The bolt carrier should have a nice matte phosphated finish already. Using the powerful solvent, clean the back half of the carrier inside and out.
Try inserting the slug into the end of the carrier. Ideally, it will barely slide in without scaring the lead but with as little slop as possible. This will effect how much slug prep you're going to have to do later. It should be just about perfect right out of the mold.
Now, were going to prep the lead slug. Take the sheet of 220 grit sandpaper and cut it in half. Lay one half on a clean flat surface and tape the other half to a clean flat piece of plywood, metal plate, whatever.
With the slug sitting on the one half, place the half taped to the board or whatever on top, so that you can roll it back and forth between them.
Exerting downward pressure on the board, roll the slug back and forth pausing to inspect and realign it once in a while.
Continue the process until the surface of the slug takes on a crystalline appearance and feels rough like the sandpaper.
Check the fit in the carrier. If it's too tight to slide in, back to the board and roll it some more. When it slides in all the way, you're ready to glue. Degrease your rough slug the same way you degreased your carrier. Make sure your hands are relatively clean when you handle the slug. Yeah, it all matters.
Position your carrier in some form of retainer where it's going to reside to the next day or two undisturbed, away from pets, away from kids, away from overly tidy wife/girlfriend, etc.
Carefully measure equal amounts of JB Weld (not JB Qwik) into a container, working it until it is a homogeneous mixture. If you have a favorite two part epoxy, you can use that, but I can only vouch for my experience with JB Weld. Why not JB Qwik you ask? Time. JB Weld gives you a longer working time than JB Qwik. Once the stuff starts curing, your time has run out!. Make sure that time is not while you're in the middle of working or you'll have a mess to clean before starting over. You don't want to be rushed either. Nuff said.
Using the flux brush and/or swabs, goober the entire inside of the carrier from the end in 2 inches
and looking in the back:
You're just pre-wetting the walls, a little goes a long way. Apply a more generous coating to one end of the slug, slide it in a bit to free up your hands and coat the rest of it. There is no need to coat the ends of the slug.
Push it in all the way until it is flush with the end of the carrier and using a paper towel lightly moistened with solvent, wipe off the excess around the rear.
There shouldn't be much but clean up, but nows the time to do it. Wipe off any excess on the inside end of the slug with the swabs lightly moistened with solvent and let it cure fr a minimum of 24 hours. I don't care what the epoxy instructions say. 24 hours before disturbing! Another 24 hours before testing. You want to get this right the first time, trust me. Epoxy can be loosened with a heat gun and the slug removed if for some reason, you don't want to keep it in there, but its a lot of work.
Here's my carrier with the weight in it.
Reassemble your rifle and try closing the upper to the lower slowly. The inside edge of the slug will clear a standard hammer with room to breath. If for some reason, it touches or obstructs your hammer, you can trim a channel into the end of the slug with an Xacto knife. Remember, it's soft lead.
No, it doesn't look as nice as the Tubbs CWS, but you can spend the $55.00 or so on ammo and you can open you gun without having to completely remove the upper from the lower. I like that as I clean right at the range in a cleaning vise between different loads I'm testing and don't want to fiddle with separating and rejoining the halves.
To some, this process may appear tricky and daunting, but its very intuitive and within most guys skill set. Once you've got your parts amassed, it takes 30-40 minutes to do, not including the cooling time for the cast slug and the curing time for the epoxy. You'll feel good about having done it yourself and your shooting will be a more enjoyable experience. I swear, it tightened my groups as well. No claw marks on any of my test loads to date and some were really light. If I missed something or you still have a question, ask away.
HootEDIT: If someone wants to give this a try and doesn't have access to lead, EMT conduit and the means or desire to cast a slug, I'll make you one for $10.00 shipped via USPS 1st Class mail.
You'll may have to do some final fitting to your carrier and of course, the sandpaper roughing.