The making of a monocore on manual machines

Thought some of you might find it interesting. A majority of form 1 builds are done using purchased tubes and end caps, sometimes incomplete baffles, or maybe freeze plugs. Some guys do turn their own baffles, but I can't say I've seen many DIY monocores, and I suspect the reason is that more of the guys doing them have only a lathe, and not a very big one. But if you have something with decent center distance and a vertical mill, monocores are actually a bit easier. The only issue is that a screw up kills the whole project, not just a small part of it.

Anyway, I wanted to build a fairly lightweight hunting can with a bit more volume than the commercial lightweights like the SiCo Harvester. The Harvester is very light at just 11.3 ounces, and kinda long-ish at 9", but it's slender-just 1.375". I stepped it up a bit, went to 10" long and 1.625" diameter. After all, with cans, more volume=less volume! The monocore material is 7075-T651 aluminum, with 6061-T6 seamless tube for the sleeve.

First order of business is chucking up your stock, indicating it true and facing it off. Pretty standard stuff. Then comes the tricky part: Getting a perfectly straight hole 10" deep. The start is absolutely critical here, as even a couple thou wiggle going in will translate to a significatly off-center hole on the other end. Then there's the issue of actually drilling it. Tailstocks are generally used for boring holes, but unless you have a true monster of a lathe, you won't have 10"+ tailstock travel. Mine actually does, but it also takes way too long to plunge in and out with a tailstock, so I use a toolpost mounted drill chuck. I put the extra long aircraft drill in it, and line it up along the piece of stock to be drilled. Then we bring it back to center and go to town. It took about 20 minutes to bore the hole


Once that's done, we bring in the live center for stability and turn our outside profile


Yes, that's a 120 pound chuck winding at 750 RPM. Keep hands clear! Anyway, I turn them down to be a somewhat loose fit in the sleeve except for the last 1/4" or so, which is snug. If you make two pieces of aluminum a tight fit over any significant area, they will gall and bind. Add heating & cooling plus carbon and plasma to the mix, you may as well weld the thing together.

Now, monocores frequently have their sleeves threaded on at the base, but I prefer a retaining nut at the front, so I thread the snout of the core





Next we part off our finished solid core piece and flip it around, re-indicate, face it off, bore and thread for whatever muzzle it's going on. 5/8-24 on this guy


Now we're done with the lathe work on the core, so it's off to the mill, where we start poking holes according to our plan. This would be far, far easier with CNC, of course, but if you have a swivel vise, it's not too bad.



Awhile later, if you didn't break off all of your long end mills, you'll have something like this



Now, this would be a functional suppressor as is, but I wanted to make one that was a bit more durable than a 100% aluminum critter would be, so I made a 17-4 stainless blast chamber that inserts at the rear



Trying to create a radiused profile inside is a bit tricky, especially sine I broke all my long ball nose end mills, so I had to do it blind with the quill right up to the piece. A little ugly inside, but functional



Continued.......

Apologize for not snapping pics of doing the retaining nut, but nothing real special there, just boring and threading a bit more of the 1-5/8" aluminum stock. Anyway, now it just needs Cerakote and it's a wrap! This one has a .315" through bore, so it's not really a .30 can. I built it to go on my .17 Remington, My .220 Swift and my .25-06. Still a proof of concept prototype, and if it'll quiet the blasty .25-06, it'd do just fine on a .308 or .30-06 with a little bigger through hole.

Final weight is 16.9 ounces.



I did step out back and test it, and while I don't have a dB meter, it's noticeably quieter than my SiCo Hybrid or AAC SDN-6. We'll do a comparison with a Harvester and TBAC Ultra 9 when I have a chance





And dressed up a bit with my info engraved

Gtscotty said:

Awesome! Thanks for posting this. The can looks great, and I love that you designed it with a slide in 17-4 blast chamber.

What lead you to the particular baffle geometry you used on your monocore?

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Mostly that it's fairly simple on a manual machine. Lots of math to poke the holes in the right places, but otherwise it's just milling with the vise at 0° and 45°.

I had already established that straight baffles don't work very well, and I tried this pattern on a rimfire can with good success, so figured I'd scale it up and see how it does. Works quite well. I stuck it on my 10.5" carbine, and the sound is more tolerable than with the other rifle cans I have. Much of that is, of course, the increased volume, but it's not that much over the Hybrid.

Blkhrt13 said:

Good looking work. I got 20 years making chips so I know what it took to get there.

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Thank you. Yeah, it takes a bit. I'm into this one about 10 hours with the fluting and engraving of the sleeve.

I've already started the next one with the materials I had on hand (waiting on a titanium order for another rifle design). This one is gonna be an aluminum monocore pistol can, and I started with the recoil booster. Basically copied Silencerco's piston design, although I went with 8 notches on the piston instead of 10 to give it more bearing surface in the housing.

The piston I made from 8620 steel, single heat treated and tempered at 450°F for high hardness.



I polished it after heat treat, then tempered, which is what gave it the pretty bronze-ish luster. The booster housing is 410 stainless, as is the cap. They're not finished yet, decided I was getting too tired at 1am, and that's when mistakes happen.

Mn Fats said:

Thanks for the post. I'd hate to get my sleeve stuck in that sucker.

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You definitely do not wear long sleeves, loose clothing or gloves other than Latex/Nitrile with rotary metal working machines. Woodworking stuff spins faster and generally presents more hazards to the hands, but the brute power of metal cutting machines will break you, kill you if you get caught in them.

I'm pretty careful, always wear glasses and keep hands clear of cutters to every extent possible, but things still happen. I was polishing a muzzle crown a few weeks ago, slipped off it and got nailed by the chuck on my Hardinge at 2,800 RPM

Blkhrt13 said:

Do you do your own heat treat or send it off?

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I do it, too expensive and too far away for a part here and there when I can do a pretty decent job with many materials here. Steel color is pretty accurate, so as long as my part is small enough and cross section thin enough to heat uniformly, I do it with acetylene torch, and temper in a regular oven. Materials that need tempered higher than 600°F present a problem, of course.

A heat treat oven is on my list, but haven't got there yet!

Had a little time today, so the recoil booster got finished. Now just a few hours to knock out the monocore, and I'll have pistol prototype #1

I thought about a way to use a tool on the piston housing, but decided that just using loctite and then cranking it in by the rear housing should work fine, be nice and clean. Let the loctite set, then unscrew the rear housing.

Stay tuned!

Aaaaand I couldn't wait. Put the boy to bed, and it was either waste my evening reading or watching television, or do something productive. So I chucked up more of that 1-5/8" 7075 stock and got after it. Took about 4 hours. Still a couple things to do before I call it done, engrave and file form 2, but it's ready for initial test.

13.2 ounces fully assembled with piston. The features I'll do on the housing will look like lightening cuts, but probably only be worth .1 oz or so.

The baffle shapes are kinda random. I sketched it out a little, but ultimately just poked some 5/8" and 3/4" holes to create peaks, then blended everything out with 1/2" and 3/8" end mills. I'd be hard pressed to duplicate it exactly, since it was heavily freehand machining.

We'll see how she sounds tomorrow

And done. Tweaked on it a little, fluted the tube, engraved and painted it with cast iron engine enamel. Not as quiet as I had hoped, sounds almost identical to my Hybrid. So, funcitonal, but not any better than anything else out there, in spite of being slightly fatter. But that's what R&D is about, learning what works and what don't!

Well, all those lightening cuts on the 6061 sleeve proved problematic with more powerful cartridges, the .220 Swift bulging it a bit after a few rounds. So we revisited that, and I also decided to try a different approach with the blast chamber.

It now has a titanium muzzle brake that is an integral part of the can, which I drilled in such a way as to create a vortex flow in the blast chamber that will, in theory, reduced the stress on both the brake and the blast chamber versus straight perpendicular holes. I also went to a .028 wall gr. 9 Ti sleeve and flame anodized it. These changes made it quieter on a 16" 5.56 AR, and also got the weight down to 12.4 ounces. We'll see soon how she handles the hotter rounds!

pdsmith505 said:

The joys of being an SOT.

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I certainly do enjoy making things, seeing what I can come up with, but bear in mind that this is ultimately R&D for a commercial venture. I'm spending a great deal of money on materials and many hours on machines to build something that I then go and deliberately beat the snot out of, and do it all over again with slight changes in design, different materials, etc. in the quest to develop a marketable item. I've blown up several already, units that would have been cared for and used for many, many years if they were personal form 1 builds, but are getting screwed onto machine guns and run to failure because I need to find out just how durable they are (or aren't).

For example, this one? I took basically the same design and carved it out of 6/4 Ti, just an inch shorter and with a little thicker sleeve to be a more durable version of this. It's heavier than I want it to be, and the suppression is not satisfactory, which could be due to the slightly reduced volume, the minor changes in baffle geometry, or the material. So I get to take another $100 worth of Ti and try again. And again. And again, With 8-10 hours on the machines and several smoked tool bits for each iteration.

Gtscotty said:

Are you making CAD models of these? Using CFD and FEA in something like ANSYS to try and weed out the un-satisfactory designs before they eat up your resources?

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Sometimes, really just to help with the math to poke the holes in the right places before I start swiveling the vise away from indicated zero. And it gives weight if material is selected, so that's helpful. But ultimately I'm doing it pretty old school, knowing also that computer generated models are only so helpful with flow analysis, and certainly won't tell me how it sounds to human ears. Different materials behave differently, and there's no way to know how things are really going to work out aside from building and testing them! Since I'd rather be making chips than "building" in a virtual world anyway, I don't mind.