Sealing a monocore

[Morgan]

Making a rimfire monocore. Shell is 4130. The tubing appears not perfectly round, can see a paper thickness gap on one side of one end while the rest is tight. Any advice on o-rings on each end? Once the endcap tightens against the tube there should be a decent seal I think? I hadn't planned on o-rings, they will just take up space that could be another chamber instead is the way I see it.

Never had a monocore design, how many rounds should I expect before the tube gets really hard to remove? Should I make provisions to be able to press the core out of the sleeve?

[CMV]

Is there an end cap for the part sticking out at the bottom of the pic? If so, my vote is try it as-is. You can leave a little space to later go back & cut a groove for an O-ring if necessary. Groove it with a threading insert/tool & it won't be very wide.

How much clearance do you have between the core body and inside wall of the tube? That + how out of round the tube may be will probably determine how many rounds before it needs a lot of encouragement to separate. Ammo used might make a big difference too - copper plated, bullet lube, bullet hardness, & powder used by manufacturer probably play a part as well. Go 100 rds, disassemble & clean, go 200 rds, disassemble & clean, etc. You'll find the appx round counts where it goes from easy to difficult to break out the BFH (or little FH since it's aluminum). But you can tap w/ a hammer & something soft like a large diameter wooden dowel or section of 6061 barstock with chamfered end to 'encourage' it to separate. You don't want to go brick after brick after brick of ammo & then 'get around to cleaning it someday' since the Al will limit ultrasonic & soaking options.

[Morgan]

Haven't made the end cap yet. The tube is a slip fit with a bit of friction, probably a couple thousandths at the most where the gap is?

I guess I should re-state my question: Are o-rings necessary? Seems like the turned ends of the tube would seal against the lip and end cap tightly enough. I don't care if it leaks a bit of gas as long as it doesn't effect performance or disassembly. I made it mainly for a bolt rifle and subsonic ammo so I'm expecting excellent performance and it won't have thousands of rounds an hour through it or anything crazy.

Also on the tubing - it's 4130 and I plan to parkerize it. Inside it is very glossy and smooth. Should I blast the inside surface before parkerizing? It's 1 inch tubing, so the nozzle will be almost parallel to the surface, not sure how well it will work near the center of the tube? Shouldda just got stainless!

[Capt. Link.]

You could cut a cone taper in each end of the monocore and in the end caps.This will keep the core centered and eliminate the need for o-rings.
You can also make the tube more round by "Balling". They make carbide balls in many different sizes.A high pressure lube is applied to the tube and ball and a press is used to force it through.This is similar to reaming but no metal is removed.

[Morgan]

I like the taper, that's a good idea. Would removing the tube be easier if there was more clearance or less? It almost seems like more clearance would make it easier to remove since that means it can slide off with more carbon still stuck on the tube?

Has anybody used some sort of sealant instead of an o-ring? Again, this is for a bolt rifle and likely won't ever get very hot. Seems like there's potential for that? Also thinking about leaving room for an o-ring on the rear end only, advice?

How thin can a rimfire tube be safely? I used 0.049 wall, thinking about turning it down a bit to save weight.

[curtistactical]

I use 316l tube for my rimfires and make my tubes .03 wall, 4140 is strong stuff so you would be ok at .03

[CMV]

That's a benefit of your design - you can use thinner wall tube because you are holding the tube in compression. You don't need any internal threads so there's no need to leave extra meat to have something under the threads to provide strength. You do have to be careful when it's disassembled though - .030" won't hold up to being dropped on concrete, being banged on, etc. Fairly easy to get something that thin out of round if abused. You'll do much more damage to your AL ends though. If you leave those raw, they will shows signs of use nearly immediately.

Taking .020 off the OD of the tube isn't a dramatic weight savings. If it were me, I'd just leave it at .049. Your core will most likely be a lot heavier compared to a baffle stack anyway. It is nice to have something real light on a pistol though. My 22/45 Lite w/ suppressor is lighter than bull barrel target MKIII. That's great for kids.

[Morgan]

So I made the end cap longer than I planned so I can put an extra chamber in it. It's just a hair over 7 inches total. I think I'm going to skip the o-ring. Suggestions before I cut the chambers? The long piece is the barrel end.

[a_canadian]

Couple of suggestions. First off if your tube isn't straight and/or isn't round, turning down the thickness is problematic as you'll end up with very thin spots and other areas which are barely touched by the cutter. Unless you forced it onto a solid rod to true it on the lathe... but then you'll probably have difficulty getting it back off without destroying the tube. So I'd suggest leaving it as-is at 0.049", which as stated already isn't all that heavy.

Next I'd suggest you consider a flanged monocore design. What I mean by this is that you can considerably increase the air volume while still restricting gas flow along the tube inner surface with flanges left between the cut-outs. At the same time such a design will allow for much reduced resistance when pushing the monocore out, with each flange acting as a scraper to push gunk ahead of it rather than having that gritty rimfire mess scoring the heck out of the whole length of the core. Say you leave about 0.070" a the thinnest for your baffle elements, for example. If you're doing a straight big hole baffle design, just drilling/milling big round holes, then you could turn down the outer 0.125" or so leaving a 0.070" ring at that baffle minimum, effectively closing off that hole preventing fore/aft pressure movement beyond the flanges at either side of the through-bore. It does make for smaller baffle pockets, but the outer-most volume you've turned down more than makes up for that loss of volume in the hole, and adds to the complexity in terms of distorting/slowing gas flow. It looks like a 1" OD steel tube, so the core is about 0.90", correct? If you were to bore holes of 0.75" in a line down that core with a 0.070" of solid aluminum between them, that should leave room for about 6 holes, though I'm guessing a bit because I don't quite follow what's happening with that long threaded bit where no baffles seem possible. So you drill out each 0.75" hole or whatever, then turn down only the area of the hole by an eighth of an inch or so to generate volume and reduce friction for dismantling, while maintaining isolation of the chambers. You could even go a bit further and mill into the thickest parts between the holes, coming in from top and bottom to open out more volume, adding mouse holes to the main chambers to make more direct use of that volume.

I don't think an O-ring or any sort of sealant will be necessary for your intended use. If the ends are all neatly squared it'll seal well enough. A wipe of lithium grease ought to be more than sufficient in assembly, just to prevent galling.

[Capt. Link.]

Before you go any further I would replace the tube with DOM tubing and sand blast to no greater than a 240 finish before you park it.This will be straight and round.
1" OD x 0.049" WALL x 0.9" ID A513 TYPE 5 TUBE
http://www.onlinemetals.com/merchant.cf ... op_cat=197
If you can anodize the mono core do it.Type 2 will work and is easy to do at home.
While lithium is okay antiseize is better

[Morgan]

The tubing is DOM. I had to cut a longer piece of tube since I made the end cap longer, and it is uniform. The first piece was from the end of the tubing, I think maybe it got beat up a bit in transit.

I've been reading up on the anodizing, it seems awfully easy so I'm probably going to try it.