.223/5.56 Completed can- Build with pics

[mr fixit]

Here's a can I finished a while back and just never posted. This is a direct thread can with 4130 tube and 4140 baffles and end caps. Spacers are Titanium between baffles. The can was welded
Direct thread end cap has integrated muzzle brake. I tried to copy one from here, I think Sampson's. Both end caps had just a small ring left on the OD to match the OD of the tube to help with welding. Drawing shows threaded brake mount but that changed.
Baffles are 60* cones, 3 of them are 4140, 4 of them are 17-4. I ran out of 17-4 so I used the 4140 I had. All baffles are clipped with DHC, and all are bored .375". I know that is what is often used for a .30 cal can, but I wanted it over-sized to help with back pressure and gas in the face. Exit end cap is bored .410".

This is the second can i've made and the first using a lathe. Yes the chatter and machine tool marks show, I'm trying to get better and have improved since I built this. My first can was a freeze plug can viewtopic.php?f=10&t=133194. Compared to that can, this one is smaller diameter (1.625 vs 1.75), more baffles (7 vs 4), shorter (7.75 vs 8"), and lighter (19oz vs 24oz). This can is also quieter. I compared them side by side on 16" AR's shooting the same FMJ and the new can is noticeably quieter to both the shooter and bystander.

This can was mounted on the AR pictured below, which had already been sighted in with night vision scope. That rifle was dead on at 100 yds prior to mounting the can. After mounting we shot it and had no POI change. I'm not sure if that was luck, or the can being bored larger or due to the DHC clips (the DHC is touted as designed for minimal POI change). I'm happy no matter what.

After welding the can together, I blasted it and painted with Norrell's Moly Coat in whatever grey/black I had on hand.

[ECCO Machine]

As you've discovered, annealed 4140 is nasty, gummy stuff. With super sharp cutters and lots of cutting fluid, you can minimize the roughness, but I usually hard turn for final dimensions, since the parts will change significantly when you heat treat anyway. You can actually get a really nice finish hard turning/machining 4140.

You've already welded this one up, but in the future, one of the easiest ways to remove tool marks on a round part is to hand file it on the lathe. Just wipe your file clean between passes so the tiny chips don't gall the heck out of your part as you're trying to smooth them. following that with a little 240 or 320 will give a pretty smooth finish.

And since you're turning your own parts, skirted cones are all-around better. It shouldn't really take any longer that cutting & truing spacers, gives you more to hold onto for later operations, and also the option of welding your core, which is definitely best for a sealed can.

[mr fixit]

Yeah, I'm not going to use the 41xx steel again, only because of how it machine's. My understanding is that even annealed 41xx is stronger than the 300 series stainless that is fairly common in cans.

I really like working with 17-4, both the 1150 and 900 tempers. I even like titanium now that I have a mist cooler.

[ECCO Machine]

Yeah, I'm not going to use the 41xx steel again, only because of how it machine's. My understanding is that even annealed 41xx is stronger than the 300 series stainless that is fairly common in cans.

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They're pretty close. Annealed 4140 has a TYS of 60 KSI, 316L has a TYS of 55 KSI. 1018 is right there, too.

4140, like most other carbon steels, doesn't have very good mechanical properties in the annealed condition. All of it's considerable toughness, hardness and strength is achieved by heat treating.

I really like working with 17-4, both the 1150 and 900 tempers. I even like titanium now that I have a mist cooler.

The machinability of 17-4 is great for such a strong material. It sucks to deep drill or plunge cut compared to free machining grades, but otherwise, with a little gear oil & water, you can attack it pretty ferociously, and it tends to have a really nice surface finish as-machined in the annealed state compared to most other annealed metals.