Inconel or...? For a form 1 5.56 can from a solvent trap kit.  I see lots of options made of aluminium, but need something better for 5.56 NATO.  Anyone have sources to recommend?

17-4 H1150 would work, as well, and you might be able to order something from one of the "DIY baffle" suppliers.

Aluminum is fine for rimfire but even for a 9mm pistol can it's best to have the first baffle be 18-8 or 416 stainless or Grade 5 Ti.  For 556 I'd want the blast baffle to be 17-4 PH stainless hardened to H900.  After that titanium is OK except for full auto mag dumps where an all 17-4 stack will handle higher temps better. Even in annealed state 17-4,is pretty rough. Diversified Machine, Rusty's Cans, or Totality Industries are best sources for solvent trap cones in 17-4 or Ti Gr5.

ETA: haven't seen any pre-turned Inconel cones and Inconel is worse than 17-4 or Ti Gr 5 to drill and clip.  You need stiff powerful machines with carbide tooling and generous coolant flow to machine inconel.

17-4

Get it heat treated after machining

Inconel 718 is better. But its costly and costly to machine.

No, get the round stock in hardened state. Not only does it machine far better when hard (gummy as hell when it's annealed) the hardening can do some really weird things to the dimensions. With something as tight tolerance as a baffle being made, I sure wouldn't enjoy having to scrap the whole baffle/stamp due to growth/shrink in the wrong directions.

Eh. I meant heat treated

Heat treating is the process used to harden steel (aside from Annealing, Quenching, and Normalizing).

What pyotr_k is recommending is to buy 17-4 in the H1150 condition. It's already been heat treated and requires nothing beyond turning. Cond. A is not hard to machine, but can exhibit unfriendly characteristics. And, then, you still need to send it off to have  treated.

I guess I'm spoiled by primarily dealing with H1150... it really does seem gummy as 304, when it's annealed.

That aside, which may well be a lack of proper setup on my part, just the shift in dimensions is worth cutting it after hardening.

I wasn't talking about machining annealed 17-4.
Buy it hardened at H1150 and machine it at that.
Then heat treat it to H900

You'll have to anneal before going to H900.
Just leave it at H1150. Still strong chit.

I've used 316 SS on all my 556 and 308 cans.  316 is essentially a step down from inconel but it is cheaper, easier to find and easier to machine.  It welds to inconel nicely.

The first $100 "solvent trap" Form1 cans that showed up on Arfcom used engine parts - either Valve Stem Retainers or engine "freeze plugs" (expansion plugs).

The advantage to valve stem retainers is they are available in hardened tool-steel and titanium.  Hardened tool steel may not be Inconel, but it is a lot tougher than the mild plain steel used in freeze plugs.

The disadvantage is that VSRs are the wrong shape for optimal cone performance.

Might want to consider 1 tool steel VSR for the blast baffle, then 60 degree cones for the rest.

17-4 annealed is not gummy unless you're tooling or techniques suck.  It machines cleaner than just about any other annealed martensitic or PH grades.  As for dimensional changes from heat treatment, 17-4 is extremely stable and the heat treat temp is low.  You'll have more trouble with H1150 annealing and then treating to H900.  If you don't like dealing with it condition A but want H900, then treat it to H900 first; 17-4 never get's especially hard, still quite easy to work in H900 condition, much gentler on tooling than most tempered 400 series will be.

On tolerances, I wouldn't call solvent trap baffles especially tight.  Most of the specs I've ever seen for the tube IDs are ±.003, and the cones are .005" under specified tube ID with tolerance in the neighborhood of ±.002" to +0/-.005.  That means you could have anything from a beat-it-together fit to >.010" diametral clearance.   .005" is ideal for most purposes, will provide good alignment without having to force baffles in or out of the tube.

Fair enough, I guess I'm spoiled with other materials and honestly not much of a machinist. I find 17-4 Cond.A as gummy as 304 stainless, but since I mainly cut H1150 when I do work with 17-4, I've never looked into it much.

Agreed on just using H900 if that's the end goal; for me, H1150 is my preference, so that's what I use for stock.

As far as tolerances, the dimensional changes of 17-4 are what I had in mind, not the baffle clearances or similar. More that if you were to machine baffles from 17-4 and then heat treat them, warping may prove to be an issue (depending on design/caliber/etc.)... but, as you rightly point out, it likely wouldn't be an issue with such relatively loose tolerances.

I'd still just machine it in the desired condition. Same price stock, really.