Dimension suggestions for .308 supersonic, .338 subsonic?

[DanielWilson]

I'm working on my paperwork for my first suppressor and working on the design ... to fill up my time between now and getting the paperwork back.

I want to build a can suitable for use on my LR-308 to use with supersonic ammo. That's the highest pressure for which I intend to build. I want the bore big enough that I can run it on a .338 Federal upper with subsonics only. I have no need to build for .338 LM pressures!

Weight is low on my list of concerns. My rifle's already heavy, so I really don't think even 3 more pounds would be that big a deal.

The FF tube on my LR-308 being 2 inches in diameter, a 2-inch can (or even a bit bigger) would not be out of place on the rifle. But is that overkill? My paperwork is for a 12-inch long device as I understand I may make it shorter than the registration states but not longer. Is the 12 inches overkill? For bore diameter, I'm thinking .375 would be comfortable for those .338 subs. Again, would you recommend going either up or down a little in size?

Thanks for your help!

[propeine]

I'm working on my paperwork for my first suppressor and working on the design ... to fill up my time between now and getting the paperwork back.

I want to build a can suitable for use on my LR-308 to use with supersonic ammo. That's the highest pressure for which I intend to build. I want the bore big enough that I can run it on a .338 Federal upper with subsonics only. I have no need to build for .338 LM pressures!

Weight is low on my list of concerns. My rifle's already heavy, so I really don't think even 3 more pounds would be that big a deal.

The FF tube on my LR-308 being 2 inches in diameter, a 2-inch can (or even a bit bigger) would not be out of place on the rifle. But is that overkill? My paperwork is for a 12-inch long device as I understand I may make it shorter than the registration states but not longer. Is the 12 inches overkill? For bore diameter, I'm thinking .375 would be comfortable for those .338 subs. Again, would you recommend going either up or down a little in size?

Thanks for your help!

I won't be of much help on the 338 overal sizing side of things but .375 is what I ran for 308. I would say a long wobbly subsonic bullet may want a bit more clearance though personally but I'd rather play safe and lose a few dB than have a baffle strike.

[DanielWilson]

Thanks. If nobody contradicts you, I'll think of going up a few more hundredths.

[T-Rex]

No reason you shouldn't be able to use a 10mm or 13/32 reamer/bit. Whichever you might have laying around.
I think 2" is a bit on the extreme side. 1-3/4" might be a bit more realistic. I'm sure someone has some input.

[Capt. Link.]

I would run no more than 1.500" with a bore of .338+.060".

[DanielWilson]

OK, thank you all. In your experience then, larger can diameter does little for suppression? Obviously it adds weight.

.338 + .060 = .398, so larger than the .375 I'd initially guessed.
13/32 = .40625, so about as close to the above recommendation as a standard size drill will get.

It's good to see experienced recommendations coalescing!

[propeine]

OK, thank you all. In your experience then, larger can diameter does little for suppression? Obviously it adds weight.

.338 + .060 = .398, so larger than the .375 I'd initially guessed.
13/32 = .40625, so about as close to the above recommendation as a standard size drill will get.

It's good to see experienced recommendations coalescing!

I don't advocate for drilling either...drill to .375 and bore to size. Concentricity will be better. All bets are off even at .060 over if you plan on drilling to size IMO.

[DanielWilson]

I'm not much of a machinist. I don't follow the drilling vs boring distinction.

Is this what you mean? https://en.wikipedia.org/wiki/Boring_(manufacturing)

So are you saying to put in a basically different bit for the final pass?

[propeine]

I'm not much of a machinist. I don't follow the drilling vs boring distinction.

Is this what you mean? https://en.wikipedia.org/wiki/Boring_(manufacturing)

So are you saying to put in a basically different bit for the final pass?

Drills "walk" or follow holes which are not necessarily concentric to the axis of rotation. They also have a tendency to make triangular holes.

Yes that would accurately describe boring. I take it you aren't planning on using a lathe to do this? Can you single point threads or are you planning on buying a tube and using freeze plugs or something.

[DanielWilson]

Yes, I intend to buy a tube and do a stepped baffle involving some fender washers and some drilled round bar stock. I have a drill press and a welder, but not a lathe.

I was thinking of a monocore design earlier, but I think I can do something lighter with the tools I have. Perhaps I need to allow higher tolerances on the bore due to imprecision, but careful measure, marking, centerpunching and drilling small holes and enlarging a step at a time are skills with which I'm comfortable.

[DanielWilson]

I don't know. Maybe I should (once my Form 1 comes back) buy "solvent trap" parts, drill them where they're punched, and call it good. I just figure I have the opportunity to work what metalcrafting skills I have a little harder than that.

[propeine]

Work with the tools you have available...I would have larger reamers/drill bits at your disposal though just in case. .060 total seems to be the rule of thumb when everything is concentric. I have no idea what the freeze plug guys run for clearances but I would think larger. Especially if you're making a welded can.