I've been having fun with my newly threaded '92 in 38/357, and I decided to take a video to share with friends.  Upon the second (or so) viewing, I noticed that there is a significant amount of gas coming from the breech during firing.  I sincerely hope there is not a barrel problem (since I just spent a ton of money having it shortened, crowned, threaded, and re-dove-tailed for the front sight) and that, rather, there is simply not enough pressure to seal a 38 spl case to the chamber wall.  I'm going to attempt to post the video here.  But, does anyone have any experience with this?

38spl Suppressed

That seems normal for mine.  
Rossi 357

Mine is 44, but subsonic ammo doesn't seal.   The chamber  and outside of brass gets very dirty.

Straight wall cases in lever actions all leak, it is just the nature of the beast. That's why the originals were all chambered in tapered or necked cases. 44-40, 38-40, 32-20, etc.

Ok, good to know.  I assumed that this was the case, but it's definitely a "better safe than sorry" scenario.

Thanks all!

The sub sonic suppressed round folks are re-inventing the wheel and might benefit from some history.

Have you ever wondered why the old black powder cartridges like the .44-40, .38-40, .32-20, etc are all cases with significant taper in the body and a bottle neck, even a slight one?  Probably not.

The taper was there to ensure that the case extracted easily from a fouled chamber - a soon as the case is extracted even a little bit, the entire case wall is out of contact with the chamber.  What is significant here is that the chamber walls got fouled in the first place.    The above rounds all operated at somewhere in the neighborhood of 10,000 to 13,000 psi.   The pressure curves were much steeper than with modern smokeless powder, however the low operating pressures of black powder rounds would not have been sufficient to quickly seal the case to the chamber without a shoulder.   In the case of the short black powder rounds like the .38-40, 44-40, etc, they used a bottle neck on the case since the resulting shoulder gets forced forward and is much more effective in quickly sealing the chamber at low operating pressures.

The long, large bore cartridges like the .38-55, 45-70, 45-90, and 45-110 didn't exceed 26,000 psi, however, their pressure curves were again very steep compared to smokeless powder rounds and the pressures were nearly twice as high, so the straight wall cases still sealed pretty effectively.  However, they still had a generous amount of taper to ease extraction.

The .44-40, 38-40 and 32-20 all saw extensive use in lever action rifles during the black powder era, but the .45 Colt did not.  It only showed up in lever action rifles after the end of the black powder era.  That's because it is a straight wall case with no bottle neck.  Rather than tapering the case, they tapered the chamber by .007" (which is why brass life is short for .45 Colt, the base of the cartridge gets stretched a lot every time it is fired).  However, even with a tapered chamber, it was a bitch to extract since the chambers fouled significantly due to poorly sealing cases.  Extraction wasn't an issue in the Colt Single Action Army,  as it had a rod ejector that pressed the case out from the inside rather than relying on a rim.  And the .45 Colt was made for that pistol.  With the S&W Schofield revolvers, which used a star ejector acting on the rim, the US Army had to use a shortened version of the .45 Colt - the .45 Schofield.

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So...the take away on this is if you are using a cartridge that needs very low pressures under about 25,000 psi to keep the bullet subsonic, you really should be using a case with a shoulder in it.  If not, you are probably going to end up with gas coming back into the action due to poorly sealing cases - just like 140 years ago with black powder cartridges.

A Rossi 92 in .44-40 or .38-40 would be a near ideal suppressor host.  A .357 Magnum?  Not so much.

Lol good to know my suppressed 357 mag, 44 mag, 45 Colt and 45-70 guns are not good hosts.

I don’t think he understands that 38 spl is always subsonic. There is no “subsonic load.”  They all are. As for extraction issues: also non-existent. Several hundred rounds 38 spl through mine, uncleaned, and no failures to extract.

Remember Dakota is talking about the old black powder guns.  The amount of gas leakage you are seeing would have the chamber and bolt face covered with a thick layer of soot very quickly.

I understand just fine.  I didn't mention .38 Special at all, but I load .38 special 2000 rounds at a time - it's one of my go to cartridges, I probably  shoot more .38 Special than any other revolver cartridge (although .357 Mag and .45 Colt are close) and I'm very aware of it's velocity potential.  Saying it's never supersonic isn't correct.  A 125 gr .38+P load in a 6" barrel will go supersonic on a cold day.  A 110 gr bullet with 6.8 grains of CFE will go supersonic any day of the week - and it only generates about 17,000 psi.

Also the .38/44 was the predecessor of the .357 Magnum and it was basically a .357 Magnum pressure  load in a .38 Special case,  fired in an N frame revolver. The .125" longer case of the .357 Magnum came later to prevent folks from blowing up the K frame .38s of the era.

Some folks today will however go in the opposite direction and develop light loads in a .357 Magnum as the longer case feeds better in some lever guns, and some folks also get concerned about a carbon ring building up in a .357 chamber when .38s are shot extensively in it - although that's not a problem with regular cleaning after each range session.

What I'm pointing out is that if you're running the .357, .44 Mag and .44 mag at low pressures to get sub sonic velocities, you're going to get more leakage into the action than you would with one of the older bottle necked black powder cartridges, since they were designed to seal the chamber sooner at lower pressures that black powder produced - not more than about 13,000 psi for 30-40 grains of FFFg.

You've missed the point about the straight wall .45-70 operating at higher pressure (around 26,000 psi with black powder, and the SAAMI smokeless spec is 28,000 (which considers trap door loads and limits).  At substantially more than 13,000 psi the .45-70 does a much better job of sealing the chamber.

It also depends somewhat on the powder you use.  For example I use 9.6 grains of Unique under a 250 gr bullet for light black powder era equivalent .38-55 loads, in large part because the steeper pressure curve with the faster powder helps the bullet obturate faster, and also seals the chamber faster.  I use around 14 grains of Unique (and a poly quilt batting wad  to take up space in the case) for the same reason in 405 gr 45-70 loads to produce black powder era velocities while keeping the action clean.

Exactly.  There were no straight wall pistol sized cartridges used in lever guns in the black powder era due to the problem getting the straight wall case to seal in the chamber at pressures down around 10,000 to 13,000 psi.  The . 45 Colt, .44 Magnum, .38 Special/.357 Magnum are all modern post black powder era chamberings in lever guns.  The gas leakage that occurs is tolerable because of the smokeless powder used.

And why those cartridges have the notoriously thin necks that crush so easily during reloading.
MLG

All great info.

Now knowing that I intend to run only 38spl subsonic (I will use 357 for hunting at normal or +P velocities), do you have any suggestions on powders that might help "seal" the case against the wall of the chamber?  Or, is that pressure curve too high?  Would something super fast that burns in the first couple inches (still using a rifle-length barrel) help?  Or, would the pressure still drop enough to cause leaks?  Would bullet shape help, if it would fill the rifling grooves and cause a better seal with the barrel?  I'm looking to make this work the best way possible, and I'm not interested in "you chose the wrong caliber."  So, I'm sorry if I come across wrong.  That said, I'm always interested in learning more and fielding constructive criticism.

Better seal = quieter = more fun.  Anything to help, or suggestions for improvement are welcome.  I am a reloader, and I'm happy to run some tests on this setup, to possibly help someone in the future.

The only way for the cases to seal the chambers is through high pressure forcing the brass against the chamber walls.  As that also results in high velocities, your quest for a low pressure, low velocity rd that doesn't have blowby will be fruitless.