It's VERY mellow - more like a very hot 38+P loaded in 357 cases. Some data I've seen says that in 357 snubbies, it's barely breaking 1,000fps.
Which makes sense since it uses the same projectile as the 38+P version, with a huge gaping hollowpoint. Drive it too fast and even a Gold Dot can come unglued.
Now for the good news: it's exceptionally accurate. If I was doing hostage rescue, this would be THE top ammo I'd grab for. It did 2" groups at 25yds in my gun (4.68" Ruger New Vaquero) and the recoil felt only marginally more than the 38+P version I shot in the same session (which grouped 3" at 25yds). At that time I still had the stock checkered plastic grips, and shooting some Doubletap 125gr @ 1,600fps in the same session was downright painful (and grouped 5"...). The 135gr "357s" were pussycats by comparison and *remain* the most accurate load I've fed that NewVaq.
They may not be "power kings" but expansion failure is highly unlikely. They're a good urban defense load and superb for any situation where overpenetration is a bad thing.
You do need to check accuracy and "where they print" issues in your gun. But Gold Dots tend to be accurate, big JHP cavities tend to be accurate, and moderate power tends to be accurate, across all loads and calibers. These may be right smack in a lot of gun's "sweet spots".
Don't take 'em into the woods and expect to stop a bear though
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