"Slow" M66-3

[mckenney99]

Just a couple of interesting findings after running several different types of ammunition through several different snubby revolvers using my new Garmin Xero C1 chronograph.
I have been testing ammo through my old 2 3/4 in .357 Ruger Security Six, a (new to me) 2 1/2 in. S&W M66-3 and a 2 in. S&W M64-2 (also new to me).
My testing has involved 158 gr FMJ/PFP (factory & handloads) and LSWC (handloads) and 130/132gr FMJ Federal & PMC factory ammo.
In each case the S&W M66-3 has consistently been running velocities 60-80+ fps slower than the Ruger Security Six with each ammunition. In a couple instances it has even been running right at or within 10/20 fps of the 2 inch M64-2.
I guess I just have a "slow" M66 and it just shows that sometimes having more information creates more questions than answers.

 

[jtcarm]

Measure your B/C gap.

 

[SGT ROCK 11B]

The Speer Manual had a Section with a great explanation on why two identical revolvers will have different velocities. I had a four inch Model 19 that always posted higher velocities than six incher.

 

[stansdds]

Barrel-cylinder gap has a very small impact on velocity. What makes a larger impact on velocity would be barrel internal dimensions and surface smoothness.

 

[Alk8944]

Just one example. I had a revolver with a B-C gap of .012". I set the barrel back to a gap of .002" and saw exactly zero improvement in velocity. As some one said above, B-C gap has little to do with velocity, other factors you can't even measure are what make the difference.

If you want to see an interesting comparison of revolver vs. cartridge velocity differences look at the #9 or #10 Speer manual.

 

[Rock185]

FWIW, I've been chronographing for a very long time, using Oehler, PACT and now a Garmin chronograph. I've had both semi-autos and revolvers that produced slower, or faster, velocities than might be expected as compared with other firearms of similar barrel length.

The Speer article referenced by SGT ROCK contains a good explanation of the variables that influence velocity. It is available online.

 

[jc2721]

If your 66 2.5 inch shoots as well as mine does a little velocity loss wouldn't bother me at all.

 

[stansdds]

30 years ago I chronographed identical ammo, both factory and my reloads, from a 6 inch Ruger GP-100 and an 8 inch Dan Wesson model 15-2. I expected higher velocity from the 8 inch Dan Wesson, but the chronograph indicated only a 30-50 fps velocity advantage from that 8 inch barrel.

 

[Bullseye Smith]

No one ever thinks about blow-back in the cylinder, the barrel gap has nothing to do with it, but the head space may be the leak. But that amount isn't enough to even think about.