38 Special Super Police Problems- Need Help

[Sixgunner]

For hoots and hollers I decided to try to replicate the 38 Super Police load. From what I've read it seems that factory ammunition ran about 700fps from a 4" barrel. Here is a rundown of what I have obtained using a 4" 67 S&W and a NOE 200gr LRN boolit:

Bullseye, 3.0gr= 585fps
Unique, 3.5gr= 570fps
IMR 4227 9.2gr= 640fps
Blue Dot 5.3gr= 570fps
2400 6.5gr= 530fps
2400 7.0gr= 580fps

All loads were RP 38 Special Brass, CCI 500 primers. The velocities are an average of 10 shots using a Beta Chrony at 12'. I seem to be quite a bit lower in the velocity than the load data (mainly LEE) would suggest. Any ideas or tips to reach that 700fps would be appreciated. Thanks.

[runfiverun]

correct for the 12' and your only about 50 fps away.
try some 4227, 8.5grs would be max 7.8 to start. [not a +p load]
I'd imagine the top side would be close.

[beagle]

Check castpics/Cast in the .38 Special article and that will give you some loads in that range./beagle

[Outpost75]

Check the cylinder gap on your S&W, I get higher velocities with those same loads out of my 2" Colt, which has 0.004" pass, 0.005" hold with rear gage in place.

[Sixgunner]

Checked it. .011" That kind of surprised me but it was a police trade in.

[Outpost75]

Checked it. .011" That kind of surprised me but it was a police trade in.

That is 0.005" above mean assembly tolerance and 0.003" above customer service max. for a used gun.

You should have the barrel set back a thread, reface the barrel extension to establish gap at minimum pass 0.003" where you can insert a .003 feeler gage through the gap so that it protrudes out both sides, and be able to pull the cylinder through a full revolution, all six chambers with no felt resistance.

This is the "pass" dimension.

With empty cases in the chambers, and inserting a feeler gage, you want to be able to insert no greater than a 0.006" feeler gage where it will go through, but then you are unable to pull the cylinder through in DA. This is called the "hold" dimension.

The difference between the "hold" gage, the largest blade feeler gage you can insert through the cylinder gap with brass in the chambers, and the size you can insert when having no brass in the chambers, so that the front gage is pushing the cylinder back, is the amount of "end shake." If this end shake measurement exceeds 0.002" you want to either have the crane stretched or have an endshake bushing fitted. In normal service the crane can only be stretched twice over the life of the revolver before you need to fit a new one. That's why endshake bushings are generally preferred.

[runfiverun]

good catch Outpost.
once I re-read his post [and compared my data to his] I should have seen his numbers were waaay off.

[Outpost75]

As an good approximation in .38 Special with standard pressure lead service loads the delta-V is about 10 fps for each 0.001" increment change in cylinder gap from a mean assembly tolerance of 0.006". It is therefore completely normal for a 2" gun at minimum assembly tolerance, having a 0.003" pass dimension to give velocity higher than a 4" gun having a maximum customer service 0.008" gap.

[tazman]

I have a question that is a little off topic. Does that excessive cylinder gap cause poor accuracy and inconsistent performance? Or does it just effect velocity?

[runfiverun]

it give the gun more chance to mess up the base of the boolit.
so yeah.

[Lead Fred]

Elmer Keith's FBI load was his 158gr hollow point, and 5.0 to 5.2gr unique.