Range Report/Chronograph Numbers

[Hondo 60]

Went to the range today with 3 guns and 1 recipe.

.38 spl +P (5.0 gr of Titegroup under a 125 gr HSM-HP bullet).

The 3 guns were:
a S&W 10-5 w/4" barrel
a S&W 36 no dash w/2" barrel
a Ruger SP101 w/ 2.25" barrel.

My chronograph said the 10-5 ranged from 956 - 1013
the SP 101 from 915-961
and the M36 from 841-893

Seems odd to me that both of the 2" barrels were so different from each other.
Since I don't cast, I've never slugged the barrels.
Perhaps this data would make more sense if I did.

 

[1SOW]

I'm interested but just guessing.
You didn't give your chrono 'AVG' speeds. I assume you gave us the Extreme Spread.

Even so, there was a 74'/sec difference in the "avg's of the ES's". Not a huge difference but more than a normal ES in the "same bbl".. The minor bbl length difference and being snubbies may account for the spread.

Titegroup is fast, but with the light load is it positional in that big case?

 

[Eb1]

Could be difference in barrel and cylinder gap. Couldn't it?

 

[Hondo 60]

1SOW - Yes, I gave the extreme spreads - I didn't even look at avg.
Hodgdon's website says:

Unlike pistol powders of the past, powder position in large cases (45 Colt, 357 Magnum and others) has virtually no effect on velocity and performance.

Eb1 - Funny you should mention B/C gap!

In July 2010, I sent the M36 to S&W and one of the things they did was close the B/C gap some.
But they never did say what it was or what they set it to.

 

[cfullgraf]

Eb1 - Funny you should mention B/C gap!

In July 2010, I sent the M36 to S&W and one of the things they did was close the B/C gap some.
But they never did say what it was or what they set it to.

Get a set of feeler gauges and you can measure the barrel/cylinder gap yourself.

I have two 20" barrel ARs that the velocity differs by 200-300 fps (8-10 percent) with the same load. Firearm variances is one of the interesting aspects of reloading and shooting.

 

[poihths]

I think the answer may lie in more than one place.

1. The cylinder gaps may be different, as mentioned by others.
2. The difference in barrel length is 12.5%, which is not trivial.
3. If you are weighing charges in a truncating scale that reads to 0.1 grain, the scale will read 5.0 grains at any weight from 5.0 grains to 5.09 grains. If you're weighing on rounding scale, the scale will read 5.0 grains anywhere from 4.95 to 5.04 grains. Those errors are about both 1.8%.

If these errrors happen to be additive, the 8% or so difference between the two guns would not be unreasonable.