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Strange chrono results with .38 Short Colt?


Fishbreath

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I'm setting up to reload .38 Short Colt for next year's revolver season, and had some unexpected data from this first chrono trip.

 

I loaded 158gr Berry's plated bullets with a moderate crimp from the Lee 9mm factory crimp die, on top of charges from 2.2gr to 3.6gr of Bullseye, increasing in 0.2gr steps, some with Federal magnum small pistol primers, and some with Winchester small pistol primers, for an OAL of 1.15". The eyebrow-raising findings were as follows:

 

1. Measured velocity was almost exactly the same as with my .38 Special loads, despite the dramatically smaller case—3.4gr came in around 800fps on average, 3.6gr at about 840fps, while my .38 Special loads with 3.6gr chronoed at around 840fps on their initial test and at my last major match. I wouldn't have expected the charges to be so close for similar velocities—is that a case of mistaken expectations on my part, or actually unusual?

2. The magnum small pistol primers resulted in lower velocities than I got with the standard small pistol primers, by an average of 3-5%, which seems very odd indeed. I only got them because I couldn't find anything else suitable for light-trigger revolver use, so I guess I'll switch back to standard small pistol primers when I can? I only had a few rounds of each to try, so I can't say it's totally statistically significant, but it does seem at least suggestive.

 

Beyond the primer differences, which I can't explain whatsoever, there are a few confounding factors for the .38 Special vs. .38 Short Colt differences.

 

1. Temperature. It was 66 degrees at the range today, against 90 or so when I was testing these loads, and in the 80s at the last major match. I had a few of my chrono samples from that match left over in my bag, and all of them clocked between 820 and 830fps. The temperature might explain a good part of the surprisingly low velocity out of the Short Colts.

2. Crimp. The .38 Special was heavily roll crimped into a crimping groove, against a moderate taper crimp on this new ammo. How much of a difference does that make?

Edited by Fishbreath
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One thought on the differences with magnum primers is the real possibility that the magnum primer actually has enough umph to push the bullet a fraction further before complete powder ignition which increases capacity, lowers pressure and lowers velocity.  Kind of like increasing the free bore on a rifle so you have more volume for the powder.  Ultimately allowing for a higher velocity at the same pressure due to more powder in a larger case.

 

Also on the crimp you can run into similar issues, depending... I've not had any luck using the 9mm Lee Factory Crimp in 38 short colt especially with a plated bullet.  Remember the Factory Crimp Die actually sizes down the length of the bullet, which can then lead to a looser bullet to case fit also increasing bullet jump on ignition leading to lower velocities.

 

If you combine both of those issues it may explain your results.

Try a regular taper crimp, being careful to not pierce the plating, and I've had best luck at 1.180" oal with 158 to 160 grain bullets.

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13 hours ago, Fishbreath said:

Thanks for the tips! The magnum primer thought certainly seems plausible.

 

At present, I only have factory crimp dies, in 9mm and .38 Special. Do you have any recommendations for an ordinary taper crimp die?

I'm using a standard 9mm taper crimp die from Dillon.  Has more taper at the base than some others and I really like being able to pull the clip and drop it out of the Die Body.  I also Taper Crimp to around .370" for 38 short colt and .358 bullets,  Also crimp my 9mm's to .370".

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I was okay at 1.15", with clean-dropping moon clips, but there were slight bulges. I backed them out to 1.18", and those are perfectly smooth for me.

 

Definitely something to watch out for as I try different bullet brands, though.

Edited by Fishbreath
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Mine would chamber individually, but not in a moon clip. Good thing I checked before I left for AZ.

 

They've got back to back revo matches in October. The ICORE Southwest Regional, and the Arizona State Revolver Championship. 

 

October 17/18

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