Interesting Study

[1911Tuner]

Control subject: 5-shot RG .38 Special revolver with 2.1 inch barrel. (Rifled length)

Test subject. 5-Shot RG .38 Special revolver with 5/8ths inch of forcing cone only. All rifling in the cone was honed to provide .001 inch land/groove depth in order to prevent bullet tumbling across chronograph skyscreens.

Bores slugged and measured. .002 inch difference, with the tighter bore diameter belonging to the test gun.

Barrel/cylinder gap adjusted to within .001 inch. Adjusted barrel was lightly countersunk to remove burrs and toolmarks. Average BC gap...approximately .028 inch. (Ouch!)

Ammunition: Standard velocity 158-grain lead RN. 5 rounds per gun chronographed.

Control subject: Average 586 fps
1. 593
2. 578
3. 582
4. 588
5. 587

Test subject: Average 557 fps
1. 568
2. 546
3. 551
4. 553
5. 545



A disinterested 3rd party was employed to fire the two revolvers blind, in a back-to-back test to see if there was any discernible difference in felt recoil. He reported that there was very little difference, and indicated that the test gun's recoil may have been slightly sharper. The test was repeated three times, and he picked the test gun as producing sharper recoil all three times. He emphasized that the difference was slight...but that there was a detectable difference.


Phase two of the experiment will entail another chronograph test of 10 rounds in the control gun, followed by a second 10-round chronograph test of the same gun with barrel parted off to 5/8ths inch of forcing cone w/ full depth of rifling intact...lightly countersunk to remove toolmarks.

Stand by...

 

[Jim K]

Am I correct in thinking that the purpose of the test is to determine if recoil is dependent on chamber pressure resulting from friction in the barrel?

Jim

 

[1911Tuner]

Am I correct in thinking that the purpose of the test is to determine if recoil is dependent on chamber pressure resulting from friction in the barrel?

Nope. The purpose of this one was to show that nearly all of the velocity and recoil impulse occurs within the first half-inch of bullet travel.

 

[1911Tuner]

Interesting though, that it works out to about 18 fps per inch of barrel...methinks. About half of the accepted 35. My bet is that, with full depth of rifling in the short forcing cone, that velocity will be too close to the same to call.

By the way, Jim. We've duplicated your blocked bullet demo without firing a shot...with predictable results...and Caldwell intends to dupilcate it in its original set-up as soon as he gets outta here and back to Louisiana. Report coming soon.