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Hi-Velocity Lube Shoot-out in 7-30 Waters

Posted: Sun May 19, 2013 1:29 pm
by mtngun
Today I was testing 2 things at once -- an experimental bullet in the 7-30 Waters Contender carbine, and a lube shootout with the same experimental bullet.

The bullet, 7EL5, is a weird design with a boo-boo on the nose. It only has one 0.286" band, all the other bands are 0.279". The nose boo-boo is merely cosmetic so I decided to go ahead and shoot it.

There were intermittent sprinkles so the chronograph was covered with plastic. To my surprise, the chrono worked fine despite the gloomy light.

Specs for today's loads:
-- oven treated WW + tin
-- sized 0.2855"
-- all but one groove filled with lube (not sure that amount is optimal, but that'll have to wait for another test)
-- COL 2.595", seated just deep enough to reliably close the action
-- 42.2 grains WW760 for HVR and HVR+moly. The velocity was a bit low so I upped the charge to 42.6 grains for Carnuba Red.
-- WLRM primers
-- Procedure was to clean barrel, shoot one fouling shot, then shoot five 3-shot groups without cleaning barrel

Accuracy Results
HVR = 2.51" average (2.5, 1.7, 3.9, 2.55, 1.9)
HVR+moly = 3.17" average (2.95, 5.85, 1.5, 3.85, 1.7)
Carnuba Red = 2.71" (1.5, 2.5, 1.35, 7, 1.2)

The differences in accuracy were not statistically significant. Also, there was no significant difference in accuracy between 7EL5 and the bullet I tested last week, 7EL4.

Carnuba Red shot the best group of the day, 1.2". However, each group with Carnuba Red seemed to have a different point of impact than the group before, so that was puzzling.

Velocity Results, including the fouling shot.
HVR = 2586 fps, 19 standard deviation (for all 15 shots)
HVR+moly = 2611 fps, 22 standard deviation
Carnuba Red (with 0.4 grains more powder) = 2619 fps, 27.5 standard deviation

Not much exciting to see on the pressure traces. I was aiming for around 42 kpsi but instead pressures were only about 40 kpsi, and velocities were lower than intended as well. Apparently the 1-driving-band bullet generates less pressure (and velocity) than a "normal" bullet. Here's a sample of HVR:

Here's HVR+moly:

And here's Carnuba Red:

My weird experimental bullet didn't shoot any better or worse than my previous bullet, and there was no clear advantage to any of the lubes. However, I'd like to do more tests before I draw a conclusion about the lubes.

Things to try next time:
-- recut 7EL5 with 2 additional driving bands.
-- tinker with the powder charge to get velocities back up to 2650+ fps
-- try lubing only the bottom half of the bullet
-- make a wider forearm for the TC
-- I need a better support for the butt of the rifle -- right now I am just using a wadded up coat.