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

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

Postby mtngun » Sun May 19, 2013 1:29 pm

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.
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There were intermittent sprinkles so the chronograph was covered with plastic. To my surprise, the chrono worked fine despite the gloomy light.
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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
-- the HVR+moly was made by melting one stick of Rooster HVR with one teaspoon of moly powder

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.
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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.
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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
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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:
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Here's HVR+moly:
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And here's Carnuba Red:
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Conclusions:
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.

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mtngun
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Location: Where the Salmon joins the Snake

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

Postby mtngun » Sun May 26, 2013 6:49 pm

Today I was testing 3 things at once -- another experimental bullet in the 7-30 Contender, a different powder charge, and a lube shootout.

Today's bullet, 7EL6, is just 7EL5 with the bottom band enlarged from 0.279" to 0.286". Also, today I did not put lube in the top two grooves.
Image

The powder charge was upped from 42.2 grains last week to 42.9 grains this week. I had to compress the powder more than I prefer, and even so, velocities were still a little low.

HVR + mica lube = 1 stick HVR blended with 2 teaspoons of motor mica

This chart shows the average velocity for each 15 shot string. I expected the mica to "firm up" the lube and increase velocities, but I didn't expect Carnuba Red to boost velocities -- last week it averaged a ho-hum 2619 fps with 42.6 grains. Hard to believe the extra 0.3 grains increased velocity 44 fps ??? I'm puzzled.
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All 3 lubes showed a tendency to increase velocity as more shots were fired. Is this because the barrel is "seasoning" with the lube, or is it because the barrel is getting warmer ? I don't know the answer yet -- more testing is required. :D

Standard deviations were: HVR -- 18, HVR & mica -- 20, Carnuba Red -- 21. No significant difference there.
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Accuracy took a turn for the worse with this bullet and powder charge. Since I changed the bullet and the powder charge at the same time, I'm not sure which is to blame ? But it's safe to say that adding the 2nd full diameter band to the bullet did not help. Perhaps it didn't hurt, but it sure didn't help.

For what it's worth, the HVR & mica lube "won" the accuracy contest, if you can call 3 MOA "winning." :D The accuracy difference between the 3 lubes was not statistically significant.
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No indication that fouling is a problem.
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HVR pressures = 41 - 43 ksi
HVR + mica pressures = 41 - 45 ksi (velocity and pressure increased as more shots were fired)
Carnuba Red pressures = 43 - 52 ksi (velocity and pressure increased as more shots were fired).

Conclusions:
-- The 2nd full diameter band did not help.

-- The increased powder charge may have hurt accuracy. This bullet does not want to give me the velocity I want (2650 fps) at the pressure I want (42 ksi). It seems like I am pushing it too hard and compressing the powder too much.

-- no huge difference between lubes. Adding some sort of dry powder, like moly or mica, seems to increase velocity a bit.

Things To Try Next Time:
-- return to a 1 full diameter band bullet

-- continue experimenting with adding dry powders to the lube

-- drop the bullet weight to 115 or 110 grains so that I can get 2650 - 2700 fps without excessive pressure and excessive powder compression.

-- let the barrel cool completely between 15 shot strings


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