Moly muzzle velocity - a puzzle

[Patrick Chadwick]

Gentlemen, I have a puzzle.

Having just experienced a disaster at a no-sighters competition, where my "correction" from 100 to 300 meters for my Long Range Sharps put the shots over the top of the target, I finally abandoned mental arithmetic and bought a chronograph.

After establishing that the Sharps was indeed pushing out the bullets a lot faster than I had thought, I turned my attention to my Eddystone M1917. As this is the next rifle to be used first at 100 then at 300 (sighters allowed, but you just haven't got time for more than a couple!) I wanted to get the correction right before travelling.

I recently mistakenly ordered a packet of the 168 gn uncoated Lapua HPBTs, when I should have ordered the moly coated variety. As I had already opened the packet I could not send them back, so I tried using a moly spray can to coat them myself. The results looked rather rough, and so I polished the bullets lightly before shooting, thus removing most of the expensive coating I had sprayed on. As I cannot afford to throw them all away, I have been using these self-coated bullets for practice. They do not seem to group quite as well as the factory-coated bullets (no surprise).

The surprise came when I chronographed the two varieties. Please note that the cartriges were identical in every respect apart from one group being factory-coated and the other being spray coated.
The results for two 5-shot groups were:
Lapua Silver Jacket (factory coated) 828.5 - 838.1 m/sec
Lapua spray coated and lightly polished 837.2 - 843.5 m/sec
The groups are too small to make great statistical deductions, but
a) all spray coated and lightly polished bullets were faster than all the factory coated bullets.
b) Statistically weak, I know, but the variation was smaller for the spray coated group than the factory coated group.

These results are not what I had expected. My hypothesis at the moment is that the light polishing improved the surface of the spray coated bullets quite considerably.

Any comments or alternative explanations?

Patrick

Information

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[Parashooter]

Effective anti-friction coatings reduce the bullet's resistance to entering the bore and therefore give less pressure and velocity with the same powder charge. The factory bullets are slower because they have an effective coating compared to the spray junk.

If you want to apply moly yourself, try the dry powder in a tumbler with steel shot. See http://www.6mmbr.com/bulletcoating.html for more information but don't get the idea that it's a difficult or technically challenging job.

[Patrick Chadwick]

Thanks Parashooter, that explains it!

Patrick

[John Kepler]

Just giving a "ditto" to Parashooter's post. Your numbers are about what you'd expect between a coated and uncoated ball....the coated ball will be moving slower. Yeah, I know....counter-intuitive as all hell, for the reasons that were stated! On the "up-side", and while your data field was probably too small to show it....your coated velocity numbers, while lower overall...will be more consistent than uncoated.

FWIW, I've been impact plating my own bullets very effectively for years...as Parashooter explained, it isn't rocket science and the results are worth the small additional investment in time and equipment.

[Matt Anthony]

On cast bullets I use the Lyman spray moly along with the Lyman bore cream. I have found it be perfect for cast bullets as I do not like to vibrate cast bullets after they are sized and have a gas check on them.
I don't consider the Lyman spray moly junk, when applied properly it works just like the impact applied products. The key is to have the bullets free of any grease or oil and let them dry overnight before seating.

[Jim Tarleton]

Just a question, but why use moly when Gunjuice is available? You only have to Gunjuice your barrel once, versus coating every bullet.

Jim

[John Kepler]

Because "Gunjuice" works about as well as "Sham-Wow" and "Veg-O-Matic" does in the "real world"!

[Jim Tarleton]

That was funny. If I Sham-Wow the bullets after Gunjuicing, will it improve velocity even further?

If you fire rounds from a machine rest, which eliminates recoil effects (muzzle jump), a bullet with a higher muzzle velocity will have a higher POI than an identical bullet of a lesser muzzle velocity at 100 yards. Now if I understand the postulation, if I fire identical rounds from a shoulder held rifle, the slower bullet will have the higher POI. The recoil effect (muzzle climb) will overide the natural tendency for the faster bullet to impact higher than the slower one. This cannot always be true, since we begin with a faster bullet impacting higher than the slower bullet, and recoil effects depend on recoil force. My question is: How the dickens do you know which effect is in command?

I have used Gunjuice (many times), and the POI of my 38-55 Marlin 93 rose 12" at 100 yards. I had to replace the front sight to get POI on Bullseye. According to my Chrono, the velocity of the bullet actually increased, so you see my delimma. I had a faster bullet, with velocity due to reduced friction, that impacted substantially higher at 100 yards than previous to Gunjuicing.

Am I missing something here? Seriously, I am confused on this issue.

Jim

[John Kepler]

You assume a "single-variable" system that is acting linearly with a valid testing protocol....it isn't! There are multiple variables that you are not accounting for, the interactions are far more complex than you think, and you are making assumptions in your testing design that you take as valid that likely aren't.

Hint: Your test design protocol is significantly flawed: The 100 yd POI isn't occurring at the apogee of the bullet flight trajectory! Wanna see the test? Check out the POI at 100 yds for a rifle zeroed at 300....the POI at 100 yds DROPS with increasing velocity! For your testing system to provide meaningful data, your best bet would be to bore-sight the rifle on the 100 target, then shoot and record!

[Jim Tarleton]

John,
I am assuming your response was in reference to my post. If not, forget this post.

I am very aware of the integrated events that occur when a round is fired. There are so many variables it is necessary to make some assumptions. Barrel harmonics plays an important role with at least two harmonics involved. Case capacity, bore diameter, barrel diameter, barrel taper, fluting, bullet weight, friction energy (3% of heat generated), heat transfer to barrel (30% of heat generated), muzzle blast (40% of energy generated), overcoming bullet inertia, (20% of heat generated), rotational kinetics (2% of heat generated), temperatures, powder grain structure, burn rate, and others.

So, yes, I comprehend internal ballistics, but I am no expert in the field. I often read about slower bullets (all other variables equal) hitting higher on target than those of a faster velocity. I have heard the oft repeated references to revolver phenomenon with heavier bullets striking the target higher. I might be so bold to point out that revolvers have two recoil componenets, the original blast in the cylinder and the forces surrounding the barrel cone. I can see recoil having an effect and throwing slower slugs higher. No so in rifles. There may be some circumstances where a combination of variables rsults in a slower velocity bullet hitting the target higher than one of a greater velocity, but it will not hold in all cases - period.

One cannot say that slower velocities result in higher strikes at the target across the board. Barrel harmonics can easily over ride recoil effects. Thin barreled rifles of small caliber for instance. Will a 22 short hit the target higher than a 22 LR fired from the same firearm? I don't think so, but I haven't actually made that test.

At around 3000 fps, a bullet is in a 24" barrel about 0.0002 milliseconds, give or take a few fractions of a milliseconds. Depending on the weight of the rifle, the caliber and weight of the projectile, and the barrel design (fluted, tapered, no taper bull), barrel harmonics can be dominate over recoil effects. and throw bullets higher or lower, but in general, I would have to say that the faster the projectile, the higher on target it will hit, assuming the POI of the higher velocity projectile is dead center of the bull at 100 yards.

One example, although extreme, is a 105 howitzer. At the same elevation, a charge 7 round will travel further than a charge 3 round, and be at a higher elevation than the slower charge 3 round at any point from from muzzle to impact.

Jim