Hi Tek, enamel, polycrylic, polyurethane

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Hi Tek, enamel, polycrylic, polyurethane

Postby mtngun » Thu Nov 12, 2015 9:44 pm

More coating tests here.

The short version is that Rustoleum enamel did poorly, while polycrylic and Hi-Tek showed some potential.

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Re: Hi Tek, enamel, polycrylic

Postby mtngun » Sat Nov 21, 2015 7:06 pm

More coating tests here, at 2200 fps with plain base bullets.

Short version: both Hi-Tek and rattle can epoxy paint performed satisfactorily. Hi-Tek did equally well with or without lube. Hi-Tek did equally well with lino and with air-cooled wheelweight. Compared to uncoated bullets, accuracy with most coatings is better and more consistent.

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Re: Hi Tek, enamel, polycrylic

Postby mtngun » Sat Dec 05, 2015 5:14 pm

After having done more tests with coated bullets in the 6x45, I've started to form draw some conclusions on what works and what doesn't:

-- it seems you can use a softer alloy with coated bullets than with uncoated bullets
-- coating can improve accuracy in high velocity loads.
-- while the coatings have eliminated leading (so far), sometimes there is enough polymer fouling to cause fliers unless a lube is used in addition to the coating. Even a tumble lube seems to help.
-- shake-n-dry urethane or polycrylic seems to make a decent coating, and it's cheap and easy. Urethane is very sticky so it adheres well.
-- for the time being I will standardize on shake-n-dry urethane with some sort of lube.

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Re: Hi Tek, enamel, polycrylic, polyurethane

Postby mtngun » Fri Jan 08, 2016 3:43 pm

Well, I've done a lousy job of keeping this thread up to date, but I've been using the 6x45 Contender as a test mule for coatings, so you can find more deets on the 6x45 thread.

Last week I experimented with extra thick coatings (0.003") and to my surprise it hurt accuracy and in no case helped. Most of the thick coatings were tumbled so I'm going to guess that they were uneven in thickness which causes an imbalance and we know that imbalance hurts accuracy as laid out in Harold Vaughn's book.

Based on that theory, my next step is to focus on getting a uniform coating and a balanced bullet. So here are some measurements related to bullet out-of-roundness, I'll update this post as more data rolls in. If some of the data seems redundant it's because there's more than one batch.

3-coat poly spray, 62 gr. FB from wheelweight, average of 10 bullets randomly chosen from lot:
-- as-cast, 0.00029" out-of-round
-- after sizing, 0.0002" out-of-round and average diameter = 0.2451" (using homemade push-thru die).
-- after 3 thin coats of polyurethane spray, 0.00017" out-of-round and average thickness was 0.00055".

3-coat poly spray, 55 gr. GC from wheelweight, average of 10 bullets randomly chosen from lot
-- as cast, 0.00036" out-of-round
-- after sizing, 0.00012" out-of-round (using homemade push-thru die, sizing from approximately 0.246" to 0.245")
-- after 3 thin coats of polyurethane spray, 0.0002" out of round. Average thickness of coating was 0.0005".
-- Summary: the poly spray was 0.0005" thick, and may have increased out of roundness 0.00008". That's probably as good as your going to get with any coating.

Shake & Dry poly, 62 gr. FB from wheeweight, average of 10 bullets randomly chosen from lot:
-- unsized & 3 coats polyurethane shake-n-dry, 0.00081" out-of-round.

3-coat poly spray, 55 gr GC from wheelweight, the usual sample of 10 bullets from the lot:
-- this batch was sized 0.245" then oven treated 475F before coating
-- after 3 thin coats of polyurethane spray, 0.00024" out of round and average diameter 0.2469"
-- it seems the coating was a little thicker than normal on this batch at 0.0009".
-- I didn't measure out-of-round before coating but let's assume 0.00016"
-- Summary: the poly spray was 0.0009" thick and may have increased out of roundness 0.00008".

3-coat poly spray, 55 gr GC from wheelweight, the usual sample of 10 bullets from the lot:
-- this batch was sized 0.245" and left air-cooled. They were sprayed in the same batch as the above oven treated bullets.
-- after 3 thin coats, 0.00024" out of round and average diameter 0.2467"
-- the coating was a little thicker than normal at 0.0008".
-- I didn't measure out-of-round before coating but let's assume 0.00016"
-- Summary: the poly spray was 0.0008" thick and may have increased out of roundness 0.00008".

GENERAL SUMMARY ON POLYURETHANE:
-- these particular molds drop bullets that are 0.00029" - 0.00036" out of round.
-- this particular homemade push-thru die produces bullets that are 0.00012" - 0.00020" out of round
-- 3-coat rattle can spray gives 0.0005" - 0.0009" thickness.
-- 3-coat rattle can spray adds up to 0.00008" out-of-roundness.
-- 3-coat Shake & Dry adds 0.0008" out-of-roundness, or 10 times as much as rattle can poly.
-- for high velocity accuracy, the extra cost of the rattle can may be justified because it produces a more uniform coating.|

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Re: Hi Tek, enamel, polycrylic, polyurethane

Postby mtngun » Tue Jan 12, 2016 5:16 pm

Update: well, the nearly perfectly uniform sprayed polyurethane bullets (0.0006" - 0.0008" thick) did not shoot as well as the not-so-uniform shake-n-dry polyurethane bullets (0.0015" thick).

Theories:
-- 0.0006" thick poly is not thick enough to prevent melting and gas cutting?
-- when the shake-n-dry bullets were oven cured at 300F, they bubbled a little bit due to solvent trapped in the urethane layer. You can't actually see the microscopic bullets, but you can feel them as a rough surface. The bubbles would be a disaster for a furniture coating, but what if the bubbles are actually benficial to bullets? They might improve the insulating quality of the poly?

As usual we have more questions than answers. :lol: Anyway, more data on more batches:

62 gr. plain base with 2 coats shake-n-dry polyurethane, cured 240F between coats.
-- average thickness 0.0009"
-- out-of-roundness increased 0.00036"

62 gr. plain base with 2 coats shake-n-dry polyurethane, cured 240F between coats, then 1 coat VHT white epoxy, cured 160F.
-- average thickness 0.0013"
-- out-of-roundness increased 0.00037"

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Re: Hi Tek, enamel, polycrylic, polyurethane

Postby mtngun » Wed Jan 27, 2016 9:07 pm

As usual I haven't had time to keep up with this thread but you can follow my coating experiments on the 6x45 thread.

I happened to dump some polyurethane coated bullets back in the pot to be recycled and noticed that as the pot warmed up, the lead melted out of the polyurethane shell leaving the shell intact. The pot happened to be 640 F when I fished these out. I was impressed that it could survive at that temperature.
poly_shells_jan27_16.jpg
poly_shells_jan27_16.jpg (69.02 KiB) Viewed 6483 times


Later I tried adding coated bullets to the pot when it was 680 F, and the coating melted right away, so apparently it melts somewhere between 640 and 680 degrees.

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Re: Hi Tek, enamel, polycrylic, polyurethane

Postby mtngun » Fri Jan 29, 2016 2:25 pm

More data on coating thickness and out-of-roundness from my latest batches:

3 coats polyurethane shake-n-dry, the usual average of 10 bullets
-- 0.2451" with 0.0002" out-of-round after sizing
-- 0.2466" with 0.00026" out-of-round after coating
-- worst out-of-round was 0.0006" after coating
-- average coating thickness 0.00075"
-- average increase in out-of-round 0.00006"

a different batch of 3 coats polyurethane shake-n-dry, average of 10 bullets
-- 0.2451" with 0.0002" out-of-round after sizing
-- 0.2462" with 0.00036" out-of-round after coating
-- worst out-of-round was 0.0012" after coating
-- average coating thickness 0.00055"
-- average increase in out-of-round 0.00016"

2 coats spar urethane, average of 10 bullets
-- this stuff is slow to dry, which is a drawback for the shake-n-dry method
-- 0.2451" with 0.0002" out-of-round after sizing
-- 0.2460" with 0.00066" out-of-round after coating
-- worst out-of-round was 0.0017" after coating
-- average coating thickness 0.00045"
-- average increase in out-of-round 0.00046"

Observations and Conclusions:
--- 3 coats shake-n-dry polyurethane does not hurt the out-of-roundness much on average, but ..... some individual bullets have significant out of round, which may cause fliers.
-- the spar urethane dries slowly, which in addition to being inconvenient also results in a less uniform coating. Nonetheless I wanted to try it to see if it made any difference. Spar urethane is more flexible than standard urethane.

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Re: Hi Tek, enamel, polycrylic, polyurethane

Postby mtngun » Sun Feb 14, 2016 1:45 pm

3 coats water-based Varathane polyurethane, mixed half & half with acetone. Shake & dry. Average of 10 bullets:
-- out of roundness increased 0.0001" (0.0002" after sizing, 0.0003" after coating)
-- worst out of roundness 0.0005"
-- average thickness 0.00045" (perhaps a little thin yet)

3 coats water-based Varathane polyurethane, mixed half & half with water. Shake & dry. Average of 10 bullets:
-- out of roundness increased 0.00034"
-- worst out of roundness 0.0010"
-- average thickness 0.00055"


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