My first attempt at gel testing, could use some constructive critisism

[Altair]

Well I have finally conducted my first gel test. I shot an 87gr HotCore from a .25-223 with a 16" barrel going 2723fps at impact into a 6"x6"x12" block. It was supposed to be longer but I the cardboard mold bowed at the center and shortened the block significantly. In the future, I'll be making my own mold so I can control the dimentions better.

Anyway, the first thing I learned is that a 6"x6" block is not big enough for rifle bullets. It didn't help that I failed to hit the perfect center of the block (didn't compensate perfectly for the close range) but I also think the max crack diameter for this round would have exceeded 6". As it stands, I don't know because the crack extended beyond the edge of the gel block. I used the 6x6 block because gelatin innovations sent me the 6x6 kit accidentally and told me to keep it so I figured I would try that one first so if I royally screwed up I wasn't really out anything. Here's what I found:

Neck Length = 0"
Max Cavity = 5 1/8"+
Length of Cavity = 12"+
Penetration = 12"+
BB @ 650fps penetrated 4 1/8"
(Most say + because the crack blew out the side of the block, as you'll see in the photos below)

The bullet fragmented and you can see frag along nearly the entire cavity. I caught the bullet after it fully penetrated the block using water filled jugs (I was hoping it would penetrate more than 12" so I anticipated this with the short block) and it had a separated jacket and core. That said, the jacket and core, as well as a lot of frag, ended up in the jug.

Overall, I have to say I'm impressed with this wildcat and load. I'm still new to gel testing, so perhaps I'm misinterpreting the results but it had zero neck length, the cracks (temp cavity) extended the entire length of the 12" block, and it penetrated more than the 12" minimum standard. This all looks pretty good to my relatively untrained eyes.

Finally, here are the photos:

Right Side
http://i710.photobucket.com/albums/ww103/aplorton/test1_right2.jpg

Top
http://i710.photobucket.com/albums/ww103/aplorton/test1_top1.jpg

Bullet
http://i710.photobucket.com/albums/ww103/aplorton/test1_bullet.jpg

Frag still stuck in jug (it was still wet and they wouldn't pour out)
http://i710.photobucket.com/albums/ww103/aplorton/test1_jugfrag.jpg

[DocGKR]

Glad to see folks testing stuff on their own.

First off, don't make molds. We use large Rubbermaid 66 liter storage boxes or similar containers you can find at Target, Wal-Mart, etc... Just pour the liquid gelatin into the bin; there is no need to spray with mold release or aerosolized cooking oil. Remember, it is important for the blocks to cool a MINIMUM of 72 hours prior to use. Our block size is approximately 16” x 20 “ x 6-12”(height is variable depending how much gelatin we pour into the bin) we usually prepare block weights from 40 to 80 lbs depending on caliber being tested. The 6x6x18 blocks are really best for pistol shots. We calibrate the gel blocks using a Crossman "Pumpmaster 760" air rifle to fire a standard .177 inch BB into the blocks. Both velocity and penetration are recorded. At a velocity of 590 f/s +/- 15 f/s, an ideal range of penetration is defined as 8.5 cm +/- 1.0 cm of penetration, although up to +/- 1.5 cm is considered acceptable if you want to use more relaxed guidelines.

[Altair]

Dr Roberts, I went back and sectioned the bock at approximately 2.5" intervals giving me 5 slices. I then measured the cracks at true length instead of estimating by looking through the side of the block. Here's what I got for actual measurements:

0" - 4 3/16"
2.5" - 5 1/4"
5.0" - 5 5/8"
7.5" - 4 1/4"
10.0" - 2 7/8"
12.5" - 2 1/4"

My initial measurements in the first post were from holding a tape measure up to the side of the block, which of course didn't measure the largest actual crack diameter. That didn't account for the hypotenuse, just 1 side of the triangle and an estimate at that.

Which measurement is the correct one to report? I want to make sure I'm posting accurate information. If the numbers I got after cutting the block are correct, this round may have some promise.

Here's a pic of the sections:
http://i710.photobucket.com/albums/ww103/aplorton/test1_slices.jpg

[DocGKR]

The one at 2.5" is probably closest to the actual max TC, however since your block was so small, the actual stretch may not be correctly derived. Keep in mind that there is a standardized methodology associated with crack measurements.

[Altair]

The one at 2.5" is probably closest to the actual max TC, however since your block was so small, the actual stretch may not be correctly derived. Keep in mind that there is a standardized methodology associated with crack measurements.

Where can I find the methodology? I can't seem to find it in the FBI information I got from Agent Boone.

[DocGKR]

It is not FBI, but JSWB-IPT. You might try starting here: http://www.dtic.mil/ndia/2004arms/session9/minisi.ppt.

[Altair]

Thank you for the info sir.

[drrufo]

Does the gel need to set under vaccum? Would the inclusion of air bubbles skew the results?

[Altair]

Does the gel need to set under vaccum? Would the inclusion of air bubbles skew the results?

It does not set under vacuum. I think air bubbles would skew the results but the mix is very thin when you pour it. I had no problem with air bubbles in the block.

They do provide a defoamer with the kit which I believe combats that specific issue.

[Zhukov]

Good job, Altair. You probably realize now why more people don't do this: It gets EXPENSIVE for the amount of gel needed to capture rifle shots. ;)

[Altair]

Good job, Altair. You probably realize now why more people don't do this: It gets EXPENSIVE for the amount of gel needed to capture rifle shots. ;)

It is definitely not cheap! It would help if the gel was reusable. The FBI doesn't reuse their gel blocks and I don't think Dr Roberts does but I'm gonna melt this one down and reset it just to see how consistent it is with the results of the first test. It won't cost me anything to see.

It will also help if I can find a block size that is a happy medium between the 6x6 and 10x10 by keeping volume down. I'm gonna look for some of the containers Dr Roberts mentioned above but the problem for me will be that the fridge I have is only 18" wide, meaning I need to find a container that is tall but somewhere in the vicinity of 8"x8". I'll see what I can come up with.

Is there any reason not to use a cylindrical gel block? An 8" cylinder would use less gel than a square but, provided I do my part and hit is in the center, it should react the same way right?

[Shawn Dodson]

I had three stainless steel gelatin molds fabricated by a local HVAC/sheetmetal shop (for about $75 each) to cast gelatin blocks in the following dimensions:

6x6x16 (9 liters water, 1 kg gelatin powder)
8x8x18 (18 liters water, 2 kg gelatin powder)
10x10x18 (27 liters water, 3 kg gelatin powder)

I had the molds constructed so the surface of the gelatin solution is 1.5 inches below the rim of the mold.

After some experience with the other two molds I modified my plans for the 8x8x18 gelatin mold to have the walls gradually taper, increasing in width from bottom to top to facilitate ease of gelatin block removal. The other two molds have a straight wall design which frustrates removal. The 8x8x18 became my favorite (handgun and .223/5.56). I used the largest mold for large caliber rifle cartridges. I rarely used the smallest mold.

I think the biggest issue with casting a cylindrical block of gelatin (using PVC pipe or something similar) is being able to remove the gelatin from the mold without damaging it.

[DocGKR]

While we generally don't do this more out of convenience, gelatin can be re-used--you have to remove all the fragments and SLOWLY re-heat. A double wall steam kettle works well.

Not only is a cylindrical block hard to remove from a mold, it want to roll off the table...

[decodeddiesel]

Glad to see folks testing stuff on their own.

First off, dont' make molds. We use large Rubbermaid 66 liter storage boxes or similar containers you can find at Target, Wal-Mart, etc... Just pour the liquid gelatin into the bin; there is no need to spray with mold release or aerosolized cooking oil. Remember, it is important for the blocks to cool a MINIMUM of 72 hours prior to use. Our block size is approximately 16” x 20 “ x 6-12”(height is variable depending how much gelatin we pour into the bin) we usually prepare block weights from 40 to 80 lbs depending on caliber being tested. The 6x6x18 blocks are really best for pistol shots. We calibrate the gel blocks using a Crossman "Pumpmaster 760" air rifle to fire a standard .177 inch BB into the blocks. Both velocity and penetration are recorded. At a velocity of 590 f/s +/- 15 f/s, an ideal range of penetration is defined as 8.5 cm +/- 1.0 cm of penetration, although up to +/- 1.5 cm is considered acceptable if you want to use more relaxed guidelines.

Good Stuff Doc!