30mm Breechloader - Page 3 - Graybeard Outdoors
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post #21 of 47 (permalink) Old 05-08-2019, 01:59 AM
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You could loop a piece of rope around the rear of each wheel to prevent them from rotating. Then the friction with the ground would lessen the recoil distance. Or you could use the chains, although they would tend to scarf the wheels more.


What is the charge? Since you have the muzzle end of the barrel, the twist is going to be the greatest. Since the GAU-8 is designed for depleted uranium projectiles, the twist is going to be a little less than optimum for lead, but my guess is that the standard projectile is longer than yours so that may not be the problem.

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Last edited by GGaskill; 05-08-2019 at 02:03 AM.
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post #22 of 47 (permalink) Old 05-08-2019, 11:04 AM Thread Starter
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Originally Posted by carbineone1964 View Post
Forgot one other thing. I think someone asked this. What sort of lead do you use. I use wheel weights for my Hughes and this one. Might experiment with some lighter loads also. That may help stabilize them better.
I was using pure lead, so it would have been pretty soft. I need to see if I can find some wheel weight scrap and then get a pot to clean it up in.
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post #23 of 47 (permalink) Old 05-08-2019, 11:08 AM Thread Starter
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Quote:
Originally Posted by GGaskill View Post
You could loop a piece of rope around the rear of each wheel to prevent them from rotating. Then the friction with the ground would lessen the recoil distance. Or you could use the chains, although they would tend to scarf the wheels more.


What is the charge? Since you have the muzzle end of the barrel, the twist is going to be the greatest. Since the GAU-8 is designed for depleted uranium projectiles, the twist is going to be a little less than optimum for lead, but my guess is that the standard projectile is longer than yours so that may not be the problem.
The charge I was using was roughly 1 ounce of cannon grade Goex.

As to preventing the carriage from rolling, I don't know if it's that big a deal. As long as I have the space, I would think it would be easier on the carriage to let it roll back, rather than trying to lock it in place and have it jump. But I might be wrong.
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post #24 of 47 (permalink) Old 05-17-2019, 10:10 AM Thread Starter
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Whelp, I got the gun out to a buddy's place to chrono the gun yesterday, with the need (more exact) 1 oz charges I made, using a scale. Sadly, thanks to a rapid moving thunderstorm, it was too dark for the chrono to work. So maybe next time.

Still, though, we seem to have validate that it is indeed keyholing. Unfortunately, I still couldn't reclaim the projectile, so I don't know what it's doing. These are still the soft lead ones. I'm still sourcing some wheel weight lead that should be a bit harder to see if that makes difference.

Also, this video seems to make it clear that this gun is jumping a decent amount when it fires. So I might need to drop the charge even more from 1oz... or maybe think about putting together a welded steel carriage (which is a shame, as Bruce did a great job on this one) to give it more weight.

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post #25 of 47 (permalink) Old 05-17-2019, 10:42 AM
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With that much recoil and keyholing, could you slug be to long and heavy?
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post #26 of 47 (permalink) Old 05-17-2019, 12:05 PM Thread Starter
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With that much recoil and keyholing, could you slug be to long and heavy?
Well, for the barrel itself, I donít think so:

The standard ammunition mixture for anti-armor use is a five-to-one mix of PGU-14/B Armor Piercing Incendiary, with a projectile weight of about 14.0 oz (395 grams or 6,096 grains) and PGU-13/B High Explosive Incendiary (HEI) rounds, with a projectile weight of about 13.3 oz (378 grams or 5,833 grains).


But, honestly thatís for the full 30x173 round firing at like 3300 FPS.

Iím not really sure how to refacture for what is likely a much shorter projectile going much slower.
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post #27 of 47 (permalink) Old 05-17-2019, 12:38 PM
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Carbineone mentioned the gain twist. Helpful to measure, then compare with other barrels? Cut the load in half, look for keyhole?

Edit. To DD’s point. What does the projectile weigh? Went back and looked but didn’t see a weight. May have missed it.

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post #28 of 47 (permalink) Old 05-17-2019, 01:57 PM Thread Starter
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Carbineone mentioned the gain twist. Helpful to measure, then compare with other barrels? Cut the load in half, look for keyhole?

Edit. To DD’s point. What does the projectile weigh? Went back and looked but didn’t see a weight. May have missed it.
It's about 14oz. I can try to weigh a couple with my new scale (had to get one that could handle cannon range weights ) and get a more precise number.

Last edited by beowulf_grendel; 05-17-2019 at 02:06 PM.
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post #29 of 47 (permalink) Old 05-17-2019, 04:24 PM
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Quote:
Originally Posted by beowulf_grendel View Post
Well, for the barrel itself, I donít think so:

The standard ammunition mixture for anti-armor use is a five-to-one mix of PGU-14/B Armor Piercing Incendiary, with a projectile weight of about 14.0 oz (395 grams or 6,096 grains) and PGU-13/B High Explosive Incendiary (HEI) rounds, with a projectile weight of about 13.3 oz (378 grams or 5,833 grains).


But, honestly thatís for the full 30x173 round firing at like 3300 FPS.

Iím not really sure how to refacture for what is likely a much shorter projectile going much slower.
And how long was that barrel and how much did that gun weight?
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post #30 of 47 (permalink) Old 05-17-2019, 04:35 PM
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If you will look at our sticky at the top of the board on safe loads and construction you will see the maximum recommended safe load for 30mm (1.181") is 200 grains of FG.

Try that and see if you have better luck. If you are shooting a lead projectiles with 1 oz of powder in a rifle bore then most likely your projectile is just stripping down the bore.

The rule of thumb for building cannons load is to start ridiculously low. Try a starting load of 100 grains and work up in say 5 grain increments.

I am surprised with the heavy charge and heavy projectile, that you didn't break something.

Last edited by double d; 05-17-2019 at 04:42 PM.
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