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Airgun .308 bullet shape - Mountain Molds

Airgun .308 bullet shape

Pinzgauer
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Joined: Tue May 27, 2008 7:31 am

Airgun .308 bullet shape

Postby Pinzgauer » Sun Dec 14, 2008 8:48 am

What do you all think of this bullet shape for low energy applications.
90 gr secant spool cropped bullet.jpg
90 gr secant spool cropped bullet.jpg (12.5 KiB) Viewed 7587 times

The nose is a secant, the bands at the base and nose are 0.050 inches wide to allow easy engraving of the rifling. They will be cast in pure lead.

Mike

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mtngun
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Re: Airgun .308 bullet shape

Postby mtngun » Sun Dec 14, 2008 8:47 pm

I don't know anything about 30 caliber airguns, so I can only comment on how it will cast.

90 grains pure lead is very small for my blocks, so you would have to cast very, very hot, and it will be a frustrating experience. I suppose that is probably going to be true of most airgun bullets in most blocks, though.

Pinzgauer
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Re: Airgun .308 bullet shape

Postby Pinzgauer » Mon Dec 15, 2008 10:49 am

Well, I suppose that 2% tin would increase the fluidity of the metal without hardening the bullet too much.

What do you think?

Mike

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mtngun
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Re: Airgun .308 bullet shape

Postby mtngun » Mon Dec 15, 2008 8:52 pm

Some people think so but I don't see much difference in 30:1 vs. pure lead.

My only other suggestion is play around with the keith design, which would give you a smaller groove diameter.

Pinzgauer
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Re: Airgun .308 bullet shape

Postby Pinzgauer » Tue Dec 16, 2008 11:29 am


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mtngun
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Re: Airgun .308 bullet shape

Postby mtngun » Tue Dec 16, 2008 8:02 pm

Keith groove diameter = 85% band diameter

Most other style groove diameter = 91% band diameter

I am assuming you are trying to minimize weight or maximize length. A smaller groove diameter would help you do that.

But, a smaller groove diameter would make the bands more difficult to fill out.

Pinzgauer
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Re: Airgun .308 bullet shape

Postby Pinzgauer » Wed Dec 17, 2008 9:20 am

OK, I see...

Do you think that Cast Iron or Aluminum molds would be best?

Mike

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mtngun
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Re: Airgun .308 bullet shape

Postby mtngun » Wed Dec 17, 2008 12:04 pm

Cast iron blocks will run hotter and tolerate the high temps better. Which in your bullet's situation, is a good thing. Plus, aluminum is not available for black powder alloys for that very reason.

Pinzgauer
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Joined: Tue May 27, 2008 7:31 am

Re: Airgun .308 bullet shape

Postby Pinzgauer » Mon Oct 12, 2009 6:22 pm

This project has been moving at a stately pace :roll:

There are finally some results on an airgun forum, my original bullet did not shoot as well as round balls out of the prototype Lothar Walther barrel. Modifiction 1 was to drill out the base of the bullet to make the bullet look like an airgun pellet, that did not improve accuracy much. Modification #2 was to machine the nose of the cast bullet to a point, that made a significant improvement in accuracy. Please follow the link to see photos and text of the development work - http://airgunadvice.net/viewtopic.php?t=12293 the guy named 220 Swift is the machinist doing the airgun development work.

In the last group pictured, note the vertical stringing, this is due to shot to shot velocity variation because of a small reservoir size. The standard air reservoir size for this airgun is 400 - 500 cc, the reservoir pictured is only 174 cc so when the gun is finalized it should give 8 - 10 consistent shots.

Now for the real question, Mtngun - can you make me a mold with a pointy nose like the final iteration of the machined pellet?

Thanks for looking,

Mike

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mtngun
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Re: Airgun .308 bullet shape

Postby mtngun » Tue Oct 13, 2009 7:19 am

Sorry, I cannot cut a pointy nose.

I do admire the serious R&D you and your friends are putting into this effort. It's nice to see that there are still some intelligent shooters in this world.


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