Lyman 257420 Boattails

[shamu25]

This is sounding good

[Gippeto]

Impressive results Bob...well done.

Have a little project of my own, wondering where you obtained the McDrag software? A search turned up a program in what looks like basic, but the Vic 20 is long gone and I've no idea how to go about entering the program on a modern pc.

Al

[rsterne]

Al, I had to write my own in Excel.... I printed it out in Fortran and then just used the formulas in columns in a spreadsheet.... Took FOREVER to double check and debug.... but eventually I got identical results to the JBM online calculator.... So, it's my own version of McDrag.... I never got around to doing McGyro, although I do have the printout of the program from the JBM website (where I got the McDrag also).....

The JBM online version is great, but for some reason they decided to put restrictions on things like nose length and Meplat diameter that are unnecessary.... but it makes it quite useless for many airgun bullets....

Bob

[Gippeto]

Thanks Bob.

Al

[YEMX]

I would be very interested in seeing results from this new configuration!

[Tofazfou]

I would be very interested in seeing results from this new configuration!

+2

[UncleDevo]

I had Arsenal Molds redevelop the Lyman 257420. Everyone likes the round, no one likes the 2 cavity Lyman mold. I have the Arsenal 257420 mold in 4 cavity aluminum. It has a Gas Check (GC), like the original Lyman Round. We shoot subsonic. I understand aerodynamics and have bevel bases on the molds I got from Lead Bullets Technology (LBT) but saw no need to modify such a short and highly effective round. Might I ask those who are so keen on a boat tail:

What range do you shoot? I shoot long distances (547 yards have been my longest hits to date).

What advantage do you perceive in a small light round having a boat tail? 257420 has a flat tip (meplat for those who like to sound fancy), so its not Spitzer like with a sharp point. I
It has limited aerodynamics, and the air envelope coming off the front may create a shock wave that never has the tail engaged with pulling much drag.

These shots were  done with 25420 rounds from my Arsenal Mold. You might want to get one of their molds instead of re-inventing the wheel.

[UncleDevo]

Arsenal also has produced a mold for the 257388 Spitzer. Carl sent me this picture of his best group that came from that mold. These shots were done at 100 yards. I know, this is a tad off topic, but hey, if you want a great mold for $75 plus shipping (mine came to $82.50 delivered), then go to arsenalmolds.com and order the 257420 and the 257388 at the same time...save a bit on shipping!

[UncleDevo]

In my previous replies I mentioned an 80 Grain Spitzer I have from Lead Bullets Technology. This bullet has a bevel base, not a boat tail, but at subsonic speed it serves the same purpose well. If you order from LBT make sure you state you want an air gun specific round, include this picture and spec. 2575

[nielsenammo]

A lot of guns can not shoot that heavy of a bullet so not everyone has a use for it.

[UncleDevo]

I sent Arsenal a picture of Bob's Modified Boat Tail 257420, as it has similarities to the rounds I get from the LBT molds, which have slick aerodynamic properties. I like the fact that it is an air gun specific round. The biggest advantage I see is the lack of lube grooves between the bearing bands. The difference between the boat tail and the GC is rather minor in my mind. I'd love it if Bob's calculation could compare the Modified Boat Tail (lube grooveless design for both) with a GC back vs the Boat Tail.

[rsterne]

The calculated difference in drag is in the first post.... in theory about 1/3 less drag for the boatttail in the subsonic region.... None of the drag programs address the lube grooves at all, they assume the bullet is smooth and full diameter between the driving bands (like a jacketed PB bullet)....

Bob

[boothm]

I'd be interested in your 257420 modified BT in HP when you get it going...looks like sweet well thought improvement in design on top of existing winner.

[rsterne]

Arsenal Molds started making the 257420 in a Boattail version some time ago.... http://arsenalmolds.com/products/257-Bullet-boattail?limit=99999999999

They do not, however, make HP molds, you would have to send it to Erik at Hollowpoint Mold Services to have it converted.... I have not yet purchased one of these molds, and so far Al at NOE hasn't decided to go forward with a BT version, probably because Arsenal already has one....

Bob

[Wayne52]

Well...count me in on a group buy for the 257420 Mod BBT HP.

This could be a fantastic high velocity ground squirrel round here in California...

There's a really good chance that I'll be getting an M10 soon which would probably love these bullets, I think I've read that these have a 1 in 21" twist but I could be wrong

I'd be game for the hollow point cavity too