.30 cal Boattail Bullet Designs

I've been working on this idea for a while with my partner-in-crime Sean Pero.... We wanted a heavier bullet that would fit into the .30 cal MRod magazines supplied by Lloyd at AirGunLab which we have designed our new repeating breech around for the Disco Double featured in this thread.... http://www.canadianairguns.com/showt...l-Disco-Double

I've been playing with boattail designs for a while, looking at their subsonic BCs, which are significantly better than a flat based bullet.... Anyway, here is what I came up with for the .300 cal barrels that Sean is supplying.... It's a 70 gr. in solid form, and would be about 65 gr. as a hollowpoint.... and has a Stability Factor of 1.5 at 900 fps in our 26" twist barrel (increasing below that).... The subsonic BC is supposed to come in at 0.16....

http://i378.photobucket.com/albums/o...psf8c47a60.jpg

While I was at it, I did another design, slightly heavier, for the commonly available .308 cal barrels.... It's 79 gr. as a solid, and about 73 gr. as a hollowpoint, and will have lots of stability in any barrel 20" twist or faster.... It will just fit into a .30 cal MRod magazine.... The subsonic BC should be 0.19....

http://i378.photobucket.com/albums/o...psf8dc7f83.jpg

I have been in contact with Tom at Accurate Bullet Molds, who make custom molds that are CNC bored in either aluminum, brass, or iron, and in 1 through 5 cavities.... You can use any of the bullet designs in his online catalogue at.... http://accuratemolds.com/catalog.php .... You can even order a mold with different cavities, which is my plan, I will be getting an aluminum mold with one of each of the above bullet in it.... I have submitted the drawings to him, and I'll let you know when they are in the catalogue.... I'm really looking forward to testing these new designs....

Bob

After a couple of very pleasant emails back and forth with Tom at Accurate Molds, I got an email telling me that the new boattail airgun bullet designs have been added to the catalogue as numbers 30-070A and 31-079A.... They are on the first page of the catalogue, so they are easy to find.... I went through the extremely simple order process on their website, and I was able to order one cavity of each design in a single aluminum mold block (which uses 6-cavity Lee handles).... The mold was $100 plus $15 extra to have two separate designs, and the shipping fee was a startling low $5.00.... The turnaround time is 3 weeks, so in about a month I should have it in my hands....

I'm really excited about the opportunity to get a custom bullet mold at no extra cost, and in such a painless manner.... My hat's off to Tom for all his help, and his excellent website....

Bob

I received my new mold from Accurate Molds today.... Tom did a fabulous job, superb service all around.... The sprue plate, per my request was sent semi-finished, with the conical wells finished but the holes not drilled through.... I have started with a hole of 0.100" so I can enlarge them if necessary.... The mold fit my Lee 6-cavity handles great....

http://i378.photobucket.com/albums/o...ps7cc7d72d.jpg

There is one of each of the above two bullet designs in the block so I can try them both out with a minimum of expense....

http://i378.photobucket.com/albums/o...ps7b3d763f.jpg

The smaller, 70 gr. .300 cal bullet is on the left in the photo and the larger 79 gr. .308 bullet on the right.... I hope to get a chance to do some casting tomorrow and find out how close the diameters and weights are to what I designed and ordered....

Bob

Well I spent a couple of hours casting and another couple counting, sorting, weighing, and measuring today.... Here is what just over 500 bullets look like, fresh from the mold....

http://i378.photobucket.com/albums/o...ps35b0868f.jpg

I started out with a 0.100" hole in the sprue plate, but that was a bit small, so I drilled it out to 7/64" (0.109") and that seemed to work just fine.... With that small a hole I am not getting any bent bullet bases like I was getting on the .25 ACP bullets from the RCBS mold.... I sorted the bullets into two piles for the .300 cal 70 gr. and the .308 cal 79 gr., and that turned out to be a lot harder than I thought it would be since they look so similar.... I did the first sort by appearance, and then I weighed 3 bullets at a time to make sure I didn't mix any of the wrong weight in and found a handful of bullets that were in the wrong piles.... I ended up with 258 good bullets in .300 cal and 256 in .308 cal, with about half of those with no visible imperfections, so I'll save those for accuracy testing and burn up the rest through the Chrony.... I only had about 20 bullets that were destined to go back into the pot to be remelted, however, which is about the best I've ever done....

I measured and weighed 20 of each size.... The .300 cal weighed an average of 70.4 gr. and measured from 0.2995" - 0.3010", they were 0.414" = 0.416" long, and they looked like this....

http://i378.photobucket.com/albums/o...ps834e3469.jpg

The .308 cal weighed an average of 79.5 gr. and measured from 0.3080" - 0.3095", they were 0.449-0.451" long, and they looked like this....

http://i378.photobucket.com/albums/o...ps49acaa7c.jpg

One of the criteria for both these bullets was that they fit in the 7-shot Marauder magazines that have been modded to .30 cal by AirGunLab, and they do indeed fit, and function perfectly....

http://i378.photobucket.com/albums/o...ps5a3bbf0b.jpg

I'm very pleased with the way these Rebated Boattail bullets turned out, let's hope they shoot as good as they look....

Bob