PC Borerider

[405grain]

It took a while but I was finally able to do some live fire testing. The nearest shooting range to me is a 90 mile round trip, and it's only open to the public on Thursday through Sunday. Because there's always a big crowd on the weekends I try to go there on either Thursday or Friday.
I had reservations about the 31-150E, and testing bore these doubts to be true. The nose on this design does not have sufficient support at both the chambers ball seat and the rifle's bore, and as a result of this the accuracy is dismal. To test out this bullets performance I made up identical loads using the Saeco #316 and the Accurate 31-150E. Both bullets are 150 grain 30 caliber. The test rifle was the most plain Jane 308 Winchester imaginable; a sporterized Mauser 98 with both the stock and barrel from Brownell's. The shots were taken off a shooting bench at 50 yards. The day was warm and clear with very little wind.

As a reference I shot a 5 shot group using the Lyman #311299 and 24.0 grains of Shooter's World Buffalo Rifle. The 311299 is a very accurate bullet, and shot a 3/4" group. This demonstrates that accuracy, good or poor, is the result of the cartridges being used and not the rifle. Eight shots using the Saeco #316 shot a 1.5" group (a flier opened the group up, otherwise it would have been a 1" group) The 31-150E was a dismal failure, and an eleven shot group opened up to 7" at 50 yards. I also tried the 31-150E in a bolt action 7.62x39 (.308 caliber barrel) and the results were similar.

Designing a bullet is a learn as you go process, and by the time I was able to test the 31-150E I have already made several revisions. I'll be shelving the 31-150E and moving on to the next design. To incorporate the features that I believe will be necessary for a cast bullet to work properly using the idea of making it specifically for powder coating I have had to change so many parameters that the bullet's design has increased from 150 grains to 170 grains. This new design differs so much from the "prototype" 31-150E that it is a completely different bullet. (see the print on post #17) I'll be submitting this new design to Accurate probably next week, and will then begin testing on it.

Bullet Test.JPG

[popper]

My 31-145C is very close to your design, Shank and nose undersized for PC. Even with BLL & from an AR, works good. 50 yds and different powder than your. 100 yds is a long walk for me. PB version does good at 100, coated and 2150 fps. Design is not the problem.
TgtGfx54.jpg

[405grain]

popper: Your 31-145C is well thought out. I'm still learning from my mistakes. When I contact Accurate next week I'm going to advise them to drop the 31-150E from their catalog because their customers won't be satisfied with that design. On your 31-145C I noticed that you have the bullets diameter just ahead of the driving band at .297". What is this diameter on the nose after the bullet has been powder coated?

Your design has a groove in the driving band for the material to displace into when it gets engraved by the rifling. (nice feature) I assume that you have that step near the base for this same purpose. I want to go with a gas check design, so I'm making the gas check shank 0.09" long to create a gap between the top edge of the gas check and the base of the driving band for this same reason. Also, after some consideration I've decided to go back to a meplat that's .18" in diameter. I had considered a .2" diameter meplat as this would increase efficiency as a hunting bullet, but I think that the slightly smaller meplat and more gentle angle on the bullets nose would make for more reliable feeding.

The accuracy that you're getting with your bullet is excellent. My self imposed standard is 3" at 100 yards. If I can't make a bullet that will shoot into a 3" circle at 100 yards I have failed. With both the Lyman 311299 and the RCBS 7-168-Sp I have shot 1" groups at this range (on those days when the stars align), so 3" is the upper limit, and I want a bullet that will do better than that, and can be used in the maximum number of 30 caliber cartridges.

[Cord]

Maybe there is something to interest you in the Accurate 30-140A.
It was designed as a powder coated bore-riding boolit for 300 blackout,
the lube groove is only to reduce total weight.

30-140A-D.jpg

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[405grain]

Cord: Thank you for the suggestion but the 30-140A doesn't have a bore riding nose section. It has the same tapered nose design that has doomed the 31-150E. There just isn't enough support at either the chamber's ball seat or with the barrels bore. All of the centering with this bullet is dependent on the driving bands, which means that it would work best in fire-formed neck sized brass. If you are having good accuracy with this bullet then it is a good match for your rifle, but may not work as well in a variety of firearms. A "lube groove" is unnecessary on a bullet designed for powder coat if there is a gap between the driving band and the gas check.

[popper]

Add 2-3 thous for PC. I haven't measured.

[405grain]

Thanks popper. In post #5 I did an experiment testing to see how much powder coats add to a bullets diameter. I came out with an average of one and a half thousandths. (some powders slightly more, some slightly less) I was just wondering if your measurements had similar results. I think that if I have the bore riding section of the bullets nose cast at .298" it should come out after coating between 0.0005" and 0.0003" under bore diameter, but that depends on how accurately the mold drops the bullet. When I have Accurate cut the molds I specify COWW + 2% tin because this seems to be the most common alloy.

[405grain]

I have a redesigned mold on order with Accurate. The revisions should address the deficiencies in my first design attempt. I'll begin testing with it as soon as it arrives.

[405grain]

The new bullet mold design arrived today. Accurate is calling it the 31-159A. I designed this bullet to work in almost any 30 caliber cartridge, and hopefully it will preform with only a shake-n-bake PC coating, and a run through the sizer to crimp on a gas check. The nose is dimensioned so that if should be the correct diameter once the PC is applied, so the nose should not get too fat to chamber and there should be no need for nose sizing. I included a crimp groove because I want this bullet to be a jack of all trades and work in both box and tubular magazines. The shank for the gas check is longer than normal so that there will be a gap between the top of the gas check and the bottom of the driving band for the material that gets displaced by the rifling to have a place to go. The big test will be if it shoots accurately. I'll cast up some bullets this week and load up some cartridges. (the 308 Winchester has been elected as my test mule for this) It might be next week before I can get to the range and test them, but I can't wait to see how they'll do.