Powder Coating and gas checks...

[Dragonheart]

To answer the basic question, I know of no one who knows more about gas checks than the designer and builder of the Freechex Gas Check Tools, Charles Darnall. We have spoken about this subject countless times and Charlie will tell you PC does what a gas check does, it seals & protects. When you get into the accuracy issue, a PC bullet with a GC base will function without the check but it is not going to be as accurate as it would be if it had a properly seated GC. A PC cast bullet with a plain base can be driven in excess of 3500 fps, I have done it. So as far as I am concerned the polymer jacket has no limit. A PC full power load should be more accurate with a properly seated gas check because the base of the bullet will be perpendicular and flat. However with full power loads, whether you PC or not or use a check or not the inherent issue of a non-concentric cast bullet remains. The only ways I know to overcome the lopsided bullet problem is swagging, using a bore rider design bullet or shoot at short range, less than 50 yards.

[Vettepilot]

What causes the "lopsided cast bullet" problem, and why is it not effectively ironed out during sizing? Is this problem the effective, definitive reason for cast bullet accuracy loss at higher velocities? If so, why does it only manifest itself at higher velocities?

Thanks for any info/insights/sources on this subject,
Vettepilot

[mattw]

I am a firm believer in this statement... if it is in a rifle and it has a check shank use it! I am shooting the NOE 47 grain WFN in my 221 Fireball bench gun, one of the accurate loads pushes a PC'ed, checked bullet to 2775 fps. I am getting 0 leading, a tiny bit of copper fouling and they shoot well. I have been working with this one in anticipation of moving up to my 222 Mag next with 55 and 60 grain cast. I have no concerns about the bullets performing up to jacketed velocities at this point.

[Dragonheart]

What causes the "lopsided cast bullet" problem, and why is it not effectively ironed out during sizing? Is this problem the effective, definitive reason for cast bullet accuracy loss at higher velocities? If so, why does it only manifest itself at higher velocities?

Thanks for any info/insights/sources on this subject,
Vettepilot

Good question. For full power accuracy at distance, bullet design is a big factor. "Bama' proved a bore rider design bullet sized with his custom dies so the bullet fit his barrel was capable of very good full power accuracy beyond 300 yards.

When a bullet is cast the bullet leaves the mold out of round. This has nothing to do with the quality of the mold, alloy or the user, it is just the physics of the casting process.

In a normal bullet sizing die process we make the bands round, but the nose of the bullet is left original, not concentric (lopsided) and unbalanced.

If we size the nose of the bullet or what a die can touch using something like a NOE nose bushing, the bushing will indeed make what it touches round, but the problem is it is a two step process; the bullet's base is not held in line with the nose bushing. This results in two perfect but separated circles. Just like laying a nickle on a quarter, you have two perfectly round surfaces, but that does not mean they are perfectly in line with each other (concentric). Additionally, there is likely an area that neither sizing die touched, so the bullet remains lopsided and unbalanced.

A vibrating tumbler it is driven by an electric motor with a concentric shaft. To create the vibration an eccentric is added to throw the normally smooth turning shaft out of balance.

When a lopsided bullet is fired the same thing happens; rifling imparts a spin, but at some point the eccentric bullet is going to start to wobble because of not having its axis centrally located. Once the wobble starts is is only going to get worse with distance. To increase the distance we increase the pressure driving the bullet increasing the velocity. As the speed increase so does the wobble. For this reason lopsided cast bullets can perform pretty well at short distances with full power loads. Or they can perform pretty well at longer distances with low velocity loads. But what an as cast lopsided bullet can't do is perform well at longer distances with full power loads, unless the extra effort is made, like Bama's Bullets.

Hope that answered your question.

[charlie b]

The reason I limit the speed of bullets is due to the rotational speed, which kinda equates to the wobble issue.

The faster the rifling twist, the lower the 'max' speed of the bullet. Slower twist means you can get higher velocities.

I wish I had my lathe back. I want to try a 'stepped' sizing die that sizes forward and driving band portion at the same time.

[Dragonheart]

The reason I limit the speed of bullets is due to the rotational speed, which kinda equates to the wobble issue.

The faster the rifling twist, the lower the 'max' speed of the bullet. Slower twist means you can get higher velocities.

I wish I had my lathe back. I want to try a 'stepped' sizing die that sizes forward and driving band portion at the same time.

I wish you had your lathe back also, because I think a stepped die would definitely help and a complete swage of the entire bullet might fix it all together.

[charlie b]

Yep, I can understand why no one makes one, simply because of all the combinations out there.

Like seating a gas check with a special die that holds everything concentric.

If I could make one I'd probably try out a few of the 'PC' bullet designs with no gas check.

[Vettepilot]

I am presently reading an older RCBS book on cast bullets. It states, and I quote: "Experience has shown that each .001" of sizing results in about an extra inch of group dispersion at 100 yards."

No explanation. Why would they say that??

Thanks,
Vettepilot

[Dragonheart]

I am presently reading an older RCBS book on cast bullets. It states, and I quote: "Experience has shown that each .001" of sizing results in about an extra inch of group dispersion at 100 yards."

No explanation. Why would they say that??

Thanks,
Vettepilot

I have never heard that statement and without an explination for their statement I would be just hazarding a guess.

When a bullet is sized metal is moved and it has to go somewhere. Logic would tell us the less metal moved the better, but I don't necessarily think putting a flat 1" per .001" is correct.

Until someone comes up with something better I think bullet design is the most important thing to accuracy. But in general, if the metal moved from sizing increases the out of axis of the bullet then accuracy would be worse. If the metal is deposited on the base of a bullet creating a skirt of altering the base, so the base is not perpendicular to the bore axis the accuracy is compromised.

One law of physics states that pressure can only act perpendicular to a surface. When a bullet exits a barrel the base of the bullet is still under pressure and if the base is angled or deformed instead of being completely flat and perpendicular to the bore axis, the bullet's flight path is altered. Basically stated, a bullet is steered from it's base.

In a casting manual, I think this statement might be referring the importance of bullet molds that drop bullets closer to the final bullet size so they do not require moving a lot of metal. Or it may refer to using a mold designed for say a 30/06 rather than a mold designed for a British .303.

Proper sized molds is something I have said we need ever since I got into PC. Undersized molds especially for rifles would allow for build out of the polymer jacket.

Well that's my best guess, maybe someone else knows for sure.

[Dragonheart]

Yep, I can understand why no one makes one, simply because of all the combinations out there.

Like seating a gas check with a special die that holds everything concentric.

If I could make one I'd probably try out a few of the 'PC' bullet designs with no gas check.

I know of no one that knows more about gas checks than Charlie Darnall the designer and owner of the FreeChex gas check cutting tools. Charlie will tell you flat out that a properly powder coated bullet does not need a gas check.

I absolutely agree with charlie, but with one exception a gas check that is perfectly installed can create a completely flat and and perpendicular bullet base. A PC base covers the imperfect cast base where the sprue was cut. The PC makes the plain base better, but it is still not perfect. Why don't mold makers consider this and give us some nose pour bullet designs?

[charlie b]

Agreed. If the base is nice and square with sharp edges just PC the bullet and shoot it.

Why not any more nose pour molds. 30-40 years ago I would see one every now and then, usually advertised as a target bullet. Why no more? Maybe because the nose is not perfect and 'they' consider that worse than a base that is a little off? Or, 'they' feel that a gas check is the 'solution' the the flawed base problem?

IIRC, aren't there some Accurate or NOE molds that are nose pour with a base pin to adjust the weight of the bullet?