Ballistic Coefficient Explained… In Practical Terms
- Thread starter PracticalTactical
- Start date
I hate the new long skinny high BC bullets that you have to seat like .08-.10+ from the lands in SAAMI chambers. Something ain't right, man. Even Berger had to publish they had a problem after a lot of complaints and came up with a solution. More seating depth, a lot more, than in the lands as originally directed by them. That is on Brian. Now if you choose these bullets you have to buy more bullets to develop a precision load because seating depth is not compatible with SAAMI. I stick to tried and true precision bullets regardless of BC. Does that give me a handicap? Depends if the long skinny guy next to me is shooting long skinny high BC bullets and figured out his seating depth for that day. Blackjack is another good example. Designed a .257 bullet that is not intended for the typical .257 the rifle manufacturers produce. Blackjack states it's high BC 131 will breath new life in your 25-06. It will do no such thing.
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BTW, those that are having trouble with the long skinny high BC 110 gr .243 SMK in a .243 Win can switch to the .244 Rem, which has a little more capacity and longer neck. It will act like a regular SMK bullet during load development. That was by accident on my part. I got the .244 Rem barrel then tried the 110 SMK. Somebody with a .243 Win couldn't get them to shoot. Then another one couldn't either but first bought like 2,000 of them. So, Sierra is no monument to justice as well.
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With High BC for the weight, bullet jump is best starting at 40/1K " even better (more consistent) at 80/1K ". Nothing wrong with that if the barrel has a long throat. Most new fast twist barrels would have such a long barrel throat.
Excellent read
precisionrifleblog.com
Excellent read
Bullet Jump Research: Executive Summary & Load Development Tips
This is the last post in a series of articles focused on bullet jump research that has been conduct...
I remember reading that article. Chasing the lands is one thing. Designing a bullet, selling it in mass quantity, only to later have rifle builders design a barrel for it is what I'm referring to. Most of us don't shoot precision higher than local and maybe state levels. It amounts to reverse engineering. Now, on the other hand, you can send in a few dummies rounds to some barrel makers and they will send you a barrel designed just for that bullet and it is on you to get those dummy rounds correct. I prefer a little SAAMI slop for utility. Also, fast twist barrels is another almost after the fact specification and most barrel makers are not going to compensate with a longer throat unless requested. Blackjack changed their recommended twist at least twice now. And the jury is still out with customers figuring out a better BC to use. Weatherby is a factory manufacturer known for long throats that has little to do with bullet design. Long Weatherby throats go back decades way before long skinny high BC bullets. At least Berger sticks with typical twist rates, admits they may have initially made a mistake and offers a work around that may or may not work. They don't recommend getting a custom barrel.
bergerbullets.com
Getting the Best Precision and Accuracy from VLD bullets in Your Rifle
VLD bullets are designed with a secant ogive. This ogive shape allows bullets to be more efficient in flight (retain more velocity = less drop and wind deflection). While this result is desirable for many rifle shooters the secant ogive on the VLD bullets produces another result in many rifle.
bergerbullets.com
I think there's a reason different people have different opinions about the ideal bullet jump.
As stated in the video, the clearance in the freebore has an affect on accuracy, but I would speculate that also translates into shot to shot BC variation as well as muzzle velocity variation.
If a guy has a sloppy freebore, he will likely find that he gets best results with a hard jam, but a guy with a tight freebore can jump a ton and get away with it since alignment is essentially perfect if he jumps or not.
As stated in the video, the clearance in the freebore has an affect on accuracy, but I would speculate that also translates into shot to shot BC variation as well as muzzle velocity variation.
If a guy has a sloppy freebore, he will likely find that he gets best results with a hard jam, but a guy with a tight freebore can jump a ton and get away with it since alignment is essentially perfect if he jumps or not.
Good thread here.
I wanted to use the Blackjack 131gr when it first came out, but ran into the following problems:
1.) Long skinny ogives that don't touch the lands from magazine length, and I don't like to single load.
2.) Very small windows of adjustability because of the overall length of the bullet being confined by the magazine box - a very typical issue is an AR15 with a 5.56 chamber using 77gr bullets.
3.) Loss of powder capacity (and ultimately velocity) to seating the bullet in the powder chamber.
4.) All of the cartridges available had excessive freebore. It was like throwing a hotdog down a hallway to the rifling and hoping for the same engagement each time.
So I did what anyone would do if they wanted to stay up at night wondering, and spend large sums of money - I designed my own cartridge to eliminate the issues above. It has been a journey to say the least. Here's how I went at it using .308 as the parent cartridge:
- I started by designing from the lands backwards
- Placed the bullet ogive (for the BJ 131gr) at the lands at 2.860", 20 thousands shorter than the standard AISC magazine overall length
- Placed the neck junction of the base of the bearing surface to boattail transition
- Made the neck 1.33 bullet diameters
- Maximized the chamber volume by using a 40 degree shoulder
I started the process a year and a half ago, and I am expecting not one, but two rifles to be delivered in a couple of weeks. One is a 32" McGowen barreled 1:7 on a Defiance Ruckus with a TT diamond, the other is a Falkor 7 Proof 1:7.5 26" also with a TT diamond. Both are in XLR Envy chassis. A good thing that happened is the release of the Berger 135 gr which has almost exactly the same profile, and the soon-to-be release of the Berger 133 gr with a very close profile. I now have three choices of bullet with a chamber ready-designed.
I think I have covered my bases, but I am sure something will pop up. No lawyer would ever approve this chamber, and I am fairly certain that reason is why most offerings do not take full advantage of these high BC bullets. They are just too finicky and require more than a little knowledge to tune for.
That is why we reload!
NZ_Fclass
Silver $$ Contributor
Well...you are kind of correct. But - and I have no axe to grind, as most of my rifles are single shot, with enough access to seat the bullet where I want, unconstrained by SAAMI.
Let's take the 223. Originally designed as a military round for the M-16, the magazine length was compatible with the 55g. And the barrel twist was 1/12. Later on the 62g was used and the barrel twist was increased to 1/7 to allow tracer rounds to stabilise, whereas the 62g would be happy in a 1/9. The mag length was not increased to accommodate the longer tracer projectiles, they just sat back in the case. SAAMI bought out the specs for the commercial market and all was right in the world. But you cannot shoot 90g projectiles on an AR length magazine - successfully - and why would you want to? Oddly, many US manufacturers only make 1/9 twist for 69g projectiles, that will seat in SAAMI length magazines. Knowing this, you can still make decisions on purchasing an AR or bolt gun that has SAAMI length restrictions. Or you could buy a Tikka and others with an 1/8 twist that will stabilise 77/80g bullets, has a longer magazine and action length to accommodate the longer OAL. Is there a SAAMI spec chamber for 80g VLD projectiles? I don't know and honestly, don't care. I don't run factory ammo.
Your SAAMI spec rifle fails on 2 counts anyway. The magazine length is too short for 131g and the barrel twist is likely too slow - probably 1/10. That rifle that will perform the same as the day that you bought it. Yes- the 131 Black Jack projectiles will transform the 25/06 cartridge - but obviously in one with a custom chamber, the correct twist and magazine length - or a single shot. Who knows? One day SAAMI may bring out a chamber spec that will accommodate the longer for weight bullets. They can be a little slow if not pressured by ammunition manufacturers.
The same goes for my experience with 223. I had a Savage 10, 1/9 twist. Shot well with 69g - but I grew out of it and, wanting to shoot 75/77/80g, I bought a used Tikka T3, had a 28 in.Tru-Flite 1/8 barrel chambered with a longer free bore allowing the bullets to sit out to my preferred length, a decent stock and new trigger. As it is a range gun, I have a "sled" in the mag well, although i believe that the rounds will fit in an after market magazine. Initial testing has shown promise with 75g Hornady's, and like many of us, I am waiting for supplies of Sierra and Berger to show up.
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You got a name for that wildcat yet?
I don't shoot with magazines. I'm referring to having to push that bullet too deep into the cartridge with these particular bullets. Seeing how long they are, finding some ridiculous sweet spot, then looking at the finished loaded cartridge is a WTF? moment. @miningshawn has it right. You need to design a cartridge for the bullet rather than a bullet for the cartridge. I wish him the best of luck.
Ya the mag length problem is misunderstood by most, but its nice to see you guys get it. I learned about the problem the hard way.
I ran a custom Sako in 223 with 80 grain SMKs for a long time and there was no way rounds would feed from a mag and I could not eject a live round without removing the bolt.
Same problem with my 308 short action Rem 700 with heavies.
I recently put together a sweet 223 though to overcome this problem. Used a Defiance action so its long enough to eject a live round and I found it easy to modify Accurate Mags to run 2.650 OAL rounds. Now I can run F Class loads from my repeater.
This allows me to run 90 grainers at 2900 FPS with what I'm sure are technically on the warm side, but nothing I would call unsafe. Primers are still rounded after firing.
For a 308 these days I would base it on a long action, not a short action for the same reason.
I ran a custom Sako in 223 with 80 grain SMKs for a long time and there was no way rounds would feed from a mag and I could not eject a live round without removing the bolt.
Same problem with my 308 short action Rem 700 with heavies.
I recently put together a sweet 223 though to overcome this problem. Used a Defiance action so its long enough to eject a live round and I found it easy to modify Accurate Mags to run 2.650 OAL rounds. Now I can run F Class loads from my repeater.
This allows me to run 90 grainers at 2900 FPS with what I'm sure are technically on the warm side, but nothing I would call unsafe. Primers are still rounded after firing.
For a 308 these days I would base it on a long action, not a short action for the same reason.
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A couple nit pix on info put out in video.
#1 Stability does not change a significant amount one way or another with velocity unless on a hairy edge of stable. It's a common mistake for people to think stability problems are overcome with velocity.
#2 Maybe I missed it but I didn't see mentioned that BC and stability are heavily tied to air density. Different bullet makers declare these attributes based on different sea level standards, so it's not always a cut & dry comparison. YOUR BC & stability are some local values, and NOT what's on the box.
Beyond the video;
As far as best seating, this is only known when tested for, never predicted.
About bullet lengths;
In reality, all things begin with a bullet. It's absurd to buy a gun and then complain about bullets.
So I don't think bullet makers should be disrespected for offering high BC bullets.
I'm glad Berger is doing just what they're doing, and I do MY part by setting throats for them with my reamers. I call it a 'plan'
#1 Stability does not change a significant amount one way or another with velocity unless on a hairy edge of stable. It's a common mistake for people to think stability problems are overcome with velocity.
#2 Maybe I missed it but I didn't see mentioned that BC and stability are heavily tied to air density. Different bullet makers declare these attributes based on different sea level standards, so it's not always a cut & dry comparison. YOUR BC & stability are some local values, and NOT what's on the box.
Beyond the video;
As far as best seating, this is only known when tested for, never predicted.
About bullet lengths;
In reality, all things begin with a bullet. It's absurd to buy a gun and then complain about bullets.
So I don't think bullet makers should be disrespected for offering high BC bullets.
I'm glad Berger is doing just what they're doing, and I do MY part by setting throats for them with my reamers. I call it a 'plan'
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You have to understand Mikecr that I don't know how much the viewer knows when I post a video and I'm trying to walk a line between getting my point across and not losing a newb with lingo guys in this thread will understand.
I just prefer a cartridge and chamber that is easy in load development and is accurate with more than just one bullet in it's weight class. Not a bullet manufactured with work arounds because it wasn't designed by industry standards to reach Max BC. I mean even Berger admits it. I'll take the cut in BC any day. That is just me.
25 Norton (Quarter Norton)
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