Litz tests the BC of ABLR's...

[Ridgerunner665]

And the news is good...provided you have a fast enough twist...which is a bit different from the previously accepted idea of "no faster twist than necessary"...it seems BC is closely associated with twist rate/stability factor.

Anyway...his tests showed the BC's to be pretty darn accurate with proper twist rates.

http://www.longrangehunting.com/forums/ ... ts-137554/

 

[Ridgerunner665]

Litz's findings on stability factor affecting BC are intersting...gonna have to read his new book I guess...

Its seems that getting advertised BC's correct is a lot like trying to hit a moving target...anyways, just glad to have the AccuBond LR in the lineup...per the findings above, I'll probably be shooting 150's in my 280 Ackley.

Nosler...crank up production...I bet those tests will boost sales a bit...even with the twist rate issue, which is minor...accuracy is fine at lower SG factors, just don't get all the BC.

 

[gerry]

That is very interesting information and does also help to explain why some people clamed the b.c. was dead on and others claimed it wasn't. The 129 gr 6.5mm is a very sleek bullet so I can see it easily being bang on. The results with the 277 calibers is very interesting and makes me happy there is a 1 in 9 twist barrel sitting in the loading room waiting for the funds to get it done. It does look like guys with 1 in 10 twist 270 Win's and 280 Rem's will see a fairly big reduction in the b.c. but even with that most guys will never notice and the small group of dedicated long range guys will likely get a fast twist tube anyway.

 

[Ridgerunner665]

The 7mm 168 ABLR is no slouch in the BC department even from a 9 twist...it still has a higher BC than either of the Berger 168 VLD's.

The same goes for the .277 ABLR's...while they don't quite make the advertised BC from a 10 twist, they are still the highest BC available in that caliber, without getting into very long, heavy bullets.

Nosler made some awesome bullets...Thank You Nosler!

 

[HOGWILD338-378]

I would sure like to run some 210's thru my 300 Weatherby :mrgreen: from using my JBM program it always marks during flight with a yellow line when the stability is at it's worse? Even with the 1-10 twist I think I will still try some if ever delivered!

 

[Ridgerunner665]

10 twist should still be fine even with 210 grain bullets...10 has always been a fast twist in 30 caliber, the original bullets for 30-40, 30-03, and 30-06 were all over 200 grains, and at pretty low velocity too...by today's standards.

I wouldn't expect to need more than 1 in 10" in that caliber.

 

[Ridgerunner665]

I just ran the 210 ABLR through the stability calculator...

In a 1 in 10" twist...it has a stability factor of 1.51 even at only 2,500 fps muzzle velocity...

In a 300 Weatherby at 2,900 fps muzzle velocity the stability factor is 1.59...well above the 1.5 that seems to be the new minimum.

P.S. I only guessed at the muzzle velocity of the 300 Bee...but it should be close.

 

[JD338]

Great info, thanks for posting the link.

JD338

 

[Ridgerunner665]

Great info, thanks for posting the link.

JD338

You're all very welcome...I'm glad I stumbled across it...I do follow Litz's research and books pretty closely.

I could be wrong...but I'm betting ABLR's are gonna be very hard to come by now, and sales of 7-8" twist barrels will go up too...people tend to listen when he speaks.

There has to be a downside to twists that fast though...especially if not used with some type of radiused rifling (5R and such)...

People will try to get SG's up to at least 2.0...I think I'll stick with 1.5, and wouldn't feel left out using 1.3...there has to be a "happy medium" in there somewhere.

 

[gerry]

Have been doing some playing with the stability calculator he posted in his thread, pretty neat stuff.

http://www.bergerbullets.com/litz/TwistRuleAltWP.php

Note to Nosler, my 1 in 12 twist 35 Whelen will stabilize a 250 gr bullet 1.6" long nicely

 

[gerry]

The 1 in 9 twist 270 Wby will spin the heavy weight 277 bullets nicely according to the formula, the 150 gr ABLR, 160 gr Partition and 180 gr Woodleigh all do really well 8)

 

[kraky]

I always wonder about he plastic tip regarding calculators. It weighs almost nothing...should it be deducted from the bullet length? I would think it should...?

 

[Ridgerunner665]

Litz seems to think the tips don't matter much...

At any rate...the higher spin rates do seem to improve the BC, and the more I think about it...the more I wonder why this wasn't known sooner...because it makes perfect sense.

I also believe, depending on ones purpose, that there is a point of diminishing returns....1 in 8" is a pretty tight twist...not sure I'd want any tighter for any reason, except in an AR15.

With conventional rifling, and .284/20mm Vulcan wildcat rounds (not an actual round, yet anyway)....slinging 190 grain J4 jacketed bullets at 4,000 fps...I can't help but wonder about in flight bullet disintegration...that is from a target shooters perspective.

From a hunters perspective...using less "quality controlled" bullets...with more imperfections...the tighter twists will be less accurate due to spinning the not perfectly balanced bullets at tremendous RPM's.

 

[Oldtrader3]

All this tells me is to save my money by not buying the ABLR. For my shooting the Ballistic Tips, Accubonds and Partitions will more than take care of my needs. As they have for 50 years.

 

[Ridgerunner665]

All this tells me is to save my money by not buying the ABLR. For my shooting the Ballistic Tips, Accubonds and Partitions will more than take care of my needs. As they have for 50 years.

That's probably true...but it won't stop most people from using them anyway...even those that have no need at all for long range bullets.

 

[RiverRider]

At any rate...the higher spin rates do seem to improve the BC, and the more I think about it...the more I wonder why this wasn't known sooner...because it makes perfect sense.

I always thought the concept was well known. I recall advertising for a chronograph system that utilized screens at or near the target in addition to those near the muzzle, and the stated advantage was that actual achieved BC could be derived from the velocity loss over a known distance. I don't recall whether it was explicitly explained, but it made sense that the difference between theoretical BCs assigned to bullets and the realized BC calculated on every shot fired would pretty much HAVE to arise because of stability, or lack thereof. Maybe someone with a better memory than mine (which should be just about everyone) will recall more details.

 

[kraky]

Fwiw...I've read reports that bullets fired out of tight twist barrels are stressed more at impact on an animal. Actually some people I think are pretty knowledgable say its pretty significant.

 

[andrewctillman]

Back in 1980-82 when I tested most of the then available 375 bullets out to 600 yards, I got a couple inches less drop with my quick twist (1-8) barrel than a std 1-12. I used a quick twist to over stabilize bullet so it would mushroom perpendicular to base. Bill Steigers and I observed that the slower twist bullets were almost always canted when recovered from game or our 5 gallon water buckets. He began advocating a quicker twist for hunting rifles and I drank that cool aid after doing my own tests which confirmed that. Added bonus was a small but measurable increase in BC. Plus you could shoot almost any heavy monometal ever made then or since. Downside was that "tin foil" bullets lost more weight and FA than a premium bullet which would stand up to the extra rotational velocity. I was probably considered a cook in 1982! Glad to see there was some truth to it.

 

[RiverRider]

Maybe I'm vapor-locking here, but for the life of me I can't come up with the meaning of "FA."

Is it me, or a typo?

 

[kraky]

I guessed "frontal area" when I read it...made sense to me but probably wrong...lol!