Max Velocity for low drag bullets?

F

fleetus

Guest
I'm a newbie and an engineer by trade and after reading Precision Shooting at 1,000 yards and a bunch of other info I've started to think to decide what kind of rifle to build I need to start with the bullet I intend to use and work backwards from there. Reverse engineering. So I've read what everyone is using and the trials/tribulation associated and made a fairly common list (assuming use of short action in 6, 6.5 or 7:

6mm
115 DTAC
117 DTAC
105-107 Berger, SMK, Clinch, Lapua

6.5mm
139 Scenar
142 SMK

7mm
175 SMK
180 Berger

Given this list, with special regard to the highest BC's in each caliber, is there a MAX velocity/twist combination where a proverbial brick wall is? Where a slower twist won't stabilize and proper twist will cause the bullet to come apart at a certain velocity?

I'd like to be able to figure what max velocity I could stabilize the specific bullets and work back from there into choosing cartridge, how much maintenance for that cartridge (brass quality, cost, dies available, neck turning required etc.) how much recoil and efficiency.

Is this a good way to go about things? Is this kind of max bullet velocity vs. max twist a real limiting factor to consider?
 
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fleetus

Call the guys who make the bullets. They will tell you, and the info will be a lot more useful than what you might get on a Forum. Walt Berger is a particularly good source as is his sidekick, Eric Stecker.

Ray
 
Eric Stecker spends a lot of time on this forum, he may answer directly if you ask the question here. Berger Bullets is at 714-447-5456 if it's Berger you're mostly concerned with.

Shilen has a handy twist rate chart FWIW.

http://www.shilen.com/calibersAndTwists.html


There is no better source of information on earth than this forum, this is where the manufacturers get a lot of their information, from the end users. Eric Stecker is one of them. I don't know why some folks feel compelled to down-rate "the quality of information on this forum"................Cheech, if someone had a question about cartridge variants, where would you send them?


al
 
Al

I didn't mean to put down us Forum users. But for technical matters it's always best to go to the source. When it comes to the "best" velocity for VLDs you'll get a lot of anecdotal answers, most of them contradictory. What's a fella to do when one guy says 3050 fps and another says 3600 fps?

You'll notice that I never fail to add my two-bits worth of expertise, on anything from shooting to advice for the lovelorn.:rolleyes:

Ray
 
fleetus said:
Given this list, with special regard to the highest BC's in each caliber, is there a MAX velocity/twist combination where a proverbial brick wall is? Where a slower twist won't stabilize and proper twist will cause the bullet to come apart at a certain velocity?

Is this a good way to go about things? Is this kind of max bullet velocity vs. max twist a real limiting factor to consider?
Click to expand...

It's wise to consider this with wildcats, and to approach a gun project -bullet first.
But it would be difficult to cause failures with your listed bullets by accident.
Maybe you could kill a DTAC in 6WSM in 7.5tw. I don't know.

People don't run into alot of problems in these cals using heaviest bullets(except for the 115Berger). It's in 22cal, ~90gr, that narrow windows exist between tumble and blow-up.
 
Cheechako,

:)


As a construction guy I get the dubious pleasure of dealing with "technical experts" every day......"expert" designers and engineers and architects, most often directly from the manufacturing companies. "Expert" salesmen more like! Simpson Strong Tie is an example of a "Leader In The Construction Fastener Industry" that has no freakin' CLUE how their stuff works in the field! I've got a particular bracket that I work with that's on it's fourth go-round.........it's been re-designed four times as a result of us guys on the user end saying NO! I guess I'm more chary than most about getting my information from manufacturers and engineers. I'm currently in the market for a portable gang-nailer for truss mfging.......I've done online research and contacted the various companies but the ANSWERS come directly from the guys putting the trusses together, they can tell me exactly which tools work and last and which ones suck.




The facts are always to be found on the ground, end-user. Sure, it's all anecdotal and sure some folks do have an axe to grind but at least it's the folks actually USING the product.

I applaud Eric Stecker and the folks at Berger for coming to this forum for information regarding how their products perform. this post on this exact subject is an example....

http://www.benchrest.com/forums/showthread.php?t=40028&highlight=eric+stecker

This is as good as it gets.




fleetus,


You've asked some very broad questions.

No, there isn't a brick wall, more like a slippery slope.

Short answer??? Although it sounds like a cop out the old saw "everything's a tradeoff" certainly applies here. May I suggest that you have a 6BR built in 8" twist so that you'll have a platform with which to experiment, there will be no downside. You will learn enough with this one chambering to PERHAPS change your mind such that when this barrel's worn out you'll change to another chambering, but take it from one who's already spent a lot of money and time in experimentation...........the 6BR is a solid all-round choice.


My second choice would be the 6.5X47, also in 8" twist.


I personally wouldn't consider a 7MM, if you want a bigger hammer just jump up to 30 because the 7mm VS 30 is like a 16ga shotgun VS a 12ga in this analogy.


sorry to be so imprecise




al
 
well....since u asked..

Al and Ray are rite on ....there are several guys that have tried it all and then some like me that dabble....I can only expound on the 6mm --105-107 class bullets that u asked abut....
I once uppon a time...had a 6 x 284 ...in a land far away I tried just about every bullet out there....and had terrible results with any of the 105 class (berger and sierra) bullets....some did not make it to the target...some shot huge groups at 100yds...the bbl was 8 twist...it would shoot just about anything 100gr or smaller very well...but the 105's terrible...
I finally gave up and got a 6mm BR !!!! well let me tell u there is/was nothing wrong with the 105-107's that I had....I am shooting from the same lots of bullets as used in the 6x284 yet today...and they are performing perfectly.....the vel is just under 3000....in the 6x284 the vel was 3400 +++++......
If you go much slower than 8 twist the big un's wont stabalize .......sooo there seems to be a twst threshold around 8 or 9 and a velocity threshold around 3200 +/-.......hope this helps ...I have no documented pass/fail data about the 6.5 mm's or 7mm's......Roger
 
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Al

As the old saying goes, there are "experts" and there are "exspurts". (My wife thinks the young kid who works at the WalMart tool section is an expert on tools.) But it's my humble opinion that the artisans that Benchrest shooters deal with on a regular basis do know what they are talking about and I value their opinions and observations much more than my own. Who knows bullets better than Walt or Eric? Who knows barrels like Ed Shilen or Dan Lilja? Who knows how to smith a rifle like Mike Bryant or Dave Tooley. I know I'm leaving a lot of names out, but you get the idea.

Beginners often hold these guys in awe and hesitate to call them with questions. But you and I know that they are shooters just like us and are eager to help. Everytime a young shooter comes to me with a question I'll gladly give him my expertise but I also give him the phone number of a "real" expert.

JMHO

Ray
 
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Cheech I gotta' agree one the awe and unapproachability thing. Although for me it was a pleasant surprise to call Berger when my 7.5gainer was blowing up 115's, and the guy who picked up was Walt. And Walt told me "yup. some barrels do that"........ BUT...... answer my question. :D


WHO would you send someone to who has a REAL question about cartridge design and variations??










My point is that some of the best ON EARTH are right here! And Walt can't opine on Sierra bullets and the Lapua factory is a long ways off across't the sea.......and last time I talked to Sierra's tech guys.......


I actually wish the Sierra ballisticians WOULD show up on here sometimes! :D


LOL


al
 
Al

Who would I send someone to who has a question about cartridge design and variations? I don't know if there is such a person. I know a little bit, being a wildcatter and collector, but certainly there are a lot of gaps in my knowledge. There are guys on these forums who know as much as I do, such as the ex-pipefitter whose post you'll notice earlier in this thread. And others here and on other forums too.

One other mistake that young shooters often make is to mix product with expertise. You mentioned Sierra. Not too many BR shooters use Sierra bullets so they are inclined to say, "What the hell does Sierra know?" But, again, IMHO the Sierra ballisticians are some of the best, maybe better than Isaac Newton and Mother Nature herself. I've shot with some of the Sierra Tech guys and they are a pleasure to be around but those Ballistics guys are real nerds, and I mean that as a compliment.

Go Seahawks! No, wait . . .:rolleyes: We're off to Nevada tomorrow morning where I'll make a modest wager on the Super Bowl. I was hoping it would be on the Seahawks - but wait til next year.

Ray
 
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Is this a good way to go about things? Is this kind of max bullet velocity vs. max twist a real limiting factor to consider?
Click to expand...
Yes and no. The interesting thing here is that with your engineering background you are making the assumption that you can "determine" the proper answers to a set of conditions.

As Ray points out, a lot of the evidence is anecdotal. The other side to "anecdotal evidence" is that while such reports are not proof, they are evidence. So the short answer is, nobody knows all the variables. There are 6mms, 6.5mms and .30s which will shoot bullets at 3,500-plus. All bullets? No. All chamberings? No.

I'll bet that if you take up the sport, and if you keep with it a while, you will wind up building at least three new rifles, as you learn things & want to try something new. The time to use your background & figure things out isn't with the first rifle. Pick a gunsmith, and go with his/her recommendation. If you are building your own rifle, visit the match reports & pick a set of components that seem to place in the top 10 fairly often, and not all by one or two shooters.

As for Ray's advice, it will work, because the manufacturers will all give you safe, conservative numbers. But that is far different than a number where you "hit the wall" & no further (pick your variable) gains can be made.

BTW, when you look at BC with such fondness, consider both (1) the method of calculation, and (2) the real-world SD with respect to that number.
 
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10yrs or so ago, I sought a combination producing lowest point blank range for deer hunting. I dug into every shooting forum(including Canadian) and set up a table of common failure points as discussed by shooters. It was amazing to me how consistant this information was, and with it I could easily define 'the wall'.
I saw no correlation with any particular barrel, or loads, and only a few distinct trends w/resp to bullet brands.
But for the most part there were not significant differences with heaviest/cal jacketed bullets.

This is how I defined it:
Vlimit = 1.389*(238*(0.308-D)+290)*T

Over the years I've watched and tested, and have yet to find hard contradictions.

If you care to see a 'window' where this comes into play, you can dig up 220swift shooters pushing 90JLKs. Those at lower altitudes normally find that due to the twist requirements for these bullets, they cannot push them as fast as their capacity allows. They blow up at a very consistant point. But they cannot go to a slower twist to prevent this(like other shooters) unless local air density allows for it. Believe me, they tried. This is a window they create, and it can be done in each cal. But you really have to go out of your way to do it, usually sacrificing barrel life and accuracy..
 
Thanks all for some very helpful responses. I am leaning toward a 6mm and was wondering if I should consider the 115-117's rather than 105-107's. Reading here and the 6mmBR site, there were some reports of instability when pushing the DTAC and Berger 115 beyond various limits. I guess, based on what I'm hearing from all of you, the real limit is in barrel life and recoil of a light gun. The bullets may hold up but for diminishing returns, the barrel and/or recoil may become problems.

I may take Charles and expipers advice and start with a gunsmith and/or look for a deal on a 6BR or similar, maybe used. I have a couple rifles I can shoot for now, maybe only in factory class and 600 yds. Heavy class. So I will use them and keep an eye out for a good deal.
 
Cheechako,


You just don't GIVE do ya' Ray :):):) The answer is YOU because even if you do have "gaps" you've also got contacts and resources with which to fill those gaps. I've seen your posts here........


Your quote, " don't know if there is such a person. "


Well duhhhh :) Is there "such a person" regarding the OP's question? It just bugs me when knowledgable guys like yourself downplay "this forum"..........I spent twenty years collecting books and burning up the phone lines across't the nation, acquiring and sorting conflicting information (opinions) from all sorts of legendary gun-folks..................and when I klikked on this forum 10-12yrs ago and saw Borden and Wright and Murphy and Gammon and Dohrmann and Carstensen etc etc etc ,,,,,, well I thought I'd died and gone to heaven. I will NEVER back down on my contention that THIS BOARD is the single most valuable resource on the planet for cutting-edge knowledge accuracy-related.

I REMEMBER posting about shooting the 6BR at 1000yds and being ridiculed. AND I remember no less the The Bill Shehane coming on in support of it. AND I watched as this silly little cartridge went on to become it's own WEBSITE for cryin' out loud!!! The SECOND great website on the net....I remember when 18" twist 30cal barrels were unheard of. I ordered a Krieger and had it sent to Art Cocchia to be put on one of my rifles and he very nearly sent it BACK to Krieger assuming it was some sort of screwup! He'd never HEARD of such a thing.......and within the year Randy Robinette and his cronies had single-handedly revolutionized the Score world, the modems were burning across the land HERE on Wilbur's Board.


And thru the years us outsiders read about stuff like "barrel stretching" and "externally adjustable scope mounts" and "100lb guns" and have no WAY to really learn the truth............until here. I talk with Ellertson and Tooley and Pendergraft and Rogers, and I watch them hash stuff out right here. It's like sitting in on round tables where I'd NEVER be invited for real because I'm not currently a member of their circle. Guys from all over the world comparing details in real time. I'm here to see guys go from relative obscurity to setting world records, I'm here joshing with Rich DeSimone one week and the next week he's famous :D


Anyways, maybe it's the winter blahhs (it's snowing like a banshee outside, my kid just came in to tell me that the Sub's all chained up so's we can get out the driveway to get some Super Bowl food ;) ) but I really appreciate this resource and the AWESOME guys who're here.........including even YOU Ray :D:D



Ooops......rant off. :eek:



LOL



al
 
117 Dtac

Only a small part of your post I know , even so , dont go there .I have ( hearsay ) word that says that these are no longer being manufactured .

My personal experience with them in two different rifles indicates that they are not able to withstand 7.5 twists ( needed to stabilize them ) at 3000 or so fps . They dont make the trip an unacceptable amount of the time ( 10% or more ) .

Jim Brown

but ..................on the other hand if you want some of them I have a few thou I coul d sell you :eek:
 
New bullet

Just read this morning about Tubbs plans to offer a 111 DTAC. Read below:

"David Tubb’s Superior Shooting Systems currently offers two high-BC bullets, both produced by Sierra Bullets to David’s specifications. The original DTAC is a 115-grainer with a normal match hollowpoint. The second bullet is a 117gr MJPT (Metal Jacket Plastic Tip), with a super-high 0.600 BC, confirmed by actual field tests.

We’ve just learned that DTAC plans, shortly after SHOT Show, to introduce a new, 110 or 111-grain 6mm bullet. Like the 117 MJPT, this will have a plastic tip. However, it should have a shorter base-to-ogive measurement than the 117-grainer. Hopefully the new bullet will be short enough to work in rifles throated for the 105s and 108s. It should look like the 117 in the photo below, but with a shorter bearing surface, and a BC around 0.545.

David explained that the shot-to-shot BC variance of his bullets has been substantially reduced by the addition of the polymer bullet tip. With conventional bullets, true BC can vary from bullet to bullet because the meplats aren’t consistent. David tells us: “With the new bullet tip you no longer have to uniform the meplats to get a consistent BC shot-to-shot. As a bonus, the BC is higher overall due to improved aerodynamics. What we’ve seen in field testing is a spread of only 2% in actual bullet BC. This has reduced the measured shot-to-shot velocity spread at long range.”

Independent testing confirms many of David’s statements. A series of dual-chronograph tests done by Larry Bartholome and Ken Oehler showed that there IS significant bullet-to-bullet BC variance in most boxes of bullets. After testing over 30 brands of projectiles, Larry and Ken found the average extreme spread in BC was 0.019. On the other hand, plastic-tipped Hornady A-Max bullets showed the smallest BC variance of the samples tested. So maybe Tubb really is on to something here.

Bullet pointing tests also suggest the importance of reducing bullet-to-bullet BC variance. Jason Baney’s recent work with the Whidden Pointing Die showed that the reduction of bullet meplat diameter (by pointing) produces a significant increase in effective BC–as demonstrated by less bullet drop at long range."
 
A series of dual-chronograph tests done by Larry Bartholome and Ken Oehler showed that there IS significant bullet-to-bullet BC variance in most boxes of bullets. After testing over 30 brands of projectiles, Larry and Ken found the average extreme spread in BC was 0.019. On the other hand, plastic-tipped Hornady A-Max bullets showed the smallest BC variance of the samples tested. So maybe Tubb really is on to something here.
Click to expand...

At one point, I had the raw data from that set of tests. It is a generalization. Sample size wasn't great, and not all "untipped" bullets showed the variance mentioned. Some untipped bullets were extremely good, rivaling the one A-max the was lowest (maybe 10 shots for that A-max).

Further, not all tipped bullets showed the smallest variation. As I remember, the smallest ES/SD for BC was with a particular A-max, but that wasn't true for all A-max in different sizes/calibers.

Dave Tooley did some further work on this -- he too had all the original raw data. Dave both put plastic tips in bullets, and developed the meplat trimmer as an alternative approach. The tips helped some bullets. They didn't help (very small sample size) a bunch of Clinch River 106's, where the meplats were quite small and very even to start with.

By in large, Dave's conclusion was that trimming the meplat was the simplest, most effective way to get low SD in drag. You have to remember this was aimed at benchrest group shooting, where the target is not pulled after each shot (you can get a string off fast), and the 10-ring is not anywhere near as large as it is in highpower.

What is "best" depends on what you compete in. As a new shooter, you just are not going to get a competitive edge through technology, there are too many of us who have been around for a while & understand the compromises in making any choice.

So I'd repeat, build that first rifle & get some experience. Then decide where you'd like to make your compromises for the particular discipline you shoot.
 
Charles,

Thanks for the advice. I didn't post the information regarding my plans to build a particular rifle. Just happened to read that article this morning and though it might interest some of you veteran competitors. I started to begin a new thread but thought our discussion was in the same ballpark.

I do have my eye on a used, 6BR, Rem 700 SA trued, with Krieger 28" HV, Jewell trigger, McMillan HBR stock, 8" tw, .269 neck which weighs less than 16.5# with scope and has less than 300 rounds usage. If you have any thoughts on a rifle like this, would like to hear them.
I also already have a 284, Rem 700 with fat 1.25" straight Lilja, 25.5 length that I thought becaus of its 20+lbs. weight and short barrel, could use for 600 yards Heavy. Lastly, have a Cooper in 243WSSM, 10" twist that just traded for. Might try some 88 FB VLD loads to see if it might be a factory class option. Thanks again.
 
Lynn said:
Are the ones you are having trouble with boron nitrate coated or plain?
Lynn
Click to expand...

Lynn,

They are the boron nitride coated bullets . I spoke with a friend on the phone yesterday while he was at the shot show . He had just finished talking to David Tubb and had explained to him the problems we were having with 7.5 twist Schneider bbls and the 117 Dtac . He was informed by Tubb that the 117 was no longer in production . Bet he still has a lot of them on hand though .

Jim B.
 
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