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Old February 3, 2011, 11:42 AM   #1
tpcollins
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More bullet bearing surface equal better stabilization?

I'm trying to compare my 70gr Nosler varmint tip in .243 versus the Barnes 62gr granades (haven't shot the Barnes yet). The Nosler is .909" overall, about .766" not including the tip, has a .370" from ogive to base but with about a .060" boat tail, the actual bearing surface is only about .310". The Barnes grenade is .980" overall (longer due to solid copper), and has an ogive to base of about .464" with the base is basically square.

This gives the Barnes about a 50% more of bearing surface contacting the rifling compared to the Nosler but the Nosler still has a higher BC (.310 to .199). In the ballistic charts the Nosler may have less "drop" over a given range but does the increase bearing surface of the Barnes allow for more consistant "tighter groups" over the same distance? Thanks.
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Old February 3, 2011, 12:09 PM   #2
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Quote:
does the increase bearing surface of the Barnes allow for more consistant "tighter groups" over the same distance?
Not really.

The bullet spin is determined by the barrel twist, and you have a lot of other problems if the bullets are skidding on the rifling and not getting the rifling's twist.

If anything, more contact increase friction.
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Old February 3, 2011, 12:45 PM   #3
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I do not think the issue is skidding the rifling.
The issue is having the bullet enter the bore square and straight.
If things work out right,the higher BC bullets can shoot with superb accuracy.The record 1000 yd bullets shooting under 4" groups are VLDs
But with an average factory throat,maybe seating depth controlled by a magazine,etc,a light boat tail with a skinny ogive may not give you the accuracy.Or,if your rifle likes it,it might shoot great.
Its not an either/or deal,you may play with seating depths or try a flat base with a fairly high BC.
An example,in 2 AR's.one a very accurate Badger bbl with some throat wear,the new .308 155 Sierra Palma with the over .500 BC does not group well for us in our rifles,based on a limited experiment.It is no doubt a world class match bullet in a properly setup rifle.In our rifles,the older Palma bullet,now the 155 MK,BC about .435,shot extremely well.
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Old February 3, 2011, 04:56 PM   #4
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This may not answer your question, but............. It’s been a few years ago and I don’t remember all the bullets I tested with, but my .243 Ruger shoots better groups with flat based bullets than with boat tails. This proved true regardless of brand.

By the way, I haven't done any real testing, but this also seems to be the case with my 30/06 Model 70.
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Old February 4, 2011, 12:13 AM   #5
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Flat based bullets are supposedly better for shorter distances because they clear the barrel end slightly faster so the gas has less time to give it that "wobble" the boat tail are supposedly better for long distance because they are more aerodynamic. I didn't test it, but I read about it on the internet so it must be true.

On a side note, BC is really a myth used to sell bullets. Enviromental effects do more to the bullet's trajectory than the BC ever will. If you look up how they get the BC of the bullet you'll know what I mean. Its basically comparing how long it would take the perfect bullet, at the ideal temp, to get from point A to point B in a vaccuum to bullet x. Or something like that. I read it all a long time ago and then quit worrying about it and just started experimenting with bullets that fit the job I was trying to do.
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Old February 4, 2011, 02:25 AM   #6
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Semi-problematic,I have to say my experience is different than yours.Long enough ago it came on a floppy disc to load in my HP 386 SX 20 mhz computer,I bought Sierra's ballistic software.I live at near 5000 ft elevation.I have a good Leica rangefinder and access to private ranches where I can shoot off by myself at ranges over 1000 yds.I also have a good chronograph and a wind meter.
One of the moments of satisfaction I enjoyed was taking the Leupold B+C reticle data,and studying different cartridges,bullets,BC's,etc.I wanted an elk cartridge that,with a center crosshair 300 yd zero would follow the B+C reticle to 600 yds at around 8000 ft elevation.I ran the numbers,studied loading data,ordered a Lilja barrel (30 cal,26 in,#3 contour,1 in 10).I blueprinted a Husky 5000 smallring magnum action,Canjar trigger and put it in a Hi-tec specialties 20 oz stock.Cartridge was 30-338.I predicted I could get 2900 fps with a 200 gr Accubond.It would be a trajectory match.Built the rifle,made the loads.Used a VX3 3.5-10 B+C. Got my velocity,sighted 300 yds at the N Sandhills near Walden,Co..Put out a lasered 500 yd target.Fired one round cold bbl @ 500 and walked down..It was an x ring centered hit using the B+C.
I nearly always load boat tail bullets,and the accuracy keeps me happy.
I have noticed the secant ogive VLDs,with a long meplat and short bearing cylinder,may be harder to get to shoot.They are picky.That does not mean they will not shoot.
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Old February 4, 2011, 07:26 AM   #7
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It’s been over 50 years since I shot any 1000 yarders, but if my old memories are correct there wasn’t much difference in accuracy,if any, between flat based and boat tails at that range. I shot both, in 30/06, but mostly 168 grain flat based. The argument as to which was best raged on back then and is still going strong today. I always leaned more towards it being the rifle than the bullet.

Of course a lot of water has passed under the bridge since then, so maybe more scientific studies have proven differences that we old timers weren’t aware of.

Hmmm.... 1000 yards with open sights......... I couldn’t hit a water tower at that range today....... I’m not sure if I can even see one that far away now........
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Old February 4, 2011, 03:19 PM   #8
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I'm not really sure which experience you're talking about... Boat tailed vs flat based; or the holy BC of a bullet.
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Old February 4, 2011, 04:00 PM   #9
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Boat tailed vs. flat based........ I've never put much stock in BC.......If that was directed at me.
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Old February 4, 2011, 05:23 PM   #10
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Oh no, it was for hibc, he said his experience was different and then went on to describe his awesome rifle and all his shooting gear. Which got me drooling so much I lost track of his point.
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Old February 4, 2011, 05:47 PM   #11
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At the risk of being thought a spoilsport, I'll address the original question with another-or two--What is your barrel's rate of twist? --- and have you thought about contacting the manufacturers of the bullets in question and ask their recommendations as to the best twist?
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Old February 4, 2011, 05:59 PM   #12
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Smart thinking
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Old February 4, 2011, 06:28 PM   #13
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In short, my opinion is "yes". When the 60 gr. Sierra HP came out years ago, I tried like the dickens to get a load to shoot in my Rem. 788 with IMR 4064, 4320, and Win. 760. Nothing would do better than a little over 1" at velocities over 3600 fps. This gun routinely shoots 85 gr. FACTORY loads less than 3/8", and most 100 gr. BTSP's in 1/2". I surmized through measurement that the short bearing surface and longer nose profile was at fault.

At extreme velocities, small bullets ask a lot of the shooter, load, and firearm. That 60 gr. pill was just too short to do any better in my setup. As you may know, typical loading formulas suggest you seat the bullet at least the same depth as the diameter. Sometimes you just can't achieve that. Forget twist rates, unless you're willing to spend $$$ just to get one load to shoot (new barrel). Standard rates are set for each caliber averaged for the nominal length of the entire bullet range.

Another factor most shooters arguably ignore is your barrel length. Time in the lands is also required to stabilize the bullet, maybe more or less for short, light, fast projectiles. Definitely more for the longer, heavier submarines. If you don't give the bullet time to complete the revolutions necessary to stabilize those violent harmonics, it makes little difference that you were ATTEMPTING to twist it faster or slower. If it doesn't rotate EXACTLY in line with its axis, it's just not stable enough to fly well.

I wrote several posts years back on my experiments with three varying barrel lengths in different rifles I shot- all chambered in 7mm Rem. Mag. The 22" gun (odd?) loved the 139 gr. Hornady, but would not shoot well with much over 150 grs. The 24" gun shot 150-154 gr. loads in less than 3/4". My 26" M70 shoots 160-165 gr. bullets about the same, but nothing any lighter will go less than 1 1/4". All three were 1 in 9 1/2" twists.

I only have two rifles in .243, but my guess from experience so far is they are doing exactly the same thing. Twist is 1 in 9" for both: one wears a 22" barrel, the other a 20" youth lightweight job. It really shows up when you go for the 100 gr. loads. Sometimes sectional density is a better baseline to judge from.


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Old February 4, 2011, 09:51 PM   #14
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I figure if it starts into the rifleing crooked, it will come out the other end of the tube just as crooked no matter what bullet you choose. Concentric loads will always be more accurate than ones that are not, and Ive always had slightly better luck getting the flat base bullets to seat better (straighter) than boat tails no matter what dies I use. VLDs have proven to be the toughest nut to crack for me. In short I think seating them straight plays a more significant role than bearing surface when it comes to accuracy. This rambling is just my 2 cents.

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Old February 4, 2011, 09:53 PM   #15
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So I wonder how well my 525 grain beer can is going to shoot out of my 20 in barrel
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