Ogive Shape vs COAL/Jump to Lands

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edwardware

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I'm addressing an interesting issue with my Rem 700 SPS Tactical (16.5", 1:9" twist). I've loaded three bullets so far, with radically different results. All loads are in LC brass, FL sized, S&B SRPs, BL-C(2). Groups are always 5 shots, and repeatable on different days. Loading with a micrometer dead-length seater.

1) Sierra 1360, 55gr soft point with a tanget ogive. Tuned load yields 0.5 MOA repeatably.
Sierra%2B1360.jpg Zoom

2) Hornady 22271, 55gr VMax, with a secant ogive. First time out (untuned) several different charges shot 0.75 MOA groups; the worst charges shot 2+ MOA. Tuning OAL and charge should improve this.
Hornady%2B22271.jpg Zoom

3) Hornady 2266, 55gr soft point with cannelure, with an abrupt secant ogive. I have run the range of charge and OAL, and cannot make a group better than 2 MOA.
Hornady%2B2266.jpg Zoom

So what is going on with the Hornady SP? I don't expect the cannelure is helping, but it can't be that bad; semi- rifles shoot sumMOA with cannelured and crimped ammo all the time.

I've read that secant ogive bullets are very sensitive to jump-to-lands; how sensitive? Should I recover the COAL range in increments less than 0.012"? How much jump should I start with? Jump from jam, or just touching the lands?

I called Hornady, and they blamed the BL-C(2); I called Hodgdon, and they blamed the bullet. . . go figure.

Any suggestions?
 
I have used the optimum charge weight method to make bullets with a cannelure that were crimped shoot sub moa. If one powder won't work, just try another. They can be made to shoot just fine.
 
edwardware ran the range of both charge and OAL, but the bullet won't shoot in his gun. Good methodical workup. There are so many, many different variables that we can only guess why your rifle doesn't like that particular bullet, but the conclusion is the same:

A good methodical process in edwardware's known-good gun with the combination of premium components listed proves that this particular batch of Hornady SP doesn't work in this gun. Might work in other good guns, but not this one. Good work. You might test different powder & primer, or just move on with other bullets.

Just one note: We came across a lousy batch of Hornady FMJ BT with cannelure two years ago, they shot 2 to 4 MOA in every possible combination. Hornady took them back and sent a new batch, the new ones shot perfectly. Sometimes a bad batch gets through.

I say Good Work. Now move on.
 
Hornady bullet # 2266 @ 2.225" OAL. BHA Match brass sorted by weight. IMR 4198 @20.0grs. CCI 400 primer.

5 groups of 5 shots each = .712" @ 100 yds.

Due use wind flags.

Savage Axis 223. Good Luck.
 
. . . Just one note: We came across a lousy batch of Hornady FMJ BT. . . Hornady took them back and sent a new batch, the new ones shot perfectly.
Interesting possibility! I'll have to try the other batch and look for a difference.

. . .this particular batch of Hornady SP doesn't work in this gun. Might work in other good guns, but not this one.
That's certainly what it looks like, but I'm not sure I can stand to leave it alone until I understand WHY.

I'm still interested in learning about the apparent difference in sensitivity of secant vs tangent ogives to seating depth. Anyone have experience with this?
 
They didn't shoot very well for me in .222 Mag. The 2245 & 2265 shot great in the same gun.

It is what it is sometimes.
 
edwardware, I ran into this earlier this year. I bought a 6k case of the Hornady 55gr FMJ-BT for general plinking. My gun is a home built AR-15 using a Cheap Anderson 18" Wylde Chamber w/1:8 twist. The jump to the lands is extreme on this chamber. I did a full workup using these powders H335, W748, TAC, CFE-224, Varget, H4198, and IMR3031. After the best load was found I even played with the OAL to try to get better group. I eventually gave up trying to get anything better than a 1-2" group at 100 yrds with this gun. The OAL it preferred was 2.240-2.250" with most any load. This AR will shoot the Sierra 65gr HPBT & 69gr HPBT-M less than 3/4" with no problem. My conclusion is that this chamber does not like light bullets. The best group came with using TAC, with CFE-223 a close 2nd. I even tried premium bullets (55gr) in this barrel too, Hornady V-Max, A-Max, Nosler Varmageddon very little improvement. I shot well over 1500 rounds trying to get this gun to shoot the cheap bullets accurately, before I gave up on it.

The best load I found in the 18" Wylde chamber worked in my 24" Match Chamber (1:10, min spec 223R) AR-15 with a minor OAL change, had to shorten them. The shortened length put me almost back almost to book values. All testing was done using LC-15 brass once fired, that was annealed sized and trimmed after every firing. I even went to turning the necks to see if it would help, no go.

My conclusion, Some guns just will not like some bullet no matter what you do. I thing this is probably related to the long jump to lands.

Now these cheap 55gr FMJ-BT bullets will shoot 1/2" groups with TAC if I sort my brass by weight in my 24" Match barrel. 1" is the average with a few fliers now and then. I can't complain too much since I got these bullets for < $0.08 each. My most accurate loads for my 24" Match barrel has been with TAC using Sierra 52gr HPBT-M. Or 69gr HPBT-M using Varget. Varget seams to do better with the heavier bullets.
 
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My theory is that the sharper corner of the secant ogive increases pressure at a more specific point and is therefore is less forgiving when it comes to distance from the lands. But with a bolt rifle that's using the lands to seat the bullet, that same corner may actually increase OAL consistency when there's variation in neck tension.
 
I think the biggest contributor to a given bullet having good quality but poor accuracy is twofold and relates to the barrel. All bullets from major companies that are 33 caliber or smaller should shoot inside 1 MOA through 200 yards properly loaded and shot in decent rifles.

One's the barrel's groove diameter is larger than bullet diameter. It can be .0002" to .0015" smaller and accuracy will be excellent.

The other is its twist rate and/or bore/groove diameter isn't constant.
 
I think the biggest contributor to a given bullet having good quality but poor accuracy is twofold. . . the barrel's groove diameter is larger than bullet diameter (or) its twist rate and/or bore/groove diameter isn't constant.
I measured 5 samples of the three bullets; both Hornadys are very consistently 0.2242, and the Sierra's are 0.2240. They're as perfect as I can measure with a Mitutoyo mic.

I like your theory better than "It just doesn't work", but if it's the rifle I don't understand why the other bullets work well.

My theory is that the sharper corner of the secant ogive increases pressure at a more specific point and is therefore is less forgiving. . .
You got me thinking, while I was mic'ing the bullets in question: the cannelure is right near the front of the driving band. I wonder if the leading edge of the lands (rifling lead?) are angled just right so that the irregular cannelure is the first thing to touch them instead of the very short section of forward driving band. I have no way to measure this, but I do observe that my Sinclair Bullet Comparator (supposedly cut with a throating reamer) seems to rock and shimmy on the irregular cannelure rather than resting solidly on the driving band.

Has anyone ever seen an interaction between the rifling lead angle and the front edge of the driving band?

edwardware, I ran into this earlier this year. I bought a 6k case of the Hornady 55gr FMJ-BT for general plinking. . .
Yeah, I know the feeling! I have 5k of these, and I don't do many mag dumps. . . Maybe they'll work better after I shoot out and replace the barrel.
 
Rifle bullets don't have ""driving bands." See https://en.m.wikipedia.org/wiki/Driving_band

Knurling cannelures into bullet jackets unbalances them a little and if at the ogive large diameter, itmakes their ogive shape irregular at that place which degrades accuracy.

Some combinations of bullet diameter/ogive, bore/groove diameter and leade/throat angle produce better accuracy than others. Slug a 22 caliber bore with carefully pulled 22 rim fire bullets whose body isn't deformed.

SAAMI specs for bullet diameters have a .002" spread; .003" for bore/groove diameters.

Crimping case mouths into bullets adds another variable to their internal and external ballistics.

And us humans can't hold, aim and fire rifles 100% repeatable from shot to shot.

All of which means accuracy based on a couple of few shot groups is statistically insignificant. Shoot 20 shots of each load and get 4 times better data. And because all firearms shoot groups between zero and some value, use the biggest group shot with a load to represent it's accuracy. None will be smaller than zero; there's no limit on how big they'll be. And the biggest ones happen just as often as smallest ones. So regardless of how many groups you shoot, there's only one of each; all the others fall somewhere in between; most are about 1/3 that of the largest.
 
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Longer bearing surface and thicker jackets increase pressure using lead core jacketed rifle bullets.

All the pressure charts i have seen, show a pressure spike, when a jumping bullet makes contact with the rifling.

The FMJBT bullets with the lead exposed base will not produce the best groups, in my experence.
 
FMJBT bullets with hollow/exposed bases can shoot very accurate if well made. Sierra's first 30 caliber FMJBT match bullets would shoot inside 5" at 600 yards. When Sierra started work on their 30 caliber168 gr match bullet, they learned 165 gr BTHP hunting bullets made with good jacket copper, they shot more accurate in their test range than heavier FMJBT bullets. Their 168 gr. Int'l hollow point bullets had the least runout on their heel and exited muzzles better balanced. Some of their 10-shot test groups at 100 yards were under .100 inch. Sierra soon changed their 180 and 200 gr Match Kings to HPBT design; they easily shot under 4" at 600 yards.

A Nat'l Champion sorted a bunch of 185 gr Lapua FMJ rebated hollow base bullets for perfect balance spinning at 30,000 rpm. He shot several 10-shot groups at 600 yards all under 1.5", then shot a 40-shot group at 1.92".
 
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Bullet jackets are very important to bullet accuracy as well. Sierra, and all the others, only use the best jackets in their match bullets. Best meaning the most even all the way around. If they are thin on one side and fat on the other the lead core will be out of balance. So, the most consistent jackets are used for match bullets. Consistent in thickness not just all the way around, but from cup to cup. Guess where the lesser jackets are used.
 
but I do observe that my Sinclair Bullet Comparator (supposedly cut with a throating reamer) seems to rock and shimmy on the irregular cannelure rather than...

yes, the accompanying photos illustrate pretty clearly how little room for error there would be with this bullet, especially with any asymmetrical throat erosion. A standard neck size might not be helpful with such short bullets, either...

excellent illustration btw
 
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