Bullet stabilization question

R

RJC

New member
I am currently trying to work up a good Long Range Elk Hunting load for my 300 Win Mag. (accurized Rem 700, Pillar Bedded, 27” Lilja barrel, 1:10 twist).
I am trying to use the 180 gr Nosler Accubond bullet. I get ¾-1” Inch group @ 100 yds with 76.0 grains Reloader 22 and average muzzle velocity of 3172 FPS with a standard deviation of 4 FPS. However, the bullet hole looks very ragged and somewhat unstable at this Load. I am seating the the bullet .015 off jam.
I tried changing seating depth at Jam and .030 off . However, the group size goes really bad, but the muzzle velocity and SD still apprear Ok. As a relative novice to Long Range Shooting any advise would be appreciated.
 
Wife says 10 minutes until dinner, so I'll probably screw this up. A few things you should know: (1) *stablity* in ballistics is divided into two parts: gyroscopic stability, and dynamic stability. (2) Rate of twist affects only gyroscopic stability. (3) If a bullet is gyroscopically sable at 10 yards, it remains so downrange (actually, it becomes "more stable") . (4) We don't really know what causes a bullet to become dynamically unstable, but usually, if the bullet remains above trans-sonic speed (around 1400 fps) -- it will remain dynamically stable.

If a bullet is groscopically unstable, you'll get pie-plate size groups I'm talking 8-10 inches. at 200 yards. I think you need to look elsewhere for your .75 MOA groups -- which aren't bad, BTW.

FWIW
 
Bullet holes

RJC said:
I am currently trying to work up a good Long Range Elk Hunting load for my 300 Win Mag. (accurized Rem 700, Pillar Bedded, 27” Lilja barrel, 1:10 twist).
I am trying to use the 180 gr Nosler Accubond bullet. I get ¾-1” Inch group @ 100 yds with 76.0 grains Reloader 22 and average muzzle velocity of 3172 FPS with a standard deviation of 4 FPS. However, the bullet hole looks very ragged and somewhat unstable at this Load. I am seating the the bullet .015 off jam.
I tried changing seating depth at Jam and .030 off . However, the group size goes really bad, but the muzzle velocity and SD still apprear Ok. As a relative novice to Long Range Shooting any advise would be appreciated.
Click to expand...

1:10 twist should certainly stabilize the 180 gr Accubond. What do mean by the bullet hole looks unstable; are the holes oval rather than round? Trying taping your targets flat on a new piece of cardboard and staple that up.

Just curious how you arrived at 76.0 grs of RL 22 because that should be a rather compressed load. The Nosler manual lists 75.5 grs. of RL 22 as maximum and most accurate at 107% load density. Must be a beast to shoot.

How many shots per group and are your groups more vertical or horizontal? - nhk
 
I think I would look at loaded ammo runout, this can give the appearance of a stabilization issue, and the twist rate is OK. While you are at it, it also would be a good idea
to confirm the accuracy of your seating depth. Use an OAL gage and a mic seating die, Good ammo should have less than say .002 run out and seating accuracy at .001
I got the following from a post on Handloads.Com
Ok, you need a bullet to start out as straight as possible into the rifling. If it does not start out straight it will just force its way through at a tilt. Many thousands of pounds of pressure have a way of forcing a bullet in slightly crooked. Now when it goes in crooked it comes out crooked, no matter how long the barrel is.
When a bullet comes out nice and straight the aerodynamic forces act on the nose equally in all directions letting the bullet fly straighter. Now add a slight tilt to the bullet as it comes out and the aerodynamic forces can and will act with more force on the section that is displaying the larger surface area to the wind. This will eventually cause the bullet to yaw and tumble depending on the range.
 
Dirty Dan,

here's a problem. The amount of inbore yaw (your 'force it through at a tilt' reference) is directly controlled by neck clearance. "Concentricity" of the loaded round has nothing to do with it. As that bullet's getting hammered into the lands, the case is GONE from it, all influence from "concentricity" is over because the case has slapped out against the chamber walls to act as the gasket which keeps all that high pressure gas inside where it belongs......


This neck clearance issue is the single biggest reason a factory rifle CANNOT really shoot well and the reason "straightening cases" via folding/spindling/mutilation is an exercise in futility.

Now.... those concentric case which fireform more straight than their brethren absolutely will shoot better, in anything, but IMO this has to do with vibration characteristics more than inbore yaw.

opinionsby


al
 
Neck clearance/case straightness -- if by that you mean the amount the bullet may be off-center -- is only one factor in "in bore yaw." Center of gravity offset in the bullet is another. The late, great Bob McCoy allowed as how we do not know all the factors contributing to in bore yaw, and we could not, even with known values of the dimensions we know contribute to it, predict in bore yaw.

We can, however, measure the bullet's tip off rate with spark photography. A large part of the tip-off rate is determined by in bore yaw

* * *

In my first post, I said that .75 to 1 MOA groups from a hunting rifle is not bad. I still say that. If you want better accuracy, try changing the bullet -- no , wait, this is a hunting rifle; bullet performance is not determined by the size of the groups.

I don't know hunting bullet performance. Some people have reported good accuracy with the Barnes XXX, and I guess Berger is touting their bullets as hunting rounds as well.

I think, but do not know, that your load is up there. I shoot a 190 grain bullet at a bit over 3,100 in a marginally smaller case, essentially a .300 Norma Magnum. That's a benchrest round, and I know pressures are high in my rifle. In my rifle, built around a 2-inch diameter BAT action, I can safely load it up until I see the ejector marks in the case head. I do back off from there of course, and don't under any circumstances recommend use this as a technique. It shows a load is too damn hot. It may be far too hot in your rifle long before the ejector hole makes a mark of the case head.

The Sierra manual, for a 190 grain bullet, lists 73.5 grains of Rel-22 as maximum.I know it shows 76.1 as max for a 180. Well, different bullets, and just in case you didn't know it, the burn rate of Rel-22 has been all over the map. Canister powders are allowed a 10% variation, and a couple of times, Reloader has pushed the 20% variation allowed by bulk powders, where it is assumed the loading company will do further testing to ensure performance IN ALL ASPECTS, which includes safety.
 
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in bore yaw

Sorry to dissapoint, but even with a fitted neck you can still get ammo with (in my own case
I use .001 neck clearance in the gun and the reloading die) I still see reloaded ammo that has .0005 runout on the shoulder and the neck and have bullet run out between .0005 and
.011, this is possible because the neck o.d. is.310 and the bullet o.d. is .02845, and since the primer will drive the bullet into the lands before the neck stretches it will enter at its loaded angle.Quote (Experienced shooters know that accuracy is degraded when the bullet is misaligned with the cartridge case centerline and the bore axis. Bullets entering the rifling at an angle will show a phenomenon known as “in-bore yaw.” Well-studied by American Rifleman Ballistics Editor William C. Davis and his associate, Charles Fagg, in-bore yaw can contribute significantly to group dispersion. Unfortunately, even the best ammunition may exhibit an undesirable degree of bullet misalignment or runout—generally, more than 0.002-0.003 inches.)
 
Dirty Dan said:
Sorry to dissapoint, but even with a fitted neck you can still get ammo with (in my own case
I use .001 neck clearance in the gun and the reloading die) I still see reloaded ammo that has .0005 runout on the shoulder and the neck and have bullet run out between .0005 and
.011, this is possible because the neck o.d. is.310 and the bullet o.d. is .02845, and since the primer will drive the bullet into the lands before the neck stretches it will enter at its loaded angle.Quote (Experienced shooters know that accuracy is degraded when the bullet is misaligned with the cartridge case centerline and the bore axis. Bullets entering the rifling at an angle will show a phenomenon known as “in-bore yaw.” Well-studied by American Rifleman Ballistics Editor William C. Davis and his associate, Charles Fagg, in-bore yaw can contribute significantly to group dispersion. Unfortunately, even the best ammunition may exhibit an undesirable degree of bullet misalignment or runout—generally, more than 0.002-0.003 inches.)
Click to expand...

whatever :rolleyes:
 
Neck concentricity

Since I went to no-turn neck chambers and Lapua brass my groups have improved and I get more sleep... not turning necks or measuring run out. nhk
 
Dirty Dan,

I find it interesting that with all the studies done on inbore yaw and loaded round concentricity, that nobody bothered to make a set of dies in one operation so they were straight. You ever seen ammo out of a straight die? My guess, from your posts, is no.

You'd be surprised how much nicer things are when you have a set of dies that's not in the shape of a banana. You could use a piece of my ammo to check your concentricity gauge.
 
Dirty Dan said:
(Experienced shooters know that accuracy is degraded when the bullet is misaligned with the cartridge case centerline and the bore axis.
Click to expand...

So, Creighton Audette was not experienced?

He did test, though, and his results were the opposite. 'Course even though published in Precision Shooting, Audette was highpower, not benchrest. Maybe that's the reason.

@Phil

As I'm sure you know, dies are only one part of the equation. Straight dies are nice. So too is brass of equal wall thickness. Even a straight die won't "straighten" banana brass when it is pulled out of the die.

Still, ideally, as far as I'm concerned, if the neck is true to the bore and the case head square to the boltface, the rest of the case can do whatever it wants. Not that easy to arrange, I'll allow.
 
Charles E said:
as far as I'm concerned, if the neck is true to the bore and the case head square to the boltface, the rest of the case can do whatever it wants
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This is where alinwa's declaration comes into play.
The neck is not true to anything if there is high clearance and you are not fully jammed into the lands. With this, the neck is laying against the chamber far from centerline.

And I wonder... Did Bill Davis actually measure & quantify in-bore yaw to respective cause? It seems that if he did, we'd all know the numbers off the top of our heads by now..
As I consider a primary law in our cosmos: ONLY A TRUTH PASSES ALL TESTS
If even one BR shooter does well with high loaded cartridge runout, then many notions here will fail tests.
 
Charles, even with some of the rather poor brass I've had, I've never seen runout in cases. After fireforming, I don't generally move brass more than a max of about .004 anyhow, (cept the neck of course). And most times, way less than that. Probably closer to .002. You can't really introduce much change in shape to the brass like that. I usually stay out of concentricity discussions, but, it seems crazy to me that you can go out and buy a set of dies that are so out of line they give people .002 of runout in a case. I sometimes think some of these companies make their dies with a hand drill or something.

mikecr said:
This is where alinwa's declaration comes into play.
The neck is not true to anything if there is high clearance and you are not fully jammed into the lands. With this, the neck is laying against the chamber far from centerline.
Click to expand...
Not really true Mike. If you think about it, it is very rare for anyone to size a case more than .001 or .002 at the shoulder. IF the shoulder is where it was before you size, then odds are the neck is somewhere pretty close to centered, even if you do use a lot of clearance. Regardless of how much clearance you have, the neck does not support the case, ever. (less you use a press fit neck, and I think that's rare).
 
I'm followin what you're sayin. But I get the impression that FL sizing is all the rave in BR.
Easy bolt turning, less bag upsetting.. I would think they would atleast be custom FL dies.

But the best die in the world is likely your smoking chamber. This is what straightens cases.
Downsizing dies, no matter how perfect, do not straighten brass. They cycle brass, bringing the devil out of it.
This shows up plane as day -as runout. Ever increasing with each cycling of the brass..
It's NOT because dies aren't straight!
Before long various stresses in the case add & subtract to cause inconsistent contact in chambers. And who knows where perfectly concentric bullets (to case centerline) are pointed then?
Two things are essential to low runout:
Culling cases for lowest thickness variance -anywhere, and minimal sizing -anywhere.
 
MIke,

It's not so much that it's all the rave, but, its almost a necessity in long range br. A long range gun is a very different animal than a short range one. It's really not fair to compare a ppc with 1000psi muzzle pressure to a long range gun with 6000psi. It's the difference in powders. Guys shooting smaller cases that have a shorter pressure spike might not need to fl resize every time. Guys with a larger caliber shooting slower powders and heavy bullet, do.

Most commercially made dies, that I know of anyhow, have the bodies made in one step and the neck/shoulder cut in another. These are not even done in the same machine. So, as soon as the setup changes, that die is no longer straight. Or, it's a one in a million. I've observed this with enough brands of die to know I didn't want any of them, and began making my own.

For those guys who are using custom made dies, I think many of your statements don't apply. For those using typical off the shelf dies, they usually have trouble.

I've been at enough 1000 yard br matches, and seen enough guys have difficulty with case feeding to know that just about everybody on the line uses dies that are pretty close. Or they size so little as to keep the cases close. I don't think you can really apply the generic stereotype of FL resize to a BR gun where, yea, its a FL resize, but it barely touches.

As for a chamber being straighter, mine are cut with the same boring bar that the dies are made wtih. But the die is tool steel and it's larger in diameter than the barrel that contains the bang. They are always a high chrome steel, if I had a second over that would do 2200f, they'd be made from 52100. Mine are not carborized and quenched, so they're not distorted, and I go to pretty great length to make certain the heat treat process does not change that.

All I'm saying is, there's always blanket statements made about case runout, many of which are believed to be gospel. I disagree with most of them. My brass with 50+ firings is as straight as it can be. It's never had influence to be otherwise, and I stand by my statement that most dies that make cases bend, are bent. Throw one in a CMM and check it.
 
No turn neck?

nhkuehl said:
Since I went to no-turn neck chambers and Lapua brass my groups have improved and I get more sleep... not turning necks or measuring run out. nhk
Click to expand...

You know, I read all that stuff about no turn necks, so I got one on my latest custom 6BR. The Lapua brass consistently was .0005 thicker on one side of the neck. When loaded, the runout gauge needle swung .003 on every cartridge seated with the wilson seater. I turned the necks just enough to get them round and the runout reduced to .001 on every cartridge. Did it make a difference at the target? You bet it did! Groups shrunk from 2 inches to 1.5 inches at 500 yards.
 
lrgoodger said:
YDid it make a difference at the target? You bet it did! Groups shrunk from 2 inches to 1.5 inches at 500 yards.
Click to expand...

Sample size? That is, how may groups, of how many shots, to determine the improvement of .5 inches at 500 yards?

For example, I went out and tested a new bullet yesterday, In the process, I did some primer testing, and thought I was on to something. Then realized I was basing this on a couple of groups.

Oops. Good enough to encourage more testing, not good enough give numbers. And for me, not good enough to draw firm conclusions, still in that large "can't hurt, might help" category.
 
Run out

lrgoodger said:
You know, I read all that stuff about no turn necks, so I got one on my latest custom 6BR. The Lapua brass consistently was .0005 thicker on one side of the neck. When loaded, the runout gauge needle swung .003 on every cartridge seated with the wilson seater. I turned the necks just enough to get them round and the runout reduced to .001 on every cartridge. Did it make a difference at the target? You bet it did! Groups shrunk from 2 inches to 1.5 inches at 500 yards.
Click to expand...

Good for you. #1-I match the bullet and twist. (Don Miller twist formula) #2-I use bushing dies and a competition seater. #3-I load for the node. In recent years I've taken machining classes and do some machining work and have a friend that has been a machinist for over 40 years and does precicion work and will be the first to tell you that unless you work in a controled atmosphere anything 'more accurate' than 0.001" is suspect. At 500 yds wind is a big factor and you may have shot under better conditions that day or read the wind better. If your bolt, chamber, throat and barrel aren't all concentric to start with you won't get much improvement with .001-2" less runout. I threw together a .243 Win with a Shilen barrel and a Savage action in a Bell & Carlson stock and loads with Lapua brass straight out of the box and it shot .25 MOA at 200m for three different shooters. - nhk
 
Off the track

I looked back at where this thread started and we haven't seen any more of RJC with his 300 Win Mag and 180 gr Accubond bullets, but we're talking about run-out, etc. There are so many mechanical factors that RJC could be (have been) dealing with long before he would progress to turning case necks on a hunting rifle and I think we lost him. I think he discovered that .015" jump was best. His load may be a little hot. Other than that everything else has been an assumption.... and I got into it too :) - nhk
 
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