Lets discuss "Accuracy"

[Team Sergeant]

Originally Posted by longrange1947

Just to throw some crap out there, transitional ballistics is a form of external and is actually more pronounced in some barrel twists than others.

What it really effects is a near range zero. Remember that the bullet crosses the line of sight (LOS) twice, once on the way down range and when, hopefully your LOS and POI coincide on the target. With some barrel bullet combination, your grouping potential at say 35 meters is worse than your grouping potential at 200. Reason is Transitional Ballistics and this is when the effect of the rifle is still present and before only external forces effect the bullet.

Clear as mud?

Is this the reason (transitional ballistics) some have taken to "Barrel De-Resonators"?

[GratefulCitizen]

Not being a frequent shooter, I've looked at some of these accuracy issues from afar.
Curious as to what the sources of "error" are in accuracy.

Given several sources of error (call them e1, e2, etc.), statistical variation implies that the bigger sources dwarf the smaller ones to insignificance (at least until the bigger ones are reduced to near parity with the smaller ones through improved equipment, loads, etc.).
Total error = square root ((e1)^2 + (e2)^2 +...)

In the opinion of the experts, what are the biggest sources of error?

[longrange1947]

Trans sonic flight can be a problem due to the turbulence that can effect the bullet. This can be seen in the Ballistic Coefficient (BC) that, unlike published numbers, change through the flight of the bullet.

The BC decreases as the speed of the bullet decreases until trans sonic and it crashes. Once through to sub sonic it again climbs to the same level just prior to trans sonic or in many cases even higher.

The problems in bullet stability in some cases is not instability, but rather over stabilized gyroscopic problems. As soon as the bullet leaves the barrel the bullet becomes more and more gyroscopically stable. Reason is that while the MV slows, the spin rate does not slow hardly at all. This means that bullet is now becoming more and more like a gyroscope. And like a gyroscope, while hard to bump off its course, when bumped sufficiently it will do a radical change. The is where transonic can be a problem

Barrel de-resonators are an attempt to insure that the bullet comes out of the barrel at the exact same time in the barrel impulse. This increases accuracy. Most barrels, match barrels especially already do a pretty good job of that, but too many things can change the harmonics and change where the barrel is when the bullet exits. The De-Resonators are supposed to help fix that problem.

Biggest source of error? The shooter. Next is gun and ammo. Look at the statistical error of a .5 moa shooter, .5 moa gun, and a .5 moa ammo. Now change any one of them to 1 moa. Now change anyone of them to the normal hack shooter of 4 moa. Take a round and leave it in the chamber too long or out in the hot sun, you have induced an elevation error. Let the rifle set out in the sun to long and the top of the barrel heats more than the bottom. Top expands more that the bottom, elevation error. Get a crap gun and or crap ammo, and well, now you have errors compounded as the consistency is all over the map.

After that the biggest error, in rifle and long range, is air resistance. Be it wind, altitude, or whatever.

Still mud? I may be trying to answer is too short of a form. Let me know.

[craigepo]

I have two bolt guns that shoot really, really well. I also have a short distance, group therapy rifle. I'm thinking that I need more.

I'm thinking about getting, not necessarily an M21, but a highly accurate self-loader. .308 would be an acceptable caliber, as anything farther out would be bolt gun territory.

I have a friend who does a great job building bolt guns. He doesn't even touch autoloaders.

I'm curious if anyone has any expertise building such a rifle. What are the differences in building an accurate autoloader vs. a bolt gun? Can a person build an accurate self-loader while keeping the weight down to less than an M60?

[HOLLiS]

LR1947, I was told that Trans sonics was responsible for a anomaly with BP rifles. At 100M it has a 2 in group and at 200M is has 2 in group, after that it behaves normally after that.

Wasn't there some companies that would deliberately put a pressure point under the barrel? Other wise the barrel was free floating.


@ craigepo, Auto loaders as in the M1 Garand or the M14/M1A1?

[longrange1947]

Hollis, not trans sonic, your bullet is doing what the Brits call sleeping. It is what I was talking about above, if I have read your explanation correctly. The round is under spun to make it more accurate at your desired range. Brit Palma rounds are famous for this. The round is rotating around the flight path but not on the flight path, sort of a wobble. The bullet will slowly come back on flight path as the bullet slows and it becomes more gyroscopically stabilized. If a bullet was to go trans sonic while in that condition, the round would really take off due to the turbulence at trans sonic.

On the pressure point, that was for the lighter skinner barrels to prevent barrel whip. That is one of the reasons the SVD has such problems is simple barrel whip, well that and crap QC. The pressure point you can find right at the end of the fore stock in which the barrel rests on that pedestal. The heavier barrels do not have a barrel whip problem so the barrels are free floated. This gives about 17 pounds of up pressure and stabilizes the barrel so the bullet comes out of the barrel at the same point, or there abouts.

craige, how far out, I have shot my AR15 to 600 yards and have watched others shoot it to 1000 yards. The AR platform has really great potential. My OBR in 7.62 will shoot to over 1000 meters with no real problem. I would stay away form the M21/M1A platform unless you like messing around with a weapon keeping it tuned, and that is experience speaking.

[GratefulCitizen]

Originally Posted by longrange1947

Biggest source of error? The shooter. Next is gun and ammo. Look at the statistical error of a .5 moa shooter, .5 moa gun, and a .5 moa ammo. Now change any one of them to 1 moa. Now change anyone of them to the normal hack shooter of 4 moa. Take a round and leave it in the chamber too long or out in the hot sun, you have induced an elevation error. Let the rifle set out in the sun to long and the top of the barrel heats more than the bottom. Top expands more that the bottom, elevation error. Get a crap gun and or crap ammo, and well, now you have errors compounded as the consistency is all over the map.

After that the biggest error, in rifle and long range, is air resistance. Be it wind, altitude, or whatever.

Still mud? I may be trying to answer is too short of a form. Let me know.

I understand how increasing the error from any one source dwarfs the other sources, especially when it comes to the shooter.
IIRC, TS once said something to the effect of "expensive golf clubs won't make you golf like Tiger Woods, neither will an expensive gun make you a good shooter".

Was curious as to some of the gun/ammo aspects purely from the technology standpoint, and what order of priority the experts would put on them.

There is just plenty of stuff in there that "I don't know that I don't know".
Trying to figure out what exists in those "blind" areas of ignorance.

At what point are there diminishing returns on barrel thickness?
How important are quality scope rings?
How important is parallax adjustment on optics?
Which aspect of handloading tends to matter most (precision in overall length, precision in powder charge, bullet choice, etc.) and why?
Should different bullet weights be selected to take advantage of the stability issues mentioned for different ranges?
It's my understanding that hollow points improve interior ballistics due to the rearward shifted center of mass.
-Is this true, and how important is it?
-Do hollow points suffer from less stability with exterior ballistics?

Those are a few of the thoughts wandering through my mind.

[longrange1947]

WOW, let me see if I can touch on these for you.

TS is absolutely correct, top gun will not make you a good shooter, but it will prevent a good shooter from shooting rat shit in a dresser drawer.

Weapon/optics

Barrel, needs to be heavy enough to not whip but not so heavy as to be unwieldy. Forget flutes, they are a way to make money for the gunsmith. The barrel on the M24 is about the limit on thickness and that is pushing it a bit. The bore needs to be enough to have a good throat but not so new as to have not settled in, a reason for the first 100 - 150 rounds. Once the throat starts to erode you have problem with free bore but you do not want to pre-engrave the bullet by making the throat too tight. That horse is dead, it also leads to making it so tight that the care becomes pre-engraved, which in turn pinched the bullet and you get one hell of a pressure spike, not good for gun or shooter, let alone accuracy.

Barrel needs to be free floated and allowed to vibrate from the round and explosion that just took place. The ideal situation is that the barrel harmonics allow the round to exit the barrel in the same point of the sin wave. I use sin wave loosly here, as the wave can be on any plane around the barrel and in some cases loops around the barrel as the bullet spins down the barrel. This error is measured in MOA and is more pronounced as the range increases. Anything, and I mean anything that disrupts this harmonic will cause a loss of accuracy. This is usually a shooter error that allows the barrel to become trapped and not vibrate freely.

Action and recoil lug needs to be fixed, usually by bedding and only the rear of the recoil lug will touch the bedding/stock. If the action begins to shift in the weapon due to collapsing bedding, crushed wood/fiberglass, then as the action shifts so does the alignment of the barrel.

Stock needs to fit the shooter so that he can get a natural stock/spot/cheek weld. This sets the eye relief which sets the sight alignment. Sight alignment errors are measured in MOA and as with above becomes a greater miss at longer ranges. Sight alignment plays in scopes as with iron sights, when you do not have a parallax adjustable scope.

Scope rings, buy good ones, cheap ones will loosen or break at the worse possible time, and will not hold zero or will not return to zero if the scope needs to be removed. An example is the Redfield ring/base combo on early SWSs. The scope rings were not fixed well in the base and the rings would begin to drift.

Parallax error is measured in MOA but to see the actual error, look through the scope and wiggle your head, when you see the cross hairs move from one side of the target to the other, and off the target, that is your potential error. Very important. When we did not have parallax adjustments, I would wiggle my head and make sure that I not only did not have shadow, parallax indicator that your head is not aligned properly, but that the reticle moved evenly left right up and down on my target, took a second, but helped negate the error.

Handloading is all about consistency. All cases should weigh the same. Why, because a difference in weight means that there is a difference in case capacity which means there will be a pressure differential. That pressure change is a MV difference. Also, powder charge needs to be trickled to the correct weight, again MV changes if you have a change in powder weight. There are so many little things in handloading that will bite in when you are looking to accuracy. From touch hole being clean and concentric for even powder burn to case length for the same free bore shot after shot.

Bullet weights are important, I shot 77gr for 200 and 300 yards, and 80gr for 600 and 1000. Most people shoot the round that gives them best overall. Along with that bullet weight is the powder charge for the different bullets, of course I had more powder for the 80gr and wanted a round moving to buck the wind, for the 77gr I lowered the powder for not only the bullet, but so that during rapid fires my sights would not leave the bullseye.

Ballistic hollow points were originally made by swagging the bullet from the rear and drawing the copper gilding to the point. This created a bullet with less turbulence in the rear and thus less drag. Through experimentation and never letting things stay too stagnant, several of the bullet manufacturers moved to a plastic tip to move the CG more to the rear. This helped in some things and hurt in others. When a bullet becomes over stabilized it acts as a gyroscope. When this happens as the bullet falls back to earth it will still stay nose high due to the over stabilized bullet. This leads to other problems when wind, pressure changes, etc hit. It also is the leading cause of key holing besides shooting the berm.

A rearward shift would not effect interior ballistics, but the VLDs and semi bore ridding bullets does and they are finicky as hell due to it. I would leave them out of the mix unless you are very good at reloading. The rearward shift can effect exterior ballistics especially in the case I sited above where the bullet starts flying butt low/nose high.

That should get you started. Let me know if I can answer more questions and if these help. When you start to talk about extreme long range, then a whole new set of problems set in to include the rotation of the earth.

[GratefulCitizen]

Thank you LR.
I find the physics of this stuff fascinating.

<edit>

Another question:

The Nosler partition bullets would tend to have slightly more mass distributed to the front and rear than a conventional design.
While this would not change center of mass, it affects angular momentum along the longitudinal axis relative to bullet mass.

Looking at the math, this would have an effect on reducing wobble while in flight.
Would the effect be neglible?

[PRB]

I like a swamped barrel with round rifling and a relieved crown for easy loading.

[mark46th]

Craigpo- My son has a flat top AR10 in .308. The snipers in his agency took it to the range and said that it shot as good as or better than their bolt guns. It has a 20" bull barrel and some trigger work. The scope is a Leupold Mk4 4.5-14X40.

[pcfixer]

Originally Posted by longrange1947

WOW, let me see if I can touch on these for you.

TS is absolutely correct, top gun will not make you a good shooter, but it will prevent a good shooter from shooting rat shit in a dresser drawer.

Weapon/optics

Handloading is all about consistency.

Many very good points, LR! As a handloader for many years I do understand all dynamics and consistency problems of loading many 06, 243 and now 5.56 ammo.
I also load my own 45 Auto, 45 LC ammo. I enjoy this port, sometimes get a little frustrated over the shooting ie bullets don't hit the target consistently in a group. I've learned guns sometimes don't like a particular powder or bullet to be accurate for me.

Also after replacement of 06 barrel with a Douglas XX Premium barrel, Bell & Carelson Stock that is bedded there is still some inconsistency. After a few phone calls to Douglas I found more of the science of barrel whip or vibration.
http://www.stocks-rifle.com/harmonics.htm

From this I gather that each gun has it's own 'sweet spot' for ammo that is being shot. Being a hand loader it takes a number of trips to the range.

[Guymullins]

I was looking at a Rigby .416 a couple of days ago. The new Rigby company is back in England, making handmade rifles which are based on the original Rigby's of old.

They are crazy expensive, although not in the Holland&Holland league, but I always fancied one as it is a caliber I greatly respect, and getting it in a Rigby is the cherry on top.

With the rifle, came a sample target and I was shocked to see that it was marked as shot over 65 yds and the group was well over three inches. This put me off the rifle and the company completely as I consider that unacceptable accuracy for any rifle, apart maybe for a double, but even then, I would be disappointed. My Remington .375 will shoot to a half inch over that distance and I question a manufacturer who would proudly include a target showing that kind of accuracy for a very expensive gun. The old Ruger .416 Rigby I have shot with in the distant past would beat that hands down and cost one tenth the price.

[Rob_Frey]

Originally Posted by PRB

I like a swamped barrel with round rifling and a relieved crown for easy loading.

Whitworth?

[jw74]

Originally Posted by Guymullins

I was looking at a Rigby .416 a couple of days ago. The new Rigby company is back in England, making handmade rifles which are based on the original Rigby's of old.

They are crazy expensive

it was marked as shot over 65 yds and the group was well over three inches. This put me off the rifle and the company completely as I consider that unacceptable accuracy for any rifle, apart maybe for a double, but even then, I would be disappointed. My Remington .375 will shoot to a half inch over that distance and I question a manufacturer who would proudly include a target showing that kind of accuracy for a very expensive gun. The old Ruger .416 Rigby I have shot with in the distant past would beat that hands down and cost one tenth the price.

I'm guessing that they are touting the handmade 'old-world' aspect of the rifle and holding the current desire for ultra-accuracy in disdain and perhaps unneccesary when their rifle is meant for something cape buffalo-sized at 30 yds.
I'm with you though. If all I wanted was an old, heavy, inaccurate rifle I wouldn't compund the problems by emptying my bank account also.

Was the target you saw shot off hand?