Bullet run out how much matters?

[Alex Wheeler]

One reason is that seating force is mostly a friction measurement, it shows up big on the dial but actual tension is what shows on the target. The other is when you have a rifle with a very long freebore and have very little bullet in the neck, you may see the neck not expand at all when fired, in that case the bullet did slip from the neck allowing pressure to equalize around it. I also can't agree with the idea the bullet slows as it hits the lands. Theres so much pressure behind it that I dont believe it slows down at all. Its rate of acceleration may plateau in some un measurable amount, but no way it slows down.

 

[Alex Wheeler]

why do you think a larger freebore vs bullet diameter increases accuracy?

Wish I knew. But we know accuracy suffers when we get too tight around the neck as well. I had a .30 cal with .002" neck clearance that would not shoot and I could not get es under control. Increasing it to .004" cured the problem. .002" should be enough and in some cases it is. I dont think its a case of more clearance being more accurate, rather not enough being less accurate.

 

[Uncle Ed]

German Salazar sez: He forgot to mention the extractor can push the case body rear end against the chamber wall. And inline ejector's can push cases full forward in chambers like firing pins do.
Case droop?

The rear of the case is held and centered by the recessed bolt face. Case droop is gravity pushing down on the cartridge and Mr. Salazar explains "Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway." Sometimes explained by "the cartridge should fit the chamber like a rat turd in a violin case". Meaning the full length resized case body has no effect on bullet alignment with the axis of the bore.

 

[Scott Harris]

Wish I knew. But we know accuracy suffers when we get too tight around the neck. I had a .30 cal with .002" neck clearance that would not shoot and I could not get es under control. Increasing it to .004" cured the problem. .002" should be enough and in some cases it is. I dont think its a case of more clearance being more accurate, rather not enough being less accurate.

Ah, neck not FB. I totally agree, like .006 clearance in the neck.

 

[Bart B.]

I also can't agree with the idea the bullet slows as it hits the lands. Theres so much pressure behind it that I dont believe it slows down at all.

I don't think there's much pressure in my my 2 examples with each bullet .001" short of touching the lands, 27 and 51 psi.

 

[dmoran]

If a 30 caliber bullet needs about 2 pounds of force to seat it, it will start moving out of the case neck when pressure in the case is about 27 psi. A 22 caliber bullet the same, it'll start moving out at about 51 psi. They slow down as they get engraved, then speed right up.

What are you basing your release pressure amounts from?
If it's a mathematical formula, what is it?

As to bullets slowing down when engaging the barrel: from actual pressure traces, I have seen that to occur occasional, dependent on circumstances, but more typically will not see it occur. Bullet entrance pressures, are dominantly controlled by neck tension and/or neck preparation steps, that can be easily tuned from about as low as 2500-psi to +10,000-psi by either one and/or combinations of both. Between 5000 to 8000-psi being a typical pressure range for bullet entrance.

 

[Alex Wheeler]

Ah, neck not FB. I totally agree, like .006 clearance in the neck.

I was only using the neck as another example of more clearance giving better results similar to what I see in the freebore.

 

[Bart B.]

The rear of the case is held and centered by the recessed bolt face.

Are all case head's recessed bolt faces the exact diameter of case rims? Surely, there are tolerances. And in bolt body and receiver boltway

SAAMI specs have about .010" tolerance on case rim diameters.

Don't think this is reality. Never come across such stuff before. Unless it's a secret and you just leaked it out.

 

[Bart B.]

What are you basing your release pressure amounts from?
If it's a mathematical formula, what is it?

Let me check with the gun God to see if he thinks you're worthy of knowing what the simple grade school math formula is.

 

[Bart B.]

Case droop is gravity pushing down on the cartridge and Mr. Salazar explains "Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway."

So the case body doesn't touch the chamber anywhere because of diametrical (radial) clearance all around the case?

Or does he mean the case body rests on the bottom of the chamber?

 

[dmoran]

Let me check with the gun God to see if he thinks you're worthy of knowing what the simple grade school math formula is.

If it is as simple as a "grade school math formula", you can skip checking with your gun God, because it would be nothing more then a in general inclusive reference prediction. For a conclusive mathematics formula, it would have to be fairly complex, that would have to include both coefficients of friction of the case neck and bullet jacket material, as well as tensile strength input based on the amount of interference fit, and both neck wall thickness and hardness, in order to have any factual bases for predictions.

 

[Uncle Ed]

Simple question I ask?
How much bullet run out does it take to make a difference? I am not interested in theory and the obvious answer only in answers that have been tested and proven.

Below the rat turd in the violin case separated from all the bovine scat and higher math.

Bullet Concentricity & Related Issues
https://www.sinclairintl.com/guntech/bullet-concentricity-related-issues/detail.htm?lid=16572

Total Indicated Runout

Bullet run out means simply means the way the bullet “runs out” into the rifling. The ideal desired cartridge concentricity is zero Total Indicated Runout (TIR), measured with a concentricity tool with the dial indicator on the bullet about 1/16th of an inch above the case mouth. If you want to get really technical, do the case neck when using military brass, so you can check the concentricity and any variation in case neck walls. Do the measurement on the case neck slightly below the case mouth. Factory loaded match ammunition usually exhibits no more than .0015" TIR, which is deemed excellent.

If you load for accuracy, especially for distance shooting; you want no more than .002" to .003". Ammo with a TIR of .005" is used for shorter ranges. If it goes beyond .005", either use it for practice ammo or very short ranges because accuracy will fall off quickly with that kind of TIR. Even M118 7.62 NATO ammo had problems with TIR depending on the lot, from early M118 to M118LR.

 

[Intheshop]

Hard to put this in a condensed form but here goes..... cast bullets @ high velocity.

Get "leading" out of your thought process... even though it's going to be discussed.

I measure bullet runout using one support at case head and one just below shoulder/neck. Instrumenting on the bullet right where it engages the rifling leade in the throat. I use a med heavy jam that results in very short engravings that actually show up on the bullet.... VERY easy visual to see if the alignment,and throat machining are "happy". The D.I. is located central to where this engagement takes place.

One major advantage to cast is we get to manipulate not only the bullet diameter but the alloy...... so,we can change the neck in several key areas. Annealing, tension,turning necks, AND total chamber clearance. Each combination will see changes or effects in one of the other criteria. Think carbon blowback.... and looking for perfect sine wave patterns left on the neck.

Antimony wash is a term that comes up every once in awhile.... and don't confuse this with "leading". Now back to deadnuts ammo,perfect engraving,and chamber clearance. After the carbon patterns.... what happens when you get the combination tuned is we start to get a little antimony wash on the case neck. Wipes right off. Make no attempt to control the parameters and the launch cycle goes to heck.

So,even though jacketed will never leave a trace of this order on the neck.... don't think that the forces aren't there. And sorry to any past or present English professors on board.

 

[Bart B.]

If it is as simple as a "grade school math formula", you can skip checking with your gun God, because it would be nothing more then a in general inclusive reference prediction.

Pressure (psi) = force (lbs) / area (in²)

Force (lbs) = area (in²) x pressure (psi)

Area (in²) = force (lbs) / pressure (psi)

Ivory soap percent good enough, that's 99.44% accurate. It's all included in the bullet pull force that's easy to measure that includes all that stuff that effects bullet pull. I don't care what all contributing factors are, you gotta overcome all of them in one fell swoop to start moving the bullet out

Don't like simple truths? Go ask a hydraulic or pneumatic engineer. More important, master grade school stuff first. Otherwise you won't grasp the details you think come first. Don't think backwards, you'll never move forward.

 

[Nature Boy]

Thats a good experiment Nature Boy showing a difference. Now, im not doubting anything you've done here, intact i commend you for taking the time to do it. But, what if you did the same experiment and shoot the .003 group first? Im thinking that the .001" group im assuming you shot first. Cold barrel, clean barrel. You may well have let the barrel cool right down for the other two groups as well. But it would be interesting to see if you get the same results if shot in a different order.
Cheers

I should have mentioned that I shot that test round-robin.

The real issue with my test is the lack of a statically significant sample size

 

[dmoran]

Don't think backwards, you'll never move forward.

The simple truth is, your not formulating for the variation of effects that apply from the grip of cartridge brass onto the seated bullet.
Nor do your pressure references have anything to do with internal ballistic pressure that move a bullet.
But do go on your marry way with your erroneous pressure references to actual bullet release.
I hope you obtain what you strive for with those references in your replies.
And have yourself a Happy Christmas !.!.!

 

[jimmymac]

Go to a SR group match where reloading occurs between relays, then report back how many competitors are checking for runout. While there, also take note of the group sizes.

 

[Uncle Ed]

Pressure (psi) = force (lbs) / area (in²)

Force (lbs) = area (in²) x pressure (psi)

Area (in²) = force (lbs) / pressure (psi)

 

[Bart B.]

The rear of the case is held and centered by the recessed bolt face.

 

[oldduc]

So, is Bart B. replacing the missing F. Guffy?