Bullet run out how much matters?

[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?

 

[Uncle Ed]

"a full-length sized case in which the neck is also fully sized. There is clearance at the neck and in the body of the case, the closest fit anywhere is the bullet in the throat. If the neck to bullet concentricity is good (although it needn't be perfect), then the bullet will find good alignment in the throat and the case body and neck will have minimal influence. Let's not forget that the base of the case is supported by the bolt face or the extractor to a certain degree as well; this is yet another influence on alignment. As you can see, there are several points from base to bullet that can have an effect. My procedure is to minimize the influence of those that I can control, namely the case body and neck, and let the alignment be dictated by the fit of the bullet in the throat and to some extent by the bolt's support of the base. Barring a seriously out of square case head, I don't think the bolt can have a negative effect on alignment, only a slightly positive effect from minimizing "case droop" in the chamber. 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.

In conclusion, I believe that allowing the bullet to find a relatively stress-free alignment in the throat by full length sizing (including the neck) and turning necks to enhance concentricity gives the bullet the best probability of a well-aligned start into the rifling."

The Rifleman's Journal
Germán A. Salazar

 

[Bart B.]

"As you can see, there are several points from base to bullet that can have an effect."

He left out the major contribution to repeatable neck and bullet alignment to bore center. Smart folks know what it is.

 

[oldroper]

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

I think it uncle ed,

 

[JFrank]

My good friend Mr. Guffey has been in his mountainous cave in Tibet developing a new method of bumping a shoulder using a Die with full body support.

 

[Uncle Ed]

I think it uncle ed,

You wouldn't of said that if you knew that Bart B. said Chesty Puller was a Navy cook.

 

[Bart B.]

You wouldn't of said that if you knew that Bart B. said Chesty Puller was a Navy cook.

The needle on your stupid meter just pointed higher.

 

[jimmymac]

God Bless us, everyone!

 

[oley55]

You wouldn't of said that if you knew that Bart B. said Chesty Puller was a Navy cook.

he better had not!

"Good night Chesty, wherever you are."

 

[Bart B.]

You wouldn't of said that if you knew that Bart B. said Chesty Puller was a Navy cook.

He really was. We told him to do his best over the 3 daily meals his first day aboard. He did so we gave him a little star for each one. Then had him serve shiverin' Liz in a snow storm for dessert, clean the scullery then feed out pet sea bat.

 

[INTJ]

The best course of action is to not use any expander ball in a sizing die at all. Forster hasnt figured out any magic there- it still plows an expander back thru a case. They just put it in a different place to make you think it must work better (but it doesnt)

I used to remove all my expanders, but now I only remove expanders when using bushing dies, and I only use bushing dies for neck turned cases.

A neck turned case is consistent in thickness so as the bushing sizes it down its the same diameter inside as outside.

An unturned case is not the same thickness. So if you don’t have an expander ball, all the irregularities are transferred to the inside of the neck when the necked is sized smaller. The bullet is then seated into a neck of irregular inside shape.

When an expander ball is used, the irregularities are transferred to the outside of the neck so the bullet is seated against a consistent surface. In a typical non-neck turned chamber, there is enough clearance so that the irregularities on the outside of the neck aren’t a problem.

Not sure any of this makes any difference on paper.........