Bullets too tight in the neck?

[Yankee]

Just started reloading 308 using a standard RCBS two die set. The internal diameter of the necks on my fired cases is somewhere in the vicinity of .315 and after resizing, they come down to around .306 to .307. The expander ball on my die is exactly .308 and so I'm assuming that the brass is springing back a little bit after the expander ball passes through the neck. Is this normal? Having a neck diameter a .001 or .002 inches smaller than the projectile means that I have to support the bullet all the way up into the seating die and be very careful to ensure that it is centered in the case. I've only loaded pistol up until now and just want to make sure that I am not doing anything wrong. I am using Sierra 150grn Gamekings.

 

[243winxb]

Over Working the Brass

Is this normal?

Yes. This is why some people buy the Redding FLRSing Type-S Bushing die, so they have more control. The reason for this is not all case neck walls are the same thickness. The dies must work with the thinnest wall made. Plus the expander should measure .307" then with spring back this give .002" tension. You may also find the neck diameter of a loaded round may get smaller with a few loading. This is caused by over working the case neck and thinning the neck wall diameter.

 

[fguffey]

Recovery/memory, then there is 'spring back', I am not a fan of spring back, there are many things that can not be done because of spring back, I have crushed cases with a hammer, not one of the cases crushed displayed spring back, I have dented cases with a punch and hammer again none displayed spring back. I have formed 30/06 and 280 Remington cases to everything from 257 Roberts to 35 Whelen, in all of those cases I have never had one spring back, none ever recovered and not one of them had a memory of ever being a 30/06 or 280 Remington.

Measuring the inside diameter of the neck after sizing requires a different tool then the dial caliper, if it is important I will use a hole gage/wire gage. New (annealed) brass is malleable and has what was once called bullet hold, now it is called bullet tension, the diameter of your sizer ball should not be 308 if the bullet diameter is .308, the sizer ball can be ordered in different diameters, some grind, file, sand etc., the sizer down but that does not seems to be the problem, seems the mouth of the case needs a bevel on the inside and or the flat base of the bullet is square.

Not practical: I made a tool for seating bullets in 25 cal cases, it sits on the shoulder and is larger in diameter than the outside of the case neck until the bullet is seated, then it fits, the hole in the top is .250 in diameter, the bottom of the tool centers the neck, the hole in the top centers the bullet, the bullet can not get off center, canted or crooked, the bottom of the tool sits on the shoulder, I set the case, bullet and tool upright on an aluminum can crusher and pulled the handle, it worked. The RCBS competition/precision seater die works in a similar manner except there guide is pushed up inside the die by the case and the bullet is held up by the case mouth until seated. This design greatly reduces the chance of something going wrong after the pullet is released when seating, Hornady uses a bullet guide in their New Dimension seater dies.

Bullet hold is determined by the condition of the brass in the neck neck and difference between the inside diameter of the neck and outside diameter of the bullet, meaning the hole in the neck is smaller than the bullet, when the bullet is seated, the neck stretches, measure the outside diameter of the neck before seating the bullet, measure again after seating the bullet, the difference determines the amount of case stretch, again if the hole is .308 and the bullet is .308 there is no bullet hold/neck tension or stretch.

Stretch/flow and spring back, or memory / recovery, then there is 'it can not be done because of spring back'.

F. Guffey

 

[sumpnz]

fguffey - You are completely misunderstanding the term springback. This does not refer to a phenomenon where you can hit a case with a hammer and then have it return to its original shape all on its own. SPringback referes to the fact that when you crush that case (or run an expander ball through the neck) there is a small amount of elastic response that moves the deformed shape slightly back towards its previous shape, but by an amount that is difficult to see without precision measuring equipment.

Think of it like this. You have a piece of metal plate that you want to put a 90deg bend in. It has to be 90.000deg, or else it won't fit into the widget you're making. It's a delicate part, so there can't be any internal stresses from slight mismatches so it really can't be beat to fit.

So you take it to a large table that you know is totally, perfectly square between the top and the sides. You bend that piece of plate over the edge of the table until it's bent that full 90.000deg. You take it over to your widget to install it and find that it doesn't quite fit. You scratch your head as you realize that somehow the plate wasn't quite bent to 90.000deg. Then you take a precision compass to check the angle of the bend and find that it's only 89.000 deg. You check the table and find that, yep, it's exactly 90.000deg. That 1 deg of difference is due to the effect of springback. Although you exceeded the yield point of the metal and induced significant permenant deformation, there is still a small amount of elasticity that tries to return the plate to the original shape.

In order to get that 90.000 deg bend you have to exceed that amount during the bending operation so that after the part has undergone sprinback it will be at the correct dimension.

In the case of the neck sizing that sprinback is causing the case neck to go from .300 or whatever back to .306 after a .307 ball has been pulled through it.

 

[loadedround]

The word is malleable which simply means in this case a metal that's flexible or pliable. Brass needs to be malleable to expand to seal the chamber upon firing and return to normal allowing you extract the fired case easily. Same thing happens when you seat a bullet and have it be held tightly by the bullet's neck tension. Are you sure you're chamfering your case mouths enough prior to seating?

 

[Yankee]

I should have mentioned that I am using a flat bottomed bullet - there wouldn't be an issue if I switched to boat tails. Looking at the chamfer, it could probably be a little more pronounced so I might give the cases a bit more and see if that helps.

 

[USSR]

Yankee,

If your inside diameter after sizing is between .306" and .307", that is exactly where it should be. I would suggest that you buy a Lyman Type M Expander die to help you in seating those flat base bullets. I just got one for loading cast bullets in my .30 Carbine brass, and it is the schitz.
Don

 

[something vague]

As posted above me, this is perfectly normal! This means that you're getting in the vacinity of .001"-.002" of neck tension, which is exactly where you want to be. After a few firings you will find that spring back is going to get worse as the brass is becoming work hardened.

For seating, just hold the bullet all the way into the die and kind of work the press until it feels like you're seating properly. Forster and Redding both sell seating dies that hold the bullet in alignment until it starts seating in the case. I use the Forster and love it.

 

[Walkalong]

After a few firings you will find that spring back is going to get worse as the brass is becoming work hardened.

Yep. Starts out almost dead soft with no "spring back", but gets harder every time it's shot and then sized, called "work hardening".

When sizing for match chambers when you are bumping shoulders back .001 or less, you have to keep adjusting your sizer to keep up with this work hardening/spring back. You will start with the sizer in one spot, and end up in another. (Screwed down farther) If you don't keep adjusting it, you will end up with brass that is very hard to chamber as the brass gets harder and the shoulder is not being bumped back as far to fit the chamber. If this happens it is extremely hard to bump that now work hardened brass back enough without really moving the shoulder back more than you want.

If you anneal, or start with new brass, you will have to adjust the sizer back up to keep from way over bumping the soft brass. (Pushing the shoulder back a few thousandths instead of one or less)

Learned that one the hard way. Hard to "run" a group if you are having a hard time getting them to chamber.

The pressure of your loads affects this as well. The higher the pressure, the faster it happens. When shooting hot 6PPC loads, it is critical to keep track of this and adjust as you go. It will eventually slow down to almost nothing. Our cases are such a close fit to the chamber we can get many, many reloads out of them without annealing etc, as long as we don't let the shoulders get out too far by not readjusting the sizer as needed in the beginning as the brass goes from new dead soft to work hardened.

AC

 

[fguffey]

"In the case of the neck sizing that sprinback is causing the case neck to go from .300 or whatever back to .306 after a .307 ball has been pulled through it"

I understand the theory of Glupe as it applies to a fluid (something that flows including brass, steel and water), I understand and have used heavy metal brakes, the inside compresses, the outside stretches (even fractures), and there is the radius, I have the tools required to measure just about anything, a new one on me is the .300 neck, where did it come from, what was the outside diameter of the case after firing? after necking down (sizing)? after pulling the sizer ball through it?


Not practical: I always shoot 8x57, 8x06 and 30/06 etc. when I go to the range, as part of my stuff I include a fired and full length sized 30/06 case and use them as gages, the full length sized case will not fit the 308 bullet (without effort), the fired 30/06 case will slide over the 308 bullet and stop at the mouth of the of the unfired case. The fired 30/06 case mouth will not slide over the 8mm (.323) bullet in the 8/06 or 8x57, cheap gages?

Not practical: I use a 30/06 full length sized case to check the outside neck diameter of a loaded 270 round, with little effort the neck of the 30/06 case FITS, if the fit is tight or will not fit I can expect the neck of the 270 to be tight in the chamber, it is not necessary for me but the 30/06 case has been been necked down to 270, this could cause the neck to be thick and as much as .025 shorter than the 270 case.

Precision measuring? I have a Pratt & Whitney electronic gage that measured .00001 to a maximum of .0002, I removed the electronics and installed a dial indicator on the stylist, it is set up with standards to a height of 10", again I make gages, I have the equipment to measure (verify) gages, fired cases and sized cases, I have no hang-ups because of spring back, I want bullet hold.

Then there is spring back of the case after it is fired, at best the amount is described as being a small amount, few thousands, little bit or just enough to allow the case to release from the chamber. My brass does not have an exemption, if I place a flat piece of brass in a press between two flat surfaces and apply 58,000 psi to one square inch of brass, the brass yields, flattens and increases in area, when I expose my brass to 58,000 psi on the inside of the case and press the case against the chamber wall I believe it gets hammered, thins and increases in area and might even require trimming, now if I could get someone to weigh there cases before firing them 50 times with maximum loads the case wall thickness could be measured to determine if the wall of the case got thinner and by weighing it could be determined if the brass compressed or flowed/stretched, and if the case flowed forward on the outside, where are the skid marks.



F. Guffey

__________________

 

[fguffey]

Again:

Not practical: I made a tool for seating bullets in 25 cal cases, it sits on the shoulder and is larger in diameter than the outside of the case neck until the bullet is seated, then it fits, the hole in the top is .250 in diameter, the bottom of the tool centers the neck, the hole in the top centers the bullet, the bullet can not get off center, canted or crooked, the bottom of the tool sits on the shoulder, I set the case, bullet and tool upright on an aluminum can crusher and pulled the handle, it worked. The RCBS competition/precision seater die works in a similar manner except there guide is pushed up inside the die by the case and the bullet is held up by the case mouth until seated. This design greatly reduces the chance of something going wrong after the pullet is released when seating, Hornady uses a bullet guide in their New Dimension seater dies.

It has nothing to do with understanding, it is about alignment, there is a RADIUS on the bottom of a flat base bullet, the inside of the neck has a bevel/chamfer, preventing the problem is about keeping the bullet centered and preventing it from canting or leaning on the way up inside the seating die, for most reloaders the bullet is on it's own after the bullet is released until it gets to the seater plug,

"I made a tool for seating bullets in 25 cal cases" the tool eliminates the twilight zone between the releasing of the bullet and it's contact with the seater plug. If the tool is difficult to remoe after seating the bullet (back to the 30/06 sized case on the 270 neck) the neck is thicker or the bullet is too large in diameter.

F. Guffey