Mandrel as last step?

[Mike Matteson]

You mean inside turning?

No! the outside of the necks.

 

[Mike Matteson]

You absolutely can do that. Turning necks is an expensive and time consuming process. I went down that road several years ago but have been trying to simplify my process lately.
Also, most SAAMI chambers are cut with 0.010 clearance between the brass neck and chamber wall. Most SAAMI brass diagrams show an 0.016-0.018 thick neck wall. You start turning necks down and you increase that clearance which also works the brass in the neck more.

Neck turning isn't that big of a deal. Generally you are cutting thickness of 0.013. Now I use a tighten chamber in one of my rifles. I have turned necks for over 20 years now. I really haven't had any problem doing that. I want my necks to be the same thickness on all sides.
I have just beginning to use reduced chamber dimensions. Alone with bushing dies. So far I' ve been able to use bushing to acheive ID of neck to be .002 under bullets size. That after spring back. Now I haven't set up yet to see what the spring back is after several days or a week or so. I will when I get back to it.

 

[Mike Matteson]

Mike, this is the easiest thing to test. Many things can move the node, like a primer change. However a bushing does not seem to do that. You can simply take your best load and just change the bushing. If I want to find the correct bushing first, I load a mini ladder, 5 shots around the node with each bushing. Usually its pretty obvious. Im not saying you dont already have to best nt for your combo, but I have turned rifles I was about to pull the barrels into excellent shooters by changing nt. It can make a huge difference. You need to shoot this at distance. I have had rifles shoot well at mid range, but were un tunable at 1k until testing this at 1k.

Interesting! I'll keep that in mind. Infact I have placed that into my notes. I hadn't put much though into it. Another trick to make your rifle shoot a little tighter.

 

[MagnumManiac]

I can give all you guys a perfect example of how bullets are NOT pushed out of necks with neck tension (interference fit) but are released by neck expansion.
How many times have you seen a fired case with the case mouth expanded to fit the chamber (less spring back), but see that the case mouth is turned inward almost to bullet diameter with only the springback amount being left?
This is bullet release by expansion, it shows up perfectly that the rear of the neck expands towards the case mouth but the bullet has moved to a point where the expansion stops.
The ONLY thing that changes start pressure and hesitates bullet movement is a crimp. The ammo factories know this, use this with faster burning powders to get higher velocities without going to bulkier slower powders.
Ponder this, it makes sense even if you don’t have your own pressure testing equipment.

Cheers.

 

[Tree Farmer]

So, if increasing interference fit has no affect on bullet release/start pressure, what difference does reducing inside neck diameter have on accuracy?

 

[Mike Matteson]

I can give all you guys a perfect example of how bullets are NOT pushed out of necks with neck tension (interference fit) but are released by neck expansion.
How many times have you seen a fired case with the case mouth expanded to fit the chamber (less spring back), but see that the case mouth is turned inward almost to bullet diameter with only the springback amount being left?
This is bullet release by expansion, it shows up perfectly that the rear of the neck expands towards the case mouth but the bullet has moved to a point where the expansion stops.
The ONLY thing that changes start pressure and hesitates bullet movement is a crimp. The ammo factories know this, use this with faster burning powders to get higher velocities without going to bulkier slower powders.
Ponder this, it makes sense even if you don’t have your own pressure testing equipment.

Cheers.

Question?
Is it expanding equally, or the neck that is thicker on one side takes just a bit more to move. creating an unequal release. Again back to the metal being unequal in thichness. Thinner metal is easier to move, than thicker metal. Or another way is less pressure to release on one side than the other. I realize it's not much, but different. People go to great lengths to have uniformity in there cases for there reloading process. Being case volume, powder, case length, primer pocket, and seating primers, bumping shoulders, annealling, flash hole work over, and neck tension. Blank bullet seators cut from your reamer to achieve a better alinement of your bullet. So why not even neck thickness.
Ever have a tires out of balance or out-of-round? Going down the road. Can't see it, but sure can feel it. That how I see it with necks being uneven.
If you don't want to cut your necks that's find by me. You can leave out other steps of the case workup too. I don't think you will get quite the harmonious outcome.
That part of reloading your own ammo. You can experiment or develop a better load for your rifle.
Interesting! I don't have much choice because I an using a tighten chamber. Thats what I wanted, and got.
Enough on to other things, like where the primers?

 

[Dragoon300]

I guarantee the bullet is moving forward while the neck is expanding, the bullet does not stand still and wait for expansion. Pressure causes both to happen incrementally at first. The rear of the bullet has x square inches that are directly exposed to thousands of pounds per square inch pushing the bullet forward, the inside of the neck is filled and not directly exposed to pressure until the bullet moves forward. The bullet would be pushed out of the case overcoming even the normal .005" interference fit friction of standard dies quite easily, as long as the chamber did not squeeze the case tighter and lock the bullet in. Pressure will likely be higher in that situation, but consider how a low pressure squib load doesn't fully expand the case to seal off, or how just a primer without powder pushes the bullet into the rifling where it stops. The case neck does not expand before the bullet moves, but as it moves. It is when the bullet reaches the rifling that the pressure builds enough to expand the brass, and completely seal the chamber.

 

[Mikecr]

It IS released with expansion.
The entire case (connected to neck) is expanding. That's a lot of area, and even a billionth of an inch worth of neck expansion in it (unless crimped), leaves bullets free in the wind.

You can test it yourself.
Take a neck to squeaky clean and rough up the ID. Note all the frictional force needed to seat a clean bullet.
Take another neck and coat the ID with WS2, (slipprier than moly), coat the bullet too, and note how much lower seating force is needed.
Fire both across a chrono, NO DIFFERENCE.
The truth is: if you ever rely on a load to push a bullet through neck friction, it could be your last testing. The gun will blow up.

Now, at a set interference, size 1/3 of the neck and size another neck 1/2 of neck, and seat bullets, both with bearing depth same & beyond sizing length. The 1/2 neck length produces more tension (grip) than the 1/3 neck, and a chrono will show it.
This is what affects normal bullet release -NOT friction.

 

[SSgt G Cody]

In my 6.5x55 AI (Swede) heavy barrel rig I take great pains to make my ammo as perfect as possible. First couple of FL sizings I use the tuned Lee collet die (rotating 180 degrees), then turn and shave necks inside and out to .013"or so. Then I trim and fully prep the brass, clean and dry brass, then start my reloading. I have seen this process make huge differences downrange at the target.

 

[SSgt G Cody]

I almost forgot my real reason for comment. In re-sizing brass, I use bushing to squeeze neck to .003" undersize, then the polished mandrel stretches it back to within .oo1-.0015" of actual chamber neck size. This definitely helps accuracy! We all pursue perfection!

 

[MagnumManiac]

Question?
Is it expanding equally, or the neck that is thicker on one side takes just a bit more to move. creating an unequal release. Again back to the metal being unequal in thichness. Thinner metal is easier to move, than thicker metal. Or another way is less pressure to release on one side than the other. I realize it's not much, but different. People go to great lengths to have uniformity in there cases for there reloading process. Being case volume, powder, case length, primer pocket, and seating primers, bumping shoulders, annealling, flash hole work over, and neck tension. Blank bullet seators cut from your reamer to achieve a better alinement of your bullet. So why not even neck thickness.
Ever have a tires out of balance or out-of-round? Going down the road. Can't see it, but sure can feel it. That how I see it with necks being uneven.
If you don't want to cut your necks that's find by me. You can leave out other steps of the case workup too. I don't think you will get quite the harmonious outcome.
That part of reloading your own ammo. You can experiment or develop a better load for your rifle.
Interesting! I don't have much choice because I an using a tighten chamber. Thats what I wanted, and got.
Enough on to other things, like where the primers?

Of course uneven neck thickness will expand very slightly differently, but we are talking ten thousands of an inch, not one thousands of an inch.
The time it takes is also a valuable number to know.
Light interference allows the bullet to engage the rifling earlier sealing the gap between the case mouth and chamber wall.
This changes start pressure and the node…so does using a dry bullet lube.
If the case is sloppy in the chamber, then erratic results occur between shots, as each case moves differently in the chamber.
Having pressure testing equipment has learnt me many things.
Tight neck chambers are actually detrimental to consistent bullet movement, .003” is ideal and trimming necks to a minimum of .014” is about perfect. Any thinner can cause erratic expansion.
Necks, and cases, are thinner on one side due to the drawing process, this doesn’t change after you trim to get them the same, this continues through the life of the brass.
Anyway, this is the fundamental way to be consistent. Some fliers will for sure be caused because a case that you cannot measure will have expanded unequally.
Culling is the only answer.

Cheers.

 

[MagnumManiac]

So, if increasing interference fit has no affect on bullet release/start pressure, what difference does reducing inside neck diameter have on accuracy?

Very little.
Across a chronograph you can SEE start pressure changes with altering bullet depth…you cannot SEE a change in start pressure altering neck interference.
This may/may not change accuracy, but if you’re talking PRECISION grouping then that is completely different.

Cheers.

 

[Tech4]

You are testing different neck tension as part of load development, how are you doing that?
Trying .001 shooting 10 or 20 shot group and doing this each step up to .006 or what is your process?

 

[cape cove]

@

Having pressure testing equipment has learnt me many things

Just wondering if you are a QL user. Reason I'm asking is QL gives a start pressure of 3626 psi. When you use a COL that touches the lands QL says to increase the start pressure by 7200 psi for a total of 10826 psi. Some users agree with this # and other users do not. Just wondering if you ever tested this with your pressure testing equiptment. What would be your take on this. TKS