Not meaning to hi-jack but how would you approach the factory chambers? Can much be gained or lost triming necks for a factory chamber?
If you read carefully you will see the way to handle a factory chamber with neck turning . Do not listen to those who say it does no good they have no clue.
Neck turning is a process of machining the external neck walls of a cartridge case to an even thickness and an accurate diameter.
This is achieved by the use of a neck turner, of which there are numerous brands.
The reason this is desirable is to achieve better concentricity and minimum clearance in seating the case in the chamber as in tight neck chambers.
To gain better neck seating tension and concentricity of the projectile, due mainly to the fact that the seating tension is more equal around the diameter of the case neck.
Even neck tension on the projectile also helps the seating die do a straighter job.
The even thickness necks allow more precise neck tensions from case to case, and assist the neck sizing operation and bullet seating operation to do a straighter job.
When turning for a factory chamber it is not necessary or desirable at the first turning to achieve 100% cleanup of the case necks as long as most of the neck is turned say about 75 % of the circumference area called skim turning .
When turning for the first time to get a case to fit a tight neck chamber it is best to reduce the necks to the correct diameter in several finer stages of cut. Two separate cuts will work ok.
This results in a better degree of case neck diameter uniformity across the batch of cases. Tight neck cases should have a neck clearance in the chamber of not less than .001 of an inch all around the circumference, that is .002 clearance across the diameter with the projectile seated , unless you are an experienced bench rest shooter and know enough to do otherwise.
The trick to getting good results is the inside fit of the case neck onto the mandrel of the neck turner.
It must fit perfectly with no sideways clearance or slap, but be able to turn easily and not jamb as the neck heats up.
This is easier said than done. Inside neck reaming or polishing before sizing to the mandrel will help in this regard and there must be no donut inside the neck.
A donut is a circular ridge inside the case neck at the junction of the neck and the shoulder.
Lubrication of the turner mandrel is absolutely necessary, to stop heat lockup. Use gun oil with a small amount of moly powder mixed in on the mandrel. Sometimes small amounts of brass will build up on the mandrel and cause the case to get sticky. If this happens polish the mandrel with fine steel wool by hand .
Don't use harsh abrasives as you do not want to reduce the diameter of the mandrel. I use a Sinclair neck expander die to expand the necks to the correct size , if they are too big to begin with , neck size them down with a standard neck die without the decapping rod then neck expand them up to the turner mandrel size.
The mandrel in this die has been polished down a bit at a time so it is just a fraction larger than the mandrel in the neck turner.
Remember case necks spring back smaller after coming off the expander mandrel.
When the cases come out of the expander die they should be a neat fit on the turner mandrel, trial and error will be required.
When turning up to the shoulder of the case it is necessary to allow the cutter to run onto the shoulder just a slight amount to be sure that you do not leave a ridge at the junction of the neck and the shoulder. This is an outside donut, which will turn into an inside donut upon firing.
You will need a 0 to 1 inch Imperial micrometer and to learn how to use it. I use Imperial measurements ( thous ) because everything from America to do with firearms is usually Imperial.
Take a small batch of cases and polish the inside of the neck.
This can be achieved using an old bore brush wrapped with a very small amount of fine steel wool in an electric drill, don't force a great lump of steel wool into the case mouth as it will taper the inside and that is not good we just want a light polish.
Then trim the cases to length.
Then size down (if required) and then expand the inside necks with the expander die to fit the turner mandrel, use case lubricant.
Measure the outside neck diameter of every case in the batch that you are doing and start with the smallest diameter neck .
Lubricate turner mandrel and clamp turner handle to base of case.
Ease case neck onto turner mandrel with a circular twisting motion while keeping it as straight as possible and move the case mouth up until it is just past the cutter edge. Adjust the cutter down until it gently touches the surface of the brass and lock it. Now move the case back away from the cutter and readjust the cutter down say .001 and lock it.
Turn the case again into the cutter, if you get a fine cut going continue to the shoulder slowly and evenly. When you have finished at the shoulder slowly back it off allowing it to cut on the way back as it sometimes will.
Measure the case neck and work out how much more needs to be removed to fit the chamber .
You must work out how much your case necks will expand after seating a projectile.
This can be done by neck sizing a case as normal for reloading and measuring the neck diameter then seat the projectile you are going to use, remeasure the diameter on the sized portion of the case neck near the mouth and the difference between the two measurements is the expansion.
Add the expansion and the neck to chamber clearance together and subtract the answer from the diameter of the rifles chamber neck .
Example only :--- Seating expansion .003 , Neck to chamber clearance ( across diameter) .002 = .005 .
Rifle chamber neck diameter .338 . .338 - .005 = .333
The cases are turned to this final diameter of .333 .
Or if you are turning to just clean up the necks for a factory chamber keep readjusting and turning until the necks clean up say 75% of the circumference, once you have a satisfactory cutter setting you turn the whole batch of cases at that setting then readjust. Try and split the turning up into 2 or 3 turnings with the finishing cut to final size being the lightest cut.
Remember this first case is one of the smallest so as you work through the batch they should clean up more of the neck.
After changing the setting of the cutter blade, measure the next case you turn to make sure you are not removing too much brass, this way you will only wreck one case if you make a mistake.
You must remember that the final diameter is with a projectile seated.
Patience and turning of a few test cases is required here.
Use old worn out cases to learn on as you are going to ruin a few before you get it right, everybody does.
For your first attempt at turning new cases just do a batch of 10 cases , then test them and see on the target and in the rifle that they are working ok.
To be on the safe side start with a powder load that is 10% lower than your normal recommended load . The amount removed from the diameter for seating expansion will be recovered upon seating the projectile. The final result should be a case with a seated projectile with an outside neck diameter of .002 thou less than the stated diameter of the chamber neck.
Upon firing , the brass will spring out .001 thou. in a radial direction and as this is approximately within the elastic spring back of most cartridge brass should spring back to about the same internal diameter as the projectile requiring only minimal resizing to reload , which is good for case life and maintaining neck concentricity.
For target work neck resizing must be accomplished with a recognized bench rest die system such as a bushing die of correct diameter.
To find the correct diameter for a standard 1/2 inch x3/8 bushing measure the neck diameter of a case with the projectile seated and turning finished.
Measure across the turned neck with a micrometer use a thumb and index finger grip on the mic ratchet and make it a snug fit then subtract .001 to .002 from the case neck diameter, the result is the size bushing to order - .003 is better if you want extra neck tension for a special purpose eg. hunting loads .
If using a tight neck chamber in a hunting rifle it would be better in increase the neck to chamber clearance slightly.
Partial Neck Sizing for Skim Turning for Factory Chamber
I have read many times the statement that neck turning is a waste of time for standard factory chambers.
Well it depends on how you do it .
If you also want to skim turn the necks study the article on neck turning and learn how to turn an accurate case neck. However it's not absolutely necessary in order to do partial neck sizing it just makes it work better .
There is no denying that turning a case neck for a factory chamber will increase the clearance between the case neck and the wall of the chamber, but you can retrieve this clearance for a section of the neck to a tighter fit than before turning .
With partial neck sizing and body die sizing .
The idea is that you leave a portion of the neck , about one third of the length from the shoulder , unsized at all times.
To achieve this a bushing type neck sizing die or a Lee Collet neck sizing die is used to size the neck only . To shorten the length of sizing in a Lee collet die place a machined washer of correct thickness over the case and between the collet skirt and the shell holder .
This section of neck never gets sized that is why it must be kept short .
If it is too long it can make chambering difficult and there will not be enough sized section to hold the projectile concentric and secure especially in short neck designs like 243 W .
A body die is used to size the remainder of the case when necessary and it doesn't touch any of the neck .
This way you gain some of the benefits of neck turning , without the disadvantage of excessive neck clearance in the chamber.
This is a technique for a bolt action rifle that has already shown to be accurate and you want to improve it .
It is definitely a waste of time employing this idea in a rifle that doesn't shoot well enough to see any small improvement in the groups.
Other methods such as pillar bedding , hand load development , quality projectiles etc, would be more likely to improve the bad shooting rifle .
So work on everything else and when you run out of things to improve , it may be the icing on the cake .
There is no one system of anything that suits every rifle , the secret to performance is experimentation.
Some rifles break all the rules such as shooting better with Full length sized cases than Fire formed cases.
Things like this can usually be traced back to some inaccuracy in the original manufacture e.g. crooked chambering job.
It's your job to figure out what works and what don't.
This article is designed to help you think about ideas you may not have come across before.
I have been using this system in some of my rifles for many years and find it improves accuracy .
25 / 10 / 07. Copyright.
