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Author Topic: Handloading; Accu-Loading Part 2 Case prep  (Read 475 times)

Offline TalkHunting Mag

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  • Join Date: Mar 2013
  • Posts: 44
Handloading; Accu-Loading Part 2 Case prep
« on: April 03, 2013, 06:40:31 AM »
I am breaking this into two areas, 1, case component and 2, operation. In either case the physical work is described and the benefits of doing it.
PRIMER POCKET…. On new brass, this tool will cut the primer pocket to the correct depth and remove the fillet radius at the base of the pocket. This cutting process only needs to be done once to new cases. For each reloading, the primer pocket can quickly be cleaned with the same tool. If your loads are hot, you will be able to cut metal at the base of the primer pocket after each firing. This is an indication that you are yielding the brass case head and setting back the base of the primer pocket slightly. When you clean the primer pocket this way, you will get a better "feel" when seating the primers (no variable fillet at the base of the primer pocket), and you will not be shooting extra primer residue down your nice shiny barrel.
FLASH HOLE BURR.... When the brass is formed and they punch out the flash hole, a tiny raised burr is left around the edge of the flash hole where it enters the inside of the case. The theory is that this burr could cause variable ignition from round to round depending on its size and location. The K&M's Internal Flash Hole Deburring Tool is simply a tiny center drill in a mandrel that it will make a cut with a limited depth. A couple of turns on each new case are all that is needed to remove the burrs and make all of the flash holes uniform. It sounds like a good thing to do and I perform this operation on all of my brass.
CASE LENGTH TRIMMING.... For really good accuracy, you need to have all of your case neck ends cut square. If one side of the neck is longer than the other, it would tend to tip the base of the bullet to the side as it exits the neck. Also, excessive case neck length can force the end of the case neck into the end of the throat and "clamp" the bullet in the neck. The extra force to start the bullet in motion causes excessive pressure with an otherwise safe round. I did use an RCBS case trimmer, but now use my Mini Lathe with a dial indicator. If you cut your case lengths too short, there is a large unsupported gap that the bullet passes by that does nothing for accuracy.
MEASURE THE CHAMBER LENGTH.... Here is another accuracy aid. I purchased the Sinclair case length measuring plugs for .17, .224, and 6mm calibers. These are very simple steel cylinders turned to the bullet diameter, leaving a rim slightly less than the case neck OD. To use, you merely drill through the primer pocket (so you can later push the plug out) on an expendable cartridge case and neck size it. Trim the case length about 0.100 of an inch short so the case mouth will not touch the rim of the plug gauge. Insert the Sinclair plug gauge as if it were a bullet, leaving it long and then chamber the case. The plug will be pushed deeper into the case neck and when you extract it, you can measure the chamber's actual length with a dial caliper. I usually find that the factory recommendations for case length leave a 0.050 inch to 0.070 inch gap between the end of the case and the actual length of the chamber. This is a factory safety concern and you can get high pressures by forcing a long case into a short chamber. The factory wants to be on the safe side. But like everything else, if you want the best accuracy, you can minimize this gap down to 0.005 inch and still be safe. You will get better accuracy and find that you can use much longer necks, in most cases, than the factory recommendations specify. The extra case length will better allow you to load the bullet farther out to touch the lands. I have found that, typically, factory .243 Win brass, is already 0.050 inch too short and there is no way that I can think of to lengthen it. I don't trim to the lengths specified in the loading manuals, but use my measurements as a guide. All of this sounds like a lot of trouble to go through compared to walking into a store and asking for a box of 30-30's, but it makes a big difference in the confidence level of your accuracy potential.
MEASURE THE CHAMBER LENGTH WITH A POOR MAN'S GAUGE.... I went through this method in Typi-Loading Part 3 but thought I’d quickly run through it again. This method uses a cleaning rod, a blunt patch jag and two rod stops. If you’re unfamiliar with rod stops, they are just that. Small round collars that clamp onto you rod to allow it only to go into the bore so far. First let’s wipe off the lugs on our bolt as well as the locking lugs of the action to ensure they are engaging bare metal to bare metal, without powder residue, grit or carbon pinned in between which would throw our measurement off by many thousandths. Make sure the bolt face is clean as well. Close the bolt on an EMPTY chamber and to make this is an idiot proof operation let’s go ahead and put the trigger safety on. The bolt actions are easily done by sitting the butt of the rifle on the floor with the weapon vertical. Secure the barrel to the workbench so it’s firmly held in place (always be careful to not bump the scope). I in the past also have sat in a chair, placed the rifle butt on the floor and held the rifle vertical between my knees. Either way you need both hands free to manipulate the rod and rod stops. Warning; be careful anytime you run a rod into the muzzle you don’t want to damage the crown. Now with the rod stops and blunt jag already on the cleaning rod go ahead and carefully insert the cleaning rod into the muzzle end of the barrel and down the bore until the blunt jag is resting snugly against the bolt face. Now we need to “zero out” our rod stops. We do this by holding the cleaning rod into the bore snug against the bolt face. While holding it there slide BOTH rod stops down firmly against the muzzle and tighten down (snug is enough) the thumbscrews locking them in place.
Now we need to take a resized, unprimed (as in no primer) case, containing NO POWDER and seat a bullet long. Let’s say .200” longer than book spec for the bullet you are using. Take this dummy round and gently slide it into the chamber. Bring the bolt up VERY gently behind it until you just feel the bullet touch the rifling’s in the bore. Now take a good rubber band and loop it over the scope and onto the back of the bolt to hold it in a forward position. Do not lock the bolt, the rubber band is just keeping enough pressure on the bolt and dummy load to hold it jammed (into the lands) in place. This insertion of the dummy round needs a gentle touch with both your hands free, and in the holding of the bolt with the rubber band they are. With the keen angle of the bullets ogive and the gentle angle of the lead in on the rifling it is EASY to jam the bullet deeper into the rifling and not know it; this is why just gentle pressure is all that is needed. Avoid exerting too much pressure, but no need to have worrisome sweat beads up on your forehead. If you do jam it in an extra couple of thousandths it’s not the end of the world. We are only trying to find a good estimation here. Now again with the weapon fixed in a vertical position slide the cleaning rod back down the bore until the blunt jag delicately comes to rest on the meplat (tip) of the bullet. Now loosen and slide the lower stop (the one already closest to the muzzle) down until it’s firm against the muzzle and tighten the thumb screw. Remove the cleaning rod from the bore being careful not to bump the stops out of position. Take your callipers and measure the distance BETWEEN the rod stops. This is your jammed cartridge overall length. Write down that measurement. Now repeat the whole process two more times. If you’re not getting greatly differing measurements, average the three dimensions and you now have the distance to rifling. If you’re getting more than a few thousandths difference between each measurement something is wrong and you'll not end up with good data. Start over!
We must now translate this to the reliable measurement off the ogive, which is the same from bullet to bullet and use that figure from now on. Take the dummy round that you used with the Rod and Stops work carefully and place it in the loading press. Thread in your seating die to the lock ring as per normal. Back the seating stem or micrometre if you use one WAY out. Now raise the dummy round up into the die all the way. While holding sufficient pressure on the press handle, begin screwing down the seating stem until you feel it touch the bullet. Now raise the press handle removing the dummy round from the die. Screw in the stem just a little (1/8 turn) and raise the dummy again and seat the bullet to that depth, remove and measure the dummy load from case head to meplat. You are looking for the exact same dimension between the stops you found in step 5. Continue seating the bullet in the case a little more each time (1/8 turn per stroke) until you get it to the exact length you came up with from the cleaning rod and stops routine. This will get your die calibrated to the exact ogive measurement of your rifles chamber. So get out your callipers, comparator body & the proper insert. This time you’ll only need one body(holder) and one caliber appropriate insert. Open the jaws and attach the comparator assembly to one of the jaws. Now measure the dummy round we have set up to our case head to ogive length. The comparator measures off the ogive instead of the meplat. We CAN use this measurement bullet to bullet to bullet for this particular bullet make, weight, length and style in order to maintain good consistency.
MEASURING NECK RUN-OUT… Run-out is generally measured in thousandths of an inch with a concentricity gauge. There are many options of concentricity gauges to choose from that work well. Some work on loaded rounds only, some have a bullet straightening feature, and a few do both loaded rounds and empty cases for checking concentricity. I’d suggest getting one that will measure both case and bullet runout. You may also want to get a Sinclair Case Neck Sorting Tool this may help you speed up your case prep work.
The indicator is set on a height adjustable swiveling base on a stand that can be used for checking bullet or case neck run-out. The adjustable blocks ride aligned in a precision milled slot. The entire set up is on an anodized base plate that gives excellent support during the process that is crucial to operation and accuracy. Basically the operation consists of placing a loaded round (for checking bullet run-out) or an empty case (for case run-out) on the bearings with the indicator end touching the chosen point to be measured. The case is easily spun with one finger as the indicator measures the amount of run-out. Once this process has been done a few times it is a fast and accurate means of measurement. In terms of indicator type being used, whether dial or digital, I actually prefer a standard dial indicator over the digital type. My reason for this choice is that you can see the needle jump when run-out is present. I believe this to be easier and faster than looking at digital numbers while measuring.


Offline TalkHunting Mag

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  • Join Date: Mar 2013
  • Posts: 44
Re: Handloading; Accu-Loading Part 2 Case prep
« Reply #1 on: April 03, 2013, 06:41:06 AM »
NECK MOUTH CHAMFERING.... After you trim the case lengths, there will be a burr on the ID and OD of the case mouth. I use one of a standard inside/outside neck-chamfering tools and make a very light cut on both the inside and outside. I just want to barely break the sharp corner. I don't want to sharpen the end. After these two light cuts, I smooth the case mouth with very fine steel wool. If you look with a magnifying glass, what the steel wool smoothing process does is remove all the tiny burrs on the chamfer cuts at the case mouth. It does not polish the neck OD or ID. This smooth mouth is a very important it will make seating the bullets easier and smoother without scratching the bullet.
NECK MOUTH.... You may see the rolled over edges of the mouth do to the hammering that occurs in the tumbling process. Also the hammered area is work hardened and locally is no longer in the annealed state. If you have ever noticed a tiny ring of gilding metal scraped off when you seat a bullet, it is this hard rolled over ring of brass that does the scraping. Even after inside and outside chamfering, there is still a burr left at the edge of the cut surface. This rolled edge can be removed with steel wool but it will take some work, you may just want to toss it or save it to make a dummy load in the future (if so label it as such and put it elsewhere). With the smooth annealed neck and no rolled over burr, bullets seat very smoothly without scraping gilding metal of the bullet.
POLISHING BRASS.... Smooth and uniform case mouths are very important in producing accurate loads. Therefore, I don't polish my carefully prepared brass in a tumbler. For my "fitted neck" cases, I polish the neck OD and shoulder with a polishing cloth (any silver or brass polishing cloth would work) or a bit of Flitz Metal Polish on a cloth before each reload. I swab out the neck ID with a cotton cleaning swab to remove the carbon and dirt. Keeping that case mouth smooth can't be over stressed.
OUTSIDE CASE NECK TURNING.... I started to get true accuracy when I began outside neck turning to true up my cartridge case necks. Neck turning provides a neck with uniform wall thickness, helps to center the bullet on the bore axis, and reduces split necks. Neck turning also sorts out the cases that have large variations in wall thickness because, once turned, the poorer cases are easily identified and can be tossed into the scrap bin.
NECK TURNING FOR FACTORY CHAMBERED RIFLES.... Here is how I adjust the neck turning tool for my factory chambered rifles that usually have a sloppy 0.010 inch of neck clearance. I pick out 10 new cases at random. Then, as I always do even with new cases, neck size them, including the expander plug, so the neck ID will be round and tight on the neck turning mandrel. I also lightly chamfer the ID and OD of the neck mouth to remove the "rolled over edge" from factory case polishing. The mandrel needs to turn hard inside the case neck even when there is no cutting action. A tight fitting mandrel is the only way you can really make accurate cuts. I adjust the depth of cut so it barely cuts any material and then go through all 10 cases. Usually, there will be one or two cases that clean up practically all the way around and a few that cut heavily only on one side. I increase the depth of the cut a slight amount and go through the 10 cases again. I continue this process until about 75% of the cases clean up about 80% to 90% of the neck outside surface. Caution: Do not set your neck turning tool so it makes a clean cut on all of the cases, because it will make the necks too thin and you will have ruined all of the cases. Therefore, with the correct setting, it means I will reject 2 or 3 out of 10 cases to the bone pile. I keep that setting on the neck turning tool and turn all the cases in that lot of brass. No more neck turning is required for the life of these cases. The neck turned cases will improve accuracy by decreasing the group sizes approximately 50% and get rid of most of the wild fliers. Another advantage of neck turned cases is the reduction of split necks. The uniform wall thickness causes uniform stretching of the neck wall during firing and uniform compression during neck resizing.
NECK TURNING FOR CUSTOM CHAMBERED RIFLES.... For my Spin Doc with a tight necked custom chamber, I use "fitted neck" cases. Once made, these "fitted neck" cases need no resizing and all that is required for reloading is to clean the primer pocket, clean the neck ID, prime, throw the powder charge, and seat the bullet. It took a while to figure out how to reliably make "fitted neck" cases and it cost me quite a few good pieces of brass in the learning process. The first step is to turn the necks on 3 or 4 sacrificial cases so that there is approximately 0.005 inch of neck clearance with a bullet seated. Load a standard load and fire form these cases. Carefully measure the neck diameter of these fired cases and record this diameter. I call it the "spring back" diameter. This diameter is actually the diameter the brass neck will spring back from elastically after being forced against the rifle chamber's neck diameter, including the elastic expansion of the chamber. The difference between the barrel's chamber neck diameter and this fire formed case neck's "spring back" diameter is usually about 0.0013 inch to 0.0015.
FITTED NECK CASES.... I take another 4 or 5 cases and adjust the neck turning tool so that the neck diameter (with the bullet seated) is the same or 0.0001 inch larger than the "spring back" diameter above. This is a trial and error process and takes some very careful adjustments on the neck turning tool. After the neck turning tool is adjusted correctly, I load and fire the 5 cases and neck size them and repeat the neck turning without changing the setting on the cutter. This final neck turning will usually take a slight skimming cut of less than 0.0001 inch. I load the 5 cases again without doing any resizing and fire them and then clean the neck IDs with a brush and load them. I feel the neck tension by the force it takes to seat the bullet. If there is ample neck tension so that I can't pull the bullet out or seat it deeper with my fingers, I have the correct neck turning setting. I make no further adjustments to the neck turning tool. At this point I turn all the cases in the lot without changing the turning tool setting. I fire form the cases, neck size them, and take the final skimming cut. At this point, I have "fitted neck" cases for this particular custom chambered rifle (Spin Doc). These cases give me the optimum in accuracy and I never have to resize them again. If they start to get the least bit sticky in the chamber (hard to open or close the bolt), I reduce the load and check for accuracy. The cases should last indefinitely, since, after the first firing, they are only exposed to elastic stress levels. Most cartridge cases have a limited life because of high stress levels and the plastic deformations of the brass during firing and resizing.
TURN TO THE SHOULDER.... I have very carefully dressed the tool bit with a fine diamond hone so that the cut on the outside of the neck looks like polished brass. I also made a small fillet radius (approximately 0.010" radius) on the leading edge of the tool bit that matches the fillet at the neck to shoulder junction on new brass. I turn the neck so that the bit cuts slightly into the shoulder approximately 0.002" to 0.004". I have had no necks separate from the shoulder from doing this and it decreases the chance of developing the "dreaded doughnut" (a constriction of the neck ID at the neck to shoulder junction).
ANNEALING CASE NECKS.... After 5 or so loadings for factory chambered rifles and the associated neck sizing, the case necks are strain hardened due to the cold working of the brass. Eventually, if you don't anneal, you will start to get split necks. Also, after wildcat case forming from one neck size to another, the necks and shoulders will be hardened. The necks may be easily annealed to remove the high residual stresses and restore the desired low yield stress and desired annealed (yield stress of 19,000 psi) condition. Here is how I anneal case necks. I use a Propane Torch, fancy tool huh. I stand it up on a table and adjust the flame until the inner blue cone flame tip is about 1 inch long. I make a case spinner out of a bamboo shish kebab skewer. I cut a piece about 4 inches long and whittle down about 3/8 inch of one end so it will easily fit in the flash hole and slip a small hex nut over the end for a stop. I put some tape or glue behind the nut to hold it in place. I fill a big bowl with cold water. I do the annealing in a darkened place, like in my loading room at night with the lights dimmed or just a candle burning (just enough light to keep me from roasting my fingers). I put the stick through the flash hole and, holding the stick, spin the case mouth in the flame while holding the center of the neck right at the tip of the blue center cone of the flame. When the neck just becomes a visible dull red (about 750°F), I drop the case in the bowl of water. The neck and most of the shoulder are now stress free in an annealed condition and my case neck is in the "like new" condition. Do not anneal the necks in a lighted room. You won't be able to detect the dull red color and by the time you see red, the brass is already too hot. This burns out the zinc, ruining the brass. Caution: Do not anneal any other part of the case. An annealed case head does not have enough strength to support the high gas pressures and would probably rupture. After annealing, I remove the cases from the bowl and let them air dry overnight.
ANNEALING AND NECK TENSION.... Uniform neck tension is another reason to anneal your case necks. Each time you neck size and then the expander ball opens the neck up to the correct diameter, the brass' yield strength increases. It is called strain hardening. As the yield stress increases, there is more “springback” (to a smaller neck ID) after the expander ball opens up the neck. This effect increases the neck tension. A new annealed neck will have less neck tension than a case that has been fired and neck sized a number of times. Cartridge brass is 70% copper and 30% zinc and its yield stress and strength is increased by cold working.
Annealed cartridge brass has a yield stress of 19,000 psi.
¼ hard cartridge brass has a yield stress of 40,000 psi.
½ hard cartridge brass has a yield stress of 52,000 psi.
So the neck tension on a ¼ hard neck will be twice that of a freshly annealed neck. If your rifle's chamber neck clearance is large, then you could easily get to the ¼ hard condition in 5 or 6 reloading cycles. It would take more cycles if your chamber neck is close fitting.
ONLY WORK WILL HARDEN BRASS.... Cartridge brass is only hardened by cold working. The crystal dislocations caused by the cold working lock the crystal lattice and make it harder and more difficult to form more dislocations thus increasing it strength. When brass is heated, new crystals nucleate at the dislocations and the new crystals are small. If the brass is quenched at this point, the brass retains the small crystals and is annealed with very few dislocations and is stress free. This is the condition you want for your case necks. If the brass is slowly cooled, the small crystals begin to coalesce and grow into larger crystals and the properties suffer because the large crystal boundaries are not strong. Also stress corrosion cracking can more easily occur at the larger crystal boundaries.
SPLIT NECKS.... Finally, the high stress with the hardened neck is what leads to split necks. It is a process called stress corrosion cracking. Increasing the stress level increases the initiation of cracks and crack propagation. Split necks are not hazardous, but they are a problem that can be prevented by annealing. It is easy to just buy some new brass when you start to see some cracked necks and do all the case prep on the new brass. If you mix old and new brass, your neck tensions will be different and this is detrimental to good accuracy.
Now you have the cases all uniform and as identical as you can get them. We are now ready to work up the bullets with the same methodical and meticulous manner. So moving onto; Part 3: Bullet Prep.

 

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