Article #7: Crafting accurate ammunition

[Ian]

The Basement Articles #7: Crafting accurate ammunition


There is a lot more to crafting truly accurate rifle ammunition with cast bullets than simply stuffing powder and bullet in the case, but basically that's it. The HOW part is the difference between a rifle that shoots so-so and one that drills holes.


This article will be heavily equipment-oriented and discuss some simple modifications often necessary to make ammunition that fits our particular guns, as well as to continue previous discussions involving just exactly what needs "fitted", and why it matters. In previous articles I discussed the aspects of static and dynamic bullet fit, how alloy plays into this during the firing cycle, and a few objectives I've found it beneficial to meet while preparing brass that fits your rifle and supports the bullet. These are some methods and tools that have helped me improve my accuracy.


Let's start with the reloading press. Maintaining concentricity and trueness in every operation while building a self-contained cartridge is essential to accurate shooting. The press used needs to have the ram square and centered with the dies, and the shell holders need to fit the ram well. Most good presses accomplish this, but some of the center-mounted turret types (Lyman, RCBS, and a few others) need to be carefully adjusted to keep the turret head from rocking under stress and literally bending things like a banana. Run the ram and shellholder up into the empty, threaded die hole and eyeball it from the top to check that the shellholder is centered on your setup.


Next, sizing dies. I'm not a brand snob, I don't care who makes the die, but it needs to do the job you need it to do, and most of them don't out of the box. I'm a fan of Lee dies because they are easily modified and cheap donors for parts. They also have a high degree of interchangeability of internal parts compared to other manufacturers who change designs and thread sizes frequently. Since the best accuracy with cast bullets is usually obtained through minimal sizing, and cast bullets are almost always considerably larger than the jacketed ones that most production dies are intended for, the neck sizing part of most full-length dies are very much too small for our needs. Through measurements of chamber casts and fired cases, case neck thickness, and through determining bullet size to be used based upon throat entrance size and other factors, one can establish just how much (or little, really) the full-length sizer die's neck needs to be enlarged to prevent unnecessary overworking of brass. In the case prep article I explained why I prefer to use customized full-length dies rather than bushing neck size or even collet dies for the majority of my work, although the other types do have their place, particularly the RCBS Gold Medal Match bushing sizer dies with the choice of body sizing, shoulder bump, or neck only die bodies. I'm only presenting the way I do this, not everyone will agree or do it my way, but I'm only attempting to outline A way that accomplishes the needed goals. Lee dies are open at the top which makes them easy to hone out with strips of emery paper wrapped around a drill shank or brass rod. I use a drill press to drive the spindles and oil the sandpaper. Once I get the neck portion honed out enough to size the brass "just" smaller than what I want it when loading (usually about .002"-.003" smaller on the ID than the bullet size), I focus on the case body portion of the die. Most standard resizing dies squeeze the body too small for best alignment in a typical rifle chamber, so I like to hone these out until a sized case just "kisses" the chamber when dropped in and has virtually no felt lateral wiggle. Modifying a sizer die to do minimal sizing will still allow you to "bump" the shoulder of a bottlenecked case back a thousandth or two from its fire-formed state without squeezing the body so much that it rattles around in the chamber like a BB in a boxcar. Every time you reload the case it will be exactly the same dimensions as last time and not get tighter and tighter in the chamber or change bolt preload over time as neck-sizing tends to do. All that leads to better consistency through the life of the brass and multiplies brass life without annealing.

 

[Ian]

(Continued)...

Annealing brass for smokeless powder, cast bullet loads is not something I usually do unless doing a severe re-size from another caliber. The reason is simple: Harder case necks have proven to shoot better than annealed ones in some situations. Of course there are always exceptions, and I DO anneal some brass for some calibers periodically, but generally for “production” chambers like most of us have, harder necks give better groups. Generally. Remember that. Sometimes I like to have an un-modified, factory sizer die with expander ball inside so I can take once-fired brass and work the necks several times before trimming, prepping, and loading. This work-hardens the necks quite a bit and helps shorten the "break-in cycle" of the brass. Hold the case up to your ear by the rim and flick the mouth with a fingernail to observe the sound it makes. A sharp "tink" sound indicated a hard neck, a "tonk" or thud means it's soft. This is one of those nuances that's tough to describe, but if you pay attention to it you'll catch on over time to what the "right" sound is when your targets begin to tell you that the necks are good for that gun, bullet, and load combination.


In some instances it is necessary to "draw" the case necks after many firings to keep them from splitting. This is NOT annealing per se, but a very mild tempering that just barely broaches the threshold of anneal. For this I use my casting pot filled with lead alloy at about 600 degrees. Just quickly dunk the necks almost to the shoulder, shake off the lead, and drop them in a pot of water. If you allow your cases to build a natural patina over time, the lead won't stick to them. Some dip the necks in mica to keep the lead from sticking. I recently read about one individual who uses a small lead furnace filled with fine sand to anneal his necks (similar to how eyeglass frames are heated and adjusted), this may be the best method of all but I have yet to try it. Use the "tink" method to observe the effect of the draw.


After you have your cases cleaned, fire-formed, and resized/deprimed, the next reloading is "for real" and I like to do the detail prep at this point. This means a final trim length check, mouth chamfer, and neck uniforming. I like an RCBS "cricket" deburring tool, but several companies offer handles with interchangeable tips for the job if you don't mind spending the extra bucks on them. The handles reduce finger fatigue. Some of the motorized case prep centers are excellent, too if you have the money to spend on them and a lot of cases to prepare. For inside deburring, I have been using the "VLD" type cutters as they require less mouth belling when loading cast bullets than do the 45-degree tools. After chamfering the inside of the case mouth, I measure the neck thickness with a ball micrometer in about four places all the way around to find thick or thin spots that will need to be turned off. Most brass has terrible variances, often upwards of .004" which will cause all kinds of misalignment problems and erratic bullet release. I settle on a dimension that will clean up most of the cases in the lot and set up my Forster bench-mounted trimmer with the neck turning attachment so that it will clean up at least 2/3 of the high spots, or leave the cases with no more than a couple of ten-thousandths variance in thickness from thickest spot to thinnest. If fitting closely to a match chamber, or if using extra-thick brass, you'll want to turn the necks based on a precise dimension, not just clean up to an average like you will with most production rifle chambers that need you to leave as much "meat" on the necks as possible. Other brands of cast trimmers work fine, I just like the Forster. Use what suits you, just get the necks uniformed. Once the necks are all turned, the outside gets the standard 45-degree deburr, just barely enough to remove any trimming ridge, not to round over the mouth.

I like to uniform my primer pocket depth with a Redding or Sinclair tool (thanks to Rick for getting me hooked on that). Uniform ignition and proper seating depth are assured by squaring the bottom corners of the pocket and ensuring that none of the pockets are too shallow.

Prime your cases. I don't care what tools you use, they all do the same thing, just make sure that you have some way to "feel" the seating pressure, and concentrate on developing muscle memory to achieve consistent seating pressure.


Expand your case necks to obtain the exact amount of case tension you need on your cast bullets. "What is the exact amount of case tension I need?" you ask? I don't know. It's up to you and your rifle to discover, but generally I like exactly .0015" interference fit from 6.5mm to .35 caliber, a half thousandth more for larger and a half-thousandth less for smaller. Self-loading rifles or lever-action rifles may prefer more neck tension, as do most magnum-level revolver loads utilizing extremely slow-burning pistol powders. There are several brands of tools available to expand the case necks uniformly and bellmouth slightly, and I'm very particular about ONE brand here: RCBS. RCBS makes a universal cast bullet expander body, stem, and lock nut and a variety of interchangeable spuds that do the job nicely. You can also modify them for your specific size needs, or have them made. I do not like Lyman "M" dies because they are almost never the right size, and the two-diameter "step" on them rather than tapered bellmouthing shank is also almost always the wrong size and damages the brass. You can, however, very easily buy an "M" die of the next caliber up and turn the spud to the size you need in a drill press with a file and put your own tapered expander shoulder on there as well. The bottom line is to make an expander that will uniform the neck ID to hold the bullets with correct tension (factor in springback here, spuds need to be a thousandth or two larger than final desired neck ID) and to bellmouth without stressing the mouth too much. The spuds also need to be long enough to work the case to 20-30 thousandths past the base of the neck or past the place that the base of the bullet will be seated if a straight-walled case.


The neck expanding operation is also a culling operation. Learn to "feel", or measure with a trigger pull gauge, spring pull gauge, or fish scale the amount of pressure it takes to WITHDRAW the case from the spud. Sort cases into at least three piles, Goldilocks-style. Shoot each batch separately and see which ones group the best, and observe the different average points of impact where each group prints. You may be surprised how much a neck tension change can affect group placement and dispersion.

 

[Ian]

(Continued)....

So FINALLY, you're ready to put in the powder and seat the bullet. Everybody has their own preferences for weighing powder charges and getting them in the case, use what suits you as long as it's reasonably consistent. I'm going to drop the bombshell here as well as again later in the powder article that exactly consistent powder charges are not as important to accuracy as conventional wisdom would have you believe. Fit of cases and careful preparation can make far more difference to accuracy than a +/- .1 grain of powder ever will. Felix Robbins made a so-true observation once that you should consider finding a powder/charge combination that can tolerate a few percent deviation from the mean with no appreciable effect on point of impact or group dispersion. The biggie here is landing your load into the center part of a harmonic node of the system. Temperature changes, slight altitude changes, humidity, and lots of smaller factors affect burn rates slightly, thus affecting the bullet's time in the barrel and how that coincides with muzzle harmonics, so finding a load that can tolerate some variances helps build reliable, trustworthy ammunition. So pick your powder and dump it in there.


Fillers and buffers deserve their own discussion, as does duplexing and other fancy stuff, so I'll leave that out and we'll go straight to seating the bullet. This is where a large percentage of us screw the pooch because we use dies that don't seat the bullet straight and nose punches that don't fit either the bullet or the die cap that supports them. Lee Precision has the worst seating dies that I've ever seen, and there isn't a good way to fix them, so when I can afford it I buy the Forster Benchrest dies. You don't need precision, micrometer depth seating adjustments, just buy the $50 seater die with the sliding case support sleeve and it will be light years ahead of what you were using before. It may be necessary to hone out the sliding sleeve to accept your carefully prepared, oversized brass, necks, and bullets, but it's worth it because they do a good job of getting the bullet into the case straight. There are other good dies out there that accomplish this so I hear, but I like the Forster dies so much I never tried them.


Seating depth is a variable. Sometimes it works well to seat a bullet out until it pilots in the rifling when chambered, sometimes that's not possible. Sometimes a little jump improves accuracy, sometimes seating to engrave does. There is no "best" way here except what each gun and combination of components assembled by YOU happens to like best. Experiment here and you'll likely see very noticeable changes for better and worse with each gun. Also keep in mind, for safety, that the closer you seat a bullet to the lands, the higher the peak chamber pressure tends to be. This is more of a concern with copper-jacketed bullets, but the effect is still there with cast bullets, though lessened to a degree.


After seating, the proof of your die quality is in the concentricity of the loaded round. Here's a "quick and dirty" trick to check concentricity that I learned from a fellow on another website: Roll the loaded cartridge on a smooth tabletop (or put a piece of glass on a tabletop and use that) while looking along the surface and watch for the tip of the bullet wobbling up and down in relation to the glass. Your eye can detect as little as a few ten-thousandths of runout here, so there's no need to spend a hundred bucks on a concentricity gauge if you don't want to. If you have runout, something is out of whack somewhere and you need to hunt it down and fix it if you expect any of the rest of the work you've done to help your accuracy any.


Last thing is crimp. I usually don't use any on rifle rounds unless it's for a levergun, semi-auto, or pistol-caliber rifle or pistol. I like a roll crimp, even on automatic handgun rounds, but suit yourself here, just make it consistent, don't over do it, and be prepared to experiment with it as an accuracy-tuning tool.


By now, you're probably beginning to see a need for some very detailed record-keeping to sort out all the variables we've learned to pay attention to and control. Just write it all down and change ONE thing at a time at the range. I like to write directly on the targets all the critical stuff about load, alloy, lube, weather, powder, neck tension, crimp, seating depth, number of case firings, etc. and start to put it all together into a "best of the best" load for that gun. Over time, a number of people I know (many who have taught me quite a few of these tricks for cast bullet accuracy) have learned to build ammunition for bone-stock military rifles, hunting rifles, and leverguns that shoot astonishing groups at much higher velocities and longer ranges than most cast bullet shooters will believe. I'll just say that consistent, ten shot groups at minute of angle or less at 75-85% of full, factory ammo velocity out to the subsonic transition point of the trajectory are possible, and many are doing much better than that.


I'm still learning, but getting better at this all the time.

Link to Article #8: http://www.artfulbullet.com/index.php?threads/article-8-barrel-harmonics.140/


Ian

 

[JWFilips]

Ian,
Again another outstanding article!

I customize all my FL die necks for cast boolits ...but how do you customize the body ( since all have a different tapers) I would love to be able to push my shoulders back without shrinking my case head area ...can you elaborate?

 

[Ian]

Good question, and it is a bit of a problem sometimes. You can hone out the body portion of your sizing die too, so that sized brass fits your individual chamber better, or buy a shoulder-bump die that takes neck insert bushings and bump the shoulder back every few firings. The ultimate solution is a custom die for each rifle from CH or one of the reamer manufacturers, but it's spendy.

 

[JWFilips]

Can a hone be made by using fired brass The brass in question being turned in the die with griniding compound...yes the brass would give first but persistance?

 

[Ian]

I bet it would work. I'd be inclined to start with a resized case since they don't exactly drop right in after being resized, then graduate to a fired case or one that has only been partially resized. Perhaps cut off the case right at the body/shoulder junction to prevent altering the shoulder of the die. The grit will tend to embed in the softer brass rather than wear it. Just my off-the-cuff thoughts, never tried it. I did enlarge one die by simply taping a single layer of medium-ish Emery paper to a resized, cut-off case and turning it with my drill press by chucking the rim in the press. I don't remember how many times I refreshed the abrasive to gain a couple thousandths diameter but it was a bunch. Transmission oil or similar is essential, and the die will get very hot.