This is one of several section of a guide for reloading your own ammo.
Rifle Cartridge Reloading Accuracy Guide:
Written by: Kim Lockhart.
Hand loading, loading, re manufacturing, reloading ammunition for a rifle is serious business and should never be taken lightly! When done properly and precisely real gains in rifle accuracy can be achieved.
a. Reloading manual loads and factory ammunition are loaded to fit and function in all guns of a certain caliber.
Manufacturers and factories do this with reasonable accuracy, but the ability to customize a cartridge to your firearm leads to excellent accuracy.
b. How you sort and assemble all the cartridge components have major consequences on harmonious ignition and accuracy.
c. As a reloader, you control many of the variables of a cartridge. You select the cartridge case, the primer, the powder, the powder charge, the bullet and most importantly the seating depth of the bullet. You customize the load for your firearm.
Note: This is a critical point to remember when you are adjusting and working up a load for your rifle, fact is, you are actually tuning and adjusting the barrel vibrations of your rifle.
The purpose of this short brief guide is to point out the small things in reloading that the average reloader may not be aware of or their importance are overlooked by experienced reloaders.
While some of the things described in this guide offer only a small seemingly insignificant gain in accuracy it is a combination of all the little things that add up to a large gain in accurate handloaded rifle ammunition.
Rifle Cartridge Powder / Load Density:
There are many rifle cartridge powders to choose from for the avid reloader today each of which vary in their burn rate. With all the powders that are available how does anyone know which powder to select for their particular rifle cartridge reloading.
Load density is the determining factor in selecting powder for a particular rifle cartridge with 86% density just about ideal in most cases. Load density is the ratio between case capacity and actual powder charge. Most factory ammunition is loaded with a density of 80% - 90% of the cartridge case capacity.
1. You should never exceed 95% load density.
a. Primers need room to flame through the powder charge which gives uniform velocity and pressure.
b. Cases that are full or compressed charges of powder will accelerate barrel wear in the rifle barrels throat area.
2. You should never drop to far below 80% load density.
A known condition named detonation (excess pressure spike) can occur with cases that are not signifacantly filled with powder. Some years ago the U.S. Ordnance and DuPont ballistics laboratories were able to duplicate the strange phenomenon called detonation and they had determined that excess air space in the cartridge case to be the trigger for detonation.
How to figure load density.
Powder charge weight divided by case capacity equals load density.
Example: Powder charge 40 grains (divided by) Case capacity 50 grains = .8 or 80% load density.
Case capacity is the amount of volume inside a cartridge case that is available for the powder to fill.
How To Measure Case Capacity.
Measuring case capacity is actually quite simple. Once you have established your bullet seating depth in the bullet section of this guide.
1. Weigh one case with bullet seated to proper depth without powder or primer.
2. Now fill the case with water through the primer hole using a hyperdermic needle and weigh again.
3. Now subtract dry weight from the water weight and this will give you your case capacity.
470 grains = water weight with bullet.
- 420 grains = empty weight with bullet.
50 grain = case capacity.
Once you have your case capacity using your reloading manual select powders that fall into your load density range.
In the above example of a 50 grain capacity your range would be.
a. 50 grain capacity x 80% load density = 40 grains of powder.
b. 50 grain capacity x 90% load density = 45 grains of powder.
Rifle Cartridge Case / Brass:
The cartridge case is the one component in reloading that is so generally passed over when looking for accuracy, when in fact it is one of the most critical for accuracy. It is the cartridge case that has to hold the bullet in perfect alignment with the rifles bore, any deviation here and accuracy will suffer.
The first rule when it comes to cartridge cases is never mix cases from different manufacturers or even same manufacturer with different lot numbers or batch run. If you really are looking for accuracy loads, bulk brass is cheap so when ordering order a minimum of 100 cartridge cases before standardizing cases.
Weighing Cartridge Cases.
1. The first step in standardizing cartridge cases is weighing each and every one and then seperating them by weight, seperate in 1 grain increments or less.
a. If there is even 1/10 of a grain difference in weight between the cases that means there is a difference in the internal dimension and strength structure of the case. This will change stress expansion areas of the case which in turn will change the way the cartridge headspaces in the rifle chamber when it is fired.
Each time the cases are loaded and fired the heavier cases will stretch less between the cases shoulder and head than the lighter ones. Evidence of this can be noted by measuring case length after firing the cartridges, they simply do not stretch the same and this does affect accuracy.
b. The cartridge case capacity is directly affected which is nothing more than the volume of the cartridge case but of which in turn affects velocity hi-lo spread and will affect bullet impact or accuracy.
RCBS Powder Pro Digital Scale With a 1500 grain capacity, you can weigh powder, bullets and
cartridge cases with complete accuracy to within 0.1 of a grain quickly.
Case Neck Thickness
2. The one case dimension that really helps shrink group spread is uniform neck thickness. Ideally, necks shouldn't vary more than .0015" in thickness. Before measuring, bulk brass should be run through with an expander ball to remove dents (resizing die with expander ball).
All cartridge cases should be checked for this condition after every third loading because brass flows forward and will thicken the cartridge cases neck.
Case Neck Thickness Gauge
How the complete cartridge fits in the chamber and throat of the rifle barrel directly affects accuracy!
A quick, way to determine several important case and cartridge dimensions is using the
RCBS CaseMaster® gauging tool,
case neck concentricity,
case neck thickness,
case length and
Listed May 1,2014The poor mans bullet seating gauge.....
With a new rifle comes a new load workup, and more details on that process later.
What I want to discuss here is a way to determine the distance from the camber mouth to the beginning of the lands, or what is commonly termed the 'Throat'. For hand loaders seeking maximum accuracy, this can be an important measurement.
The idea is the distance a bullet moves forward from the case before it engages the rifling can greatly effect accuracy. This I know to be true. If the handloader can find the 'sweet spot' for his best load, usually something like .005-.010" from the lands, then peak accuracy is one step closer.
To measure that distance, special tools can be purchased that are designed to perfectly gauge the 'freebore', or distance from case mouth to rifling. Being a frugal (read that as CHEAP) old fart, Carteach prefers using a little ingenuity to achieve the same results.
Here, we see a full length sized un-primed 30-06 case that's been sliced with a diamond wheel on a Foredom tool. Slicing the case almost to the shoulder seems to work well, although I've seen good results from slicing a little farther, about halfway down the shoulder.
The idea is to have the case neck pressure relieved just enough that a bullet will slide into the case, but still be tight enough it won't shift or fall out on it's own.
What we'll do is hand start a bullet into the case mouth, and then carefully... but firmly.... chamber the round in the rifle. It's important the bolt not be slammed home, but be moved slowly into full battery. Treating the operation roughly will result in false readings.
In a bolt action, the bolt must be fully cammed into lockup. With a pump or semi-auto, assuring full lockup is a little more difficult. Since most rifles will not fire out of battery, if a dry fire gives a satisfying click, the bolt is usually closed all the way. It's critical beyond my ability to stress.... UN-PRIMED cases are used for this! If a live primer is in the case, it can propel the bullet far enough into the bore to create a deadly dangerous situation.... a blocked bore.
Carefully open the bolt, and draw it backwards slowly. Try not to let the ejector kick the case out, but preferably lay the rifle over and drop the case into your hand. The bullet should have contacted the rifling, and been pushed back into the sliced case neck.... where it should have stayed.
There is something to be said for repeating the entire trial multiple times. If the final measurement is the same every time, it's probably being done right.
Regarding the resulting measurement..... how is it done? Well, a simple vernier caliper will give a total overall length for that case, with that particular bullet. You DO own a good vernier caliper, RIGHT?
Using that measurement, the overall cartridge length can be set up with the desired bullet-to-land spacing. Simply set the seating die to seat the bullet at maximum length, and dial in the a few more thousandths depth at a time till you reach the length you wish to try.
It's rather important not to set the bullet to seat right at the rifling with a field rifle. If done so, a loaded round in the chamber may have it's bullet pulled simply by camming the bolt open... leaving the bullet stuck in the rifling. Bench rest shooters often seat right at the lands, or a few thousandths in, but that's a different game.
Now, back to measuring the overall length of the 'gauge' cartridge we just invented..... it must be understood..... if measured as found, the resulting length will be for THAT bullet design, and no other. Different bullets come with different ogives, or curves, and will impact the rifling at different spots along their length. A spitzer bullet will not hit the lands at the same place a round nose bullet does.
The answer here is a widget called a 'comparator'. It's a big hex-nut looking affair with six precise holes drilled in it that mimic bore dimensions.
Including a comparator to the measuring process gives a number that can be used with any bullet the handloader wishes, as long as the comparator is always used in measuring overall length during seating die setup.
In a field rifle... hunting or match.... there is another factor that must be considered. In the case of The Fat Man's 30-06 Mauser... it overrides the accuracy potential of seating to the lands. That factor is magazine length.
On a rifle with a long throat (as I have here), the longest cartridge that will fit the magazine will not even come close to the rifling when chambered. That's just the way it is, and must be accepted as a limiting factor. In the case of this rifle, it effectively nullifies the idea of seating to the lands, as this is clearly a hunting rifle and the magazine will be used.
High power match shooters often have two completely different overall cartridge length loadings in play in the same match.... a short one that fits the magazine for rapid fire, and a longer one that will be loaded singly for the slow fire stages.
Okay....THIS INFORMATION COME’S FROM the Carteach cheat for measuring case mouth-to-rifling. Any questions or concerns?
HOW TO CHECK HEADSPACE
Here’s how to use the tool needed to check your rifle’s chamber dimensions.
By Patrick Sweeney
A three-tool set of Go, No-Go gauges represents an easy way to check the headspace of your favorite rifle.
To many shooters, headspace is a mysterious term, one to which many evils can be attributed. I’ve had shooters come in to my shop expressing the belief that their rifles had too much, not enough, none at all and even the wrong kind–I’m still not sure what that guy was talking about. In simple terms, headspace is the dimension of the chamber of your rifle, the gap between the face of the bolt and the stopping surface for the cartridge. To be precise, it is the distance between the face of the bolt and the datum line, which is a circle of stated diameter, along the slope of the shoulder of the cartridge.
On a rimless cartridge such as the .308, the stopping surface is the shoulder. On a rimmed cartridge like the .30-30 or .303 British, the headspace is the gap for the rim. On a belted magnum, headspace is the gap for the belt. Since not every rifle or cartridge can be made to exact dimensions, with perhaps the best custom rifles being one exception, headspace is deemed to be correct if it is within a certain range.
The specs for a cartridge involve a minimum chamber/maximum cartridge drawing. Headspace for a cartridge is the minimum dimension of the chamber plus .006. If your rifle’s chamber is not cut within this range, some extreme situations can be dangerous. If your chamber is below minimum, and thus too small, you can have problems with bolt function. The cartridge, being crammed into the short chamber, prestresses the locking lugs of the bolt. Once fired, the bolt handle may be hard to lift. Or, in a self-loading rifle, empties do not eject far, or at all. The extra force can wear the engagement surfaces of the locking lugs, or even wedge the action closed and locked.
A chamber that is over maximum may not show any signs of trouble at all. Unless you reload, you may never know it. A rifle with excess headspace can eat reloaded brass quickly. Upon firing, the expansion of the case blows the shoulder forward. When you resize and set the shoulder back, you set up the excess headspace condition again. The stretched brass will eventually crack and break. A prime example of this is the .303 British. It headspaces on the rim, and the shoulder is left with large amounts of space for reliable function under adverse conditions (I’ve seen rifles with more than .050 extra). I’ve never been able to get more than three firings from reloaded .303 brass before the case separates. You can have the same problem with belted magnums if the belt headspace is correct but shoulder space is excessive.
There is an easy way to measure the headspace of your rifle–even if just for peace of mind. You’ll need headspace gauges, precision-ground cartridge-shaped measuring tools. There are three kinds: three-gauge sets, multi-gauge sets and micrometer gauges.
Multi-tool headspace gauges are generally used when building rifles with exact tolerances, such as beanfield rifles or benchrest models.
The three-gauge set consists of “Go,” “No Go” and “Field” gauges. The Go gauge is the one which corresponds to minimum chamber dimensions, and your bolt should close on it. The No-Go gauge corresponds to maximum dimensions, and your bolt should not close on it. The Field gauge measures the largest safe dimensions, and any bolt that closes on it should be immediately tended to.
Multi-gauge sets are used by gunsmiths who work on super-accurate rifles for match or long-range shooting. A multi-gauge set will have a precision-ground gauge at each .001-inch interval along the headspace spread. Using such a set, a gunsmith can ream a chamber to an exact specification. The micrometer gauge is a chamber-shaped adjustable measuring tool not commonly seen outside of factories or arsenals.
To measure headspace with these gauges, first strip and clean your rifle. Chamber and bolt must be squeaky-clean. Then disassemble the bolt; if your rifle has a spring-loaded ejector, you must remove it. Luckily, they are usually held in place by a cross pin which can be drifted out. If the extractor can be removed easily, do so. The extractor on a Remington 742, for example, is staked in place and cannot be removed. But get the ejector out. On a bolt-action rifle, remove the cocking assembly. You do not want the reading to be muddled by the spring pressure of the striker.
When using headspace gauges, the bolt must be completely disassembled, including the cocking assembly, where applicable, and the chamber should be as clean as possible.
Slide the Go gauge into the chamber, and gently close the bolt. On a bolt-action rifle you should be able to close the bolt handle without feeling any resistance. On a multi-lugged bolt, like the AR-15, you should be able to turn the bolt by hand without resistance against the locking lugs. If there is resistance, or the bolt handle stops before it is completely closed, headspace is under minimum dimensions and must be opened up. For that you’ll need a finish chambering reamer, which is a subject to be covered in a future column.
Next, remove the Go gauge and slide the No-Go gauge in place. Again, attempt to gently close the bolt. You should not be able to do so. Do not try to force the bolt–use only fingertip pressure. The bolt handle will usually stop halfway down. On an AR-15, you might be able to catch the leading edge of the locking lugs under the shoulders of the barrel extension. If you had not removed the ejector, you could not feel the resistance, as the force needed to overcome the ejector spring would be too great for the delicate feel needed.
If the bolt closes on a No-Go gauge, you’ll need a Field gauge to check it further. If the bolt closes on the No-Go but not the Field, you simply have a rifle that is going to be hard on brass. Be careful that you don’t set the shoulder back while resizing, and you can get many years of use out of both rifle and brass.
If the chamber swallows a Field gauge, you’ll have to have a professional look at it. Most likely, you’ll have to have the barrel set back and rechambered by someone with riflesmithing experience.
And the rimmed and belted magnum rifles? Dealing with the rim or belt and the shoulder at t
he same time is a reloading problem, involving expanding the neck and resizing it down to create a false shoulder, then fire-forming the brass to your chamber. On a .303, I wouldn’t waste time. When I tried it, I got one extra loading out of my brass. On a .300 magnum, it is definitely worth the extra effort.