Return of the Accuracy Testing Protocol

Additions, comments, opinions?

HOW TO SEARCH FOR ACCURACY

            This article describes an importance-ordered set of the things we can and must do to get a rifle to shoot accurately with cast bullets.

            It is not going to explain how to do any of these things; only when, in what order, to do them. In the background is the element of cost; it's always there but seldom mentioned.

            So we start with either a new or used rifle that we want to get going with cast bullets.

            The first step is to acquire a notebook in which everything, yes everything about the rifle and what is done with it is written down.

            A rifle must have sights that allow the shooter to shoot accurately.

For young persons with good eyesight interested in hunting or generally less precise shooting, open sights or peep rear and blade front sights may be adequate, telescopic sights are much better.

For precise shooting, good quality aperture front and rear sights are threshold sights; and telescopic sights are in virtually every case, better.

With a new rifle, make sure that:

There is no obvious bedding or barrel problem

Sights are mounted solidly and correctly

Screws are tight

 With a used rifle, make sure that:

There is no obvious bedding or barrel problem

Sights are mounted solidly and correctly

There is no damage to the muzzle crown

Screws are tight

             The barrel is clean, no copper or other fouling is in there

            New rifle barrels may be “broken in” by the new owner. Since instructions and opinions abound and conflict, this is the shooter's call.

With either a new or used rifle we need to know the twist, to measure the groove and if possible the bore dimensions at chamber and muzzle ends, and to slug or make a cast of the throat. We also need to find out if there are tight or loose spots in the bore, and may need to fix such spots. 

            Testing a rifle for accuracy requires a solid bench rest on a sold bench, and a good chair or stool.

The target used must work for the shooter-target types, shapes and styles  affect group size.

            When the above is done or ready, it is time to select one or more starting loads from published sources such as reloading manuals. Here we select a set of cartridge cases, bullet, alloy, diameter, lubricant, primer, powder, charge and OAL.

            Depending on what is or can easily be made available, several combinations of powder, charge and bullet may be prepared and used for testing.

            Vary powder charge weight in half grain increments.

            Chamfer the mouths of the cartridge cases and always “bell” case mouths.

            Visually inspect the cast bullets and recycle those with flaws.

            Always clean primer pockets

            Always brush or clean inside case necks.

 

Intermission             I test at 100 yards, five shot groups, five groups to a test, group sizes and average recorded. Two or three foulers and ten shots = two five shot groups are shot in about a 15 minute relay, followed by a target-change period of 10-20 minutes. All in reasonable-not perfect and not blizzard, conditions.

            The group measurements mentioned below are average group sizes for bolt action or single shot rifles of about .30 caliber with telescopic or aperture front and rear sights, tested per the paragraph just above.

            If you test in a different way, the group sizes mentioned below may not apply to your testing, but the remainder of this article applies.

Now back to our show.               In this phase of accuracy testing the “Tic-Tac-Toe” chart method, or “Ladder Testing” may be of  value. 

            It is my experience that using recommended loads from reliable sources, with reasonable bullets and powders and primers and lubricant, that average group sizes of 2” or less are fairly easily obtained by varying the powder, charge or bullet. If the best average group sizes that result are over 2 1/2", there is probably something wrong with the rifle.

 

            Now to get from 2” to 1 1/2” average groups.

What do we change next?

            The things we CAN change are legion. The things we SHOULD change are limited somewhat by costs, but should follow a reasonable scheme that works.

 

Second Intermission             There are a number of things that can be done that probably won't help get from 2” to 1 1/2” group averages but that may help later in getting to very small groups.

            I do the following because I've got the time and tools on hand:

                        Select ~100 cases with the same headspace, from the same lot if possible

                        FL size, fire and trim to length

                        Uniform Primer pockets

                        De-burr flash holes

                        Turn case necks

                        Weigh and segregate cases by weight

                        Weigh and segregate bullets by weight, keep those +/- .5 grains, recycle the rest or use for flyers

Now back to our show.  

            Changing the bullet, diameter, powder and charge will get us down to 1 1/2” groups with some more testing. Read anything available about who's doing what with cast bullets, the powders and bullets used.

            Keep the barrel from overheating, cooling methods are available.

 

   

Getting from 1 1/2” groups to ~1” groups is tough.

Based on the CBA National records over several years, competitors average around 1” over the classes. Means that those who shoot in each of the four classes, all told, average about 1". Averaging 1” with cast bullets is tough.

 

            Here are the things that can be done to reduce group size below 1 1/2":

            If you haven't done it yet,

                        Select ~100 cases with the same headspace, from the same lot if possible

                        FL size, fire and trim to length

            Segregate bullets by weight, classes of .5 grains

            Vary bullet diameter in .001” steps

            Vary the alloy, harder is almost always better

            Vary OAL in .005” steps

            Anneal case necks

            Try different barrel cleaning methods and frequencies

            Check and fix cartridge concentricity

 

 

            Here are the things that can be done to reduce group size below 1":

            Change primers

            Get “better” (Lapua, Norma) brass

            If you haven't done it yet,

                        Uniform Primer pockets

                        De-burr flash holes

                        Turn case necks

                        Weigh and segregate cases by weight

            Get cartridge case length closer to chamber length

            Vary the lube

            Vary the number of lube grooves filled

            Vary OAL in .002” steps

            Control bullet weights to .2 gr.

            Control powder weights to .1 gr.

            Orient cases and bullets in the preparation and shooting steps

 

 

 

A Warning: It takes a lot of shooting to find and verify a small change in accuracy-in group size. Simple and easy to use statistical tests are available. (Add references)