ACCURACY TROUBLE SHOOTING REGIME
Accuracy Trouble Shooting Regimen Example
The following is an example of things that must be checked one by one to solve accuracy problems,
submitted by local gunsmith associate, Jim "SHOTS" Hendershot.
Not long ago I had a customer ask what caused his Encore to “Shoot all over the place”. After a long talk on the phone about what was going on, he decided to ship it to me to check out.
In our conservation I determined it was more vertical than all over the place. There are quite a few things that can cause this. So approaching it can be a series of elimination of one thing at a time.
The most common is a very tight headspace. It can be caused by the ammo you are using or the fit of the barrel against the frame or bumping it or both. The next area to check is the forend. It will also cause “Vertical Stringing”, but is less a problem than headspace.
The first thing I do when I get a “Problem Child” barrel is to give it a good visual look at the chamber and the crown. I then do a Cerrosafe casting of the chamber so I can get good measurements of the chamber. This barrel was a TC 24” SS 7mm08, and to my surprise, had one of the best aligned chamber, neck and throat I have seen in a long time. The crown also looked good. So now it is time to shoot it.
I started at 75 yards just to make things easier to see what it was doing....yep....pure vertical. This barrel had a “Barrel to Frame” gap of .0015 so I selected the factory ammo one by one from the box and dropped them into the barrel (barrel off frame) to see how they fit. The ammo ranged from -.001 to +.004, this is quite a range, but by selecting only those that read “0” (by using a Bellm headspace gauge and dial indicator) gave me a headspace of .0015. And you guessed it, vertical stringing.
Noted that as the barrel warmed, the shots went higher and higher. The barrel to frame gap did not change as the barrel warmed, but it also appeared that the barrel was bumping the frame. So the next thing to try was to face off a few thousands from the end of the barrel, thus eliminating any chance the barrel was making contact with the frame. And by the way, this will not change the headspace.
Running low on factory ammo that I needed to meet the headspace requirement, I started working up reloads to work with. The first few reloads showed less vertical stringing, but it was still there. Knowing the headspace was correct, I started to look at the forend. I removed it and put a couple of small washers in place to give it a little more float. Helped but did not stop the vertical stringing, just got a little shorter. Next I removed the forend and did some more testing....did not help much, if any more than the washers. The customer had a 3 to 9 x 50 with no AO. I noticed a lot of parallax so I put one of my big scopes (6-24x50) to eliminate the parallax and make it easier for me to get a good solid POA... So started to think the barrel was the only problem. Thick and thin areas within the barrel causing it to warp as it warmed up.
I talked Mike into looking down the barrel to see how straight it was. With many years of making barrels, he can do this with his micrometer eyeball. He said it looked too straight to be causing all this vertical climbing. So now it is time to work on the forend. With all the other causes removed or corrected it had to be the thing causing most of the problem. I machined a couple of steel pillars and installed them in the forend giving it a good .025 off barrel except for the pillar contact. Also removed a lot of material off the sides where it had been touching the barrel. After the epoxy got good and cured, off to shoot it again. Same drill.
Fired five rounds as fast as I could letting the barrel get good and hot. The first three shots were inside a three quarter inch black spot on the target (POA), and the next two were only a quarter inch above the three, and side by side. This was now acceptable to my customer. I still feel the barrel will climb a little as it warms up. But now he has a few shots that go into at least 1MOA. Starting with a cold barrel.
Just what you want when hunting. He is talking about not wanting to shoot only a few rounds of factory from a box that will give him the proper headspace. He is thinking about getting into reloading....good move...and a lot of fun. But he did buy a Bellm Headspace Gauge and a Dial Indicator so he can use factory ammo until he gets into reloading. If you are having a problem like this, check that forend along with the other causes mentioned.