Why does my rifle shift its aim point? – Part 1
by B.B. Pelletier
Before I start, Pyramyd Air is closing out the Walther RedStorm pistol and is offering them at a terrific savings. This will be your last time to get this pistol.
This will be a series that explores one of the most interesting and confusing conundrums of airgunning – the point of impact shift. I hear about it frequently and the complaint sounds like this. “I get my rifle sighted in, then come back to it in a day or so, only to find that the point of impact has shifted. If I sight-in again, when I come back to the gun, the POI has shifted once more. The gun is very accurate, but why can’t I keep the groups in the same place?”
Here is a second variation of this same theme. “I’ll shoot a group of several shots and then suddenly the gun throws two or three shots wide of the group. Sometimes if I continue the shots will go back to the first group but other times, the new POI is where all the pellets will land.”
I actually did a report on the problems of scope shift that you might want to read, though this series will be detailed in far greater depth.
This series is prompted by a reader comment that came in while I was at the SHOT Show. Hegshen said “I own an AirForce Condor and have been experiencing POI shifts that I can’t solve. I’ve tried everything and have sent my rifle back to AF for them to inspect.
Hegshen and I then had a lengthy discussion about his problem, which you can read in the comments section of the third installment of the Benjamin Discovery report. Normally I would play 20 questions with the person until something I said triggered the right neurons and he did something that corrected the situation. But this time was different.
I happened to be at the AirForce plant testing the final prototype of the new Diana scope base (it works well, by the way), and I asked if they had any guns in for repair. They had two, and one of them was from a guy with the same problem as Hegshen, so I knew I had found his gun. This time, I figured I would test the problem rifle myself, and see first-hand if the gun was shifting its POI. What’s more, I would document the entire process so you could see what I go through when analyzing a problem like this one. POI shift is one of the most common problems airgunners have today, so what we do here should really help a lot of you.
Step one – clean the barrel!
I did all the repairs at AirForce when I worked there, and whenever guns came in with complaints of poor accuracy, I always cleaned the barrel first thing. Of all the guns I ever tested for accuracy, I only found one barrel that was bad. It had a poor choke and I couldn’t get it to shoot no matter what I did. But dozens of other rifles shot perfectly. I didn’t take the time to test a rifle before cleaning because no one cares what it was doing before it got fixed and time is money. So, cleaning the barrel is always the first step, unless the barrel cannot be cleaned due to gun construction.
I’ve already described how to clean a barrel, and there are several posts in which I list the materials and steps to do the job right, but this time I took pictures to show you what I’m talking about. Here we go.
The cleaning rod and brush meet with a lot of resistance when I first try to push them through the bore. Part of this – maybe most of it – is due to the friction of the brand new brush, and some is due to the crud in the barrel. I don’t know until the session is over – after the brush has passed through the length of the barrel 20 times in both directions – how dirty the barrel really is. A lot of dirt and some lead flakes usually come out of the barrel.
Stroke after stroke, the brush is passed through the length of the barrel. Whenever possible, I try to hold the Dewey cleaning rod by the ball bearing handle to let the rod rotate and the brush to follow the rifling. However, for the first 14 strokes, there’s too much resistance in this particular barrel to allow that. Either this was a very dirty barrel or this brush was very large.
Following the cleaning, the rod is wiped clean and the brush is exchanged for a cleaning jag. Clean dry patches are then pushed through the bore in one direction, only (breech to muzzle). Continue pushing clean dry patches through until the come out clean. In this case, I was having difficulty getting the final residue out of the bore, so I wet a patch with Otis bore cleaner and pushed it through to soften the residue. The job was easier to finish after that.
Now that the barrel is clean, I’ll mount the scope and start testing next time.