Trouble dialing in .22

Gentlemen,

This is going to be long, so buckle up. I just want to give as much information as possible to help diagnose my gun’s problem.

When I first got my Vulcan Pup Gen4, it was shooting like a dream compared to my springer, but I thought it could be better.

Around the 2000 shot mark, things started to go wonky. I would be hitting bulls-eyes, and then for no apparent reason, it would start grouping low or really high or to the left or right. I would re-zero the scope, and everything would be fine for a bit. However, eventually it would start all over again.

I clean the barrel after every 500 pellets using Kleen Bore Formula 3 on cotton patches pulled through the gun from the muzzle end. The patches are pulled with a piece of weed-wacker string that has a piece of 50# test fishing line taped to the end (in a loop).

Things I have checked:

1. I removed the stock and side-plates at the back. All screws were checked in the area around the rear block and all moving parts were cleaned/oiled.

2. I checked for an air leak at the probe by using the tissue paper method.

3. Scope rings and picatinny rail bolts were checked.

4. Bolts holding the trigger assembly checked.

5. Side plate removed and barrel bolts (One side only) were checked and found to be tight.

6. Shroud removed and gun was shot, which actually made the POI worse.

7. LDC removed and inspected inside for evidence of pellet clipping.

8. Stock bolts checked for tightness.

9. Gun shook listening for rattling.

10. Breech o-ring gets lubed with silicone (from the dive shop I work at) every time the barrel is cleaned. Applied with a Q-tip.

11. Tried shooting AA Diabolo Field 5.51 16gr. They seem to shoot a little worse than the JSB 18.13gr that I am currently using.

12. Parallax error minimized by proper scope setup. Scope Werks side-wheel was calibrated in 1 meter increments by myself using a scope visual target (from 10m to 41m) (took me all freaking day to do). Scope is an Althlon Argos BTR 6-24×50.

13. Bubble level on scope checked before every shot. Scope, bubble, and barrel are inline and re-verified using a string and electric level.

14. 11 pellets were shot into the pool at work and retrieved. Pellets were inspected for irregular grooves, damage, etc. I *think* they look fine.

Here are some photos of the crown:

The first couple are after shooting around 400 pellets today.

And then after doing some cleaning. The only thing I did differently with this cleaning is that I ever-so-carefully ran a nylon brush up and down the barrel twice. I did not run the brush into the barrel far enough to reach the breach o-ring.

Today, my chronograph arrived, so I put the gun through the paces. I also wanted to know when the gun would fall off the regulator. I used the JSB’s mentioned above. Is the gun shooting too hot for the JSB’s?

Now that the chronograph has arrived, I can start my big pellet experiment. Using the JSB’s from above, I first Yrrah rolled them and divided them up into groups. Those groups were then subdivided by head size using a PelletGauge. Then, those groups were further divided by weight. I will be shooting groups of approximately 5 provided there are enough pellets in each group.

Could my issue simply be that the gun has a specific requirement for a pellet, which I have yet to discover? Or, am I just expecting too much? After all, the Vulcan isn’t a competition rifle? Or is it…?

Again, sorry this is so long-winded. I hope I’ve given enough information. I really want this to be a pellet-on-pellet gun.

Cheers!