.177 P-rod conversion help!

August 9 2012 at 1:12 AM

Chris  (Login Loki_762)

Okay, I took the plunge and bought parts to convert my P-rod a .177, and it hasn't gone as smoothly as I hoped. I bought a LW barrel from a 1701, and I had Jim Gaska turn down a .22 bolt to fit it. All I had to do was put in the new barrel, file a small flat for the set screw for the shroud bushing, and swap out the bolts. Pretty simple. I already had a single shot adapter for it, so I was set. Today I got to shoot the gun for the first time, and after getting the speed where I wanted it (starting in the low 800's and peaking at about 825 fps), I shot it for groups. I was sorely disappointed. Of the 5 pellets I tried, not one would group consistently! The pellets were CPHP's, RWS Hobby, RWS Meisterkugeln, Crosman Destroyer EX, and Predator Polytips. I shot mostly Destroyers, as they shoot well from my Benji 397, and I had a bunch on hand. No matter what pellet I shot, groups would shift, seemingly randomly. Sometimes it would stack 3 right in the same hole, then the next one would go an inch left or right. Then the next one would be half an inch low. This happened with all brands and types of pellets I tried. Here are the things I checked:

-Barrel set screws were tight
-All scope ring screws were tight
-Pellets were going into the barrel straight
-There were no errant limbs or blades of grass to deflect the pellets
-I kept the magnification of the scope the same throughout the shooting
-Shroud was not touching the barrel band
-Breech seal was tight
-Consistently placed the forearm in the same spot on the rest each time
-Consistent cheek weld
-I shot my Talon SS to make sure it wasn't something I was doing - stacked pellets in the same hole, and trimmed blackberry vines at 30 yards, no sweat

With the exception of the occasional flyer, I did not have any problems like this with the gun when it was set up as a .22 (after I crowned the barrel.) I don't think it's the barrel - LW barrels are NICE, and the crown looks good. The only other thing I can think of is my transfer port. I opened it up to .109 (7/64ths) when it was a .22 to optimize air flow. Do you think it is possible that too much air is getting through to the small pellet, and creating turbulence of some sort that is throwing my accuracy? I have an extra port - should I stick it in and see how it does, and just open it up to get the speed I want? It is an aftermarket port made by Mark Gravelle, so it is extra tight - I could start small and just increase in size a little at a time, I suppose. If it isn't the transfer port, what else could it be? Is there something I am overlooking?
Thanks in advance for the help,

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