Muzzle Velocity differences

[DaveT1]

Just received a new .22 Superior barrel for my DreamTac. I began testing with both JSB 18.1's and NSA 17.5's in .218. I noticed a couple of odd things. Even though the the NSAs are a bit lighter than the JSBs they shoot about 10 FPS slower. I used two different power settings: HS preload at 17mm HS at 5 & Max and the Reg set at 115bar.

The other thing that I noticed is that once I got the scope re-zeroed the JSBs were scary accurate. One hole, with 10 shot groups, at 15 yards (the max shooting distance in my backyard). The NSAs shot low and to the left and the groupings were 1/4 to 1/2 inch. All groups were shot from a bench with a bipod and rear monopod. I had similar results from some FX Hybrids.

I haven't tried indexing the barrel. It is shooting so well with the pellets that I didn't want to mess with success. The slugs chamber with virtually no resistance, where with the JSBs I can feel them seating. Also, I am using a stock transfer port and pellet probe.

Has anyone else experienced this situation? 

 

[nervoustrig]

Generally it’s due to more friction in the bore. A pellet only makes contact in two tiny rings whereas a slug has much more area in contact with the bore.

 

[qball]

Superior barrels seem to like .217 but at 15 yards you are much better off with pellets at much lower speed. I’ve had pellets ricochet back and when I shoot slugs the ricochet sound is really loud so at that 15 yards I would shoot 12 FPE max. Most of my target practice shots are 7fpe. 

 

[Kevin23]

Same thing in my gun. Nsa 17.5 are 10-12fps slower than jsb 18.13

 

[DaveT1]

I hadn't thought about the friction aspect, thanks nervoustrig!

 

[tor47]

It could also be the slug is not sealing as good as the pellet if they have a loose fit. The skirt on the pellet will expand and make almost an airttight seal.

 

[bandg]

Tried some slugs in my Pulsar today. 12.5 grain NSA slugs shot at almost the same velocity as H&N Sniper's that are just under 15 grains. Could be either additional friction or less sealing in the bore. As Forrest Gump once said, "maybe it's both". Accuracy at 940-960 fps was excellent with the slugs (better than any of the heavy .177 pellets by a noticeable margin out of that rifle and they matched the best accuracy of the 10.34 JSB's).