Lighter projectile with same velocity as heavier one?

[mmahoney]

I've come across a phenomenon the last few days that I'm having trouble getting my head around. I can crank the hammer spring tension on my Veteran to shoot the 25.43 grain JSB Monster redesigns at 900 fps. If I shoot a 23 grain NSA slug with the exact same spring tension, the slug also travels at 900 fps and not faster like physics would suggest. This is the only pellet/slug combo I have found to be doing this. Anyone have an idea what might be going on?

 

[BigTinBoat]

Even though the slug is lighter is is likely a tighter fit in the barrel causing more friction.

I've also had the same thing happen with 15.89 JSB's (5.52) vs the H&N 14.66 (5.55) the H&N were only slightly faster at the muzzle.

 

[Long_Shot]

Like BigTinBoat said. 

I have a .2495" Dia. 31gr. slug that is a 886 FPS @ the muzzle. 

In the same gun a 30.5 at .2500" Dia. is only shooting @ 872 FPS. 

Lighter and slower. Both are extremely accurate though......

 

[JimNM]

?? how far from the crown are you running the chrono? Stretch it out to 50 yards and I bet you will see the difference.

 

[mmahoney]

@JimNM

Only about a foot away, but I'm not talking about velocity retention. The lighter pellet is not starting out at the faster velocity that it should.

@BigTinBoat @Long_Shot

Your experiences are helpful. Thank you. I dropped both the Monster pellets and the Slugs in a pellet gauge, and both were pretty consistent at 5.55mm. I have other slugs that are 5.52mm and they might have the same problem, but I don't have any similar weight pellets to compare them to. Is it possible the shape of the slug is contributing to the increase in friction? 

 

[Skip-in-WV]

I experienced the same thing with JSB Monsters (13.4g) and the Baracuda Match (10.65g) pellets. The Baracuda velocity is a 100 feet faster.

 

[Sigma]

Even though the slug is lighter is is likely a tighter fit in the barrel causing more friction.

I've also had the same thing happen with 15.89 JSB's (5.52) vs the H&N 14.66 (5.55) the H&N were only slightly faster at the muzzle.

Not only a tighter fit, but also increased bearing surface in contact with the barrel.

 

[mmahoney]

@spladd1ct

I bet your are right. The slug shape does seem like there would be more surface rubbing along the inside of the barrel. I'm guessing this will cause my barrel to foul faster than when shooting pellets. I feel like cleaning it right now!

 

[Guest]

Even though the slug is lighter is is likely a tighter fit in the barrel causing more friction.

I've also had the same thing happen with 15.89 JSB's (5.52) vs the H&N 14.66 (5.55) the H&N were only slightly faster at the muzzle.

Not only a tighter fit, but also increased bearing surface in contact with the barrel.

Exactly.