That is normal, a bullet won't drop in.
The barrel has internal, raised lands ( rifling) that slightly cut into the bullet.

The lands are twisted in spiral down the barrel. This rapidly spins the bullet which stabilizes it since it is moving at high speed .

If the bullet could just slide in, it wouldn't contact the raised lands.


You can see the cut grooves the rifling lands made on the fired bullet on the right.

 

That is normal, a bullet won't drop in.
The barrel has internal, raised lands ( rifling) that slightly cut into the bullet.

The lands are twisted in spiral down the barrel. This rapidly spins the bullet which stabilizes it since it is moving at high speed .

If the bullet could just slide in, it wouldn't contact the raised lands.

You can see the cut grooves the rifling lands made on the fired bullet on the right.

Great answer and if loose fit lots of gas would blow by..and not accelerate bullet properly...its snug + fit to seal gasses and accelerate bullet to its max..

Remember Bullets are made of lead/copper both are malable and form somewhat of a gas seal..

Hope thats clearer than MUD

 

The "30" in 30-06 refers to Bore diameter-the ID of the barrel before rifling is cut (or however the mfr. does it). The rifling grooves will be 0.002"-0.004" deep. or thereabouts deep. Again varies by manufacturer.- Therefore to get rifling purchase and gas seal the 30 cal bullets will be about 0.308" in diameter. Hope this doesn't further muddy the water.

 

In your 30-06 the bore diameter is .300 and the groove diameter is .308

Bullets are .308

Yes, a very tight seal

 

30-06 loads are around the 50,000 psi mark. There needs to be a good seal to contain it.

 

Here if you are talking about a 30-06.
https://en.wikipedia.org/wiki/.30-06_Springfield