Forward Driving Band, What is it?

[Maxwell]

Could someone explain what the forward driving band is on a round of ammo please?

I ask because someone on another board stated that the rim thickness of a round of 22lr ammo does not allow a bolt to close easily on a Cooper 57M has nothing to do with the rim thickness of CCI SV vs SK Standard Plus but the forward driving band. When I look at the rim of a CCI SV round & a round of SK Standard Plus (after I take my contacts out) the SK looks a tad thinner.

What am I missing?

Maxwell

 

[Badshot308]

They're probably referring to the most forward portion of the bullet that engages the rifling. Some rounds will engage the rifling in certain .22 match chambers as the bolt is closed causing slight resistance.

 

[Kebo57]

most lead bullets are not shaped like the typical jacketed bullet. There is a cylindrical section that resides in the case mouth of the loaded round and then the nose. Often times the nose is bore diameter while the cylindrical section is groove diameter. The step in diameter at the transition from nose to cylinder is the beginning of the front driving band. Since lead bullets, whether for a 22LR or a buffalo rifle, need lubricant, many times the cylindrical section has grooves to hold the lube. This divides the cylindrical section into bands of which the one closest to the bullet nose is called the front driving band and the rearmost is the base band. They are called driving bands because they are the portion of the bullet that engages the rifling and allows it to be "driven" down the bore following the rifling. 22LR match chambers are tighter and the front driving band is actually engraved by the rifling when the round is chambered. Depending on reamer design, some brands of 22 ammo are much more difficult to chamber fully than others. Those of us that shoot cast lead bullets for accuracy typically use a cartridge O.A.L. that has the front driving band into the rifling.

 

[Maxwell]

Thank you all. I appreciate it.

Maxwell