Bore Riding Question

[thirtythirty]

Hello, I was looking for "dumb question" section of the forum but I couldn't find it, so its going here. If there is a more appropriate place please let me know.
I am somewhat confused as to what a bore riding Boolit is. I get that there is a bore and groove diameter, however isn't the basic theory for all Boolits to fill the entire bore, otherwise you get gas cutting? Wouldn't something skinnier cause problems? Thanks for your help.

[kens]

. I get that there is a bore and groove diameter, however isn't the basic theory for all Boolits to fill the entire bore, otherwise you get gas cutting"

A bore rider is a rather long nose section that rides the bore diameter, while the driving bands in the rear of the bullet engage the bore + groove.
A bore rider would have a rather long nose, of the bore dimension.
the driving bands would still engrave the rifling.

[Hannibal]

The 'basic' theory is that the bullet fill the groove diameter, 'lest you get gas cutting.

In the case of a bore rider, the nose of the bullet contacts the bore diameter/rifling, while the base fills in the groove diameter. This allows the nose to extend into the throat/rifling further in an attempt to start the bullet down the bore straighter/more consistently. Yes, there will be some distortion on the driving bands/base where the rifling/bore diameter displaces material. It's inevitable.

Arguments abound about how to best address this situation.

Many will tell you to size your bullets to the freebore diameter.

I'm not saying they are wrong or right, but I suggest you try it and make up your own mind.

[JSnover]

The bore rider nose is supported by the bore, centering the whole boolit and reducing 'slump' upon firing. This should make for a more accurate load.

[Oklahoma Rebel]

that's what I am hoping for when I get the accurate 37-286C, it is a bore rider, I am just trying to figure out, if the bore is say... .355, and his tolerances with the bore riding section is +0-.002, what if it comes out too small? well, I guess to small is better than too big, because if it is too small, I could send it back and have him lap it out a bit.

[Rcmaveric]

Its as kens describes it. The bullet has a longer nose bore diameter to increase bearing surface. The bore rider bullets have around 2 or more bands pluss the gas check acts as a driving band to engage the riffling. The base of the bullet still obturates. Its the base obturation that prevents gas cutting. All my riffle bullets are bore riders

[MT Chambers]

I've found that if the bore riding portion is too tight in the bore, accuracy suffers, it also suffers if the bore riding portion is to narrow.

[Wayne Smith]

You are right, bore riders have much more critical dimensions. Fit to the rifle is important for any boolit, but the nose of the bore rider has to be pretty close to right. That's why he makes nose sizers.

[farmerjim]

All of my bore riders show accuracy superior to my other boolits. They do need to be cast and sized to your gun for both the nose and the base.

[Digital Dan]

.30 caliber bore rider:

https://i.imgur.com/rnGSDMC.jpg




.430/320 grains NOT bore rider:

https://i.imgur.com/7Hk8Q6C.jpg

[farmerjim]

Digital Dan,
Did you use a NOE nose sizer on those 30 cal's ? I think I see a slight ridge above your top driving band, or it could be just my imagination.

[Cowboy_Dan]

FarmerJim, I think what you are seeing is a sharp shoulder between the nose and the shank.

[thirtythirty]

So is it harder to paper patch a bore riding Boolit? Because of the reduced clearance?

[oldblinddog]

So is it harder to paper patch a bore riding Boolit? Because of the reduced clearance?

For paper patch the entire bullet should be sized to bore (not groove) diameter. Better if it is cast at that diameter, i.e. for .30 caliber 0.301".
204572

[Bama]

that's what I am hoping for when I get the accurate 37-286C, it is a bore rider, I am just trying to figure out, if the bore is say... .355, and his tolerances with the bore riding section is +0-.002, what if it comes out too small? well, I guess to small is better than too big, because if it is too small, I could send it back and have him lap it out a bit.

That would almost be ideal, if small, then you would powder coat, size nose and you are set. If you put much of a load the bullet will obstruate and be full bore size within a VERY short distance anyway.

[Oklahoma Rebel]

do you guys use a caliper to measure bore on a slug or chamber cast, because it would seem the ends of micrometers are too fat?

[Bama]

Rebel Slug or chamber cast, then check in end of barrel. I personally do not like the thought of possibly pushing a bullet down in the case if it is oversized because I neck size only and have about .002 tention on neck. If a 200 gr. catches, a lot of case volume can be taken up if bullet gets pushed back with unpleasant results. Did one time and forced bolt close- gun was OK but I flinched for weeks from the added recoil. Lessoned learned--will not knowingly do again ever!

[Outpost75]

The "bore riding" section of a cast bullet is analogous to the bourrelet of an artillery shell.

The "bourrelet" is an accurately machined surface slightly larger than the body and located immediately to the rear of the ogive. Its purpose is to align and center the forward part of the projectile in the gun tube and to bear upon the lands in the tube. When the projectile travels through the bore, only the bourrelet and the rotating band of the projectile bear on the lands of the tube.

[Oklahoma Rebel]

stil want to know if micrometers are used to measure a bore slug, I know it could read the groove diameter, but would it fit between those to get the bore diameter? or is a caliper necessary? and also, which are more accurate from best to worst? micrometer, digital caliper, dial caliper? I have a digital cal. but not sure I trust it

[Oklahoma Rebel]

so the noe 280gr is also a bore rider?

[runfiverun]

micrometer is more accurate.

[Oklahoma Rebel]

are they usually small enough too measure between the rifling on a barrel slug?

[Silverboolit]

Pin gauges are your friend.