I’m not a novice to casting/loading/shooting but I am to Black Powder.   I’ve poured over chamber and bullet diagrams and got a few questions.

First, what is the benefit of the of .600 neck over the .500 neck length.   Is it primarily to contain the lube grooves of bullets like the Snover and RCBS 40-400-CSA, or does it go beyond that?

Second, for those images I see of bullets cheated way forward, is the purpose mostly to increase BP capacity or is it to get more bearing, or both?

Third, when employing reduced driving bands, it seems like you’d create opportunity for blow-by or is that prevented entirely with bump-up?

Fourth, let’s put a value of .408 for groove, is the conventional wisdom to still fill the groove with a .408 or greater diameter, or, since we have the bump-up is diameter considerably less important, so long as you are getting adequate bump up, say with a .407?  In other words, I’m wondering why worry about a chamber fit to accommodate a .409 or .410 if I’m shooting BP exclusively.

Last one… I read it both ways but for bore riders, do you favor right at, say .400, or do you go .001 or .002 under bore size?

Thanks in advance.

Gert has summed it up quite well.  Just to add a little, I like to be at groove diameter or slightly larger; so .408" or .409".  I've also found that nose diameter is dependent on whether you are a wiper or blow-tuber.  1-.002" under if you blow tube and close to bore diameter if you wipe.  Good bore alignment without distorting the bullet is necessary if you're going to shoot the longer ranges.  My most accurate moulds have a reduced front driving band and then I extend the bullet out so that about half the front driving band is engaged in the leade when I load the cartridge. Bob

Thanks fellahs.    Still working on the boat so not sure what floats best yet.

The neck question came from thoughts about containing the lube.   I have no idea what the rifle will like insofar as seating depth so thought it might be prudent to have a long neck.

Old-Win,   “Wiping or blowing” makes perfect sense.     I’m thinking wiping would be best if that’s the profile I select.

svartkruttgris, thanks for mentioning Wads, I should have - had concern if seated deep might push the wad into the tapered zone, as in .600 worth of lube grooves seated deep in a .500 length neck.   Maybe not be an issue but it was a question I had.  The wads I use with some smokeless loads seem to have springback in the diameter. From what I understand the compression of BP does not have a lot of springback so, again, maybe that’s a mute point.   

I’m hoping I get the measurements close enough for a slip fit in a fireformed case.   I’m thinking chamber with a neck diameter  maybe .001 over the OD of a case with a seated bullet would do that.    Then again if you started out with a .410 bullet and then the rifle told you it liked a .409, you’d be turning necks or have a sloppy fit over what your .410s had.

Seems the bullet diameter is not so different than smokeless so should be comfortable there.  Currently shoot anywhere from groove to .002 oversize.   Thanks!      

Schuetzendave, are your Starline reformed 45-70 or 40-65?   I did a volume test with water & Black Powder and looked like the 45-70 would hold 2gr more powder.   45-70s should give less cause for seating forward I’d think.    

One other question I’m trying to wrap my head around:  Is there any correlation between reduced bands and freebore?   In other words, are you more likely to find reduced bands proving useful with chambers that do or don't have freebore?    Can’t answer that for myself as I’ve yet to select a reamer or a bullet.   I’m just wondering if either ‘accuracy’ in the load development stage, or if more ‘velocity’ in the quest for bullet ‘stability’ forced you to cheat your bullet forward --  then reduced driving bands, and maybe even freebore, would give greater flexibility if the need arose to seat further out?

John,

Before possibly over thinking it too much, make up some reasonable loads and see how well they shoot. Some rifles, like my 40-65 seem to shoot well with numerous loads, all with 20:1 Pb:Sn alloy and 0,410" or 0,409", 0,40 cal fiber and LDPE wads under. I get no leading with any of these loads, so, either wads are being excellent gas seals or bullets are "bumping" up, or both. 

Bullets are Lyman Snöver 400gr and Lyman 425gr flat point hunting bullet, RCBs 350, Saeco 370grs, a Lyman 300gr Win 405 plain-base bullet, and a Paul Jones 400gr tapered bullet. Powders have been 45 to 65 gr of Swiss FFg or 1,5Fg, lube SPG. Rem 2,5 large pistol primers. Kinda outa box, mix and match.

Groups at 100yd are 1,0-1,5 for 5 shots. Groups at BPCR distances have given as good as 8-10 hits per 10, if I don't screw up (which I am seem to be getting better at).

Grisen

Selecting moulds and reamers can complicate matters!!

I am sorta an Off The Shelf kinda guy as well as loading BP since age 13 and nearly all my CF rifle and revolver ammo for 50 years.

I am sure you will enjoy the journey!!

Grisen

john,
here is what happens when you fire a black powder cartridge.
first thing is any bullet in the case bumps up as the case obturates to the diameter of the internal obturated case.
second, a bore riding nose bumps up into the rifling.
then the bullet starts to move.
from this we learn that a bullet that slightly friction fits fired cases is the way to go.
oversized chambers are not good here.
bore riding noses can cause leading.
how you deal with this can be quite problematical.
keep safe,
bruce.

John,

i suspect that leading with soft alloy boreriders and BP has to do with lack of lube on bore riding section. Think I have read of a few instances where shooter started carefully wiping lube off bore-riding section (to keep if from accumulating dirt??) and got leading where there was none previously.

I too use bore riders with nitro powders, generally with gaschecks and nitro lubes only in GGs, at BP chamber pressures, and never have any noticable leading for up to at least 100 shots, no wiping or brushing. Most (all?) of my BP bullets have at least a thin layer of lube from GGs to nose and don't lead. I have never attempted to recover fired bullets from my 40-65 loads, so, no info re bump up ahead of driving bands.

For what it might be worth,
Grisen

Grison, my experience is similar to yours with smokeless.

Old-win, thanks for the tip.