Groove Bullet - Diameter for bore or groove?

[roscoe]

What is the rule of thumb for the correct diameter of a grooved bullet?

Should it be bore size, slightly over bore size or maybe the groove size?

[BRUCE MOULDS]

roscoe,
if a groove bullet is a greaser, there is one simple answer.
its diameter should be a neat sliding fit into a well fireformed case.
keep safe,
bruce.

[Travelor]

From what I have read, the bullet should be sized .001" over slugged bore diameter.

I'm open to be corrected.....................

[Tom Myers]

From what I have read, the bullet should be sized .001" over slugged bore diameter.

I'm open to be corrected.....................

And corrected, ye shall be.

We are probably dealing with a case of semantics here. Many times the concept of BORE and GROOVE are unintentionally interchanged.

Usually, the grease groove bullet should be sized to at least 0.001" over GROOVE diameter and not large enough to expand a fired formed case when seated.

[country gent]

While Paper patched can be wrapped to bore or groove dia, they are done both ways. The grease groove is normally cast or sized to .001 or .002 of groove dia ( the large dia) this helps facilitate the bullet sealing the bore well and saves on bumping up of the bullet. Other things to consider is nose fit in the bore length and alloy

[Don McDowell]

The correct diameter for a greaser is something from groove diameter to .002 over groove. The nose on a greaser is best to be just under bore diameter to prevent leading due to the lack of lube on the nose, and to make chambering easier.

[roscoe]

Thanks for the information This is what I needed. Having been reloading since the late 60's, I have never worked with black powder. Wow what a difference and learning curve. This forum has really helped me out. Thanks again

[BRUCE MOULDS]

roscoe,
the 001 to 002 sizing rule is an urban myth, suited to smokeless and hard cast.
with black and the alloys that suit it, here is what happens when you light the fire.
the powder ignites, and before anything else happens the case obturates to the chamber wall at the same time as the bullet bumps up to fill that dimension.
the smaller the bullet, the more it bumps up.
then it starts to move forward through the transition/ leade area, being swaged to barrel dimension as it goes.
having the bullet at the diameter of internal unsized case reduces most of the bumping up, eliminating one deforming action and thus aiding accuracy.
this is also why having a loose chamber can reduce accuracy.
save the time and money sizing bullets because it is more work for less accuracy.
not having bore riding noses also helps accuracy because they bump up into the rifling and being unlubed can potentially add lead to the bore.
keep safe,
bruce.

[Gunlaker]

I've found the same as Bruce with respect to bullet sizing. The biggest that fits the case usually works best for me. If the chamber is a good one then it'll shoo well.

I also agree with Don about the bullet noses. As an example I have two of Steve Brooks Creedmoor molds. They are nearly identical, except one has a nose that is about 0.001" under bore diameter, and the other is at bore diameter ( and just a little heavier, maybe 10 grains or so ). The slightly smaller nose does not significantly lead the bore, but the larger nosed bullet will led the bore.

Chris.

[BRUCE MOULDS]

chris,
you make a good point about chambers.
shilohs have tight chambers, and are noted to be good shooters.
we know that bullets bump up prior to moving from an experiment done by William metford in the 1860s
he drilled a hole in a barrel and threaded it in order to screw in a pointed rod.
the point came out in a groove and was screwed in such that it stuch out about 1/2 the depth of the groove.
it was placed such that it was a known measurement from the base of a loaded bullet.
the recovered bullet had a scratch mark on it the length that proved the bullet had bumped up prior to moving.
this was done with a bullet containing tin and antimony, so not a soft bullet.
one of the reasons metford liked harder bullets was to minimize bumpup to only what is necessary.
chronograph (pendulum in his case) testing proved that the softer the bullet, the lower the muzzle velocity.
this is because the softer the bullet, the harder it bumps into the rifling, increasing velocity robbing friction.
never be afraid to experiment with alloy.
keep safe,
bruce.

[Gunlaker]

That is an interesting experiment. F.W. Mann did some interesting experiments showing essentially the same thing.

I might do a little bit of alloy experimentation this year. The low antimony/low tin alloy that Michael Rix has been using, and written about by Dan Theodore, sounds very promising for pointy bullets. Do you have any idea of the alloy composition used by Metford? Did he write a book by any chance? I only have the North American perspective on this stuff.

I'd like to be able to get rid of all leading in my grease groove shooters, but never seem to quite achieve it. I'm at this very moment removing lead from one of my rifles . I used to think that my rifles did not lead, but it as because I wasn't looking hard enough. Interestingly, of all of the BPCR rifles I own, my Badger barreled C. Sharps rifles are least likely to lead. This is by a big margin too. This of course excludes my paper patched rifles

Chris.

[roscoe]

roscoe,
the 001 to 002 sizing rule is an urban myth, suited to smokeless and hard cast.
with black and the alloys that suit it, here is what happens when you light the fire.
the powder ignites, and before anything else happens the case obturates to the chamber wall at the same time as the bullet bumps up to fill that dimension.
the smaller the bullet, the more it bumps up.
then it starts to move forward through the transition/ leade area, being swaged to barrel dimension as it goes.
having the bullet at the diameter of internal unsized case reduces most of the bumping up, eliminating one deforming action and thus aiding accuracy.
this is also why having a loose chamber can reduce accuracy.
save the time and money sizing bullets because it is more work for less accuracy.
not having bore riding noses also helps accuracy because they bump up into the rifling and being unlubed can potentially add lead to the bore.
keep safe,
bruce.

I understand what you're saying here for the most part, but I'm a little confused on what size you're saying the bullet should be. It sounds like you may be saying the less it has to bump up the better, so are you saying the closer the bullet is to groove size and not "over" groove size the better?

[Gunlaker]

Rosco, basically the idea is that no matter what, the bullet is going to get as big as the case is inside. So lets say your case is 0.460" inside, but your groove is .458". In this case a .460" bullet will be distorted less than a .458" that gets bumped up to .460" in the case, and then swaged back down to .458".

I've got two rifles just like that and they both like .460" bullets best. I'm sure that smeone has the exact opposite experience, but that idea work for me.

Chris.

[roscoe]

Rosco, basically the idea is that no matter what, the bullet is going to get as big as the case is inside. So lets say your case is 0.460" inside, but your groove is .458". In this case a .460" bullet will be distorted less than a .458" that gets bumped up to .460" in the case, and then swaged back down to .458".

I've got two rifles just like that and they both like .460" bullets best. I'm sure that smeone has the exact opposite experience, but that idea work for me.

Chris.

So are you getting the bullet diameter from a fire formed case?

[martinibelgian]

No, much easier... If the unsized bullet fits the fireformed case, then don't size it, but use it as cast - much simpler, no? Whatever the dimension is, when the hammer hits the primer that bullet will indeed set up as big as it will possibly can. Which actually is the diameter of the fireformed case + springback of the brass.

[BRUCE MOULDS]

roscoe,
what gert and chris said.
but that is why good chambers are important.
if you can finger seat a bullet 0.001 to 0.002 bigger than groove in a fired case with a little friction, that is the optimum.
for those buying a reamer, the place to start is to buy your brass and barrel
from here you can establish bore and groove diameter, and neck thickness of brass.
so you know what the bore ride of the nose needs to be, what 0.001 bigger than the groove is, and can easily calculate the neck diameter of the chamber.
now you can order the reamer and a mould.
if this is put together by a competent gunsmith you will have a shooter, and will have great accuracy for little work.
keep safe,
bruce.

[BRUCE MOULDS]

chris,
it seems to me that metford was constanly experimenting and had no final perfect alloy.
what is clear though is that he preferred a harder alloy for groove diameter pp bullets than for bore dia bullets.
he also had a lot of trouble getting lead/tin/antimony bullets to retain constant hardness.
he referred to bullets "ripening" which seems to mean aged and stabilized.
I have been making some notes on metford's alloys, and will post either here or Shiloh when it is clearer in the brainbox.
keep safe,
bruce.

[roscoe]

Bruce, thanks a lot for the information. I re-read all the post here and you pretty much told me what to do on post #2. Sometimes you just can't see the forest for the trees. I'll try this out. Thanks again.

[Gunlaker]

Thanks Bruce. It would be interesting to hear about his experiments. I think I've seen just a litle bit of that posted here once. If I remember correctly it was a guy named David from ResearchPressUK... He has some really interesting articles.

Chris.

[Lead pot]

Antimony in bullet alloy is a plus, but the balance using it in a PP bullet patched at bore diameter or slightly under bore diameter the percentage of the mix can be a problem without a good wad seal under the bullet to hold the gas back for reducing gas cuts and getting enough upset to get enough engraving for proper rotation. This is something you don't have to worry about using a groove diameter GG or PP bullet. Just .8 oz of antimony and 15 oz tin mixed in 18 lbs. of lead will hold the bullet nose profile with minimal setback and expand well enough to fill the grooves for good rotation better then 1/16 T/L alloy.
Here is what that 523 gr PP bullet patched to bore diameter will look like shot with a 89 gr load of 2F powder from a .45-2.4.
Kurt