.510 vs .509 Diameter Projectiles

[Aussie_Hunter]

I'm hoping someone here can shed some light on this topic for me? I have had a bit of a look online and can't really find an answer.

I have noticed that there is a few manufacturers making projectiles with a .510 diameter and then others making them at .509 diameter with the 2 different diameters intended for use in rifles such as the 500 Nitro Express & 500 Jeffery.

Woodleigh and North Fork list their projectiles at .510 while the likes of Barnes & Swift list theirs at .509. Does anyone have a definitive answer as to why some manufacturers are going with .509 diameter? And does it make a difference in performance - velocity, pressures, accuracy etc? I have only used .510 diameter projectiles in my 500 Jeffery so far but I have ordered some Swift A-frames which as per Swift's website are meant to be .509.

 

[Pheroze]

I was told that the swift .410 would work fine in the 400 H&H .411 diameter with no problems. So I suppose the same holds true in your case. Although I have no answer as to why they chose the .509 diameter.

 

[MRBlack]

I have loaded both the Barnes banded solids at .509 diameter and Woodleigh Weldcore Softs at .510 diameter for my 500 NE. It is my understanding that Barnes has designed them a thousandth under bore to ensure there isn’t a pressure issue. That is the reason for the drive bands also to decrease the bearing surface and thus pressure. In older doubles the barrel walls can be thinner. Using a “solid” solid can greatly increase pressure and cause issue with the thinner barrels and damage the rifling of older doubles. I have not experienced any issue with either bullet in my Merkel. I don’t believe that the .001 difference will cause any accuracy issues at dangerous game distances and a cartridge with major rainbow trajectories. I believe the decreased pressure is the main reason for the slight under bore diameter. By no means am I an expert of any kind and I’m sure there are others one here that can give a more refined and scientific answer.

 

[Aussie_Hunter]

I have loaded both the Barnes banded solids at .509 diameter and Woodleigh Weldcore Softs at .510 diameter for my 500 NE. It is my understanding that Barnes has designed them a thousandth under bore to ensure there isn’t a pressure issue. That is the reason for the drive bands also to decrease the bearing surface and thus pressure. In older doubles the barrel walls can be thinner. Using a “solid” solid can greatly increase pressure and cause issue with the thinner barrels and damage the rifling of older doubles. I have not experienced any issue with either bullet in my Merkel. I don’t believe that the .001 difference will cause any accuracy issues at dangerous game distances and a cartridge with major rainbow trajectories. I believe the decreased pressure is the main reason for the slight under bore diameter. By no means am I an expert of any kind and I’m sure there are others one here that can give a more refined and scientific answer.

Thanks for the response. Yeah I was also assuming it was to try and reduce the pressure curve, having said that I believe Woodleigh Hydros which are a monolithic bullet are .510 so that theory doesn't stack up 100%. You would think the Hydros would have a fairly high pressure curve too?

 

[MRBlack]

I don’t really believe that pressure is an issue with either the .509 or the .510. I think the greatest pressure decrease comes from the drive bands present on either bullet. Aside from decreasing the amount of bearing surface, it also creates cavities between the bands that allows somewhere for the material displaced by the rifling to go. These are both on the Barnes and the Woodleigh Hydros. The Hydros have more drive bands that would theoretically further decrease pressure. Barnes’ website lists a separate solids for the 500 Nitro and the 500 Jeffrey. The Nitros at .509 and the Jeffrey at .510. This makes me think the reason for the thousandths under bore in the nitro is out of concern in the barrels of older doubles. I know the owner of Swift bullets has been interviewed a few times and has made the comment that he is a big fan of vintage English double rifles. This may also explain the diameter of those bullets at .509 as well. I’ve attached a picture of Barnes’ solid selection

 

[Aussie_Hunter]

I don’t really believe that pressure is an issue with either the .509 or the .510. I think the greatest pressure decrease comes from the drive bands present on either bullet. Aside from decreasing the amount of bearing surface, it also creates cavities between the bands that allows somewhere for the material displaced by the rifling to go. These are both on the Barnes and the Woodleigh Hydros. The Hydros have more drive bands that would theoretically further decrease pressure. Barnes’ website lists a separate solids for the 500 Nitro and the 500 Jeffrey. The Nitros at .509 and the Jeffrey at .510. This makes me think the reason for the thousandths under bore in the nitro is out of concern in the barrels of older doubles. I know the owner of Swift bullets has been interviewed a few times and has made the comment that he is a big fan of vintage English double rifles. This may also explain the diameter of those bullets at .509 as well. I’ve attached a picture of Barnes’ solid selection

Very interesting, I didn't look to see if they made projectiles specifically for the 500NE and the 500 Jeff. I found some 570 grain Barnes TSX for sale and it was the first I noticed the .509 diameter. The other issue I have noticed with bullets designed for the 500 NE (570grain bullets) is the position of cannelure, obviously the 500NE has a longer COAL compared to the 500 Jeff so seating them for the 500 Jeff is not perfect, I have already experienced this with the 570 grain Woodleigh RNSN.
I just looked up some Barnes load data and they list 500 Jeff load data for both the .510 and .509 solids as well as the .509 TSX.

 

[MRBlack]

That is very interesting. I would venture a guess that the solids specifically for the Jeffrey would feed much better in a bolt action also. The load data seems to in part confirm the theory that the difference in pressure from the .509 diameter is minimal or it would be able to have separate load data with increased powder charge and velocity. One thing I will say in regards to reloading the Barnes Banded Solids is that the number and size of the bands make crimping almost too easy. It worked out for me that the end of the case was perfectly in between two of the bands

 

[Capt_Oscar]

In some cases the minor differences are due to the age of the cartridges. To mean, tolerances of rifles from early 1900s aren't what they are now. There are more 500 Nitro Express from high end double rifle manufacturers in the 1920-30s. Even from when they were black powder cartridges. As such, barrel tolerances make it more commonplace for .509 diameter. If you forced a .510 down an old bore you might end up with a metal flower on the end of the forend. Many manufacturers recommend slugging the bore to determine true diameter of old rifles for this very reason.

 

[bruce moulds]

interesting question.
if you set your vernier on 0.001" the gap does not look big.
halve that assuming the bullet is central in the barrel and it is even smaller.
how this affects pressure, only the good lord knows.
riverbrand used to use the same projectiles for 308 and 303 reloads and it seemed to work ok.
303 barrel specs allowed a fair bit of variation in the lee enfield, but mkV11 ammo shot to the sights out to long ranges in any rifle.
this is really discussing the irrelevant though as we are talking your gun in a different age.
bruce.