Two diameter GG bullets

[flatsguide]

I am a total noobie when it comes to BPCR loading and shooting, so please hang with me.
I just bought a NIB Browning BPCR in .45-70.
I made a Cerro cast of the chamber and a couple of inches of the bore, the measurements are as follows;
Bore dia. .450
Groove dia. .458
Chamber dia. At mouth. .481
As I'm sure most know, there is no free bore and the lead is a very sharp angle and only .048 long on my rifle.
Bought 200 Starline cases. Thickness at mouth, .011.
Thinking of a bullet weight around 530 gns.

If my math is correct, the case mouth inner diameter, ID, when expanded to the chamber wall will be .459 ID.
I have not Fireformed any of these cases so I have no idea as to the amount of spring back of the case at the neck region.
What I was thinking, is to get a two diameter GG bullet with a base diameter of .458 to .459 about .250 long for the driving bands and the forward portion from the driving bands to where the ogive starts to be at bore diameter +.0005 -.0015. This section would have GG's also. Seating this bullet only .25 inches into the case would give me more powder capacity and the base would not have to be bumped up then swaged down if I understand one of the problems that need to be controlled.
The bullet would be loaded at "as cast diameter".
So, a few questions please.

Has any one have first hand knowledge of this type GG bullet being tried before?

Would a .25 long driving band with a grease groove still have enough material to engage the rifling?

With a 1:30 alloy would part of the bore riding section of the bullet slump enough to provide adequate lubrication?

And last, how would one go about lubricating this style of bullet.

I know it would be easiest to cut in some free bore but modifying the rifle is not an option. Thinking resale later on.
Thanks guys,
Richard

[Hiwall55]

Go to BACO and order a mould with one or two reduced driving bands. .450 dia . And .449 nose dia. Should take care of your rifle. My Browning likes a 520 creedmoor from Brooks with 2 bands reduced and drops at .460

[bruce moulds]

Richard,
depending on the requirement, buffalo arms no 460535m5 could be a good choice.
it can be ordered in 0.458 and 0.459, as well as 0.460.
good for long range in conjunction with wiping, and mid range could be shot blowtubing with a tallow wad under it.
the nose has minimal bore ride reducing the possibility of leading.
keep safe,
bruce.

[Kurt]

Richard.

It's best if you want to shoot a GG bullet to have what ever design you feel you want to shoot that you go with a reduced driving bands then go with a bore rider like say a Government .457-125. The 125 is a good bullet but it has a lot of dry lead ahead of the front driving band that might leave a lead smear in the bore. A postell type of bullet with some front bands reduced so the bullet that is riding tight in the bore is lubed to minimize the chance leading the bore. It would take a mould from Brooks or another custom mould maker.
Or use a PP bullet.

Kurt

[Don McDowell]

The buffalo arms jm459525m3 cast from 20-1 shoots very well in my browning

[flatsguide]

Well thanks guys. That will get me going in the right direction, although Kurt's suggestion of going to a PP bullet has crossed my mind. It seems like the chamber of the Browning might favor a PPB wrapped to or .001 over bore dia. One could then seat the bullet well out into the lands and gain powder space, as opposed to a GG bullet that one would have to seat deeper into the case.
But that last statement begs the question why can't a GG bullet that casts bore diameter, .450, be seated out into the lands just like the PP'd ones?
I mention powder space because It seems to come up so often, particularly when it come to .45-70 for the longer, 600 + yard! shooting. I guess I should add here that I plan on shooting Silhouette, but did enjoy long range shooting years ago. My line of thought, that may be in error, is that a good load that would work for Rams may not work for 1000 yard target work, but a good load for 1000 yard work would be good for Rams, so why not develop a long range load that will work for both.
Just trying to get a handle on which direction to go and in the meantime I'm building a PID temp regulator.
I do appreciate your insights guys.
Regards, Richard

[Kurt]

You can use a GG or use a what was called a ringed gullet that is bore diameter. It was common practice back in the 1800's. I have seen bullets at collector shows that where loaded in cartridges side by side. They react just like a PP and performed like a groove diameter GG from what I found using a .447 diameter soft postell GG in a .45-70. It gave me a little more leading being a little undersized but when I put a knurl on them to expand them to .451" they shot great.
Remington also had a hollow based bullet, not quite as deep of a base but a very thick skirt that looked similar like a mini that had 2 and 3 grooves that they seated right on the powder charge.

[flatsguide]

Thanks Kurt, I will look around and see what is available at that diameter.
Regards, Richard

[bruce moulds]

Richard,
the nasa bullet design will give you more powder capacity, but comes with problems.
first is the creedmoor nose design which carries more drag than optimium.
replacing this with a money or elliptical will solve that problem.
the other issue is the long bore riding, bore diameter nose.
it will bump into the rifling just like a pp bullet does, but lacks the protection of a patch.
guess what this means when you are not blowtubing or the barrel is clean?
putting micro mini grooves on the bore ride section will stop the leading, and barely increase the drag.
off to a custom mould maker for you.
keep safe,
bruce.

[Don McDowell]

Richard as you are just getting started, I would really caution you to keep it simple. If you don't want to go with the bullet I use from BACO then simply go with the lyman postel.
There's an awful lot of internet fluff tossed around about the 45-70 not having "enough case capacity" and like most things if someone with a large post count posts something then it has to be real, whether or not that person even owns a rifle , or if he does, even shoots that rifle is another question that seldom brings a satisfactory answer.
With the energetic powders we have available to us from Swiss, Schuetzen and others, the case capacity of the 45-70 is more than adequate to produce velocity enough to shoot to 1000 yds just fine.
You mentioned a bullet that shoots well at the rams might not shoot at 1000 yds, this is an especially true statement when folks try to push more bullet than the twist in their barrel can stabilize. This will become more pronounced if there is wind present.
All this was laid out for us over 100 years ago, and all we need do is don't over think this stuff.