8x75R load development

[Gankai]

Hopefully I can find some sage advice. I have come into an Austrian double rifle in 8x75R ("I") bore which slugs to .306/.316 inches. Would people start load development with a .316 or .318 bullet? I have some R-22 powder loads for 180 and 200 grain bullets listed at 71 and 68 grains respectively. Does the group have any thoughts?

Rick Hill

[mike ford]

Gankai,
The first step should be to determine if a .318"( or .320") bullet will fit easily into a case that has been fired in the rifle and not resized. If a .318" will not fit, check the neck very closely to insure the case doesn't need trimming to length.( you can obtain a fired case by cobbling together a fireforming load with a lead bullet and pretty heavy load) If you must use .316" bullets, you won't have an insurmountable problem. Just as a matter of interest, how did you determine the nominal caliber? Is it marked clearly on the rifle, was it determined by a previous owner, or did you determine it yourself? Is there a "duty bullet" shown somewhere an the rifle? If so, finding a load that "regulates" should be easier. Improper "bench procedures" may complicate finding a useable load, and could prevent it. In my opinion, you have a very interesting project on your hands, and will have a lot of fun.
Mike

[Diz]

Gankai,

If I read you correctly then you established the bore / groove diameter by slugging? I ran a quick check using a Norma Alaskan bullet of 196 grains and 68 grains of Reloader 22 and the results show a safe loading with good loading density. I can post the predicted results if you like.

Diz

[Gankai]

Mike - Thanks for the kindness of your reply. As Diz eluded to I did slug the bore (each one twice). So glad for that as I do have S bore ammo which will NEVER be shot in that rifle!! I think the fire forming is a good idea but 8x75RS (.323) ammo drops in with a slightest resistance so we should be ok with .318. I think that was the original intended caliber. I am sure of the narrowest dimensions but come to think about it I had another double rifle that had tighter sections in the barrel. I discovered this cleaning the rifle and noted the tighter areas with passes of the bore brush. As the barrel broke in the accuracy increased and the bore offered uniform resistance to cleaning. When I looked at that rifle the tool marks were visible inside the barrel! This rifle also has pristine bores and may very well range from .316 to larger as driving the slug you could feel variations in resistance with travel down the bore. I guess my main concern was generating an over pressure touching off close to 70 grains of R-22! I may download slightly or swage the bullets down at bit until the bores break in.

Rick

[Gankai]

Diz,

I am a big fan of barrel slugging and chamber casting. So far I have had pleasant but weird surprises like the 35 Winchester that was actually 9x63R. I have the listing from cartridges of the world but would never turn down more information.

Rick

[mike ford]

Rick,
Since you have tried the 8x75RS , I'm sure a .318 bullet will fall right into a fired case. The Germans used many M88s with "S" bore ammo, by reaming the necks to "S" diameter specs( and some were already large enough). It is not so much the smaller groove diameter that causes elevated pressures; but rather the chamber neck not being large enough to release the bullet. Once the bullet is moving, the pressures are moderated by the increasing volume. By the time the bullet has moved into the barrel, the length of the parallel section, it has been sized to the groove diameter. We often find we can use .320" bullets in .318" rifles. I have an 8x57R/360 that can use .3215" Remington bullets. Too large bullets may not be as accurate, due to the violent resizing, offsetting the advantage of a larger bullet centering the cartridge in the chamber better. A couple thousandths usually don't cause a problem as long as the bullet releases.
Mike

[Diz]

Rick,

Mike is correct on all counts. I find that with over sized bullets the extra material has to go somewhere and it forces them to elongate as they go into the bore. This seldom occurs in an even and symmetrical manner and leaves you with a somewhat imperfect bullet. The result is usually sub par accuracy compared with a properly fitted bullet.

The data I am posting is from my computer program and is all "computed" so I would check it against any published data you may have. One thing I noticed was that RL-22 wanted to jump a bit in pressure with a small addition of powder. This is not unusual with some powders but requires a bit of caution. My data shows the Pmax for this cartridge as 49,313 psi (3400 bar) CIP and that is the max used in the program. Two bullets were used in the calculations and I plugged in a 24 inch barrel just to run the numbers. Here is what came out:

Powder: 68 grains Reloader 22 Bullet: .318" Norma 196 grain Alaskan

Pmax = 44794 psi
Vel = 2678 fps
Fill = 96.5%
Burn = 95.5%
Eff = 24.1%

Powder: 70 grains Reloader 22 Bullet: .318" Norma 196 grain Alaskan

Pmax = 49177 psi
Vel = 2763 fps
Fill = 99.3%
Burn = 96.7%
Eff = 24.9%

Very near maximum!

Bullet: .318" Woodleigh 200 grain Weldcore Powder: 68 grains Reloader 22

Pmax = 46926 psi
Vel = 2692 fps
Fill = 97.8%
Burn = 96.3%
Eff = 24.8%

Bullet: .318" Woodleigh 200 grain Weldcore Powder: 69 grains Reloader 22

Pmax = 49205 psi
Vel = 2734 fps
Fill = 99.3%
Burn = 96.9%
Eff = 25.2%

This is only [B]one grain [B] more of powder but brings it right up to max with this bullet. The Woodleigh's are usually a bit harder and show a little more pressure.

I would like to see some photo's of your rifle if possible and best of luck with it. Diz

[sharps4590]

Gankai, are you familiar with Hawk bullets? They're annealed dead soft and I'm certain they have .318 diameter. Some folks like them and others don't for various reasons. I've always have satisfactory results with them.

[Diz]

Gankai, as Sharps mentions, Hawk shows several bullets in this caliber on their website. There is a .316" diameter 150 grain RN and two .318", one 180 grain and another in 220 grain, both in round nose configurations . Unfortunately, my program only lists the .323 diameter bullets and there can be problems trying to reconstruct them to the right diameter. Other bullets from various makers can be swaged up or down to meet your needs without too much trouble. Thanks, Diz

[mike ford]

Gankai,
The softer bullets made by Hawk may be necessary for such lower power cartridges as 8x48/58R S&S or 8x57R/360, but the 8x75R is not in this class, at all. This is a powerful cartridge that doesn't need "soft" bullets , which may not hold up to the possible velocities.
Mike