Double Rifle Load Regulation

[cal pappas]

Gents:
I'm new here and I'll try to post with a photo to experiment a bit.
Anyway, it's interesting to see a double rifle change its target grouping as the powder charge changes. Most vintage double can be made to shoot well by playing with the load--either the powder type, powder charge, bullet weight, bullet style--or all four.

A mate bought a .577-500 double from me a short while ago and came to my home to shoot it for the first time. He did the shooting and I recommended the load. We began light with 45 grains of IMR 4198, moved to 50 grains and finished at 55 grains. The bullet was the standard for nitro for black loading of 440 grains.
The three targets are here. Low velocity will see a double shoot apart, and you can see that in the first target of 45 grains of powder. As the powder charge increases thereby increasing velocity, the pattern improves. Too fast a velocity, say if we went to 60 grains and the double will cross fire.

Anyway, let's see if this works.
Cheers,
Cal
PS. I offer to you double rifle men my website <calpappas.com> to see lots of double rifle information.

 

[Bullthrower338]

Cal,
Would I be correct in assuming that as you load past the 55Gr and velocity increases you will see the shots start spreading again? Forgive me if this is a dumb question as I am just starting to learn about doubles in earnest.
Cheers,
Cody

 

[cal pappas]

Cody:
You are correct but the separation after 55 grains will be a cross fire, not shooting wide.
Cal

 

[Wheels]

Cal,

Welcome to AH.

I am not a double guy, but enjoy this post watching what the increase of powder does.

It is good having you over here. You certainly bring a lot of knowledge and expertise.

All the best.

 

[zephyr]

Why did you choose 25yrds instead of 50yrds?

 

[cal pappas]

As in sighting in any rifle, begin close to make sure the bullets print on the target.
Cal

 

[zephyr]

I'm some what stuck on 50yrds as that is what is recommended in Wright book.
I realize that we are dealing with iron sights and aging eyes but, once you get the results on your last target will not those bullets start to cross when shot out to 50yrds?
Were you shooting over a chrony? If so what sort of velocity change was between the first target and the last?
Appreciate the flow of information..

 

[cal pappas]

This was just the beginning to get a base line on paper. We will go to 59 and beyond now we have a baseline from which to begin, 50 yard will be larger--say 1-2 inches depending on the shooter and open sights. Crossfire--maybe maybe not. If so just back off bit on the powder a bit. I did not set up a crony.
Cal

 

[DUGABOY1]

Cal's explanation is correct! One always should use a close target when working up a load for a rifle that is new to him. This makes it easier to move the bullets in the proper direction to get a working composite group of bot barrels. Once this is done the distance doesn't matter as the load is regulating properly and will shoot side by side individual barrel groups centers parallel with only hold over for elevation. Double rifles are not regulated to cross those group centers no matter the distance