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Double Rifles, Single Shots & Combinations >> Double Rifles
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Spring
.300 member


Reged: 01/04/04
Posts: 104
Loc: Georgia
Adjusting your POI ballistically
      #17756 - 10/08/04 07:41 AM

I read with interest in Shooting the British Double Rifle the logistics of how to maneuver horizontally the shot placement of your respective barrel's groups by increasing the velocity of your bullet loads. But if you wanted to move the shot placement higher or lower, what should you do? Are there any alternatives besides adjusting your sights? Is there anything to be gained by changing your load or bullet? I'd like to raise my POI by about 3 inches.

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DUGABOY1
.400 member


Reged: 02/02/03
Posts: 1340
Loc: TEXAS USA
Re: Adjusting your POI ballistically [Re: Spring]
      #17758 - 10/08/04 08:26 AM

Spring , does you double regulate well, but is simply shooting 3 1/2" low? If this is the case if it is regulateing at 50 yds, try it and see how it shoots at 100 yds. Then see how it regulates at 10 yds, If it is on at 10 yds, and 100 yds, and low at 50 yds, it may be just about perfect, depending on caliber. If it is still regulateing at 100 yds, but is still low,there and at 10 yds, then you must lower the front sight. Be very carefull here, a little goes a long way with that file, and you don't want that rifle shooting 3" low at 10 yds!

I'm trying to remember what double, and chambering you have! The type of sights will make a difference in how you adjust the hight.

While I've got you here, do you have a wing shooting, or a shotgun book out?

--------------------
..........Mac >>>===(x)===>
DUGABOY1, and MacD37 founding member of DRSS www.doublerifleshooterssociety.com
"If I die today, I have had a life well spent, for I've been to see the Elephant, and smelled the smoke of Africa!"

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4seventy
Sponsor


Reged: 07/05/03
Posts: 2210
Loc: Queensland Australia
Re: Adjusting your POI ballistically [Re: Spring]
      #17761 - 10/08/04 08:44 AM

A change in bullet weight will sometimes make a double shoot higher or lower.
You will most likely have to play a bit to get the individual groups to come together if you change the bullet weight.

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500grains
.416 member


Reged: 16/02/04
Posts: 4732
Loc: Salt Lake City, Utah USA
Re: Adjusting your POI ballistically [Re: Spring]
      #17763 - 10/08/04 09:13 AM

Spring,

In your 470 you should first find out the pattern that it produces. From a rest, shoot 2 each of something like the following (500 grain Woodleigh solids), one shot from each barrel. Mark which bullet hole is from the left barrel and which is from the right barrel.

84 grains Reloader 15 - 2 shots
85 grains - 2 shots
86 grains - "
87 grains - "
88 grains - "
89 grains - "
90 grains - "

Then try it again with IMR4831

103 grains
104 grains
105 grains
106 grains
107 grains
108 grains
109 grains

The 2 shot groups should start out being HIGH and WIDE APART.

As you increase the powder charge, the 2 shots should move CLOSER TOGETHER and LOWER.

With this method you can often find a load that gives you an acceptable spread between the barrels and an acceptable POI.

Alternatively, and as a last resort, you can have a good gunsmith go to the range with you and file the sight.

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Spring
.300 member


Reged: 01/04/04
Posts: 104
Loc: Georgia
Re: Adjusting your POI ballistically [Re: DUGABOY1]
      #17768 - 10/08/04 12:37 PM

Those are some good suggestions and I think that I do need to start looking for a solution by adjusting my loads and powders. When shooting 85 grains of RL-15 my POI is just over 3" low at 50 yards. I've been working on loads for other calibers the past couple of weeks and have not had a chance to try to fine tune a load for my .470. I suspect I just haven't yet matched the load for which my gun was regulated.
I would really prefer not to have to adjust my sights if I can correct things ballisically. Coming from the bolt-action world, I still think it's amazing that you can do that to some degree.
Out of curiosity, what sort of change in my POI would you guess I'd see if I increased my load from 85 grains to 89? Would it do anything besides bring together my respective barrel groups as long as the POI's do not cross?


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bonanza
.400 member


Reged: 17/05/04
Posts: 2335
Loc: South Carolina
Re: Adjusting your POI ballistically [Re: Spring]
      #17806 - 11/08/04 12:02 AM

It took me nearly 20 different loads using 3 different powders to get my gun to regulate and shoot POA with a 235 grain bullet. I nailed the 270gr. on the second try, go fugure.

--------------------


"Speak Precisely" G. Gordon Liddy.

"Life is absurd, chaotic and we must define its purpose with our actions" Abert Camus

"I''m the dude playing a dude disguised as another dude."

"Yo! Mr. White"

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500grains
.416 member


Reged: 16/02/04
Posts: 4732
Loc: Salt Lake City, Utah USA
Re: Adjusting your POI ballistically [Re: Spring]
      #17817 - 11/08/04 03:35 AM

Spring,

Going from 85 to 89 grains of Re15 will do two things:

1. Bring the POI of both barrels closer together (or make them cross). And

2. Bring your POI DOWN. That's right, I said DOWN.

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