Riddle me this, Batman

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  • Last Post 03 July 2018
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Bohica793 posted this 25 June 2018

If a Mosin 91/30 shoots to a POI of 3" left of POA with 13gr of Red Dot and shoots POI of 3" right of POA with 22gr of H4198, with what load is POI == POA?

This is the riddle I have to decipher over the next couple of weeks.  I have been shooting the H4198 load for a while and just tried the Red Dot load.  I was surprised at the difference in POI.  Adjusting the front sight on the rifle requires a jackhammer and I am unwilling to play that game so I will be playing with different loads looking for the answer.

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Ken Campbell Iowa posted this 25 June 2018

... thank goodness i can ( barely ) resist the temptation to advise mixing the two powders .... 

ken

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4060may posted this 25 June 2018

are you shooting Arshins or Yards?

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Bohica793 posted this 25 June 2018

are you shooting Arshins or Yards?

Yards -- 100 to be exact.

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onondaga posted this 25 June 2018

If a Mosin 91/30 shoots to a POI of 3" left of POA with 13gr of Red Dot and shoots POI of 3" right of POA with 22gr of H4198, with what load is POI == POA?

Well, if you listen to the duplex load insanity of pyromaniacs, you should use half of each and you will end up in the middle. I recommend you adjust your stinking sight for the one that groups smaller.

 

Gary

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45 2.1 posted this 25 June 2018

Hmmmmm............. The new humor ^^^^^^^^ doesn't really go over well. Stay with what is published in reputable manuals to be safe............ even though we see a lot of unpublished, unpressure tested data on this site. Try another powder as there are a lot more choices, it may be on for windage.

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porthos posted this 25 June 2018

what onondaga said

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Geargnasher posted this 26 June 2018

I'm not Batman, but try 10 grains of Unique. If it still shoots to the left, try 16 grains of 2400. Have you examined your bag placement and hold setup? Could be barrel time + follow through if you're right handed.

Or stick with Red Dot and yank the trigger harder.....

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Brodie posted this 26 June 2018

Well Riddler, If I were you I would take heed of what Geargnasher had to say.

B.E.Brickey

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BudHyett posted this 26 June 2018

There is a mechanical possibility, the crown is crooked or nicked. An imperfect crown can aggravate bullet direction with different bullet exit times due to velocity variation. 

The easy away to crown a barrel is to use a brass screw head that centers in the bore:

  • Reverse the screw in an electric drill with variable speed control
  • Fill the screw slot with lapping compound
  • Run the drill with a light touch to see the if shiny spot is centered on the bore.
  • If not centered, keep going until it is
  • You might want to use several screw heads of slightly increasing size - your choice as you see the lapping working. 
  • Thoroughly clean the lapping compound off the bore before firing.
  • Touch up the crown with cold blue.  

 This has worked well for a SMLE #4 and a Winchester M70 Varmint in .243. 

Country boy from Western Illinois, living in the Magical Pacific Northwest

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Bohica793 posted this 26 June 2018

I'm not Batman, but try 10 grains of Unique. If it still shoots to the left, try 16 grains of 2400. Have you examined your bag placement and hold setup? Could be barrel time + follow through if you're right handed. Or stick with Red Dot and yank the trigger harder.....

Yes, I will be trying other powders to see what happens.  I would consider form and follow through if the groups were not consistent, but each has proved such over the course of 50 rounds each.

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Bohica793 posted this 26 June 2018

There is a mechanical possibility, the crown is crooked or nicked. An imperfect crown can aggravate bullet direction with different bullet exit times due to velocity variation. 

There is no apparent damage to the crown.  If there were, I would expect rounds to be going everywhere, not consistently in one location based on powder.

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BudHyett posted this 26 June 2018

Be open to new phenomena, the SMLE not only tightened groups, but also changed the point of impact to center. It was shooting left and went to center on all loads. It had been shooting left which with the the prevailing winds of the Pacific Northwest is a good thing. 

Country boy from Western Illinois, living in the Magical Pacific Northwest

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Geargnasher posted this 26 June 2018

I would consider form and follow through if the groups were not consistent, but each has proved such over the course of 50 rounds each.

Consistency means you're consistent in your hold, nothing else.  If you hold the same way for both loads and the muzzle is jumping to the right slightly, but consistently, the your groups will move in the direction of of the jump with the slower powder.  If you changed your body position behind the butt (squared more to the bore), or observed carefully your cheek pressure and direction of pressure, you might find a way to control your POA better.   By the same token, the particular harmonics of the rifle alone may be changing the POI with load (as has already been assumed) no matter how you try to hold it, and the powder change may be the fix. 

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Larry Gibson posted this 27 June 2018

Given a consistent hold the difference in POI vs POA of the two different loads is simply a function of the time pressure curve differences and how they affect the recoil impulse and barrel vibrations. Even the subtle differences in lot to variation of essentially the same ammunition can give similar POI variation.

LMG

 

Concealment is not cover.........

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longhunter posted this 28 June 2018

WOW!

Jon Welda CW5 USA Ret. 608 797 0056

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Ed Harris posted this 28 June 2018

Larry is spot-on.  Even minute changes in powder charge can affect POI.

In the 91/30 contact of the barrel with the handguard can also influence this.  It is often informative to shoot the rifle with and without the handguard.  If it shoots better without it, some attention to where wood contacts the barrel and relieving that point with a scraper is in order.  Normally I am not a true believer in "ladder testing"  but in THIS particular instance, it may indeed provide an answer if the handguard tinkering produces no result.

 

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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joeb33050 posted this 03 July 2018

Stevens 223 bbl, 40 gr nosler, Titegroup, left to rigt, no windage adjustment.MV 2100-2600. See the poi move left.

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