Author Topic: Changed cases - changed POI...270 Win.  (Read 582 times)

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Offline Land_Owner

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Changed cases - changed POI...270 Win.
« on: February 10, 2010, 11:48:37 PM »
My 270 WIN Model 70 Featherweight likes a specific powder charge and bullet weight.  I get very good accuracy, about an inch for hunting, and my confidence is high - usually.

I changed from brass to nickel plated cases this week, same case weights, same case OAL, same powder charge, same primers, same bullets, all necks turned and reamed, none fire-formed in this rifle though, REAL LOW and RIGHT POI at 200 yds...but the group of 10 rounds was good.  Brass cased loads, the last 9 from this deer season, were right on target.

I resighted the scope for the "new" POI and it is now ON again.  What causes this?

Offline LaOtto222

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Re: Changed cases - changed POI...270 Win.
« Reply #1 on: February 11, 2010, 01:34:35 AM »
Barrel Harmonics. Barrels are not static when fired. The muzzle moves in a small circle - a light weight barrel more than heavy weight one. A long one more than a short one. It only takes a very small difference to have the bullet leaving the bore at a slightly different time - thus a different bullet path. In your case it MIGHT be that the case is not fire formed. It MAY go back to the original POI after fire forming and it may not, if that was not the cause. It MAY be the nickle plating does not stick to the chamber wall the same as a brass case or may not stretch as much. You did not mention bullet seating depth - I assume that with all the care you took with the rest of the reloading process that the bullet seating depth was the same for a cartridge OAL the same. Or did you mean to say that? If that what you meant by case OAL - is the case trimmed the the same exact length? Did you turn the nickle plating off of the necks? Is neck tension the same? Like I said it only takes a very small difference to change a POI - especially when a light weight barrel is used. The main thing is to be constant from shot to shot. Once you change the POI and the loads are the same from shot to shot, and barrel conditions have not changed, you should have a reliable POI. It is just real hard to say for sure what caused your POI change. Guns are so predictable, but not. I have never used nickle cases, so I have not had any experience like yours. I just tossed out a few possibilities and what I know about barrel harmonics. Good Luck and Good Shooting
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Offline Dezynco

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Re: Changed cases - changed POI...270 Win.
« Reply #2 on: February 11, 2010, 02:11:03 AM »
+ LandOwner +
Little things can move POI a good bit.  Fortunately, the overall accuracy is usually good, but the POI moves.  Just changing one little thing can move things around, and sometimes can make a great shooter into a good shooter and a pretty good shooter into a great shooter.

Offline gray-wolf

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Re: Changed cases - changed POI...270 Win.
« Reply #3 on: February 11, 2010, 04:11:42 AM »
Land owner--I have been watching some of your post.
You seem to be a good shooter and a very good detailed orientated person
  Going from brass cases to nickle cases and trimming the necks AND not fire forming, gets you.
    ???  A TRIP TO THE WOOD SHED, AND NO TV FOR ONE WEEK.   ???
What happened to consistency ?
  Make two piles of brass-----Nickle over here---------Brass over there.
No more on this one.

Offline wncchester

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Re: Changed cases - changed POI...270 Win.
« Reply #4 on: February 11, 2010, 04:45:37 AM »
What you are seeing is why it's often suggested to use cases in batches of the same make, head stamp and have even been reloaded the same number of times.  Mix your old good ammo with your equally good new ammo and your "grouping accuracy" will suck.
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Offline Siskiyou

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Re: Changed cases - changed POI...270 Win.
« Reply #5 on: February 11, 2010, 05:47:28 AM »
I am a little bit of a 270 Winchester nut, and have reloaded Remington, Winchester, Federal and necked down G.I. -06 brass without negative results.  I have a hundred Remington Nickel brass loaded with WW785, 140-grain Hornady BT, and WLP primers that are real keepers.  99% of my loads work fine with all three rifles.  I have only one commercial load that did not provide good accuracy in my M760; it was WW 150-grain power point.

The WW load was not providing expected results so I decided to shoot up the four or five boxes I had for practice and the brass.  That quickly came to a halt when I started to fire it in a Remington 700.  It proved to be very accurate, but produced low velocities.  I guess high velocity is not everything because it sure has racked up the Mule deer, and the remaining boxes are reserved for hunting.  The down side is that I have a good supply of hunting ammunition and needed to load practice ammunition.  I should note the velocity of factory Federal, and Hornady ammunition was also load.  Remington ammunition met expectations.

I have been careful not to mix headstamps or brass with nickel when loading.  But at the end of the day the identical charges of the same powder, primer, and bullet provide the same accuracy. 

In my bolt action 300 Savage a maximum charge of IMR4064 pushing 165-grain Remington C-L, Hornady, and Nosler PT puts the bullets in the same tight group at 100-yards.  Like you I seek accuracy out of my hunting load. 

I hunt deer in difficult terrain, and deer are not taken over bait from a fixed positions.  Deer are taken as they are found.  One of my better shots was off hand at about 75-yards.  I had been working two bucks for about a mile in steep brushy country when I spotted one of the bucks looking around a large pine at me.  All I could see was his head and neck.  It was take the shot or forget it.  The crosshairs were steady on the neck, and I pulled the trigger.  The buck was a bang flop; the second buck did not present a good shot, and was gone.  Knowing the 270 shot a tight group was the deciding factor.  I would have passed on the shot if I was carrying my British 303.

There was a point years ago that the accuracy of known rounds dropped off.  I was in a surge of reloading and shooting.  A 200-yard walk and I could shoot my rifle a few rounds before work.  I would shoot a few rounds, quickly clean the rifle and get ready for work.  The downside was I was getting the powder residue, but not all the copper residue.  More attention to the copper residue resolved the problem.

The copper issue has been around a long time.  This past Saturday I had two family members loading at my bench.  I had them bring their rifles to make sure the resized cases would chamber in their rifles.  Their rifles had nice shinny bores but by looking down the muzzle end with a light on the side I found copper in the bores.  One cleaned bores while the other one loaded.
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Offline shot1

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Re: Changed cases - changed POI...270 Win.
« Reply #6 on: February 11, 2010, 10:15:27 AM »
It is the unfired "NEW" cases that is doing it to you. Once you fire those new cases and reload them your POI will probably change again. They may got back to where your old cases used to hit. I almost sold off a rifle because I was loading new cases trying to get it to shoot. I shot shotgun groups until one day as I was coming to the end of the 100 new cases I started loading cases that had been fired once with the best load I had found so far. It put them all in almost the same hole. That rifle would shoot under 1" with most any load if it was put up in a case that had been fired before.

Offline Land_Owner

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Re: Changed cases - changed POI...270 Win.
« Reply #7 on: February 11, 2010, 11:10:39 AM »
Quote from: gray-wolf
 Going from brass cases to nickle cases and trimming the necks AND not fire forming, gets you.   ???  A TRIP TO THE WOOD SHED, AND NO TV FOR ONE WEEK.   ???

Good one.  LOL.  

Nickel cases were given to me and shot from someone else's rifle.  I did seat the bullets to the same depth as in the brass cases.  Nickel plating was turned off of the necks, inside and out.  I have no measuring device to determine neck tension.  The brass cases were similarly turned and assume neck tension was the same or a neglegent difference.

I am an Engineer, what can I say further?  I am detail oriented, although not as "accuracy focused" as are some.  I just want confidence in my hunting rifle.  That means testing the equipment.  If my range were closer, say the back yard, versus 1/2 hour's drive away, I would test EVERYDAY and GO for that accuracy "Jones".

I will be testing more.  Shooting is FUN.  Shooting more is FUNNER!~

Offline TXSPIKE

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Re: Changed cases - changed POI...270 Win.
« Reply #8 on: February 13, 2010, 12:35:09 AM »
I bought a 100 nickle 7mag brass when I first got my 7mag 16yrs ago.That lot was the best I've seen.Many of those cases were loaded over a dozen times and I've still got some of them.I order another batch of them and they sucked.The cases were much harder than the first batch and the neck tension is much tighter too.Guess what?,my groups opened up as well.I switched backed to regular brass and everything went back to normal.One thing I've thought about but have not tried,is to anneal those nickle cases.

Offline Autorim

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Re: Changed cases - changed POI...270 Win.
« Reply #9 on: February 13, 2010, 02:11:42 AM »
I have only bought one lot of nickel cases and that was for a 30-06. They were harder with more bullet tension and I now see no real advantage. I have never bought another batch although I still have some of those. I don't recall any significant POI shift. For many years, I always pillar bed, add concealed steel crossbolts and free float all bolt action barrels. I have very little POI shifting and my Ruger M77 MKII .270 is a very consistent shooter with nearly any bullet. My one exception is a M70 .338 Win Mag which shifts significantly with lower power 200 grain bullets to full house 225 or 250's.

Rifles are like people - all different.

Ken