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Thread: Significant impact point shift with ammo change.

  1. #1
    Boolit Master tazman's Avatar
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    Significant impact point shift with ammo change.

    I own 4 different 22rimfire rifles. All are bolt action rifles. All have decent scopes. One is old. One is semi old, two are new in the last few years.
    They are a CZ 455 American, a CZ 452 trainer, A kimber 82 Government, and an old(circa 1950) Winchester 72A.
    I took them all to the range today to give them a workout. Things went well. Probably even better than I expected.
    The two CZ rifles both shot under 1/2 inch at 25 yards and nearly the same at 50 yards with match ammunition. The Kimber did about the same. The 452 trainer shot a 1.2 inch group at 100 yards when the wind stopped. I can usually put 4 out of 5 shots in one hole with a close flyer at 25 yards with any of these three rifles.
    The Winchester never has shot match grade groups for me but doesn't need to for squirrel hunting which is what I have used it for during the last 56 years. With match ammo or Federal Auto match it shoots about 5/8" at 25 yards and about 3/4 inch at 50 yards. With high speed ammo it runs about 3/4 inch at 25 yards and 1 inch at 50 yards. Basically minute of squirrel.
    This is the background for the rifles.
    My problem, if you want to call it that, is when I change ammo type or brands in any of the newer rifles, I get a significant impact point shift. Sometime up to 1.25 inches at 25 yards.
    This happens even when using differing match ammo brands. Group size stays about the same, it is just in a different spot. When I go back to the brand the rifle is sighted in for, the impact point goes back to center just as you would expect.
    I thought the heavy barrels on the target rifles wouldn't do that to the extent that it is happening. I expected the impact point to vary only slightly but the group size to change a bit.
    That isn't what is happening.
    The really funny part is what happens with the old Winchester 72A. The center of the group never moves. The groups simply change size with a change in ammunition quality. It doesn't matter whether I use target ammo or high velocity ammo, it all goes into a group centered on the x ring.
    Why is this happening this way?
    The three newer rifles all have free floated barrels. The CZ rifles are magazine fed. The Kimber is a single shot.
    The Winchester is fed from a tube magazine beneath the barrel. No possibility of free floating there.
    Another thing about the old Winchester. About 45 years ago, I mounted a 1 inch Bushnell 4X scope on it and sighted it in. I have never needed to change the adjustment on the scope in all that time. It still shoots to the same impact point after all these years.
    I expect I will take it hunting again this fall when squirrel season comes in. It will still do the job.

  2. #2
    Boolit Master

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    I'd wager you have different amounts of time in the barrel for each type of round, and you're launching at different spots in it's harmonic wiggle. The Winchester barrel is anchored by its hardware, so your major impact changes will likely be from trajectory changes, not harmonic ones. Another possibility is that the difference in speed is causing the bullet to exit at a different point in your follow-through, though your experience with the 72 seems to discount this.

    One of the fun bits of rifle lore I've picked up is that barrel free-floating ain't necessarily all that and a bag of chips. It seems to depend greatly on barrel taper and barrel shape. While free-floating has it's place and advantages, I think the industry may have sold us a bill of goods in convincing us that it's a NECESSARY thing, when one thing it's certainly doing is cheapening manufacture by eliminating ANY need to properly fit barrel to stock. They get the double bone-us of making a rifle for less and selling it for more because "free floating is GOOD"

    But then we have Remington 700's which made their name for accuracy on both a fast lock time and upward pressure against the barrel at the nose of the stock. Going back further, we have the Enfield No. 4, that got accuracy out of a portable weight barrel basically the same way. Further still, we have the WWI-era No.1 MKIII Lee Enfield which went so far as to put a spring loaded plunger in the stock to bear against the bottom of the muzzle.

    Shim up the front of your free-float with some chunks of business card in order to do a non-permanent test. If things improve, replace the card shims with epoxy.
    WWJMBD?

    "I'M MELLLLLLLLLLTING!" - Elphaba

  3. #3
    Boolit Master Ole Joe Clarke's Avatar
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    I had mine out Monday. They shot a lot better than I could hold them.

    Have a blessed day,

    Leon

  4. #4
    Boolit Master GhostHawk's Avatar
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    I agree with Bigslug.

    The easy answer is find the one brand that shoots consistently in the majority of rifles. And only stock that.

    I love the Federal Auto Match 325 round bulk packs for my Ruger Pistols. But it is not as long range accurate in my Ruger 10/22. Ok, but not the best.

    For that nothing beats CCI Mini Mags. So I stock some ammo just for that rifle.

    We expect variables in our loaded ammo. Fact is they exist in factory ammo as well.

  5. #5
    Boolit Master
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    Aren't 22LR weapons bizarre beast?

    Personally, I'm in the pressure point camp with my accuracy 22s. I'm also in the camp of find the ammo X gun likes best and only shot that ammo/ gun combination. With 22LR the lube one the bullet contributes to how it shots, you change brands, you change lube. It usually takes about 20 rounds of a differently lube ammunition shoot through a cleaned barrel to reseason it for the new lube, before you can truly determine how it's going to shoot in that barrel rifle chamber combo. But I think the chamber has a bunch to do with this ammo sensitivity as well. In another thread asking about your least ammo picky 22LR, I listed a Marlin 981T as being my least picky. It's generally MOSH (that'd be minute of squirrel head) with just about anything you feed it, in any order you feed it, but it sure ain't going to win any shooting matches! Tight target and semi target chambers tend to be more ammo sensitive, yet shoot tighter groups with ammo they prefer.
    My two main squirrel hunting rigs are a custom 10/22, and a Browning T-Bolt. The first gets CCI SSHP only, and the second only gets ELEY SSHP.

    I hope you never get a barrel that throws cold bore fliers!

    Btw, those two rifles shoot MOSE (minute of squirrel eye) with their ammo!

  6. #6
    Boolit Man JoeJames's Avatar
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    Most shooters never realize how picky a .22 rifle is. I had an old KKW .22 trainer, and out of all the ammo I tried, it liked, I think it was, RWS match. An old Win. Model 1890 liked cheapo Federal Lightnings best. You just cain't ever tell until you've tried everything you've got.

  7. #7
    Boolit Master
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    .22's are the most finicky when it comes to ammo. When you have a big change sometimes its the velocity causing the problems. Example
    You sight in with Federal lightnings est 1240fps 50 yards away and your dead on the bullseye but then You shoot some winchester bulk ammo say that 333 or what ever they are calling those floor sweepings and the next thing you know. The rifle is hitting two inches low & left and its more pattern than group. The reason is the winchester's are around 1375fps but not as consistently loaded so your velocity is all over the place which explains the pattern. The best thing to do is pick one ammo and stick with it.

  8. #8
    Boolit Master sparkyv's Avatar
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    Quote Originally Posted by 1Hawkeye View Post
    .22's are the most finicky when it comes to ammo. When you have a big change sometimes its the velocity causing the problems. Example
    You sight in with Federal lightnings est 1240fps 50 yards away and your dead on the bullseye but then You shoot some winchester bulk ammo say that 333 or what ever they are calling those floor sweepings and the next thing you know. The rifle is hitting two inches low & left and its more pattern than group. The reason is the winchester's are around 1375fps but not as consistently loaded so your velocity is all over the place which explains the pattern. The best thing to do is pick one ammo and stick with it.

    This is my experience. It's the velocity that changes the POI in my .22LRs.

  9. #9
    Boolit Master tazman's Avatar
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    I would agree with velocity changes when using high speed ammo, but, I was getting impact point shifts with different brands of subsonic match ammo as well. And not just at 50 yards. Sometimes match ammo would move a group by nearly an inch at 25 yards.

  10. #10
    Boolit Master Gunslinger1911's Avatar
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    Not unusual at all for impact shift. Especially with different brands, even if they are rated at the same velocity.
    They won't be exactly the same vel, they will have a slightly different bearing surface on a slightly different hardness bullet. All these contribute to change in impact.

    I have a stock 77/22 and a full custom 10/22, both capable of one hole 5 shot groups at 50 yds. Both can show a shift (slight) with different lots of the same ammo .
    Both like CCI standard vel, I buy as much of a lot as I can afford, just to save re-zeroing .

    As an aside, if you really want to deal with a picky gun, try an Olympic grade pellet gun.
    I have a FWB 300 - think Olympics from maybe 20 years ago. .177, No recoil springer at 700 f/s.
    Same tin of pellets; zero in the cool of morning, poi will change as the temp / humidity creeps up.
    Growing up, my sons would compete shooting 9mm casings at 50 yds (had to switch to spent 22 casings as they got better). Part of the learning curve was determining clicks on the scope as it warmed up.
    Cogno, Ergo, Boom

    If you're gonna be stupid, don't pull up short. Saddle up and ride it all the way in.

  11. #11
    Boolit Master
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    I did slug the barrel on my new CZ455 the other day. I then mike'd some of the various .22s that I had laying around. There is quite a difference in .22 bullet diameters, I found out. The one .22 round that shows the best fit seems to be the Aquila rifle match. It is about .0015 over the groove diameter of the barrel.
    Haven't had time to shoot, yet, but maybe this weekend if it is not too windy. Sorry, I don't have the measurements in front of me right now.
    IIRC, there was as much as .003 difference in different ammo brands and some brands differ in the same box.

  12. #12
    Boolit Master GhostHawk's Avatar
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    You want to talk about impact shifts.

    Had a cousin of mine out to the range with his 16 yr old boy last week. Ran through a variety of pistols and pistol caliber carbines.

    Was finishing up by checking a couple of H&R Handi rifles, single shots both in .44mag.

    We were at the pistol range, so target was at max 50 feet. I had scope zero'd for bullseye.
    Had just put 2 through one hole.

    Sat my cousin down and he shifted things so the barrel was supported at the end, instead of? the hinge.

    Next shot went 6 inches high. He shook his head, tried again. Next shot went 6 inches low.
    I put the support back at the hinge, told him to leave it there. Aim to the same spot as before.
    He put a third bullet back through the center hole.

    He's looking at me with this awe and wonder on his face. How did you know it would do that?

    Well I did not "know" but I had a pretty good idea. Handi rifles like the support just forward of the hinge.
    I did not tell him I learned the hard way like he did.

    As long as they left the support where I set it. It would stack them up.

    But there are many many variables. The trick is to identify the one causing the problem.

  13. #13
    Boolit Master lefty o's Avatar
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    different bullets even of the same weight at the same velocity can have fairly large differences in points of impact. its not a new thing, most people just dont notice it.

  14. #14
    Boolit Man JoeJames's Avatar
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    There is a wide canyon separating those who strive to put all rounds through the same hole and the exact point of aim, and those who just want something to go bang. Sometimes I've had better conversations with a Hickory stump, than with those of the bang persuasion.

  15. #15
    Boolit Master
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    .22's are not the only ones that change poi. My .40 Shield changes poi when changing from 6 round to 7 round magazines using the same load. In this case, the small finger doesn't fit the grip on the 6 but does on the 7.

  16. #16
    Boolit Master 243winxb's Avatar
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    22 rimfire rifles.

    when I change ammo type or brands in any of the newer rifles, I get a significant impact point shift. Sometime up to 1.25 inches at 25 yards.
    Different lube on the bullets, is the main cause. Clean barrel between brands/types. Or fire 10 rounds to recondition the bore.

    I have seen the first 5 to 8 shots of a different ammo shoot high and left from zero. If i keep shooting, it moves back down , close to where it should be.
    Last edited by 243winxb; 06-08-2018 at 07:49 PM. Reason: Add title.

  17. #17
    Boolit Master
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    did a test with my old Win M-70 30-06 years ago. It would shoot 1-1.5" groups with any decent ammo. I loaded 16 rounds all with the same LC53 case/lot all same powder charge, CCI primer. etc. The only difference was Hornaday, Speer, Remington and Sierra FB spitzers. I got four nice 1.25" 4 shot groups, centers spread over six inches apart

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