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can you over stabilize?

Discussion in 'Rifle Country' started by futureranger, Jan 6, 2010.

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  1. futureranger

    futureranger Member

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    I am trying to find a good load for my savage 308, its 1:10 twist so would shooting 155gr lapua’s be “over-stabilized” 168gr bergers also look good but the 155gr lapua’s actually have a better BC. Im trying to get the most accuracy out of my rifle as possible, does anyone have good tips for shrinking groups besides telling me to practice more?
    Also some loads I have made can get under .5” at 100 yards but it seems I can only get those groups after the barrel warms (8-12 shots depending on how long I wait between shots) and the point of impact shifts a good bit. How do I get a good cold barrel load? Cause a deer won’t stand around for me to shoot 10 shots before I get to my zero…

    thanks for the help
    -Pat
     
  2. Heywood

    Heywood Member

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    Hi I know someone with the same twist savage and he found 180 matchkings to be the most accurate.I think most people who shoot 155's use a 1'12 twist.hope that helps!
     
  3. USSR

    USSR Member

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    futureranger,

    Actually, a 1-10" twist is excellent for the 155gr Scenar. The reason is, determination of the optimal twist rate for a particular bullet is actually a function of bullet length, not bullet weight. While in most instances, only heavy bullets are long, in the case of the 155gr Scenar, the lead core does not go anywhere's near the ogive (there is a lot of empty space near the bullet tip), and the bullet's length is about the same as the 175gr Sierra MatchKing bullet.

    Don
     
  4. Geno
    • Contributing Member

    Geno Member

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    I read on one of the custom barrel websites that when the first few rounds down the barrel are not as-accurate-as those after it is "fouled", that it is most times due to the first 3 to 4 inches of the barrel's rifling and lands being rough.

    It said that stainless can break in about 4 times faster than carbon steel barrels. They suggested polishing the barrel, especially the first 3 to 4 inches. I did so, and now my groups are very consistent from the first 3-shot group to the final, 5th, 3-shot group. I clean every 15 rounds.

    To polish my 30 cal rifles, I used Lead Out clothes over a 30 cal bristle brush. You can also use JB Bore polish. It made a world of improvement.

    Geno
     
  5. Bobarino

    Bobarino member

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    in your case, no you're not over stabilizing your round. it's actually impossible to do that. there have been a few cases of people shooting very lightweight bullets in fast twist barrels where the bullet actually explodes from spinning so fast, but you're plenty safe. i've only heard of it in things like people trying to shoot 40 grain v-max type rounds in a 1:7 twist barrel.

    anywho, if your POI is shifting as you shoot and the gun warms up, you need to break out the sandpaper and get the barrel off the stock. sand out the barrel channel until you can slide a dollar bill under the barrel all the way to the action without it getting stuck. bedding the action is a good idea too. after that, re-zero your scope and you should be good to go with that first shot.

    there are some relatively cheap things you can do to improve accuracy like having your barrel cut & crowned, having the action trued, etc, but i think just developing the right load for it is the best way to go.

    Bobby
     
  6. futureranger

    futureranger Member

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    Geno thanks for the advice ill try that, the lapua scenar look good to me but i just wonder if the 155 gr will loose to much momentum compared to the 168 or the 180's i shoot now, to make the lighter/faster bullet worth it. anyone shoot 155's at any great distance?
     
  7. Bobarino

    Bobarino member

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    the 155 scenars do give up some energy compared to a 168 grain but the 155's with their high BC can be pushed faster and will stay supersonic at well over 1,000 yards whereas the 168's are starting to go transonic. 168+ will also be less affected by winds of course.

    if you're talking about hunting, match bullets aren't made for that and in my opinion, it wouldn't be ethical to use them for game. if you're talking paper punching, they're perfect.
     
  8. rizbunk77

    rizbunk77 Member

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    This is why I am somewhat upset that the best M4 carbine type rifles come with 1/7 twist. The average Joe is goint to want to shoot 50 gr Vmax with these for varmints or 55gr SP which are the best for avoiding over penetration in home defense situations. Is 1/7 ok for 55 gr. out of a carbine barrel?
     
  9. Bobarino

    Bobarino member

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    yes, 55 gr is find. that's what the military uses in their 1:7 twist barrels. there are also some really good 62-64 grain softpoints on the market for home defense too. i think you'd even be ok with 50 grain V-Max.

    there are a lot of M4 type rifles that use 1:9 twist out there too.
     
  10. futureranger

    futureranger Member

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    Bob i have a aluminum bedded stock and the barrel away from the stock by at least 1/8" in the tightest spot, could it be that the load i shoot now was developed in the summer and im shooting now in the winter? its about a 50-60 degree difference here in the mountains, i think ill just spend more time developing a load, the bergers are looking like a good mid point to me, im gonna buy the hunting match 168gr, and back it with varget
     
  11. cougar1717

    cougar1717 Member

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    30 caliber bullets should not have the issue of flying apart due to rotating it too fast using typical twist rates. The only problem I have heard of was AR owners using bullets advertised as being super explosive or bullets designed with an extremely thin jacket for fragmentation on impact. I have not had any issues using 55gr. Vmax and soft point bullets.
     
  12. MachIVshooter

    MachIVshooter Member

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    Seen in. A friend of mine has a .22-250 that the original owner had custom built and intended it for deer and antelope hunting. Because he was planning to use heavier bullets, he had opted for a 1 in 7 twist. Well, when my friend started trying to push 35 grainers in excess of 4,000 FPS, the bullets were coming apart on him. Bullets built for the .22 hornet are too lightly constructed to be spinning at more than 400,000 RPM.
     
  13. Geno
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    Geno Member

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    FR:

    There are dozens of fellas here who use that 155 grain projectile. Zak, BullfrogKen just to name two. These fellas shoot at some serious distances!!

    I think what you mean over-stabilize (which can happen), is to over-rotate the projectile and destroy or deform its jacket by subjecting too much centrifugal force. I'll make the example regarding a .223 cal. The larger, heavier bullets say in the 80 grain range have stronger jackets. They can handle a 1-7 twist at high velocity and hold together. However, the 40 grain hollow points have paper think jackets, and at 4,000 FPS, the 1-7 twist would deform the projectile, and so they are fired through a 1-12, 1-14 etc.

    The heavier the projectile, the faster the twist-rate needs to be. Conversely, the lighter the projectile, the slower the twist. However, in the case of a 30 calibre, a 155 grain projectile, a 1-10, 1-11 or even a 1-12 should work beautifully!

    Geno
     
  14. Vern Humphrey

    Vern Humphrey Member

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    "Overstabilization" can have two effects. The first is to destroy bullets through both the stress of passing through the fast-twist rifling and the high rate of spin. This rarely occurs in calibers over .224 or so. Larger calibers tend to have thicker jackets.

    The second effect is "trail." This is true overstabilization, where the axis of the bullet remains fixed and does not conform to the curve of the trajectory. Eventually, the bullet is pointing so far off the trajectory that aerodynamic forces make it tumble. It is almost impossible to make a conventional bullet trail from any conventional barrel.
     
  15. NCsmitty

    NCsmitty Member

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    It's easier to under-stabilize in a slow twist than to over-stabilize in a fast twist. If the bullet in a fast twist is able to tolerate the rotational speed that it develops, it seems to have less effect on the ability to group.
    The under-stabilized bullet from a slow twist, often imparts a wobble to the bullet that can get worse to the point of creating a keyhole on the target and usually poor grouping.



    NCsmitty
     
  16. Bobarino

    Bobarino member

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    if you're bedded and free floated then my next suggestions would be this; shoot it and get the rifle good and warm to the point where your POI stablizes in one spot. then, while it's still warm, loosen the stock mounting screws enough to relieve tension and then retighten them with it still hot. it could be that the different expansion rates of the aluminum bedding block vs. steel action are causing binding.

    if that still doesn't work, i'd guess that the barrel wasn't properly heat treated and is warping as it heats. you can have it stress relieved with heat or cryo-treated to try to resolve that. or just get a new barrel :)
     
  17. futureranger

    futureranger Member

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    thanks for the advice Bob, ill try the heating then adjusting the tension on the screws. i was thinking about getting one of the 30 dollar bedding kits and seeing if that would help the aluminum bedding do its job, does anyone have any experience with those?
     
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