Can changing a stock alter your average FPS?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Swifty, Jul 15, 2012.

  1. Swifty

    Swifty Active Member

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    I have a Stevens 200 in 7/08. I have used the same flimsy stock that came with it since I bought it- almost always shooting off of a bipod. I developed a load a couple years ago that I have accumilated a large amount of data with. 150gr SBT, and 40.6gr of varget (Avg FPS was 2647). The load has been quite consistent in the varying temps hat I have shot it in at 800ft ALT. I actually didnt notice any difference in flight or impact when I went out to WY last year for a hunt and we went to the foot hills and did a rock shoot at several different ranges. This was at 4600-4800ft ALT.

    My buddy just purchased a savage M10 FP-SR in 308 and changed out the stock. I noticed that the factory stock he took off the gun has the same screw spacing and same blind mag set up as my stevens. The stock (not an Accustock) was much better and much more rigid than the one that came with the Stevens. So I thought, "What the hec!" and decided to put the stock on my stevens to try it.

    I took the rifle out to rezero it and decided to run the loads over a chrony. The avg FPS is now at 2710. At first I though that I got a hot batch of Varget. But, I have never ran into this increase in FPS before because the data has pretty much stayed the same in whatever temp I shot it at (generally out to 500yds).

    Now with this stock is more rigid and has much more free float around the barrel (the stock I put on was cut for a bull barrel and I am toting a sporter weight barrel). Could the new stock be causing the FPS to increase due to different contact/ no contact with the barrel lug, action, and barrel?
     
  2. Hunter2678

    Hunter2678 Well-Known Member

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    I've officially heard it all now..
     

  3. Swifty

    Swifty Active Member

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    OK, great. So maybe you can help me out on this. Just trying to get some advice or help here.
     
  4. Coyboy

    Coyboy Well-Known Member

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    the short answer is yes, but not in your case.

    60 fps based on only the stock not likely.

    If you changed from a 2 lb stock to a 20lb stock you would likely see a small increase not 60 fps, may-be 20-30fps.

    since you don't crono all loads from the rifle, pin pointing the precipitant to the change may be difficult. Very small differences could change your speeds; barrel wear, brass lot change, hardening of the necks, neck weld, the list goes on.
     
  5. Swifty

    Swifty Active Member

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    My round count is in the low 1600s. I havent changed brass (100ct) in maybe 4 reloadings. And I have ran them over a chrony about 2 reloadings ago. I am not familiar with the two things I quoted you on. Could you please elaborate? Thank you.
     
  6. Coyboy

    Coyboy Well-Known Member

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    brass work hardens and thus increases the neck tension on the bullet,
    ammo that is loaded and left to sit for a period of time can bond to the case neck causing an increase in pressure during firing that as in hard necks increases velocity in most cases.
     
  7. cowboy

    cowboy Well-Known Member

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    I have never seen a change in stock give that kind of fps difference. In my opinion - something has changed besides the stock.

    If it were me and I had the original Stevens stock, i would go to the range with my chrony and both stocks. Play switcharew and see what you get - then you know for sure and it's not opinion, it'll be fact.
     
  8. Swifty

    Swifty Active Member

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    Interesting. I never knew that could happen with ammo that has been loaded and stored for a period of time. I'm using Winchester brass. Is there a time frame on that or is it more a case by case basis? I did load the ammo in january of this year.

    If it is a case of hardening and neck weld, is it time to change out the brass?

    Also, I think I will will take your advice and play switcharew with the stocks over a chrony and see what happens. Thank you...
     
  9. bassin93

    bassin93 Well-Known Member

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    I would guess also it is your crony. If it is in the sun it will read different then when in the shade. I have seen several that do this. Also temp will affect your powder also. By that I mean if it is hotter out when you last checked your velocity then when you originally checked it, it can make a big difference. your powder will burn hotter.
     
  10. Edd

    Edd Well-Known Member

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    I think switching stocks back would be a good test.

    Bart B has previously said that changing shooters will change the velocity using the same gun and ammo.
     
  11. Bullet bumper

    Bullet bumper Well-Known Member

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    A few months loaded will not cause serious neck weld in the true sense but every time you reload the brass work hardens a bit more and the harder the brass the quicker true neck weld will take place . However it will have more neck tension than it had when originaly loaded . How much more depends on how soft the necks were to begin with , how thick the brass is and how much neck tension was initially applied. I have done a lot of work on neck weld and completed a 10 year trial on stored reloads . When the brass age hardens it also shinks in diameter at the thinnest points that are under strain , the neck , and quite dramaticly .
    I don't think that increased neck tension is the whole issue as the velocity difference is quite small and some of it would be normal chrony error and normal shot to shot variations .
    One way to combat incraesed neck tension on stored loads is the seat the bullet long to start with and then when it comes time to use them seat the bullet to the correct depth . This helps break the grip to some degree but does not arrest long term strain hardening and shinkage .
    The military know all this and usually use and replace there ammo in around 7 year cycles .
    For pecision shooting regular annealing of the neck is a good idea as long as it is done right .
     
  12. Swifty

    Swifty Active Member

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    Well, i put the old stock back on my rifle and went to the range. Rezeroed it and shot at 400yds using the old data. Bingo-perfect. Ran it across a Chrony. Bingo- same FPS I was getting with the old stock. I agree that its weird, but it's what it is. Guess the action just didnt like the stock I tried on it.

    I did learn something though from this post about the neck hardening and I willl keep that in mind when long term storing some of my ammo.
     
  13. AZShooter

    AZShooter Well-Known Member

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    Did you shoot with the new stock right after chrono'ing the old stock? If not you don't have a good control. You cannot say the new stock causes faster velocites.... yet.

    Let us know when you test both stocks under same conditions.
     
  14. Joe King

    Joe King Well-Known Member

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    Whats the fit like for you between stocks? if your really loose with one and tight with the other it can make a difference, maybe not much of one but it changes what happens with your rifle as the bullet travels down the barrel.