bolt lug contact

Discussion in 'The Basics, Starting Out' started by Guest, Dec 9, 2005.

  1. Guest

    Guest Guest

    Is there an easy way to see what amount of lug contact a bolt has?
     

  2. sewwhat89

    sewwhat89 Well-Known Member

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    Remove the bolt from your rifle, hold the bolt in one hand letting gravity do the rest, look at the back of the bolt lugs, they are painted black. How much silver do you see? Take a peek at jb's .25-06 for sale he has two pics of a 100% contact bolt.
     

  3. Guest

    Guest Guest

    Ok. Here is what I have. To me, it looks even from one to the other. Mabe 75% contact. Is the % of contact important to accuracy or the evenness from one to the other? [​IMG] [​IMG]
     
  4. Ballistic64

    Ballistic64 Well-Known Member

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    Do you grease the lugs? It looks like a little galling going on.Im no expert though /ubbthreads/images/graemlins/confused.gif
     
  5. Guest

    Guest Guest

    Yes. What is galling.
     
  6. Ballistic64

    Ballistic64 Well-Known Member

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    Galling-scoring,pulling metal from one surface to another.Like I said Harv,Im no expert but the bottom pic looks like theres good even contact with slight galling at the top (outer edge) of the lug.The top pic isnt showing quite the same smooth contact as the bottom pic.Hopefully Fifty or someone else with a little more knowledge will see your pics posted and comment.
     
  7. wapiti13

    wapiti13 Well-Known Member

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    Harv, 100% bolt contact is important for accuracy. The contact lets the bolt react the same for every shot as I understand it, otherwise your lock up varies from shot to shot effecting accuracy. /ubbthreads/images/graemlins/shocked.gif
     
  8. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Harv,

    First off, what is that bolt out of? Looks like a Sako bolt as there is a sako extractor to the left of the lug in the first pic, or at least looks like one.

    Could be a Rem 700 with a Sako fitted but the guide groove looks to large in the right lug. Also, the groove behind the lugs on the bolt body is not right for a Rem 700 unless it has been altered.

    Anyway, the lug contact appears to be relatively even. I would say in the 70-75% range. On the leading edge of the lugs, Right side in the pics, there is a cam machined which is why that area does not contact the receiver when the bolt is locked, this is desirable and should not be machined out.

    On the left side of each lug there is that triangle pattern on the bottom of the lug surface.

    Without knowing exactly what receiver this is I would not want to say either way if this area should be corrected but I will say it is desireable in most cases to have this area fully contacting.

    As far as the gauling is concerned. ITs hard to tell in the pics if it is actually gauling or old machine marks that are present and visible through the polished areas of the lug.

    In the top pic, it appears that this is just machining marks as you can see the line on th ebaring surface near the top of the lug. I say this because the groove is consistant in width from start to finish. Generally gualing will increase in size or width as it progresses as more metal is balled up if you will.

    In the bottom pic, there is one area on the right side of the contact area about 1/3 up from the start of the bolt body that appears to be some gauling. Just to the left of this is what appears to be a brass smear. This tells me that brass chips have gotten between the bolt lug and receiver surface and may be the reason for the gualing.

    Keep thise bolt lug recesses clean and free of dirt and brass chips and use a high quality moly based lug grease to lube these surfaces when needed. I generally lube every 25 rounds.

    Most importantly, how is the rifle shooting right now?

    Kirby Allen(50)
     
  9. Guest

    Guest Guest

    Thanks for all the replys. The rifle is a Tikka 270. I loaded 130g wildcats this year and all loads shot under 1" at 100y. Best was just under 1/2". The rifle is basicly stock. I sanded the forend out so I have at least 1/8" clearance between barrel and stock. Also added about 3lb led to the syntec stock. Kirby, what's your thought on neck sizing only for this rifle. I started doing this in hopes of a little better accuracy but was wondering if I will run into any problems after a few reloads? Thanks.
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Harv,

    Really depends on how heavy you load the 270 Win. Neck sizing only works great for accuracy but if you load to top levels you will quickly need to bump the shoulder to maintain easy chambering. You can let that be your judge on when to bump the shoulder.

    Do some testing and see if the rifle shoots better with neck sized only or partial Full Length sized cases. Despite conventional wisdom, many factory rifles shoot more consistantly with partially full length sized cases because they are not baring evenly on the bolt lugs.

    If the bolt lug baring surface is not square, generally a preload on the bolt will cause unexplained fliers at times. This Bolt preload can be caused by only neck sizing so test her out and see how your rifle responds. Your lugs look relatively even but its impossible to tell if they are square without putting a mic to them.

    From what I have seen with the Tikka rifles, the most limiting factor to accuracy is their synthetic stocks, very flexible in the receiver area.

    If you get a load in the 1/2" range I would say you have done very well and to stick with that.

    Again, test the neck sizing only against the partially FL sized cases and see if there is any accuracy difference. If you decide to neck size only, it is imparative to keep those lug surfaces lubed with quality lube as there will be more force applied to them when the bolt is closed. Keep them clean as well!!

    Good Shooting!!

    Kirby Allen(50)
     
  11. Guest

    Guest Guest

    Thanks much Kirby. I will have to rethink this neck sizing only thing. I lube the lugs every time I clean the bore (25-50rounds). Been having good luck with FL sizing so mabe I'll go back to that. Just trying to get the best accuracy from this factory rifle without spending too much. Saving my pennies for a custom AM ..... some day.
     
  12. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Harv,

    Adjust your FL die a little at a time while checking how the sized case chambers in your rifle. Just when you get the case to chamber easily stop there. you will have about 0.001" clearance which will offer great accuracy but still keep chambering easy.

    I generally turn my FL die down about 1/16 a rotation at a time when setting it up to size cases. When they start getting close to chambering ease, I cut that in half again and work up to that point slowly.

    Good Shooting!!

    Kirby Allen(50)
     
  13. Guest

    Guest Guest

    I have only gone one round of neck sizing and no problems chambering them. Should I just keep neck sizing until I get resistence when chambering and than bump the shoulder a bit?
     
  14. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Harv,

    Yes, you will have to play with it a bit and see how many firings you can get before you need to bump the shoulder. If your not runnng really hot loads this will generally be every 3 firings or so.

    Kirby Allen(50)