R700/Jewell trigger, timing issue?

Discussion in 'Advanced Gunsmithing & Engineering' started by Fast14riot, Jul 8, 2017.

  1. Fast14riot

    Fast14riot

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    Currently building a R700 with a Jewell trigger I purchased second hand. Today I was looking at primary extraction to see if I was getting at least 50% of the ramp and noticed that if I cycle the bolt handle up then down only, not back or anything, the firing pin will follow the bolt back down, not catching the sear. Firing pin fall is approx .270" on an empty chamber currently. Could shortening the cocking piece .010-.020" (only what is necessary, of course) alleviate this condition?

    To be clear, if I allow the bolt to move back any amount after lifting the handle I can hear the sear reset, it was only when cycling up then down with no aft movement does it not reset.
     
  2. rayjay

    rayjay Silver $$ Contributor

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    I think you need to carefully investigate this before removing any metal. If the rubbing surface of the cocking piece is fully into the full cock notch with the bolt handle all the way up I don't see anyway for the sear not to be resetting. I think if you try this with a properly sized empty case in the chamber the bolt will be held back far enough for the trigger to reset.

    Part b. What's the purpose of wanting a sear reset in the situation you are describing ?
     
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  3. Fast14riot

    Fast14riot

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    I've tried it with a SAAMI case, and a fully fire formed Ackley case (260 Ackley 4x fired and neck sized only), same results. I am overly cautious when it comes to messing with ignition, I will gladly pay someone else to do it if I don't feel comfortable, but I do like to have a complete understanding of what exactly is going on.

    I dry fire practice quite a bit, no need to fully cycle and eject snap caps, but would like to have the sear reset.
     
  4. rayjay

    rayjay Silver $$ Contributor

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    This is how I corrected the excess firing pin fall on my actions. It would fix your 'issue' [ :) ] also.

    I might have been better off to move the full cock notch on the bolt but this is easily and cheaply fixed if I had happened to be having an oversight :) . I also rework the full cock notch to mostly eliminate the hump but I no longer sure that this is appropriate. I may be missing some aspect. You will have to study the pic and look at your own bolt to see what I did to the bolt on the left.

    [​IMG]

    [​IMG]
     
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  5. Fast14riot

    Fast14riot

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    I suspect it's due to the remington use of cock on close and combined with the Jewell trigger placing the sear slightly farther aft. I'm fine with a small amount of cock on close as long as the pin fall stays adequate.

    I will have to pull it from the stock to get the bolt out (40xb stock) and take some careful measurements to fully determine what's going on.
     
  6. rayjay

    rayjay Silver $$ Contributor

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    On my 40X stock I had to dramatically lengthen the slot in the top of the comb to allow the bolt to be removed. I did do a good bit of sanding of the bedding surface which lowered the action a good bit.
     
  7. Fast14riot

    Fast14riot

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    Ok, so after looking at things and doing some brain exercises, if I reduce cocking piece length to achieve sear engagement when just cycling up and down, I will be reducing cock on close. That will shorten pin fall, which I have total .270" currently and .034" of that is cock on close. To maintain the suggested .240" total pin fall minimum (per Alex Wheeler) I should have about .006" of cock on close remaining. No need to change the firing pin. I can live with that amount of cock on close with an otherwise untimed action. (I.e. primary extraction timing)

    Once again, I am not attempting to do this work myself yet, just trying to fully grasp the concept of things and if it worth me having it done.

    I can very easily just cycle the bolt differently when dry firing, but I'm the type of person that will not just leave it be, it should he working right.
     
  8. boltfluter

    boltfluter Gold $$ Contributor

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    Can't make out what the second picture is showing us.

    Thanks, Paul
     
  9. Fast14riot

    Fast14riot

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    Look closely at the cocking cam and fully cocked notch, the left shows it smoothed out and lowered the cam angle, right appears to be factory.
     
  10. boltfluter

    boltfluter Gold $$ Contributor

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    Ok, makes sense now. Just wasn't sure I if I was missing something.

    Thanks, Paul
     
  11. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    What your seeing is normal. Its how the action is designed. If you eliminate cock on close you will not have this. But if you eliminate cock on close on a rem 700 (without doing the whole job) you will not have enough fall. Maybe .210" Your math or measurements are off.
     
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  12. Fast14riot

    Fast14riot

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    I appreciate the advice, the difference I am seeing between cocked and and then closed is about .035", is there more going on that I am not aware of? I've read many of your posts on the subject trying to piece together exactly where and how much should be needed. Unless it's the combination of reducing sear surface and the cam that is making the larger number, which then is when you would have to shorten the pin and lower the total cam surface? Am i correct? Clear as mud?

    I will pull the action tonight and investigate more thoroughly, I'm still somewhat new to the intricate details of bolt guns, I've been a gas gun guy mainly when it comes to fine tuning.
     
  13. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    You have to measure right when the top lever touches the cocking piece and again just after the cock on close is done, subtract the amount the shroud backs up do to thread pitch and the angle at which the two measurements were taken. That is how much cock on close you have. Thats how much need to be removed from the cocking piece and how much pin fall you will lose. I have done a lot of Remingtons, the depth the the cocking cam prevents move than about .210 of pin fall if setup without cock on close. Thats what it all comes down to the cocking cams on every bolt out there except a Borden and some PTGs do not have the depth to allow smooth close AND enough pin fall. Thats what I do, I recut the cocking cam helix. Thats why timing and action is not as simple as grinding a cocking piece. My advise is, unless you are willing to recut the cocking cam to the correct angle and depth, live with the cock on close. You will experience accuracy issues in the .220-.230 pin fall range. I have cured accuracy issues due to this, it is a fact.

    Cock on close is an obnoxious feeling. But to me, it feels terrible whether you have .040" or .010". Simply reducing it doesnt really help the feel that much, you have to eliminate it. Honestly if you are gonna have cock on close I prefer a lot of it right from the start, at least its is smooth (even if its stiff) that way without the clunkyness.
     
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  14. Fast14riot

    Fast14riot

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    Ok, that's the information I was missing from your other posts on the topic. I understand that now. This is not something I am tooled up to do, but I do want a thorough understanding of the process if I do have it done.

    Thanks.
     
  15. rayjay

    rayjay Silver $$ Contributor

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    Why not put in a stiffer main spring to make the lower pin fall have the same impact energy ? Also, for a bench gun you could add weight to the firing pin. You lose on lock time but gain back ign. There is a lot of debate about this on rimfire BR rifles.
     
  16. rayjay

    rayjay Silver $$ Contributor

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    I measured my Viper and it's got about .195 pin fall if my sleepy brain is doing the math right. My modified 700s have around .235 . It looks like I ground the cocking piece about .060. Note that all these measurements are ballpark wrestling with a dial caliper, not using a dial indicator and careful setup.
     
  17. rayjay

    rayjay Silver $$ Contributor

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    Hmm, if you reduce the firing pin fall but add weight is the lock time the same as a lighter pin moving farther ?
     
  18. rayjay

    rayjay Silver $$ Contributor

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    Of course with a stiffer spring the bolt handle feel will probably let you know whether it's a good trade off or not.
     
  19. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    It just doesnt work out that way. Fall=time for the pin to accelerate. You can add weight and spring but it will not make up for lack of fall and still be an action youd like to use. The heavier the pin the more spring you need to get it moving. Its also not about energy numbers. Otherwise a light fast pin would work as well as a heavier slower pin and we know this is not the case. Light fast hammer vs a slow hammer. I am confident in standard weight pins, with standard 22-24lb springs and a minimum of .240" fall for optimum accuracy. I have seen accuracy loss with the above and .220" fall. If there was an easy way to time an action with no negatives, trust me I'd be doing it.
     
  20. rayjay

    rayjay Silver $$ Contributor

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    I just had sticker shock that the PTG cocking pieces are $27.
     

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