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Dry Firing Jump

 
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  #1  
Old 04-25-2013, 08:02 PM
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Join Date: Dec 2007
Location: Central, KY
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Dry Firing Jump

I've noticed that one of my rifles the crosshairs jump a little when dry firing. Also I did the coin on the end of the barrel test and this gun is the only one that the coin falls off.

I don't think this can be good for consistent precision and accuracy. The rifle is a Rem 700 .308 stress free bedded into a Choate stock.

I have other Rem 700s that don't jump near as much as this one.

Any ideas on how to reduce it?
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  #2  
Old 04-25-2013, 09:06 PM
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Re: Dry Firing Jump

You can reduce it and improve accuracy doing so.
Contrary to popular belief, a firing pin should not be set to excess energy. Excess being more than needed for consistant ignition.
If you load develop with firing pin adjustment you will find a sweet spot where performance is best, and it won't be at any extreme setting.

I do this, after also backing off sear/cocking piece so that it does not bottom in the shroud on release.
Also, if you whitness the bolt turning on dry firing(usually lifting) -that's evil energy right there.
So I also set a bolt turn stop so that the cocking piece will fall freely without resistance, and the bolt ceases to so much as wiggle.
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  #3  
Old 04-26-2013, 05:10 AM
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Re: Dry Firing Jump

Thanks for reply Mike, this sounds like it might need a trip to a gunsmith.
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  #4  
Old 04-26-2013, 07:16 AM
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Re: Dry Firing Jump

Quote:
Originally Posted by scsims View Post
I've noticed that one of my rifles the crosshairs jump a little when dry firing. Any ideas on how to reduce it?
Every fixed power scope I've ever used does that on all my rifles; rimfire and centerfire. Their windage and elevation adjustments are spring loaded pressing the erector tube in the scope hard against the flat of the adjustment screw. It's totally normal that that tube will vibrate a tiny bit and you see that when dry firing.

In most variable power scopes, the two lens groups that slide back and forth when changing power will shift position a tiny bit when dry firing the rifle and that also makes the reticule jump a bit when the rifle's fired; dry or with live ammo. Their fit is not zero tolerance in the tube they slide back and forth in as the power is changed. They also can change position as the power's changed; the reticule moves in an irregular pattern about the collimator. Sometimes as much as 1 MOA. Which is why many folks wanting best accuracy with variable scopes set the power to one limit and keep it there; the scope's more repeatable that way.

As long as the reticule goes back to the same position after jumping from mechanical shock, there's no problem. Put an optical collimator in the muzzle, zero the scope on it then dry fire watching the scope reticule on the collimator's reticule. If it goes back perfectly each time, no worries.

And no rifle action I've used has its bolt jump when firing live ammo. The firing pin tip does not dimple primers enough to let the cocking piece strike the bolt camming surface to push the firing pin back. But when dry firing without a round in the chamber, it's as common as sunrise every morning. If this happens with live ammo, then something needs fixed; probably the cocking piece on the firing pin needs its cam point ground back a few thousandths.
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  #5  
Old 04-26-2013, 08:55 AM
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Join Date: Aug 2011
Location: central Georgia
Posts: 300
Re: Dry Firing Jump

To reduce the dry firing jump , swap the firing pin and spring assembly. I have 7 custom rifles built on LA Rem 700 actions and Sendero stocks . They all had good accuracy potential, but when shooting from the bench I had to hold them differently to obtain the best groups.The ones with no dry firing jump could be held normally, but the ones with dry firing jump had to be held tighter with downward or side pressure applied to the stock to obtain best results. I discovered that by swapping firing pin and spring assemblies that the problem was corrected. This does not last forever, because the spring pressure changes over time. All springs do not work the same in all similar rifles. A firing pin and spring assembly that does not work well in one rifle may be entirely satisfactory in another. The assembly can be changed in a few minutes with only a dime. Gary
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  #6  
Old 04-26-2013, 09:56 AM
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Re: Dry Firing Jump

If its the factory spring on the firing pin, which I'm guess it is, i'd bet 50 bucks its way to long, thus it is binded up inside the bolt body. Check it, if it is have a smith cut it, or put a ptg or wolff spring in it and check the firing pin protrusion and the cocking piece. An aftermarket trigger can also help with the timing of things with tighter tolerances, especially a Jewell. I have had over a dozen 700s and only 1 has had a straight spring in it, the rest were as crooked as a poltician.
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  #7  
Old 04-26-2013, 02:26 PM
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Re: Dry Firing Jump

Quote:
Originally Posted by backwoods83 View Post
If its the factory spring on the firing pin, which I'm guess it is, i'd bet 50 bucks its way to long, thus it is binded up inside the bolt body. Check it, if it is have a smith cut it, or put a ptg or wolff spring in it and check the firing pin protrusion and the cocking piece. An aftermarket trigger can also help with the timing of things with tighter tolerances, especially a Jewell. I have had over a dozen 700s and only 1 has had a straight spring in it, the rest were as crooked as a poltician.
All my firing pin springs scrape the inside of the bolt body. Nary a problem with that.

And no trigger will change how the firing pin operates. It's a different mechanism and does not touch that spring in any way.

And if it's a factory spring, there's no way it would be too long. Anybody want to bet against this?
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