Cutting for cock on close

[mike a]

Is there some literature with pictures or videos out there on this. Honestly I just can’t really GET IT with text alone. Would be nice to know, even though it’s a step above what I could fix.

 

[mike a]

If I lift the bolt and the cocking piece ends up in this position is that not fully cocked? Seems to me there could be no cocking on close. It’s cocked! Showing my ignorance here.

 

[WSnyder]

If I lift the bolt and the cocking piece ends up in this position is that not fully cocked? Seems to me there could be no cocking on close. It’s cocked! Showing my ignorance here.

What they are referring to is when you go to close the bolt there is a small additional cocking of the firing pin as the lugs ramp up the ramps in the action right as you start closing the bolt. Right at this point the cocking piece is stopped by the sear bar in the trigger and as you close the bolt there is a small amount of "cock" as you start closing the bolt. You can feel and see the bump when the cocking piece moves the additional .030-.050" or so out of the shroud. Make sense?

 

[HPC]

A new example from a Remington 700 trued with a PT&G bolt and firing pin assembly.

Cocking piece protrusion with the bolt not in battery: 0.030
Cocking piece protrusion with the bolt in battery: 0.073
Cock-on-close: 0.043

Cocking piece with the bolt in battery: 0.073
Cocking piece in the fired position: 0.220
Total firing pin fall: 0.293

Total firing pin fall: 0.293
Minimum firing pin fall (my number): 0.250
Maximum amount to be removed from either the cocking piece or sear to reduce cock-on-close: 0.043

 

[Edd]

A new example from a Remington 700 trued with a PT&G bolt and firing pin assembly.

Cocking piece protrusion with the bolt not in battery: 0.030
Cocking piece protrusion with the bolt in battery: 0.073
Cock-on-close: 0.043

Cocking piece with the bolt in battery: 0.073
Cocking piece in the fired position: 0.220
Total firing pin fall: 0.293

Total firing pin fall: 0.293
Minimum firing pin fall (my number): 0.250
Maximum amount to be removed from either the cocking piece or sear to reduce cock-on-close: 0.043

What happened to the ~.020" in bolt shroud movement?

 

[HPC]

What happened to the ~.020" in bolt shroud movement?

Are you referring to the bolt shroud movement with rotation in relation to the bolt as it moves from not in battery to battery?

If it is, I ignore it, because I sneak up on any metal removal value where there is difficulty in measuring precisely what I'm trying to accomplish. Remove 0.010, reassemble and check. The 0.043 value was a maximum, and in the few that I've done, an acceptable feel was achieved before the maximum; that is, roughly 0.025 to 0.030.

What I'm looking for is just a little resistance as the cocking piece climbs out of the holding notch; but nothing that requires real effort moving the bolt handle down.

I'm open to any suggestions to more accurately measure these values in order to provide a better operating platform.

 

[paperpuncher]

So Ive mulled this around in my brain for a bit and would like to ask the experts? Could a person set up the handoff from the striker to the sear to provide minimal cock on close while disregarding (temporarily) firing pin fall. Once the proper cock on close is established and firing pin fall is measured can firing pin fall be added by changing the position of the firing pin in relationship to the striker? In other words just taking a bit off the back of the pin and relocating the pin hole that marries the firing pin to the striker to increase the firing pin fall to an acceptable amount. Im probably missing something here but was curious if this is a workable solution

 

[carlsbad]

Short answer yes but anything you do has it's limitations. Moving the hole is possible. Rotate 90 degrees and drill a new hole (machinist job, not with a hand drill, this is a precision hole).

More common people try to take material off the bottom of the firing pin shoulder. This is limited by how deep the cocking ramp is. You could end up having to reprofile your cocking ramp.

No matter what you do, you'll end up with a bastard bolt with unusual measurements which is error likely later on.

My favorite solution is to replace bolt with PTG bolt. PTG bolt is a nice upgrade and they get the extraction timing right. When you adjust the cock on close you still have adequate firing pin fall.

--Jerry.

 

[Will Henry]

My only concern, as far as additional cocking on closing is concerned, is that the cocking piece does not contact the sear until the bolt handle is lowered. This determined by the location and function of the extraction camming surface. If primary extraction is maximized, cock on close is inconsequential. When the extraction cam is right, the locking lug ramps will just clear when the bolt is opened. WH

 

[paperpuncher]

Short answer yes but anything you do has it's limitations. Moving the hole is possible. Rotate 90 degrees and drill a new hole (machinist job, not with a hand drill, this is a precision hole).

More common people try to take material off the bottom of the firing pin shoulder. This is limited by how deep the cocking ramp is. You could end up having to reprofile your cocking ramp.

No matter what you do, you'll end up with a bastard bolt with unusual measurements which is error likely later on.

My favorite solution is to replace bolt with PTG bolt. PTG bolt is a nice upgrade and they get the extraction timing right. When you adjust the cock on close you still have adequate firing pin fall.

--Jerry.

I notice this with the last ptg bolt I used it had a bunch of FP fall I dont recall the amount but i think a bit over .300" I removed material from the striker and got a nice smooth feel when closing the bolt and still had plenty of fp fall

 

[Alex Wheeler]

So Ive mulled this around in my brain for a bit and would like to ask the experts? Could a person set up the handoff from the striker to the sear to provide minimal cock on close while disregarding (temporarily) firing pin fall. Once the proper cock on close is established and firing pin fall is measured can firing pin fall be added by changing the position of the firing pin in relationship to the striker? In other words just taking a bit off the back of the pin and relocating the pin hole that marries the firing pin to the striker to increase the firing pin fall to an acceptable amount. Im probably missing something here but was curious if this is a workable solution

Thats how its done, but as you shorten the pin the cocking piece will eventually hit the bottom of the cocking ramp and or the inside of the shroud. At that point you have to re cut the cocking cam helix to a different angle based on closing cam design. I have cut 100s of cocking cams to time actions. Now there are enough action manufacturers that have gotten on board and changed things so I very rarely need to do that anymore.

 

[Ksracer]

To answer the OP question about how to cut them.
I do mine in the bridgeport with a cup shaped grinding wheel mounted on an arbor with the correct angle on the corner. I hold the cocking piece in a vertical 3jaw mounted on a rotary table. By turning the cocking piece past the grinding wheel, I can match the original shape.

 

[Edd]

Is it necessary to maintain the original angle on the cocking piece? Why couldn't you just make a vertical cut on it and round the corner a little?