Cutting for cock on close

[urbanrifleman]

So... nobody tear me apart. I have no dog in the fight.

Remington 700

So, you get the bolt handle just in the right spot for perfect geometry. Perfect bolt handle clearance and excellent primary extraction.

You close the bolt and you can see the firing pin being pushed back and there is a hard spot.

Can you cut the firing pin cocking piece to relieve the cock on close? If yes, how?

 

[Dusty Stevens]

You can move the sear surface forward if thats easier. Youll need a surface grinder

 

[Edd]

.....Can you cut the firing pin cocking piece to relieve the cock on close? If yes, how?

Yes you can. You can also buy a replacement from PTG that is already trimmed .030" shorter.

You will reduce the firing pin fall by the amount you trim so the first thing you must do is measure how much cock on open you have and how much pin fall you have. You will probably have to do some other mods to maintain enough pin fall.

 

[natdscott]

You can move the sear surface forward if thats easier. Youll need a surface grinder

We’ll all of course assume he is not using a factory XP trigger...

..but for the readership, do not be grinding on triggers with sintered metal bits. Savage 10/110 trigger(s) and I believe the Rem. XP crappers have sintered bits. Wear, or cut, through the hard case, and watch out.

 

[natdscott]

Yes you can. You can also buy a replacement from PTG that is already trimmed .030" shorter.

Or Jim Borden, if you want one correct the first time.

 

[clowdis]

You have to get a measurement of how much cock on closing you have. You can do that by measuring from the end of the firing pin to the shroud and that's how much you'll have to remove from the cocking piece to relieve the 'cock on close'. Take the cocking piece and cut the area that catches the trigger sear and move it back the required amount. Sounds easy but there are angles that need to be cut exactly right.

 

[urbanrifleman]

We’ll all of course assume he is not using a factory XP trigger...

..but for the readership, do not be grinding on triggers with sintered metal bits. Savage 10/110 trigger(s) and I believe the Rem. XP crappers have sintered bits. Wear, or cut, through the hard case, and watch out.

I have one that was trimmed. It works good but I cannot polish that surface no matter how much I try. I think it is soft.

 

[urbanrifleman]

Is possible that once the hook is relieved the FRONT of the cocking piece is now too long and will drag across the bolt body as you close the bolt?

 

[natdscott]

I have one that was trimmed. It works good but I cannot polish that surface no matter how much I try. I think it is soft.

Sure is.

It also will not hold adjustment well over time, and can eventually lead to function issues.

I stoned a Savage once, starting with about 400 grit I think, and it worked out, but it’s still sketchy and I was prepared to replace the part if I got too deep.

I am not a metallurgist though, so I have no quantitative idea how deep that case goes.

 

[carlsbad]

I adjust cock on close for all my rifles. It takes a while since you have to disassemble the firing pin between each cut.

If you cut it down on a stock remington bolt, you may find that you have inadequate firing pin fall. Opinions vary here.

On a PTG bolt, I find that before adjusting I have huge cock on close--perhaps .050". After cutting down the cocking piece I generally have around .230-.240 pin fall which is perfect.

I use a solid carbide endmill at high speed to get a mirror finish.

--Jerry

 

[Alex Wheeler]

A stock Rem 700 is designed to have .275" of firing pin fall. We have found that .240" is a good number with Remington style ignitions in custom actions that have improved firing pin guidance. Under .230 is asking for ignition related accuracy problems in a 700 style ignition.

 

[mike a]

I like this thread as it provides some information that’s not talked about much. I have a basic understanding of cock on close but wonder if there is some amount of cocking happening on open and some amount or “ the rest” on close. Speaking of Rem700 that is. I have two Bighorn TL3 and they both open and close very smoothly. I also have a Bighorn Origin and it is much more difficult to close the bolt. Sort of just like Urban is discribing. I run the Bix n Andy tacsport pro triggers. I’m wondering if a different trigger would change things. Of course I haven’t talked to the manufacturer. Why would I do that. Lol. Mike

 

[Dgd6mm]

Bighorn makes different cocking pieces for some triggers for the Origin action.

 

[mike a]

Bighorn makes different cocking pieces for some triggers for the Origin action.

Thanx, I do know the Bix n Andy makes different sears but didn’t know about different cocking pieces. I think I’ll give them a call. I feel I may be hyjacking this thread. I brought up Bighorn as it a 700 clone and cocking was the subject.

 

[urbanrifleman]

The more I play around with it it seems like it's a no-win situation. If you wanted to get it to work smooth and you remove the material off a cocking piece to wear it smooth you no longer have .25 pinfall no matter what you do. I have also noticed that if you receive a bolt with an action that's actually got the bolt handle very tight up against the bolt shroud in the back which gives you a lot of primary extraction the Bolt feels very clunky. I figured this is because it's interacting with the ramp in the back. My favorite bolts in my favorite actions that are smooth as silk aren't super tight for primary extraction it almost seems like leaving a little slop in it actually can drastically improve the smoothness of the bolt even though you lose a bit of primary extraction it still has plenty of primary extraction to function perfectly fine but not a severe amount.

 

[urbanrifleman]

I'm kind of Ball parking the measurements but it appears to be to really get one super smooth with the cocking piece you end up with about 215 of fall

 

[urbanrifleman]

The more I think about this tell me if I'm wrong, but it seems the fix isn't to remove material from the cocking piece claw but the fix would be to add material to the front post that fits into the notch which would move the entire assembly rearward which would actually give you more pinfall and move the cocking piece Claw rearward at the same time

 

[dnellans]

Adding material to "the post" that rides the cocking cam (or conversely, decrease the depth of the cocking cam cutout) it will set the firing pin back from the bolt face by the same amount and you could end up with not enough firing ping protrusion through the bolt face. If you do that, you then need to offset it with a longer firing pin.

Because you don't want to decrease firing pin protrusion (unless its too much, which is rare since that will lead to pierced primers) the pin fall stop isn't easily adjustable.

That means to decrease cock on close you're left with decreasing the total cock distance by changing the sear handoff slightly (described above filing, milling, polishing) up to the point you don't have enough firing pin fall. As Alex mentions above though, you might already have excess fall (2.75) versus 2.5 and could reduce it without issue.

Anything beyond this starts requiring "real" gunsmithing to improve it, AFAIK.

All that said - I wish my Borden actions didn't have as much cock on close as they do - but he said people prefer some to lighten the lift a bit so thats what he's doing now

 

[urbanrifleman]

Adding material to "the post" that rides the cocking cam (or conversely, decrease the depth of the cocking cam cutout) it will set the firing pin back from the bolt face by the same amount and you could end up with not enough firing ping protrusion through the bolt face. If you do that, you then need to offset it with a longer firing pin.

Because you don't want to decrease firing pin protrusion (unless its too much, which is rare since that will lead to pierced primers) the pin fall stop isn't easily adjustable.

That means to decrease cock on close you're left with decreasing the total cock distance by changing the sear handoff slightly (described above filing, milling, polishing) up to the point you don't have enough firing pin fall. As Alex mentions above though, you might already have excess fall (2.75) versus 2.5 and could reduce it without issue.

Anything beyond this starts requiring "real" gunsmithing to improve it, AFAIK.

All that said - I wish my Borden actions didn't have as much cock on close as they do - but he said people prefer some to lighten the lift a bit so thats what he's doing now

Myself, I don't really mind the cock on close really, what I hate is the "catch" as the cocking piece tries to jump on to the sear. It is right at the top.

Adding a fillet to the leading edge of the front lug seems to help with that a bit.

It's like your robbing Peter to pay Paul. You fix one thing and mess up another.

 

[carlsbad]

I hate cock on close--or more hate the difficult closing that comes with it. Reducing cock on close to minimal reduces closing force by more than half. -Jerry