Nucleus bump on close (renamed again)

TexasTightwad

TexasTightwad

Sergeant of the Hide
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May 30, 2018
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DFW, Texas
#1
I am putting together a Nucleus build, and am having an issue. The action cycles just fine by itself, but I added a Timney Calvin Elite trigger (without the Timney bolt release) and it now has a super noticable catch. It occurs as the bolt is rotating closed, and it takes what I'd guess is about 8lbs of force on the knob to overcome.

I know that you have to have the bolt pushed all the way forward so that a pin is released. It's not that. It catches after the bolt has already rotated a little bit. I'm sure it has something to do with how the part on the bottom of the bolt (which I don't know the name for) engages the top of the trigger assembly.

This is my first 700 pattern rifle, so maybe this is to be expected? I hope not, because it makes working the bolt awful.
 
#3
TexasTightwad said:
I am putting together a Nucleus build, and am having an issue. The action cycles just fine by itself, but I added a Timney Calvin Elite trigger (without the Timney bolt release) and it now has a super noticable catch. It occurs as the bolt is rotating closed, and it takes what I'd guess is about 8lbs of force on the knob to overcome.

I know that you have to have the bolt pushed all the way forward so that a pin is released. It's not that. It catches after the bolt has already rotated a little bit. I'm sure it has something to do with how the part on the bottom of the bolt (which I don't know the name for) engages the top of the trigger assembly.

This is my first 700 pattern rifle, so maybe this is to be expected? I hope not, because it makes working the bolt awful.
Click to expand...

Call Timney, they are aware of issues with the Nucleus and working on it, from what I understand. Can't remember his name, but he was looking for feedback on Facebook.
 
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#4
I'll have to do that. Playing around with it more, I've found that the more forward force applied, the less rotational force required. My guess is that the lugs are making contact on an angled surface and are not quite far enough forward to lock. To rotate and lock, they need to pull themselves and the whole bolt forward, and at that point it is being resisted by the firing pin spring. That's my guess at least, and I don't see any solution.
 
#5
Typically when moving the bolt forward the bolt will hit a hard stop preventing the cocking piece from striking the sear, at that point the bolt must be rotated to begin the engagement of the cocking piece and the sear.

On the nucleus there is a bolt shroud locking pin that makes contact with the receiver unlocking the shroud from the bolt.
This spring loaded pin needs to be depressed by the bolt being pushed fully forward allowing the bolt to be unlocked.

You need to apply forward pressure on the bolt while rotating the bolt to close it.
 
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#7
In that video, you can see that as the bolt unlocks and goes over the point where the catch is, the bolt head jumps up and to the left (toward the ejection side). It does the same in reverse when locking, but it's harder to see because it is moving fast after I overcome the catch.
 
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#11
I didn't have your issue and I can't help, but I can give you some troubleshooting advice if you're interested. You suggested you only noticed this AFTER adding your trigger? If that's the case, remove the trigger and use a black magic marker to mark the face of the cocking/trigger engagement surface. Before re-assembly test without the trigger to confirm your suspicions. Now add the trigger on, run the action a few times, again demonstrating that you've introduced this new behavior, and then remove the bolt and get a picture of the cocking/trigger engagement surface. You should have some visibile indiication of what is hanging up and where.
 
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#12
Is the cocking piece rubbing on the sear when you're running it? You may have a bunch more sear engagement than you want. Having someone tune the trigger by stoning the sear is an option get proper sear engagement. Your top sear may be running out of travel and bottoming out when you're closing the bolt, causing the cock on close condition. That looks like a pretty bad case of it, if that's what is happening.

I ended up going with Bix'N Andy TacSports because you can order the right height sear and tune the sear engagement from the bottom while in the stock. Helped my ARC actions a bunch. Timney will likely be able to help too. They may know of this issue with the Nucleus. Unfortunately even though it's all supposed to be drop in and go, not always the case with custom actions.

First part of this video goes over why you need the right height sear for trigger tuning.
This video shows a cock on close condition -
 
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#13
My Mausingfield/Huber combination had this issue. The bolt manipulation was pretty terrible. I switched to a TriggerTech and it eliminated the issue. I think it's just stacked tolerances.
 
#16
ddavis said:
My Mausingfield/Huber combination had this issue. The bolt manipulation was pretty terrible. I switched to a TriggerTech and it eliminated the issue. I think it's just stacked tolerances.
Click to expand...

Like as it was with me except my trigger was the Timney Calvin Elite.

TT won the single stage trigger wars by a huge margin IMO, nothing better than that Diamond Pro.
 
#18
TheOE800 said:
Isn’t it “be like it is” ?
Click to expand...
You are correct fellow meme god
they-dont-think-it-be-like-it-is-but-it-do.jpg
 
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#20
M5B2CFF said:
Is the cocking piece rubbing on the sear when you're running it? You may have a bunch more sear engagement than you want. Having someone tune the trigger by stoning the sear is an option get proper sear engagement. Your top sear may be running out of travel and bottoming out when you're closing the bolt, causing the cock on close condition. That looks like a pretty bad case of it, if that's what is happening.

I ended up going with Bix'N Andy TacSports because you can order the right height sear and tune the sear engagement from the bottom while in the stock. Helped my ARC actions a bunch. Timney will likely be able to help too. They may know of this issue with the Nucleus. Unfortunately even though it's all supposed to be drop in and go, not always the case with custom actions.

First part of this video goes over why you need the right height sear for trigger tuning.
This video shows a cock on close condition -
Click to expand...


Those videos were helpful. I seem to have a tiny bit of cocking on close.

Measuring the depth from the back of the bolt shroud to the face of firing pin head (the thing with the torx socket in the center of the back of the bolt) gives some insight as to what is going on. The bigger the depth measurement, the farther forward the cocking piece and firing pin are. It measures .040" with an open bolt, .0535" when rotated to the catch, .049" just past the catch, and .0545" with a closed bolt. The catch coincides with the cocking piece contacting the top sear of the trigger. After that, any changes in depth are because the bolt/bolt-shroud has moved while the cocking piece/firing pin has stayed still.

There is only .0045" of cocking on close. I really don't think that would be considered excessive or that you could blame the trigger. I think the issue lies in the locking lugs.
 
#22
I found the problem. I have two bolt heads, and on both of them, one of lugs was machined improperly. The lead-in must have been cut with a worn-out tool, leaving burrs hanging off and less material removed. That makes all the pressure be put on that one lug as it is locking up, rather than spread out among three, and kicks the bolt to the side as it rotates. Once the bolt makes it past the lead-in, all three lugs make even contact.

I took some pictures and I'll be contacting ARC monday. I may change the name of the thread, because the trigger is not at all to blame. It just made me notice the problem because there was pressure on the lugs. Everybody else with a Nucleus, you might want to check to see if yours has the same issue. It is the lug opposite the handle.

A couple of these pictures are of another lug that is properly machined, for reference. The next-to-last picture shows the problem spot most clearly.
 

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#23
Timely thread for me. The nucleus I ordered is in the mail as I type. This issue will be something to look out for. Hope your’s is a rare case and gets sorted out quickly.

This thread is also a reminder, that I need to get off my ass and order a trigger (among other things) ASAP.
 
#25
I have the same issue, the click/catch makes me think this action is worth than a normal savage. I will see how to dremel a bit off that lug, I was wondering why 3 lug look different from the back.
 
#27
Srgt. Hulka said:
You guys are making me nervous. I have $2000 committed to a JHR. I’m a poor MoFo. I can’t afford to dick around with a bunch of high dollar rifles or actions till I find the best one. This is a once in a lifetime purchase for me. If this thing is f***ed up, so am I.
Click to expand...

It’s an issue but the action/rifle still works 100%, it’s just not nice and smooth. Relax.
 
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#28
FWIW (admittedly not much), I just checked my (LA) Nucleus, and neither of my bolt heads (.473 and .535) exhibit the issue described. I also installed my trigger (basic bitch Timney 517) for a quick function check with the .473 bolt head installed, and it worked just like you'd hope... nice and smooth with no binding or other issues.

I know that does nothing to resolve the OP's problem, but hopefully it will serve as a data point regarding the commonality of the issue(s). I'm sure that Ted and the rest of the ARC crew will make things right.
 
#29
Srgt. Hulka said:
You guys are making me nervous. I have $2000 committed to a JHR. I’m a poor MoFo. I can’t afford to dick around with a bunch of high dollar rifles or actions till I find the best one. This is a once in a lifetime purchase for me. If this thing is f***ed up, so am I.
Click to expand...

I'm sure if there is an issue with your rifle that the manufacturer will take care of it. Both ARC and PVA are great companies so don't sweat it.
 
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#30
TexasTightwad said:
Honestly, I'd be surprised if mine is a rare case. I have two bolt heads in two different sizes, and they both have the same bad lead-in with burrs hanging off.
Click to expand...

Mine is the same but without burs. One lead-in opposite the handle is barely cut out. It is definitely doing the same interference as you described. For reference, mine was one of the first ones off the line.
 
#31
Well, if it is only a few raised burrs that is the issue, I’m not going to sweat ARC over it. Nothing a few seconds with a small slip stone can’t sort out. Just something to be on the lookout for. Thanks for raising awareness.
 
#32
No, it's not just burrs. If you look at my pictures, you'll see that one of the lugs has a lead-in that was not cut properly. The other two lugs have nice pretty lead-ins, and the third is almost uncut. It's maybe .010" deep, and most of the material that was there is smudged to the side. As a machinist, that tells me the likely cause was a worn-out tool.

If it was just burrs, I'd remove them and move on, but it's not. I can't close the action without significant force on the handle, and then jerking after it passes the catch. That means I'll have to reaquire the target after every shot.
 
#34
TexasTightwad said:
No, it's not just burrs. If you look at my pictures, you'll see that one of the lugs has a lead-in that was not cut properly. The other two lugs have nice pretty lead-ins, and the third is almost uncut. It's maybe .010" deep, and most of the material that was there is smudged to the side. As a machinist, that tells me the likely cause was a worn-out tool.
Click to expand...

This sounds like mine except I don't have material pushed to the side or burs. It's more like the lead-in was just cut different (less) than the others.
 
#37
TexasTightwad said:
Yes.
Click to expand...

The burrs are not acceptable.

However, the ramp on that bolt lug is shorter because of the slot cut into the lug for the ejector. If you look at the other bolt lugs, they are wider. The other two lugs are wider so the lead in is longer.

My two Nucleus have the same sort of click that yours does. One with a Huber and the other with a Diamond. I might try to look into trigger sear engagement, but I never noticed it in PRS competition. Might have something to do with coming from a Savage...

EDIT: Running the bolt full speed, I don't really notice it at all. Nuleus apparently like to be run hard for CRF and for what you are describing as far as what my actions feel like. You may have a more serious problem than me, but for me running it hard that click goes away. I suppose that is why I don't notice it at a match.
 
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#39
Srgt. Hulka said:
You guys are making me nervous. I have $2000 committed to a JHR. I’m a poor MoFo. I can’t afford to dick around with a bunch of high dollar rifles or actions till I find the best one. This is a once in a lifetime purchase for me. If this thing is f***ed up, so am I.
Click to expand...

Yup, same here... My excitement with my pre ordered John Hancock is all but gone. I’m new to this and don’t have the skill or even knowledge to have even figured this out if it was my rifle.

Perhaps, selling my spot might be the best option at this point
 
#40
Re: JHRs... I am certain that the issues described and shown by the OP would be apparent during a basic function check at PVA, and would be addressed prior to shipping. I am confident that those rifles, once delivered, will be the bang-for-the-buck for which purchasers hoped.

Regarding the issues with the Nucleus bolt heads, let's not get ahead of ourselves regarding the commonality of the problem... there are only a couple of folks who have spoken up about it, and (AFAIK) no one from ARC has yet had an opportunity to address it. The good news is that due to the design of the bolt, it would be possible for replacement bolt heads to be sent out on an exchange basis for any that exhibit the issue. Let's all take a deep breath and let the manufacturer have an opportunity to investigate/address this before we go all interwebz crazy about it.
 
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#41
BurnOut said:
Re: JHRs... I am certain that the issues described and shown by the OP would be apparent during a basic function check at PVA, and would be addressed prior to shipping. I am confident that those rifles, once delivered, will be the bang-for-the-buck for which purchasers hoped.

Regarding the issues with the Nucleus bolt heads, let's not get ahead of ourselves regarding the commonality of the problem... there are only a couple of folks who have spoken up about it, and (AFAIK) no one from ARC has yet had an opportunity to address it. The good news is that due to the design of the bolt, it would be possible for replacement bolt heads to be sent out on an exchange basis for any that exhibit the issue. Let's all take a deep breath and let the manufacturer have an opportunity to investigate/address this before we go all interwebz crazy about it.
Click to expand...

You’re right - just a bit too over paranoid on my part I guess.
 
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#42
**DRB** said:
Yup, same here... My excitement with my pre ordered John Hancock is all but gone. I’m new to this and don’t have the skill or even knowledge to have even figured this out if it was my rifle.

Perhaps, selling my spot might be the best option at this point
Click to expand...

I think that the "click" is really no big deal, and certainly not a defect with my action. And, the "shorter lead in" on the lug with the cut for the ejector is not a defect.

When running the bolt fast, there is absolutely no noticing the "click". Now, if you like to sit at the bench and run your bolt slow, then there might be a better feeling action for you. I can run my Nucleus from a barricade and stay on target cycling the bolt. There is a HUGE difference for me running it slow and running it fast. I never noticed the "click" until this thread. I think that says something about it. Here is a video of me running it on a barricade. There are many things I would change before the way the Nucleus runs...



The Nucleus is a great action, but there is no perfect action. I know lots of people who don't like one thing or another on it. That is why there are all sorts of everything we buy, no accounting for personal taste, LOL... This thread is way ahead of itself in my opinion. Before you lose all your excitement, post in the Nucleus Order thread and ask for feedback. But, I am sure that there is someone who would buy your spot in line. If I had more money right now, I would have bought some other spots in line... All my new rifles will be Nucleus actions. I'm slowly selling the odds and ends that I have, because the Nucleus bug has hit me.

If you think it is a deal breaker that it has a click, then get a different action I guess.
 
#43
**DRB** said:
You’re right - just a bit too over paranoid on my part I guess.
Click to expand...
If this is your first custom, I think you have made the best choice and wise investment. Innovative design, bomb proof construction and top layer materials.

For folks like myself who are spoiled by custom rifles, I just need to remind myself how much I paid. There are many reasons for the introductory price and potential minor issue is one of them. I totally trust ARC will address it if it’s really a common problem.
 
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#44
cageli said:
If this is your first custom, I think you have made the best choice and wise investment. Innovative design, bomb proof construction and top layer materials.

For folks like myself who are spoiled by custom rifles, I just need to remind myself how much I paid. There are many reasons for the introductory price and potential minor issue is one of them. I totally trust ARC will address it if it’s really a common problem.
Click to expand...

First “custom” and most expensive firearm I will have purchased...

Admittedly- I’m probably just being a pain in the ass.
 
#46
Yeah, you probably have nothing to worry about with the John Hancocks. As others have said, when they leave PVA they will have triggers installed, at which point if they had the same defect as mine it should get caught. I understand why it did not get caught at ARC. It's a very small detail in the midst of a lot of other details, and with no trigger on it there are no symptoms. We're all human and I am not upset that it happened, I just want it fixed.

I did not intend to scare people who are waiting on their orders. Just wait until it comes in and see. I am assuming ARC will take care of this, so as long as they do it's not a big deal to me.

I did however intend to find out if anyone else was having this problem, and make people aware that if their action is not acting right, it might be a defect that (I assume) ARC would be happy to fix. Better to have a fixed problem than have people trash-talking their actions.

@hereinaz Perhaps your bolt heads are cut correctly or at least closer than mine. It is a major catch on mine, and not tolerable on any rifle no matter the price point.

hereinaz said:
The burrs are not acceptable.

However, the ramp on that bolt lug is shorter because of the slot cut into the lug for the ejector. If you look at the other bolt lugs, they are wider. The other two lugs are wider so the lead in is longer.

My two Nucleus have the same sort of click that yours does. One with a Huber and the other with a Diamond. I might try to look into trigger sear engagement, but I never noticed it in PRS competition. Might have something to do with coming from a Savage...

EDIT: Running the bolt full speed, I don't really notice it at all. Nuleus apparently like to be run hard for CRF and for what you are describing as far as what my actions feel like. You may have a more serious problem than me, but for me running it hard that click goes away. I suppose that is why I don't notice it at a match.
Click to expand...

When I get home, I'll try to get some measurements from the bottom of the lead-ins to the grooves in each of the lugs.
 
#47
Mine has no burrs in either of my bolt heads, standard and magnum. I get the same result with either bolt head installed. With one trigger it is smooth, with the other there is a very noticable catch when closing the bolt slowly. Both triggers are trigger tech diamonds. With the trigger that catches installed you can see that it slightly cocks the firing pin as you start to close the bolt. Like others have stated, you don't really notice it when you run the bolt hard.
 
#48
I tried comparing measurements between the three lead-ins, but was unable to. There are almost no flat surfaces to measure off of, and all three lugs are a bit different.

Looking at ARC's CAD rendering pictures on their website, it does look like the lead-in next to the ejector slot is intended to be smaller than the others. So it may not be far off of what it is supposed to be, but I still say it is off. Again, that kind of burr is a sign of a worn tool; I can watch the bolt head push away from that side as it works through the catch (indicating contact on that lug but not the others) and there is no wear on either of the other two lead-ins, just that one. In fact there's globs of undisturbed grease in the action where the other two lead-ins should be making contact.
 
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