I hope you post your results, I swapped out to a 19lb spring while I only had 2 misfires on my rifle, they were my error as I assume my primers were not fully seated and I was using ammo i had loaded for a previous barrel. I may also swap back to the 16lb spring and see if I can get by. The 19lb has been working flawlessly for around 200+ rounds but I too can notice a bit of bolt lift difference. It is enough that I roll the rifle occasionally when extracting a spent round. With the 16lb spring I had zero issues with the rifle wanting to roll.
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Nucleus Light Primer Strikes
- Thread starter ThePretzel
- Start date
I hope you post your results, I swapped out to a 19lb spring while I only had 2 misfires on my rifle, they were my error as I assume my primers were not fully seated and I was using ammo i had loaded for a previous barrel. I may also swap back to the 16lb spring and see if I can get by. The 19lb has been working flawlessly for around 200+ rounds but I too can notice a bit of bolt lift difference. It is enough that I roll the rifle occasionally when extracting a spent round. With the 16lb spring I had zero issues with the rifle wanting to roll.
Shot my Lapua brass and srp for the first time and had my first failure to fire in 500-600 rounds with my LH short action 16# spring shot about 40-50 rds each with cci450s and fed205m the FTf was the first round of the day and a cci450 which is a known issue however this was my first failure I will probably install my 19# and test things out but my sd/es I’ve been getting leads me to believe I’m getting very consistent ignition otherwise
the first two strings were the first 10 shots of the day and the first string includes the ftf that went off the second time I fired
Just for more data points...
Trigger: XTSP Mod.22 (three lever model)
Pin down: .296"
Bolt up: .043"
Cocked, bolt down: .034" (9 thou cock on close)
Pin protrusion: .042"
The "critical measurement" from the tip of the striker to the castle nut is 1.343" on my action.
Total striker travel is .262", travel to the bolt face is .220".
Haven't fired anything yet, but planning on using CCI No.450's. Getting a little anxious, because using the "power factor" from the last page nets me 3.52, which seems a little weak...
EDIT: I should probably just get the 19 pound spring because that'll get me to 4.18
Trigger: XTSP Mod.22 (three lever model)
Pin down: .296"
Bolt up: .043"
Cocked, bolt down: .034" (9 thou cock on close)
Pin protrusion: .042"
The "critical measurement" from the tip of the striker to the castle nut is 1.343" on my action.
Total striker travel is .262", travel to the bolt face is .220".
Haven't fired anything yet, but planning on using CCI No.450's. Getting a little anxious, because using the "power factor" from the last page nets me 3.52, which seems a little weak...
EDIT: I should probably just get the 19 pound spring because that'll get me to 4.18
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Was The Lapua brass new? if it was measure the case shoulder datum to base of new and fired brass and see what the difference is.
It was virgin brass so that may be a factor but the virgin brass is all within 1 thou of what I bump my shoulders to max difference between the rest of that lot virgin and the 1xfired is .003 it was the first round of the day also the first round of small primer brass I loaded that night so I’m going to chalk it up to that unless It happens again
I would reduce that protrusion .010" if you can. I had far more failures at .040" than .030"
Those numbers are very similar to my 223AI build that has been running great with the 16# spring... I'd start with it and see if it gives you any issues with the CCI 450's just so we can compare. The Nucleus / Mod 22 / 16# spring has not been a problem at all with my 223AI with 7.5 Remington primers, I've only had one misfire and that was because the primer pocket was really, really deep on that one round and the firing pin barely left a mark on it. My Tikka wouldn't set it off either.
That's odd... because of how the Nucleus firing pin, cocking piece, and castle nut arrangement is designed I can't see that making a difference; as long as you have 0.030"-ish minimum FP protrusion you should be good to go unless you run into an abnormally deep set primer. Not saying there can't be a reliability difference between the two settings, I just don't see any mechanical reason why .030" vs .040" of FP protrusion would make any difference in ignition reliability on these actions.
The reason I say that is adjusting the castle nut does not alter the total distance the firing pin travels between the cocked position and when the firing pin tip intersects the plane of the bolt face-- adjusting the castle nut does not alter the dimensional relationship between the cocking piece and sear which is what would alter the amount of firing pin travel. The castle nut only serves to retain the firing pin spring as well as serving as an adjustable stop for the forward firing pin travel by contacting the back of the bolt head. Tightening the castle nut down as far as it will go will compress the firing pin spring a little more as well as allowing more firing pin tip protrusion past the bolt face in the fired position. On both my short and long action, even with the castle nut totally bottomed out I only get a maximum of 0.044" protrusion on one action and 0.047" on the other action. If you unscrew the castle nut to say 0.030" FP protrusion, that may limit the firing pin protrusion from the bolt face in the fired position but it does not alter the distance the firing pin travels from the cocked position to when the firing pin tip intersects the plane of the bolt face. Only the protrusion past the bolt face is affected.
Personally, I'd rather have a little more firing pin protrusion than less just to have a better chance of setting off the occasional piece of brass with a "deep" primer pocket or a case that was FL sized a bit too much.
I'm all ears if there's a reason for the difference in reliability from 0.030" to 0.040" protrusion... more data is always a good thing.
Also for more info, Friday at the range I decided to see if the 19# spring would make any difference on my 223AI build. So far the 16# spring has been working great in my Nucleus with the CG Mod 22 trigger. I changed from the 16# to 19# spring and noticed no difference in velocity/SD/ES on the lab radar and didn't see any difference in how the primers looked. Bolt lift may have been very slightly heavier with the 19# spring, but it was hard to tell; I use a little dab of moly paste on the cocking ramps which really smooths things out. For now I'll go back to the 16# spring, but keep the 19# spring and tools to change it in my shooting bag just in case.
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I'll definitely start with the 16# spring, but I've got a match the first week I get back from school, which is also the first week I anticipate getting it up and running. Load development Monday, Tuesday, verify drop Wednesday, load rounds Thursday, Friday, shoot a match Saturday. It'll be a busy week without worrying about light strikes!
I'm also shooting strictly handloads, so I'm going to headspace off virgin Lapua plus a couple thou, so that should eliminate any virgin brass issues on my specific rifle.
Looking at the pin, what you're saying makes sense. I don't think adjusting the castle nut will effect the pin's cocked position.
That being said, at .040ish protrusion, I had a high rate of failure.
Likewise @tomcatfan had similar issues when he switched to the 19lb spring and just screwed the castle nut all the way in to increase protrusion. After reducing protrusion to .030" or so, hasn't had issues.
If I have read and understand boehms post on protrusion correctly, the reason you have less issues with .03 vs .04 is that at .04 you have decreased the springs length of expansion from compression and thus lost some of its energy.
If you modify the pin protrusion by changing the length of the pin, yes this is the case. However with the Nucleus action, the castle nut does not modify the length, instead it just serves as a stop for forward movement. The pin should travel the same amount regardless.
That being said, my experiences have been the opposite and less protrusion has proven more reliable. However that is just one data point. It's possible I did not adequately clean out the pin when I had it set for a longer protrusion.
I will report back when I have a chance to shoot my new 6X47L. After reading all of your posts, I contacted ARC and asked if I could ship them my bolt for inspection. They changed my bolt head to the latest design and put in a new 25lb spring. They were extremely helpful and turned it around very quickly. I have nothing to compare it to since I never fired the rifle, but it still feels pretty smooth upon bolt lift. I know it’s not optimal people have had issues, but in my case they have been great to deal with.
That’s good to hear.
I have a nucleus on order and I’m going nuts waiting for it.
Well it appears misery loves company.
Today I am shooting my Nucleus and at 305 rounds total it stopped igniting primers, done, finished.
I have been using CCI450s mostly and some Federal 210Ms. Crazy it craters both.
It was shooting fine then nothing but light primer strikes.
WTF its like the spring lost its mojo.
I get home I take the bolt apart everything looks fine but there is some oil around the firing pin.
The bolt was previously cleaned spotless but it appears that some oil seeped in there.
I cleaned the entire assembly put it back together and tested it using a fired case with a new primer and it still will NOT ignite a primer
The pin protrusion and the dimension to from the castle nut to the tip is correct.
Bolt is going back. Annoying.
I think this thread jinxed my spring.
Today I am shooting my Nucleus and at 305 rounds total it stopped igniting primers, done, finished.
I have been using CCI450s mostly and some Federal 210Ms. Crazy it craters both.
It was shooting fine then nothing but light primer strikes.
WTF its like the spring lost its mojo.
I get home I take the bolt apart everything looks fine but there is some oil around the firing pin.
The bolt was previously cleaned spotless but it appears that some oil seeped in there.
I cleaned the entire assembly put it back together and tested it using a fired case with a new primer and it still will NOT ignite a primer
The pin protrusion and the dimension to from the castle nut to the tip is correct.
Bolt is going back. Annoying.
I think this thread jinxed my spring.
The trigger is a TT diamond, there is no issue with the trigger as I get .251 firing pin travel.
I started with Hornady brass and 210Ms then Lapua brass and cci450s they were working fine then someone pushed the off switch.
95% of the ammo fired in this action has been with cci450s without issue.
Yikes!
Just paid my final invoice and set up the FFL trans so hopefully I’ll be shooting my Nucleus next week.
Are we ever going to get a disassembly/reassembly video? Since there really is no manual and ARC stated that the actions they got returned from customers for light strikes were due to user error on assembling the bolt.
This is technically correct, but it misses the point.
The total amount of pin travel is the same. HOWEVER, the amount of pin travel before it strikes the primer is not the same. You're adding to the amount of travel before the pin reaches the primer, which means more usable energy (kinetic energy of the pin at the time of impact) is delivered to the primer because the pin is traveling faster.
0.030" of protrusion is plenty to ignite the primer unless you are seating them super loose inside the primer pockets. All you do by using 0.040" of protrusion instead of 0.030" of protrusion is reducing the total energy delivered because as soon as the firing pin touches the primer the pin will begin to decelerate as it starts compressing and deforming the primer cup.
Same total energy when dry firing/same total potential energy does not mean there is the same usable force applied to the primer. It's the same reason that you can remove your trigger and close the bolt on a live round without it going off if you're careful. Steady pressure from the spring once the pin is touching the primer will be less effective than a faster moving firing pin. This is because the explosive contained within primers is shock sensitive, not necessarily pressure sensitive.
What’s your bolt lift like since it’s almost double the spring weight out of curiosity? I’d imagine it would torque the rifle a bit (although I don’t know whether a heavy or light spring impacts that).
This is the diagram they posted. There is a video about disassembly, but this picture shows where grease should go and not go.
Attachments
You are in the same shape I was in,mine had around 300 rounds without a hiccup. Then out of the blue it would fail to set the exact same loads that it had flawlessly set off for 300 or so rounds. I cleaned all the oil and checked everything arc said,cleaned again and still no fix. Mine is a pretty early serial number,I just sent bolt back to ARC Tuesday,so hope the get this figured out. Been this way since last fall.
I’m only at 91 Rounds on my preorder nuk. 16lb spring. All factory ammo with LR primer, no issues of any kind yet. I am hoping things hold up. I really like the action the short throw, feeding and ejection have been smooth and robust. Curious about the 25 lb spring and the revised bolt head even though I haven’t had any issues yet. Hopefully long term reliability holds up
I’ve had no issues with any factory ammo or any primers other than the CCI 450’s.
Received an email this morning from ARC. They will be sending 25# spring free of charge. Surprised since I emailed about a month ago and got a basic reply.
Doesn't it kind of defeat the purpose that we want a light bolt lift but are given a 25# spring that makes it heavier? Am I the only one thinking that this nucleus action sucks?
You probably have more aggressive cocking cams to increase the amount of firing pin travel compared to the Nucleus action. You don't have any weight added to the bolt lift from primary extraction cams with the Archimedes, which means you can use the work that was previously used for extraction and redirect it towards additional firing pin compression without feeling any difference in the bolt lift. It's probably a very minor thing if it's anything at all though, I wouldn't be surprised if Ted is using the same design for the cocking cams as on the Nucleus.This ain't helping my Archimedes pre-order anxiety.
I'd be willing to bet dollars to doughnuts because of this that the Archimedes will come standard with the 25# spring...
So far, I haven't had any issues either. I also have a TT Diamond and also a 6.5 CM.
This may have been answered but does anyone know around what serial numbers did ARC start using anything other than the 16# spring?
I scanned back over this thread and didn't see where Ted or ARC has formally addressed this. If they have, can someone provide a link to the post?
I am still under 200 rounds. I have been diligent about keeping the bolt and the bolt internals clean so I am hoping these issues won't surface.
To my knowledge they haven't used anything standard besides the 16# spring except in actions they were sending to PVA (in standard and John Hancock form).
On the Nucleus, since the castle nut adjustment does not change the effective length from the sear catch on the cocking piece to the firing pin tip, the firing pin will travel the same distance from the cocked position against the sear to when the firing pin tip passes the plane of the bolt face regardless if you have 0.010" or 0.040" of FP protrusion set via the castle nut.
If you want to verify, try the following:
Set FP protrusion to say 0.010", then measure the distance from the firing pin tail to shroud in the cocked position (bolt closed and against the trigger sear), and then measure again in the fired position, then subtract the 0.010" FP protrusion. That's the total FP travel from cocked against the sear until the firing pin tip crosses the bolt face.
Now reset the castle nut to 0.040" FP protrusion and repeat the exercise. This time subtract the 0.040" protrusion from the cocked to fired difference measurement. You'll get the exact same number as above; with the design of the Nucleus firing pin, cocking piece, and castle nut arrangement, the firing pin falls the same amount from the cocked position to when the firing pin tip crosses the bolt face so the amount of FP protrusion you set will not affect the potential energy of the system.
On the other hand, take an AI action for example where the FP protrusion is set by screwing or unscrewing the firing pin from the cocking piece and the firing pin forward travel is stopped by the cocking piece bottoming out in the bolt shroud in the fired position. When you screw or unscrew the firing pin from the cocking piece to adjust the FP protrusion on an AI action, this changes the dimension from the sear catch on the cocking piece to the firing pin tip. For the AI action, if you unscrew the firing pin from the cocking piece for additional firing pin protrusion, the firing pin tip is now pushed farther away from the sear catch on the cocking piece and closer to the bolt face when in the cocked position, and the FP travel from cocked to when the tip crosses the bolt face will decrease-- this results in less energy being imparted to the firing pin and primer. Not so for the nucleus since the castle nut on the nucleus does not alter the sear catch surface on the cocking piece to firing pin tip dimension.
Still not sure what's going on with these actions. Firing pin travel of the Nucleus is right in the ballpark of my AIs (my AIs have about .195" of firing pin travel from cocked to when the tip crosses the bolt face when setup for 0.045" of FP protrusion-- so very close to the Nucleus.) One thing I have not measured is the mass of the firing pin, castle nut, and cocking piece in the Nucleus compared to the mass of the firing pin and cocking piece in the AI. Mass of the components in the system will have an effect on the acceleration the FP experiences during firing as well as energy delivered, but the mass of the fire control components in the Nucleus doesn't seem to be too heavy or too light compared to other bolts I've had apart. Maybe it is sear drag in certain trigger combinations robbing the firing pin of energy, the Short Action Customs video linked earlier is a good demonstrator of this and easy to test for. Might be a good idea to remove the FP spring and test for free movement of the FP assembly through the bolt shroud, over the sear, and through the bolt body and bolt head. If it doesn't move very freely you're losing ignition energy to friction somewhere in the system. I'd also check to make sure the firing pin spring when removed moves freely in and out of the bolt body and slides easily over the firing pin. If the springs were wound with too large of an OD they would rub excessively on the inside of the bolt body and also rob ignition energy, likewise if the ID is too small and they don't allow the firing pin to slide easily through the spring. A friend's Remington 700 had this problem years ago, whatever firing pin spring was in there rubbed heavily on the ID of the bolt body slowing the firing pin down. Changed the firing pin spring to one that actually fit in the bolt body without dragging heavily and all the light strike issues went away.
One thing that is crossing my mind when some of these recent posts are saying "it used to work, and then all of a sudden it isn't working anymore"-- perhaps ARC received a bad batch of firing pin springs that are suffering from an excess amount of rate and/or preload loss over time and cycles?
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I don’t have enough rounds through it with the 19# to know if it will now work 100% with cci450s I bought a few thousand 205m’s to try and avoid problems but the 19# spring has almost stopped the cratering I was getting with my nucleus entirely and was 100% reliable over 100 rds so far (20x-cci200 and 60x-fed 205m) like I said not much of a sample yet but I know some others are getting the cratering as well
Also the change in bolt lift force was negligible to me I may notice it on the bench if I’m looking for a difference but no change in functionality when actually running it at the range
Also the change in bolt lift force was negligible to me I may notice it on the bench if I’m looking for a difference but no change in functionality when actually running it at the range
Good catch there on the pin protrusion comment, I wasn't thinking quite right with my previous explanation assuming that it was the same overall distance of pin travel from start to finish regardless of where the castle nut was, not that it's the same pin travel from the start to the bolt face.
As far as the particular section I quoted goes though, the mass of the components will have no effect on the total energy delivered. The potential energy stored within the spring is the same regardless of the mass of the components and the KE of the pin when it hits the primer will be the same regardless of mass as a result when it hits the primer. The PE of the spring when compressed is 1/2 * k * x^2, where k is the spring constant and x is the distance it was compressed. The KE of the pin - regardless of mass - once it strikes the primer will always be equal to the PE from the spring compression relative to the bolt face, less the losses from friction.
The distinction here is that it's not just energy that we care about. You could have a 2,000kg firing pin spring moving at .1 m/s and it would have a kinetic energy of 10 Joules but still not set off a firing pin because it's not moving fast enough to set off the shock sensitive primer compound (it would be moving at a speed of less than 4 inches per second). Similarly you could have a .01 gram firing pin (standard USGI AR15 firing pin) moving at 44.75 m/s with 10.0128J of energy that would nearly certainly set off the primer (and probably pierce it too).
For reference, a standard Rem700 long action with a 22 pound spring and 59.3 gram firing pin will strike a primer at a speed of only 15 ft/s (4.572 m/s).
You can see this same sentiment reflected here in a PDF from David Tubb, though his focuses primarily on the topic of reducing lock time with lighter and faster firing pins/pin assemblies. https://www.davidtubb.com/index.php?route=account/download/free&download_id=28
I meant to link to that tubb article in my last post but forgot, it's good reading. I also meant to say that the mass of the firing pin and components would change the velocity of the firing pin at impact, not the energy. The potential energy is indeed controlled by the spring, but velocity of the firing pin matters too, per the exact reason in the example you gave. A very heavy firing pin moving slowly would probably only flatten the primer without igniting it even if the amount of energy delivered is adequate. As mentioned, I have not measured the mass of the nucleus firing pin components, but when I had the bolt disassembled a while back nothing seemed out of the ordinary about it being too light or too heavy.
I still really want to check out a "problem" action first hand to see what's going on and play with it. Mine is still running great, but I keep wondering what is causing these problems for other people.
I still really want to check out a "problem" action first hand to see what's going on and play with it. Mine is still running great, but I keep wondering what is causing these problems for other people.
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So you guys are saying the mass of the striker assembly is less important than the velocity of the striker? I'm asking because if you go to Ted's YouTube video on the Nucleus, at about the 26 minute mark, he talks about how the striker is hefty to allow him to use a lighter spring and keep cocking forces low. He also says the striker is about 55 grams for the short action Nucleus.
If you guys are correct, then reducing the mass of the striker may help with primer ignition?
So like 848 grains and that falls between a 700 Long action striker(914grains) and a tub b speed lock for long action(468)being much closer to the 700.
Short action 700 is 671 grains and Tubb speedlock is 422 grains so nucleus striker is pretty damn heavy for a short action.
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Correct.
@ThePretzel energy may not change with mass of striker, but force will (as F=ma). What sets off primers, force, energy, or something else?
EDIT: After some research, it seems that it takes enough energy applied over a short enough duration to set off a primer, so it may be more applicable to put firing pin "energy" in terms of energy per unit time (joules/second, aka watts). Or maybe not. Just kinda spitballing here...
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This would make much more sense to me, and I think Ted was trying to maximize the momentum of the firing pin (and thus the impulse it provides to the primer) when he designed the Nucleus with a heavier firing pin. I believe that the power transferred to the primer (energy/second, watts, etc.) is likely to be more important because the primer compounds are shock sensitive rather than just needing a certain amount of force applied to the primers.
F = ma
F = m * (dv/dt)
F * dt = m * dv
The impulse (F * dt) is the change in the momentum (m * dt) of the object in the collision. A higher impulse is created with a faster firing pin (the velocity change, dv, increases because it's a higher velocity down to zero) or a heavier firing pin (mass increases).
This is likely the reason that Ted uses a heavier firing pin spring, because the equation for momentum is p = m * v. With the same amount of kinetic energy (KE = 1/2 * m * v^2) a heavier firing pin will have more momentum than a faster/lighter firing pin because kinetic energy increases with the square of the velocity rather than increasing linearly with velocity. Doubling the velocity will double your momentum, but it will require 4x the kinetic energy. Doubling the mass will also double your momentum while still only requiring 2x the total kinetic energy.
My guess is that Ted looked to approximately match the impulse delivered to the primers by similar short action designs, which sounds good on paper but doesn't quite match up with what's been observed so far. This could be entirely wrong, but this is the best guess I can make based on the comments we've heard from him and what we know about the action. Ted specifically designed it with a heavy firing pin that would decrease velocity. The only way this would make sense is if the measurement used to determine the effectiveness of the firing pin for ignition weighted velocity and mass equally, and kinetic energy was considered irrelevant.
This holds true for momentum and impulse (p = mv and F *dt = m * dv) where both mass and velocity scale linearly, meaning you can increase the mass (heavier pin) and reduce the kinetic energy (lighter spring) while still ending up at the same value for momentum.
He does not use kinetic energy, because the spring choice alone (PE of the compressed spring = KE of the pin - frictional losses) is the only thing that could change the effectiveness of the firing pin. Changing the mass of the firing pin will not affect the kinetic energy, so he wouldn't mention using a heavier pin if his measure of effectiveness was solely based on energy.
He also does not use power, because if you use only power the light firing pin would always win. A light firing pin using the same spring would increase the deceleration of the firing pin when it hits the primer because it has less inertia than a heavy firing pin. This means all the energy is transferred in a shorter amount of time, and less time for the same energy level means a higher power (because power in this circumstance is P = KE/time of energy transfer).
TLDR;
If you want to maximize impulse or firing pin momentum, a heavier firing pin makes sense when comparing with a fixed spring weight.
If you want to maximize kinetic energy the only thing you can change is adding a heavier spring.
If you want to maximize the power delivered to the primer, a lighter firing pin makes sense when comparing with a fixed spring weight.
Ted seems to have gone the route of attempting to maximize the momentum or impulse of the firing pin when it hits the primer, because he selected a heavier firing pin to go along with his lighter spring. I personally believe that the power is more important since primers are specifically shock sensitive (and this maximizes the rate at which energy is delivered). I readily admit, however, that I have no deep experience with the mechanics behind igniting a primer and I could be entirely wrong about what the appropriate measure of firing pin effectiveness is.
Got home and decided we needed more data... this way someone can run through the math outlined in Tubb's whitepaper with the Nucleus fire control system if they want to. I'd run the numbers but I had to hurry and run off to dinner.
I then took apart one of my short action AI bolts to weigh the components. I don't think anyone will disagree when I say that AI's are extremely reliable. Also, my AI has not had a single misfire in 2900+ rounds of 6 Dasher with CCI 450 primers-- a primer that many here have cited does not ignite reliably in their Nucleus. I figured this would be a great comparison to the Nucleus.
It's obvious the firing pin and spring of the Nucleus are not all that much heavier than the very reliable AI. So, what's causing these Nucleus light strikes, now that we see that the component weight between the AI and Nucleus short action are so similar, and especially since the AI actually has less firing pin travel than the Nucleus?
I can think of a few things:
1. Nucleus needs more FP spring rate, or the springs are defective in some way from the winder and are losing preload/length/rate prematurely. I may have to test the AI firing pin spring and determine the rate, since AI doesn't publish it.
2. Excess sear drag depending on trigger used
3. Dual cocking cams and matching grooves in the bolt shroud are somewhat long, presenting a lot more surface area for lube or other contaminants to adhere and cause extra drag on the firing pin
4. Frictional losses from somewhere else in the system. Spring excessively rubbing bolt body or firing pin, insufficient clearance between FP nose and bolt crosspin and/or bore in bolt head, burr on cocking piece or in bolt shroud creating drag, bent firing pin body/tip?
More questions than answers unfortunately.
- Weight of short action Nucleus firing pin, cocking piece, castle nut, and castle washer: 810.7 grains
- Weight of 19# short action Nucleus spring: 241.9 grains
- Total FP travel from cocked against sear to crossing bolt face in my action with CG Mod 22 trigger: 0.216"
I then took apart one of my short action AI bolts to weigh the components. I don't think anyone will disagree when I say that AI's are extremely reliable. Also, my AI has not had a single misfire in 2900+ rounds of 6 Dasher with CCI 450 primers-- a primer that many here have cited does not ignite reliably in their Nucleus. I figured this would be a great comparison to the Nucleus.
- Weight of AI firing pin, cocking piece, and anti-rotation setscrews to retain firing pin into cocking piece: 798.6 grains
- Weight of AI firing pin spring: 208.5 grains
- Travel of firing pin from cocked to when it crosses the bolt face with 0.050" of FP protrusion (the AI firing pin and cocking piece arrangement will have a variable fall distance depending on FP protrusion setting, unlike the Nucleus): 0.192"
It's obvious the firing pin and spring of the Nucleus are not all that much heavier than the very reliable AI. So, what's causing these Nucleus light strikes, now that we see that the component weight between the AI and Nucleus short action are so similar, and especially since the AI actually has less firing pin travel than the Nucleus?
I can think of a few things:
1. Nucleus needs more FP spring rate, or the springs are defective in some way from the winder and are losing preload/length/rate prematurely. I may have to test the AI firing pin spring and determine the rate, since AI doesn't publish it.
2. Excess sear drag depending on trigger used
3. Dual cocking cams and matching grooves in the bolt shroud are somewhat long, presenting a lot more surface area for lube or other contaminants to adhere and cause extra drag on the firing pin
4. Frictional losses from somewhere else in the system. Spring excessively rubbing bolt body or firing pin, insufficient clearance between FP nose and bolt crosspin and/or bore in bolt head, burr on cocking piece or in bolt shroud creating drag, bent firing pin body/tip?
More questions than answers unfortunately.
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And herein lies a problem. If we follow David Tubb's analysis paper, he puts very little (read: absolutely no) weight on momentum. He thinks that the faster striker will do the job better (the more powerful striker) as you do, even with a slightly lower spring weight.
I'm working through his calculations for the Nucleus right now, but I'm estimating some numbers and my action isn't with me. If someone could give me the numbers I need, it would be very helpful (and give a restless mind something to do). Looking for:
Striker weight (firing pin, cocking piece, flanged washer, castle nut)
Spring weight (physical weight)
Free spring length (for 16#, 19#, and 25# springs if different)
Uncocked spring length
If someone could help me out, it would be greatly appreciated!
EDIT: @Kiba you had weights up before I posted. Freaking beautiful!
Still need the two spring lengths for anyone out there...
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Mine has been 100% so far with about 200 rounds (170’s serial #) My question as I follow this is if there was a bad batch of springs, why wouldn’t they be replacing them with another 16# spring vs a 19# 25# etc. unless they recognize 16# isn’t right. If it isn’t right, then why isn’t there a recall to get the proper spring?
I think Ted designed the action with low cocking force in mind first and foremost. The 16 pound spring was probably borderline (and I suspect ARC knew it would be), but in ARC's testing it apparently worked with everything up to No.34 and No.41 primers, so they figured it would be fine with everything else. They're giving/selling people heavier springs to people that call with problems, but they aren't putting out a "recall" because of numerous possibilities.
I understand that they will provide a new spring if you experience light strikes, but are we supposed to hope ours continues to function properly until we experience a malfunction? What if you spend money on a match and travel etc and then you experience a malfunction as some have stated like me (so far everything works as stated but in the middle of a match it starts to light strike). Eating a $500 plus weekend would suck in that scenario. This is my first custom action so I may be ignorant about new releases and having to roll with the nuances, but it seems odd to me nonetheless. I also don’t see the availability of springs on their site so unless I send it in, I don’t see an option to replace the spring proactively.
Yep, it pretty much seems like it. This is my first custom action too, and I'm nervous about getting light strikes already and I haven't even shot it. If you call, they should ship out a spring to you.
ARC's customer service leaves something to be desired, but Ted says they'll be working very hard to improve that this year. Hopefully they do. I like their designs, but they struggle on the follow through a lot recently. Nucleus, Barloc, ARC mags. Hell, the Mausingfield took like three revisions after it was released to get it to what it is now.
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