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ARC Archimedes sear engagement

D

ddavis

Sergeant
Full Member
Minuteman
May 26, 2011
1,336
232
Texas
#1
New ARC Archimedes SA .473
Triggertech Special

My bolt has to be slammed forward pretty hard to get it to close or start downward rotation. My Mausingfield also did this with a Huber trigger and it was just flat out horrible to run the bolt. I replaced the Huber with a Triggertech and the problem went away.

Instead of trying several triggers until one works with this action, is there something I can do to get the timing/sear engagement correct so that I can easily close the bolt? I know I've seen something about this before but can't seem to dig it up again. This doesn't seem to be specific to any one action or trigger, but so far both of my ARC actions have been guilty of it.

Thanks,
Dan
 
#2
You could try honing the cocking piece down with a stone. I’ve had to do this with a few triggers before. I’d call arc and just make sure that it won’t jack up any warranty though before you do.
 
#4
I had to shorten (length) my BnA TacSport top dear with my Archimedes. This, effectively, is like shortening the cocking piece on the bolt, but less "permanent," in my eyes (I have both low and medium top sears).

I'm guessing this is because the top sear is coming in contact with the cocking piece before it can bottom out the bolt shroud locking pin.
 
#5
HOLLYW00D said:
I had to shorten (length) my BnA TacSport top dear with my Archimedes. This, effectively, is like shortening the cocking piece on the bolt, but less "permanent," in my eyes (I have both low and medium top sears).

I'm guessing this is because the top sear is coming in contact with the cocking piece before it can bottom out the bolt shroud locking pin.
Click to expand...

I did the same thing earlier this week, both medium and low sears on my Tacsport pro did not work. Mine wasn't able to close the bolt even with slamming it forward. I've got no experience modifying triggers so I sent the action and trigger back to ARC for them to look at.
 
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#7
Stone the cocking piece, or leave rhe original and buy a second cocking piece from ARC and stone that before you do your trigger, IMO.

At this point, it will be very good to have ARC looking at these.

I am curious what is happening...
 
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#8
hereinaz said:
Stone the cocking piece, or leave rhe original and buy a second cocking piece from ARC and stone that before you do your trigger, IMO.

At this point, it will be very good to have ARC looking at these.

I am curious what is happening...
Click to expand...

That was my thought, there are too many different triggers this is happening to.
 
#12
Yep, I tried a CG Xtreme and 2 different BnA. Both work smooth as butter on my Mausingfield. So we've got

BnA
Tubb
Triggertech
CG X treme
Calvin
Geiselle

@karagias, can you give us an update when you've had a chance to take a look?

craigos said:
My two ARCs wont close on my Tubb T7T (cant push the bolt down) - worked find on my nucleus and my mausingfield. Disappointing!!!
Click to expand...
 
#13
I posted on the other arc thread...
I really don’t know much about trigger mating issues, never had one so far.

Is it a design thing
Tolerance thing
Are all the high quality triggers made to the same spec, concerning protrusion etc
Or it’s some companies have particular specs that are at the min/max of the generic numbers
Trying to get a education


Thanks
Brian
 
#14
I'm guessing it's a tolerance thing. Like I said, my Mausingfield felt just like this when I had the Huber. I took a gamble and tried a TT and the problem went away. Today I swapped the "good" trigger from the Mausingfield onto the Archimedes and it made no difference. Mausingfield bolt practically closes itself, Archimedes needs considerable force and it's just clunky.
 
#15
I mentioned in the nucleus thread quite a while back that it would be nice for ARC to offer cocking pieces with various lengths of sear engagement from standard length to -0.035" or so in 0.005" increments so you could tune the amount of overcocking with a drop in, off the shelf part.

Ted mentioned a while back there is no industry standard when it comes to sear length and height vs trigger pin location, so different brands of triggers are all over the place. Might be good info to ask ARC if they designed the action with a specific trigger brand in mind.

Excessive overcocking is the most probable cause of a difficult to close bolt or a bolt that has a "catch" on closing after a trigger is installed. My nucleus & CG Mod 22 combo has about 0.025" overcocking on closing, and if I were to tune that down to 0.005" or so it would lessen the "hitch" and decrease bolt closing effort when running the bolt slowly. When I run the bolt normally to quickly I don't notice it.

A heavier firing pin spring will exacerbate the hitch on closing issue if there's excess overcocking, especially if the sear is holding the bolt far enough back that the lug ramps aren't yet engaging-- in that case the bolt won't close until you push the bolt forward firmly to further compress the firing pin spring until the bolt lug ramps engage and allow you to close the bolt. The Archimedes shipped with a 30# spring-- that's heavier than the nucleus firing pin spring.

Since ARC doesn't offer cocking pieces in different lengths and the actions don't use a trigger hanger (offered in various lengths to adjust the trigger fore and aft) you're left with shortening the sear or shortening the cocking piece to tune the amount of overcocking on close. If you go this route, my suggestion is leave a little bit of overcocking in the system; about 0.005" or so, this way the firing pin doesn't drop against the sear when closing the bolt and instead will have good contact with the sear throughout the entire rotation of the bolt handle.

One thing to mention, even if you tune the sear or cocking piece to have 0-0.005" overcocking on close, you still have to apply enough forward pressure to compress the bolt shroud lock pin. That's a design choice by Ted; I like the lock pin for positive control of the bolt shroud rotation, but that design does require the locking pin to be compressed when closing the bolt, either by forward hand pressure only when running the bolt very slowly or assisted by inertia when running the bolt at a more normal speed.
 
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#16
these actions have life time warranty , if it doesnt go bang they aint much use. Never seen an action have so many incompat triggers. I have a Rem trigger will try and install that tomorrow - if it doesnt worn enough said.
 
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#17
Kiba said:
I mentioned in the nucleus thread quite a while back that it would be nice for ARC to offer cocking pieces with various lengths of sear engagement from standard length to -0.035" or so in 0.005" increments so you could tune the amount of overcocking with a drop in, off the shelf part.

Ted mentioned a while back there is no industry standard when it comes to sear length and height vs trigger pin location, so different brands of triggers are all over the place. Might be good info to ask ARC if they designed the action with a specific trigger brand in mind.

Excessive overcocking is the most probable cause of a difficult to close bolt or a bolt that has a "catch" on closing on these actions. My nucleus & CG Mod 22 combo has about 0.025" overcocking on closing, and if I were to tune that down to 0.005" or so it would lessen the "hitch" and decrease bolt closing effort when running the bolt slowly. When I run the bolt normally to quickly I don't notice it.

A heavier firing pin spring will exacerbate the hitch on closing issue if there's excess overcocking, especially if the sear is holding the bolt far enough back that the lug ramps aren't yet engaging-- in that case the bolt won't close until you push the bolt forward firmly to further compress the firing pin spring until the bolt lug ramps engage and allow you to close the bolt. The Archimedes shipped with a 30# spring-- that's heavier than the nucleus firing pin spring.

Since ARC doesn't offer cocking pieces in different lengths and the actions don't use a trigger hanger (offered in various lengths to adjust the trigger fore and aft) you're left with shortening the sear or shortening the cocking piece to tune the amount of overcocking on close. If you go this route, my suggestion is leave a little bit of overcocking in the system; about 0.005" or so, this way the firing pin doesn't drop against the sear when closing the bolt and instead will have good contact with the sear throughout the entire rotation of the bolt handle.

One thing to mention, even if you tune the sear or cocking piece to have 0-0.005" overcocking on close, you still have to apply enough forward pressure to compress the bolt shroud lock pin. That's a design choice by Ted; I like the lock pin for positive control of the bolt shroud rotation, but that design does require the locking pin to be compressed when closing the bolt, either by forward hand pressure only when running the bolt very slowly or assisted by inertia when running the bolt at a more normal speed.
Click to expand...


Great expectation...thanks alot
 
#18
I'm not an engineer but I don't understand why other custom actions don't seem to be having widespread problems with this issue. If it was as simple as changing to one of those $$$ BnA triggers I'd try it just to have a receiver I could use for now, but someone above couldn't get it to work even with that. I'm curious what trigger was used to design these as well.
 
#21
ddavis said:
I'm not an engineer but I don't understand why other custom actions don't seem to be having widespread problems with this issue. If it was as simple as changing to one of those $$$ BnA triggers I'd try it just to have a receiver I could use for now, but someone above couldn't get it to work even with that. I'm curious what trigger was used to design these as well.
Click to expand...

Are you kidding me? Nearly every major design i have been on the phone with either the action maker or trigger mfg when the action first arrives with issues with one trigger or another. Why do you think BnA have 2 sear bars, because I spent 4 hrs on the phone with Chris/BnA guys when they released the tacsport when they changed the cocking knob length on the TL3 (was dragging on the high sear bar) - measuring all the dimensions so Chris could quickly get a new sear bar mfg.

i.e. just because the volume of the noise isnt as lound, does mean its not as prolific.
 
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#23
I'm pretty happy with a 2# trigger, though I'd really like for the trigger I bought for this action to work with it. I don't see how going to a heavier trigger would fix an issue with tolerances within the action.
 
#24
Just had a conversation with ARC, and what I was told is that ARC bolts (on all their actions) increase in diameter towards the rear of the bolt; I'm guessing that this is so that there is adequate clearance between the bolt and the action for most of the bolt stroke to deal with debris, etc..., but that as the bolt slides into the closed position, the clearance between the (back of the) bolt and the action decreases in an effort to both positively center the bolt within the action and reduce any play between the two pieces as the case is held in the chamber.

In any event, it seems that the Archimedes bolt is slightly larger in diameter at the rear of the bolt (compared to the Nuke and the Mausingfield), and that seems to be the source of the issues that they're able to observe. It sounds like they have a handle on the issue, and are in the process of developing a mitigation plan to get it addressed moving forward.

The long and short of it is that they're working to find definitive answers and develop a plan for taking care of customers. I just wanted to post this info to let early Arch adopters know to stand by for communication from ARC, lest anyone go all "Internet" and start trash talking and/or spreading inaccurate or incomplete information.
 
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#26
Great, thanks for getting the info out. I know they will have my action and Bix N Andy trigger in hand tomorrow to experiment with. ?

BurnOut said:
Just had a conversation with ARC, and what I was told is that ARC bolts (on all their actions) increase in diameter towards the rear of the bolt; I'm guessing that this is so that there is adequate clearance between the bolt and the action for most of the bolt stroke to deal with debris, etc..., but that as the bolt slides into the closed position, the clearance between the (back of the) bolt and the action decreases in an effort to both positively center the bolt within the action and reduce any play between the two pieces as the case is held in the chamber.

In any event, it seems that the Archimedes bolt is slightly larger in diameter at the rear of the bolt (compared to the Nuke and the Mausingfield), and that seems to be the source of the issues that they're able to observe. It sounds like they have a handle on the issue, and are in the process of developing a mitigation plan to get it addressed moving forward.

The long and short of it is that they're working to find definitive answers and develop a plan for taking care of customers. I just wanted to post this info to let early Arch adopters know to stand by for communication from ARC, lest anyone go all "Internet" and start trash talking and/or spreading inaccurate or incomplete information.
Click to expand...
 
#27
BurnOut said:
Just had a conversation with ARC, and what I was told is that ARC bolts (on all their actions) increase in diameter towards the rear of the bolt; I'm guessing that this is so that there is adequate clearance between the bolt and the action for most of the bolt stroke to deal with debris, etc..., but that as the bolt slides into the closed position, the clearance between the (back of the) bolt and the action decreases in an effort to both positively center the bolt within the action and reduce any play between the two pieces as the case is held in the chamber.

In any event, it seems that the Archimedes bolt is slightly larger in diameter at the rear of the bolt (compared to the Nuke and the Mausingfield), and that seems to be the source of the issues that they're able to observe. It sounds like they have a handle on the issue, and are in the process of developing a mitigation plan to get it addressed moving forward.

The long and short of it is that they're working to find definitive answers and develop a plan for taking care of customers. I just wanted to post this info to let early Arch adopters know to stand by for communication from ARC, lest anyone go all "Internet" and start trash talking and/or spreading inaccurate or incomplete information.
Click to expand...

Excellent info, thanks for sharing.
 
#28
ARC has cocking pieces of varying lengths for the Archimedes. They are not for sale on the website but they are available for $40 if you call them.

I also asked if there was a possibility of having the action machined for a trigger hanger so I could use an adjustable hanger.
 
#29
So then is it something with the bolt diameter or the cocking piece? It felt like the cocking piece since I've experienced this same thing with the MF. I'll just give them a call tomorrow. Curious what trigger they designed this around since it seems no one has had much luck with pretty much any available trigger. Kinda fucked to make it not compatible with anything then charge $40 to "fix" it.
 
#30
100%
What trigger was it designed and tested with.

I guessing/hoping there was a bunch of testing for functionality and durability.

Give a call and find out the trigger on action #001

And that the one to buy
 
#33
ddavis said:
So then is it something with the bolt diameter or the cocking piece? It felt like the cocking piece since I've experienced this same thing with the MF. I'll just give them a call tomorrow. Curious what trigger they designed this around since it seems no one has had much luck with pretty much any available trigger. Kinda fucked to make it not compatible with anything then charge $40 to "fix" it.
Click to expand...

Spoke to them yesterday and the problem is not going to be fixed with the cocking pieces they sell.

They said they are stopping all shipments until they get it figured out. They know what the issue is and said it won't take too long to get it sorted out.

BTW, mine was supposed to ship Friday.
 
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#35
thanks for the update...

you know what would really be great

for them to tell us that the problem is, instead of this cloak and dagger stuff

they admit there is a problem

they admit they are working on a solution

now disclose the issue that we will all know immediately when the fix comes out

kicking the can down the road doesnt help anyone
 
#36
It was either an Arch or another LRI mausingfield HTR action.....really wishing I’d gone the 2nd LRI route as the one I bought was/is perfect for my uses. I knew there’d be bumps and some fine tuning but really thought they had learned from the nucleus. I don’t doubt it will get sorted....but damn.
 
#37
I guess this is the downside of getting my Archimedes delivered yesterday...

I'm going to check five triggers in my Archimedes as soon as I can to see if mine has the issue. Unfortunately my action is in the 10 day wait so it will take a while.
 
#38
I have a spare Timmey 510 and the intended TT Special to try and could swap a Diamond out of something for shits and giggles. I don’t have a waiting period to deal with but do have some other stuff going on that will prevent testing until at least saturday or Sunday.
 
#39
Kind of baffling how this happened again - im just really curious what trigger was used during testing and how this issue didnt come up.
(I had the Arch on preorder for quite awhile, but when the delays started happening, i decided to swap my pre-order for the updated Nuke as I have some big hunts starting in October. Glad i made the right choice, i usually choose wrong in those cases haha. And FWIW, the Nuke with all bugs worked out has been nothing but a pleasure to shoot)
 
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#42
UPDATE:

Spoke to Ted today and it was reassuring. They said it's the diameter of the bolt contacting the trigger. Nothing that's going to be solved with a different sear, so don't bother. Sounds like they've got it nailed down. He said the most likely course of action is for them to send shipping labels for those Arc's out in the wild to send your bolt in and they'll modify/replace whatever they need to do to make it right. Keep an eye on your email inbox.

-Dan
 
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#43
Thanks for starting the thread.

I also have the TT Special, now that I've been informed I can feel the bolt ride up onto the sear.

Frankly, I was more annoyed with the last ~0.030" of the bolt travel prior to closing rotation.
The shroud locking pin on my example does not always engage properly on opening, so sometimes the bolt goes home with less effort which is an improvement on the feel, frankly, I think the spring is a bit stiff and interferes with the most critical part of the bolt throw.
My cocking piece is ever so slightly long and the sear is engaging before downward rotation begins putting another notch in the bolt throw.

If you want to feel where the actual sear engagement on close is, just remove the shroud locking pin and spring, this can be done easily without tools. Take care to not launch it across the room.

Thanks to HOLLYW00D for the video:
HOLLYW00D said:
Hope this helps:
Click to expand...



Bonus exercise:
Once you've got the pesky plunger and spring out of the shroud you can more easily observe the actual leveraged portion of extraction by holding forward on the bolt shroud with your thumb while pulling back on the bolt knob with your index and middle fingers.
My example is measuring exactly 0.031" from fully closed bolt to maximum leveraged retraction, and there is ~0.125" of throw at the bolt knob before the lever begins acting on the receiver so lots of room for improvement here...



I'd be happy to send my trigger in with the action if it would help.
 
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#45
Got long action serial number 6 in today (but it was ordered as a short action, hopefully my long action order will ship with a short action). Doesn't work with an elf pro, tt diamond, and tt special at least for me so far. Still have a couple other triggers I could try but going to just put it away until they are able to fix the issues.
 
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#49
My ffl called that mine had arrived this morning and I don’t even want to go pick it up.

I guess the major disappointment is I have yet to see or hear a word from ARC and it sounds like this is not an isolated incident. You would think they would function check these damn things before they were shipped out.
 
#50
9 months ago when we were seeing the video of it at SHOT is when it should have been apparent the rear of the bolt is under constrained.

Here is what the TriggerTech looks like installed, the primary sear is slightly above the housing, but the bolt sags down and that is a problem.

2019-09-20 19.35.08.jpg

If you hold the action upside down you can still feel the larger diameter portion of the bolt body just touch the sear and you can see the track in the grease, if they cut another flat down that path and make some clearance towards the cocking ramps for rotation it should be good to go:
2019-09-20 19.32.07.jpg
 
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