Gunsmithing Bedding a Chassis

[B_w.]

Hi all, looking for feedback on a project of mine. I recently picked up a barreled Ultimatum Deadline long action in 300 prc and a MDT ACC CIP long action chassis. The Deadline is a 700 ish foot print action but I am having some issues and I believe bedding it may resolve them. I would appreciate some feedback. The barrel is a button rifled 1/8 from International Barrels made here in Canada.

When I first screwed it together at the specified torque from MDT (60 inch pounds) I could not insert the bolt into the action. The rear tang was not supported and the action was bindingunder the stress. Don't recall at what amount I could insert the bolt but it was probably around 20 inch pounds or less on the rear screw. I didn't feel good about that and reached out to Ultimatum for their suggestions. They suggested using a set screw to apply some pressure under the rear tang (see pictures below) so that the action wouldn't bind when tightened.

Fast forward and I have worked through my factory ammo, 225g Hornady Match, to get the brass and have started load development with 230g Bergers and Retumbo. Working through all my loads I couldn't print anything much better than 1 moa. Factory ammo was sh^t and I was recording ES's of 130 fps with my labradar so I was not too concerned with the poor accuracy at the time.

After getting initial poor results on my loads I suspected something was up because my factory Tikka CTR in a MDT ESS prints groups half the size of the best results achieved with the Deadline. I am loading with a Auto Trickler, AandD 120 scale and Coax press with Whidden dies so I am pretty sure of my process. SD was typically under 10 fps through all the loads fired and consistent with my other reloads.

Below are pictures of the action and the chassis. You can see where the two are contacting. For sure I think the rear tang needs to be bedded but not sure about the recoil lug and along the length of the action. Along the length of the action it looks like there is minimal contact.

I have already picked up the Devcon, putty, neutral polish in prep to do this but thought I would see what the team here thinks before messing the stock up.

 

[want2learn]

please forgive me if i'm off base in asking (i'm trying to think out loud and learn in this query).... but what would be the rational to not do a complete bedding having already defined the need to better accommodate the barreled action? is the concern a risk to the integrity of the chassis stock? thank you

 

[B_w.]

I would do the entire length if it would provide benefit. I am fairly certain the rear needs attention but I would prefer to minimize hacking the chassis up as much as possible.

 

[acudaowner]

I have thought about doing the full bedding with my mdt but know far too little about it yet to want to go messing around too much with it or if its even worth the effort as the gun shoots far better than I can shoot it as it is without the bedding . Maybe when i replace the barrel this might strike me more . Good luck with yours the pics look real nice hope it shoots as good as you want it to .

 

[Eric32]

Have to tried to get a hold of @MDT_Josh i remember a washer of some sort being installed or they figured the production action were diffrent. Anyways Josh will offer some info for sure.

 

[Dobbs02si]

I ended up having to bed the rear of the action/trigger hanger on my savage axis to get correct contact when tightening the action screw(sub par design). It's my personal opinion, but I would bed the lug/screw area as well as the tang. Something about the two hot spots with v beds just never have sat right with me for "stress free" bedding.

 

[Notevenonpaper]

I will readily admit to knowing jack about gunsmithing, but does it appear to anyone else that the witness mark on the chamber side looks like the contact point was shifting? On one side of the action you have a concentrated witness mark with no contact on the recoil lug vs the opposing side with witness marks on the recoil lug and what looks like rubbing/scuffing on the action.

 

[want2learn]

that was my impression as well...

 

[Mordamer]

I think bedding is probably best in this case, although I hate having to bed a chassis. It destroys resell value.

You could try some brass shim stock under the rear tang to fill the gap and see if that works.

 

[Sierra770]

Bed it and forget it. I had to bed an MDT Chassis due to similar issues. Fixed it right up.

 

[MDT_Josh]

Thanks for the tag @Eric32!

I'd like to clear up a few things quickly and offer my 2 Canadian cents (so 1.4 cents at current exchange ).

1. Our v-block design and inletting has gone through MANY revisions throughout the 10+ years we have been making chassis and learning about how they interact with different actions. The biggest thing is that no two actions (even if they are the same footprint) interact with a stock or chassis the same way. Heck, even two actions that are the same design from the same manufacturer can act differently in the same chassis due to tolerance stackup on our end and theirs. We have done our very best to mitigate these issues be designing our bedding system to work with 99% of the actions you guys will throw in there.
2. When installing an action into our chassis and torquing down the action screws, you will ALWAYS see those witness marks simply due to the fact that in the great battle of material strength: steel > aluminum. The witness marks are just showing the contact points/lines/faces between the action and the chassis and will show up even if the rifle is unfired (we see it all the time when testing prototypes). The only way to completely eliminate those marks is to fully surround your specific action with a semi-flexible material that will act as a buffer between the chassis and the action (ie. bedding it). Will it make it shooter better? We don't believe it will. Will it make you feel better? Maybe.

So now to answer the actual question asked by @B_w. ; yes, bedding your chassis will be the best/easiest solution to your problem. We have gone through many issues with the UP Deadline and have created a specific v-block profile to better support that inlet (as it is not a R700 SA drop in fit) on our SA variant of the ACC. I don't think that we have released it on any of our other chassis, but demand can cause us to do a run if need be. The problem is that the inherent design of the Deadline (SA and LA) causes their bolt to bind (as you found) when torqued down to recommended values.

By bedding your chassis, you will fully support the rear tang/back half of the action, which is causing you issues. The set screw method that big Jack from Up River precision came up with does work, but bedding is a better solution. You may also have to shorten the rear action screw to account for their lower cocking piece on the bolt and be sure to install the correct mag stop in their action based on which magazines you're running

If you have any more questions, let me know!

Josh

 

[B_w.]

Thanks appreciate it. I have a SA Deadline in the ESS and no issues there...just with the long action. I know this is not an MDT issue based on the 700ish foot print of the Deadline. Would there be any harm in bedding the recoil lug and front screw area as well as the rear tang?

 

[MDT_Josh]

Thanks appreciate it. I have a SA Deadline in the ESS and no issues there...just with the long action. I know this is not an MDT issue based on the 700ish foot print of the Deadline. Would there be any harm in bedding the recoil lug and front screw area as well as the rear tang?

No worries and that's good to hear. If you were to bed the front recoil lug and bedding surface, you probably wouldn't see any changes in performance and fit, however, the rear bedding surface/tang are the key. If you're going to bed the rear tang though, you may as well bed the whole thing to keep everything consistent.

Josh

 

[B_w.]

Here is what I am planning to do. Let me know what the collective minds here think. The blue is the current contact points and the red is where I am thinking of applying bedding. The second picture shows the recoil lug recess looking from the front back. Not much to do on the front support of the lug but lots of room on the sides. Not planning to remove much material, just rough it up a bit with the Dremel, I don't want to mess up the current contact points. Is this a sound plan?

 

[Sierra770]

A Dremel might be overkill. I have scuffed mine by hand with a piece of 220 grit sandpaper and it has held for over 5000 rounds.

 

[B_w.]

I would not have thought 220 was rough enough for the epoxy to bite into. Sand paper might be good for the v block and sides. Convince me otherwise but I don't think there is any contact by the screws so thought for sure I would want a little more scuff there where the epoxy will probably be the thickest.

 

[Dobbs02si]

I would be willing to be most chassis' are bead blasted at a minimum before annodizing, so an oil free chassis should easily hold most compounds. Same reason parkerizing is an amazing 'priming coat' for steels to be painted/ceracoated. Just my $.02.

 

[Sierra770]

I would not have thought 220 was rough enough for the epoxy to bite into. Sand paper might be good for the v block and sides. Convince me otherwise but I don't think there is any contact by the screws so thought for sure I would want a little more scuff there where the epoxy will probably be the thickest.

That was sufficient for a McRee G10 and MDT LSS-XL. Again, my experience. I was able to remove it when needed and it didn’t damage resale value.

 

[jzwolen]

I would use that set screw to find the right height that the Deadline long action likes to sit perfectly flat while torquing both actions crews to 65in/lbs, then skim bed the front, and add some extra bedding in the back to help support the tang around the setscrew.

 

[B_w.]

Finished this afternoon. Will see how it turns out tomorrow. Did around the recoil lug, front action screw, lightly along the magazine well and rear screw / tang. Fingers crossed it comes apart and looks half decent. The ACC does not support the front of the lug so put a little clay in front and built it up a bit.

Most of the time was getting the clay into place.

 

[B_w.]

Just pulled it apart and I think it looks pretty good. A bit of clean up to do with the Dremel and lots of putty to pull out but that's ok. Question is should I be drilling out the screw holes in the chassis to free float the screws or leave them as is with putty in them?

 

[B_w.]

and cleaned up. Sits in there nice and tight. Managed to break a small piece on the right side of the mag well. Should I be concerned about that?

 

[Dobbs02si]

The mounting points and lug face are the most important points of cantact from my experiences.

So..how does it shoot?

 

[Wannashootit]

I have always been a firm believer in making certain that action screws have plenty of clearance within the pillars.
I don't want any contact between screws and pillars. The principle is to have the recoil lug transfer 100% of the recoil energy into the stock/chassis.
If an action screw is in contact with a pillar that goes out the window.

I'm often puzzled by guys I see tediously drilling/reaming pillars actually trying to get minimal clearance. I don't get it...I want to see plenty of daylight between them.

JMO, YMMV.

 

[B_w.]

I have always been a firm believer in making certain that action screws have plenty of clearance within the pillars.
I don't want any contact between screws and pillars. The principle is to have the recoil lug transfer 100% of the recoil energy into the stock/chassis.
If an action screw is in contact with a pillar that goes out the window.

I'm often puzzled by guys I see tediously drilling/reaming pillars actually trying to get minimal clearance. I don't get it...I want to see plenty of daylight between them.

JMO, YMMV.

That's what I was thinking. Thanks.

 

[Heffo]

That's what I was thinking. Thanks.

Hi mate, I’m having same issue with the U300 action ( they are a punish, great once all the many gremlins are worked out) Gonna drop off to gunsmith tomorrow. Once bedded what torque are you using? Less? Cheers Luke

 

[nksmfamjp]

Well crap. I probably should bed the ol Savage.....or maybe just sell off the chassis.

 

[LRI]

This is the process I adopted years ago:

First, I didn't read through all the comments. If this has already been mentioned, my apologies for the redundancy.

It's important to understand exactly what is happening, particularly in the tang area of the rifle stock. A great many of these chassis stocks get made by cramming a ball-shaped tool down the length of the inlet.

-High 5's to the staff and call it day. . .

The problems begin in the tang because of the arrow head-like taper of the receiver. Tangent contact of the action ends ahead of where the guard screw gets inserted. Because of this, a lever-like behavior takes place and when the rear screw is snugged up in conjunction with the front, the whole action tries to hunch its back like a cat does when you pet it.

This is easily verified. Drop action into the stock, tighten the rear screw, and observe the front half. If it says put, your golden. If it tries to levitate off the front register, it's not right.

Gooping up some resin and casting the receiver in various places is one way to fix this. I personally don't care for that so I went another path. I had a tool made that has a .675" dia radius. The same as most round actions. (Remington footprint) We start by enlarging the counterbore of the rear hole in the stock and cutting 1/2-28 female threads. Next, I turn/thread a short plug of 6061 naval brass. That piece is then screwed into the hole and glued into place with some resin. Step three is poking a hole down the center of this brass tree stump-looking, thing. Last, we chuck up the form tool and begin taking passes off the top of the brass plug until the receiver lies tangent and parallel along the length of the inlet with no bias being impinged upon it.

With the tang feature now supported. There's no room for anymore bowed-up, "kitty-like" receiver issues. The old AICS stocks were notorious for this and we used to fix a boatload this way. When it's completed it just works and the usual appearance issues that bedding jobs are so susceptible to are completely avoided.

Good luck.

C.