Gunsmithing Why aren't chassis systems bedded?

[EddieE]

Hoping to hear from some of the more experienced folks on this. Been watching some videos about the pressure points related to chassis v-blocks. Can you bed these? For me, one of the draws to a chassis is not having to deal with bedding and without bedding, it actually seems cost effective vs. buying a traditional stock, shipping the gun to someone to bed it, etc. and not to mention the weeks or months without your gun.

Here is a video that I saw and found interesting

https://www.youtube.com/watch?v=_TwczrQoLek


I know Chad doesn't bed these, hoping to hear why.

Thanks

 

[Ledzep]

Problem solved literally with 2 dabs of JB weld. You can even lightly release coat the chassis to keep it from sticking too bad if you ever want to remove it.

It happens because the tang is not a complete cylinder, and the very bottom of the action is NOT supported in the typical "V" block setup. If you put a dab of JB weld near the action screws (I do infront of the front action screw, and behind the rear one, or on both sides of both if you prefer....), then SNUG (as in apply no torque) your action screws up and let it sit over night, you alleviate the issue.

A complete skim bed is not required, and I wouldn't pay someone to do it.

The other alternative is to have someone (namely C. Dixon comes to mind) surface machine the chassis to match the receiver's curvature, so it's a half-pipe instead of a V block.

 

[FatBoy]

I'll start by saying I am not a chassis fan. The only time I use them is when I build clones with one exception which was my first LR rifle, a Winchester Stealth 1. Eventually I had GAP skim bed, re-
crown and do a trigger job. If I ever warm up to shooting my Mk13 Mod7, I will have that chassis skimmed as well. It's not common, but it's also not uncommon if that makes sense.

 

[FrankieJames7]

a little off topic but similar, what does everyone think about receivers and stock material being different coefficient of thermal expansion? carbon fiber is now able to have its cte changed to the same as the steel it holds, but if it is aluminum the dimensions change differently than steel and steel alloys. aluminum reacts more to temperature than steel, so if the dimensions are perfect at 60 degrees f, at 90 degrees f the aluminum chassis is going to be proportionally bigger than the receiver and will stretch the screws holding the chassis to the gun

 

[delfuego]

It is a compromise to allow similar actions to fit. It allows the person to easily remove or change the action from the stock without any extra work. Also not all chassis are V-Block. My XLR Carbon isn't. It is exactly machined to match the action.

You can always skim-bed your chassis. People have done to AICS for a long time. Problem would be that the stock is now only for that specific action and may not be easily switched between actions.

My different chassis will shoot into one hole, what kind of accuracy is required? John Whidden builds and sells V-Blocks, he know a little more about accurate guns than all of us combined. Will it be as perfect as a benchrest bedded rifle stock? No. Will it matter to you? Are you shooting 3" BR groups at 1k or 2moa steel at 600y?

 

[Supersubes]

Most people dont bed them because they shoot just fine without it. Ive owned a bunch of chassis, and i've never needed to bed a single one. Certainly you can bed it if you want to.

 

[wareagle700]

Problem solved literally with 2 dabs of JB weld. You can even lightly release coat the chassis to keep it from sticking too bad if you ever want to remove it.

It happens because the tang is not a complete cylinder, and the very bottom of the action is NOT supported in the typical "V" block setup. If you put a dab of JB weld near the action screws (I do infront of the front action screw, and behind the rear one, or on both sides of both if you prefer....), then SNUG (as in apply no torque) your action screws up and let it sit over night, you alleviate the issue.

A complete skim bed is not required, and I wouldn't pay someone to do it.

The other alternative is to have someone (namely C. Dixon comes to mind) surface machine the chassis to match the receiver's curvature, so it's a half-pipe instead of a V block.

I've wondered if I was the only one that did this, ha. I've even used the "JB Stick" and put bedding pads in places to give extra support. On a lightweight rifle I have found putting a bedding pad under the chamber area, just forward of the recoil lug, really stiffens the forearm on a traditional stock and has improved accuracy in more than one rifle for me.

 

[EddieE]

Problem solved literally with 2 dabs of JB weld. You can even lightly release coat the chassis to keep it from sticking too bad if you ever want to remove it.

It happens because the tang is not a complete cylinder, and the very bottom of the action is NOT supported in the typical "V" block setup. If you put a dab of JB weld near the action screws (I do infront of the front action screw, and behind the rear one, or on both sides of both if you prefer....), then SNUG (as in apply no torque) your action screws up and let it sit over night, you alleviate the issue.

A complete skim bed is not required, and I wouldn't pay someone to do it.

The other alternative is to have someone (namely C. Dixon comes to mind) surface machine the chassis to match the receiver's curvature, so it's a half-pipe instead of a V block.

Does this essentially "free float" the action with the exception of the two spots that have JBweld?

 

[Ledzep]

Does this essentially "free float" the action with the exception of the two spots that have JBweld?

No. There is still contact with the V block down the length of the action on both sides. The JB weld just provides a "floor" for the action to be supported on the bottom. Two things it prevents; 1) The action screws down try to suck the action to the bottom of the V block, and likewise force open the V block (elastic deformation). 2) Prevents the fulcrum of the tang area and the rear screw by having a support behind the rear action screw.

Here's an MS paint drawing, hopefully explains it better if the words aren't doing it.

 

[supercorndogs]

I have had a banana shaped action that would not shoot in a V-block. I ended up bedding it into a pillar bedded stock, and the problem went away.

 

[The King]

I have bed actions in chassis systems. I think the best outcome I had was glue in though - shrank the groups by .25. The action was leaving a substantial movement wear mark in the v-block.

 

[LRI]

Chassis should not need to be bedded. You first solve this by designing it correctly. As the illustration above shows, the #1 parent issue is supporting the tang properly. Because the tang on a majority of action designs narrows in the rear, the tangent contact stops prior to the source of the load being applied. (the screw) This makes it behave like a fulcrum and it attempts to pull the front of the action off the stock.

Bedding the back end is one way to solve this. Another is to enlarge and thread the rear screw hole. Screw a brass pillar into it, and contour it to match the bottom of the action while also being tangent with the block that the receiver sits on. A little more work, but it's not going to ever flake off.

 

[Terry Cross]

Properly designed chassis systems will shoot with a bedded stock.
With the exception of a few odd spec'd actions, I have not shipped a bedded rifle out in several years.

I do not think the internal chassis I am using will outshoot a properly bedded rifle but I do not think it is giving anything up to one either.

By the time I bond the IMB into a stock and properly clean it up, I am not saving much time if any over pillar bedding the rifle. The cost of the IMB component is a good deal more expensive than a couple of aluminum pillars but it all works out to about the same money and labor at the end. I believe I have a superior package when complete or I would not use the technique.

The track record for the system is impeccable across a broad spectrum of temperatures and usages.

I know that some of the big name aluminum stock makers are having the same exceptional results so I think that my own experience is not unique or a fluke.

That being said, there are certain attributes that can be present in a barreled action that can make them problematic in some chassis systems, especially one incorporating a V-block design.

./

 

[Gossett6MM]

I've been shooting a manners mini chassis for a couple years now with no issues. I recently bedded that chassis with devcon and accuracy is excellent but I don't know if it's better than before. I can tell there is a noticeable difference in vibration since it's been bedded and in my mind that could help accuracy. But the only thing I really learned was, bedding the chassis will not hurt accuracy if done properly.

 

[308pirate]

Chassis should not need to be bedded. You first solve this by designing it correctly. As the illustration above shows, the #1 parent issue is supporting the tang properly. Because the tang on a majority of action designs narrows in the rear, the tangent contact stops prior to the source of the load being applied. (the screw) This makes it behave like a fulcrum and it attempts to pull the front of the action off the stock.

Bedding the back end is one way to solve this. Another is to enlarge and thread the rear screw hole. Screw a brass pillar into it, and contour it to match the bottom of the action while also being tangent with the block that the receiver sits on. A little more work, but it's not going to ever flake off.

Is a completely flat bottomed action (Howa and Winchester for ex) more advantageous in this regard?

 

[Ledzep]

Depends on the geometry. If the action is not supported behind the rear action screw, or if the chassis makes contact with the action higher, on the not-flat-bottom part, forward of the rear action screw, you'd get the same fulcrum effect. But probably less likely for it to happen with a flat bottom action like a Winchester or Mauser, Howa, etc. because you'd expect it to be designed to make contact with the bottom of the receiver, including behind the tang screw.

Round receivers kind of need to make contact with the V block on the sides, higher up than just on the bottom. The square bottom actions could squarely butt up to the bottom of the chassis (and both would back up against the recoil lug squarely) and not have rotational issues. The cylindrical receivers need side contact to prevent rotation.

 

[308pirate]

Depends on the geometry. If the action is not supported behind the rear action screw, or if the chassis makes contact with the action higher, on the not-flat-bottom part, forward of the rear action screw, you'd get the same fulcrum effect. But probably less likely for it to happen with a flat bottom action like a Winchester or Mauser, Howa, etc. because you'd expect it to be designed to make contact with the bottom of the receiver, including behind the tang screw.

Round receivers kind of need to make contact with the V block on the sides, higher up than just on the bottom. The square bottom actions could squarely butt up to the bottom of the chassis (and both would back up against the recoil lug squarely) and not have rotational issues. The cylindrical receivers need side contact to prevent rotation.

I have Howa actions on both Manners (pillar and epoxy bedded) and KRG (unbedded) stocks. The rear tang does not extend appreciably from the rear action screw and its bottom is flat. I think that is one big reason why my 308 (KRG chassis) and 223 (Manners) both shoot lights out. In fact, the Manners was inletted and bedded to the 308 action first, then I moved it to the KRG. When I bought the 223 barreled action I dropped it in the Manners (without re-skimming) torqued it to 65 in-lbs and shot lights out with 24.8 gr of TAC under a 55 gr Vmax (sub MOA 10 shot grp).