Thoughts on bedding a chassis?

[X Count]

I have an MDT ACC chassis that needs to be mated to an action.

It's getting bedded regardless but what is everyone's thoughts on where to bed. Just the front ring and tang or, full action including side rails. Note this will have a 1.25" 30" parallel barrel on it.

 

[jackieschmidt]

Nothing is better that a full contact proper bedding job, whether in a synthetic stock, a wood stock, or a metal chassis.

The object is to avoid any distortion in the action when it is tightened into what ever you are attaching it too.

Since you are hanging a lot of barrel off of the action, bed it where ever it contacts.

 

[X Count]

Nothing is better that a full contact proper bedding job, whether in a 7 stock, a wood stock, or a metal chassis.

The object is to avoid any distortion in the action when it is tightened into what ever you are attaching it too.

Since you are hanging a lot of barrel off of the action, bed it where ever it contacts.

Thanks Jackie, that's what I'm leaning towards as well. Other repeaters Ive done have been front ring and tang and have shot excellent but none have been this heavy or in a chassis.

 

[Alex Wheeler]

Like most things in rifle building you need to understand what your trying to achieve. With bedding its a interface between the action and stock that does not change from shot to shot or day to day. Its that simple. Bed as much or as little as you want so long as the interface is stable and doesnt change.

 

[eddief]

In a good chassis, capturing the lug in bedding, is all that is needed IMHO. This keeps the system from being affected from side impacts (going in and out of props, such as a metal cattle gate, etc). I have tested just torquing down with no bedding, full bedding entire action as you would a McMillan, and just the lug.

If you take a hard lateral hit metal on metal, it can shift a very small amount. A bedded lug shored this up.

This is my experience and literally seeing no change in zero or POI. In fact, last year I shot a PRS match in an absolute downpour, decided to fully tear down rifle system and even pulled barrel. Assembled everything back and neither, zero nor POI changed. Of course, there are more variables involved than just lug bedding, but this has been done over multiple chassis and it has always worked for me.

 

[LVLAaron]

Personally, I've seen very little benefit in bedding the two that I have - One is an MPA and the other is a Manners mini chassis. Both of these are higher end and the mating surfaces are all matched up well.

I had a savage with a V block that didn't mate well on the rear "V"s - bedding helped that one quite a bit

 

[X Count]

This chassis has already been bedded by someone else for a different action at the lug and tang. So I don't have the option to go direct into the chassis but I'm confident of bedding those areas and definately not making things worse.

 

[NZ_Fclass]

I would bed any factory made action - while the chassis may be to spec, the action may not. I found this out the hard way, using a Remington 700 in a Dolphin chassis. It didn't take more than a skim to correct the difference between components and the difference was immediate.

 

[X Count]

Decided to just do the front and rear and leave the middle. The ACC is very low through the central section which I guess allows a universal fit with various port openings and bolt release positions. Because of this the contact area between the chassis and the action would have been less than .250 each side and the juice wasn't worth the squeeze.

Removed the old bedding and roughed up surface. The chassis has 1/4 UNC holes in the bedding area adjacent to the action screw holes. Presume this is for fixturing during manufacture. In the rear that would be 20% of the bedding area so made up grub screws and used locktite to hold in place. Made spacers that fit in the forend and raised the action above the bedding area by .020 and milled .040 from the recoil lug face to give the devcon some meaningful thickness.

The holes for the action screws are actually slotted fore and aff to allow recoil lungs to pull up against the chassis. Good in theory but it makes for a fairly large hole which they bridge with a thick washer. Spot faced the bolt holes and made up 1/8" thick washers and surfaced both sides. Squared the back side of the action bolts.

Blanked off everything with putty, tape and kiwi polish where it needed to be. Supported the chassis under the barrel supports so that the back end of the chassis and the action were floating. Got a good layer of devcon on everything and nestled the action into its new home.

 

[X Count]

Left it a few days and it popped out nicely. Cleaned everything up and the indicator shows about 7.5 micron or about 3 tenths.

Threaded the muzzle 3/4x24 for the brake. Thread still looks small against the 1.25" barrel!

Going to a while before I can start load development but it's coming together.

 

[LVLAaron]

Very nice job

 

[tobnpr]

I'm alone on this island...
But I've always bedded an inch or so ahead of the lug under the barrel cylinder with long, heavy barrels such as yours. Ten pounds of steel hanging off the end of the receiver just doesn't sit well with my non-engineer brain. I like to have some support just ahead of the receiver ring to mitigate this.

 

[Sniperhandle]

I'm alone on this island...
But I've always bedded an inch or so ahead of the lug under the barrel cylinder with long, heavy barrels such as yours. Ten pounds of steel hanging off the end of the receiver just doesn't sit well with my non-engineer brain. I like to have some support just ahead of the receiver ring to mitigate this.

I also do my builds the same except, More like 1.5 inches, Especially with Heavy Varmint, MTU etc. hanging off the front end like that.

 

[X Count]

Yeah I'm picking up what your putting down as it makes sense in a way and I used to do the same.

The alternate train of thought says that the chamber area is getting hot and expanding, if you swap barrels regularly then each barrel is not EXACTLY the same diameter and if we are indicating and cutting the chamber and threads concentric to the bore then the OD of the barrel is not going to be concentric and will sit in the bedding differently for each barrel.

For a gun that keeps the same barrel for a period of time and then is re bedded for each barrel then sure. For chassis gun that is going to be used for shooting steel and swapping barrels then I hope some form of bedding is going to be an improvement over dropping it in and torquing it down.

 

[Alex Wheeler]

Take your barreled action and hold it in you hands by the action. Do you think your bending that action?

 

[tobnpr]

Take your barreled action and hold it in you hands by the action. Do you think your bending that action?

This is something that is easily tested, no?
Given I don't have a 30", 1.25 barrel I'll see if I have a length of 1-1/4" steel rod somewhere that I can cut down and thread a tenon on it. Challenging part will be locking the receiver down in a vise to do this without effing it up.

 

[Alex Wheeler]

This is how I tested it. Used my spring tester to push the tang down and balance the action on its lug. This a worst case, because theres no bedding to support the action.

 

[CA_Shooter]

So with a custom action Impact / Kelbly / etc + MDT ACC Elite + 1.25 straight barrel: is bedding going to help or be a waste?

 

[LVLAaron]

The problem you have on many chassis, is there’s no place to put bedding under the barrel.

Never seen an F class gun with a barrel bedded.

Personally I don’t want to redo the bedding every barrel change or if the barrel comes off and gets torqued a little differently- they aren’t perfectly concentric.

Bat actions have 1 thou of play between the bolt and the raceway. If actions were bending, we’d know without any special measuring equipment

 

[X Count]

Like most things in rifle building you need to understand what your trying to achieve. With bedding its a interface between the action and stock that does not change from shot to shot or day to day. Its that simple. Bed as much or as little as you want so long as the interface is stable and doesnt change.

Were you hacked?!

I agree with both of your posts. For this type of rifle and its intended purpose there are compromises that need to be made.

As with most guns the forend flexes at the recoil lug. This gun will mostly be shot off a bipod but could be a sandbag or backpack. That fulcrum point may be at the tip of the forend or at the mag well. So. . .. . Bedding in front of the recoil lug is going to cause varying amounts of pressure upwards on the barrel depending on where the support is positioned. Also this won't be shot free recoil so there is potential for movement on all axis depending on the tension that is applied during each shot. Combine that with a aluminium chassis being shot off of concrete, dirt, grass or mud there is going to be a wide range of harmonics at play.

None of those things are ideal but hopefully it flexes where it needs to and returns to its home position after each shot and meets its intended purpose.