robbar, Are you talking about the bedding blocks that go under the reciever and run the entire length of the forend, ala HS Precision? That aluminum block is made from CNC'd Aircraft grade aluminum, and would have to get pretty hot before you'd have to worry about heat expansion, they're all freefloated stocks anyway with a layer of fiberglass cloth, Kevlar and whatnot over it. What is your worry with , anyway? images/icons/confused.gif Jay
Robbor weight comes into play and the fact that aluminum radiates heat better than stainless. I believe the idea is to transfer the heat out of the stainless. It would be the same idea as a steel sleeve inside an aluminum block in a car engine.
I use regular 34CD4 ( US 4140 steel ) with a electroless nickel platting or hard chrome on to avoid rust , barrels are glue with Loctite in , Stainlees is more difficult to machine and except for the look you win nothing
Randy, the reason for a skim coat of bedding is because it is very difficult to have a zero interferance fit while inletting a stock. Except for CNC'ed components, there will always be some slop.
An action/barrel block can be held in place by the "lug/action", screws, bedding block or some combination of the above. I prefer the bedding block-lug/action simply because this is the largest surface area and the largest component to move during recoil. I don't feel confident in 1/4" screws holding everything together.
Machine the block so that it has some "draw" angles for easier disassembly, then bed into the stock. Of course, the screws will have very heavy pillars to ensure that the whole mess does not vibrate loose during many recoils.
The bedding just ensures a "perfect" fit. When done properly, there is no stress on the action/block when the screws are tightened. Absolutely no movement when the screws are loosened. The screws only need to be put in hand tight. I don't bother with any torque wrenching since I feel this indicates problems in the bedding.
If bedding is done properly, the material/pillars will not compress under hand pressure or move during recoil.
Sounds like a very nice cannon. I too would build the block out of aluminum for the same reason, act as a heat sink. Our rifles shouldn't get hot enough that expansion rates of metals becomes an issue, as would happen in a car engine.
Curious about your "glued in" process. Do you mean that your block only has a hole bored in it which the barrel is glued into? Or do you mean that the block is split, and the barrel clamped using glue and/or bolts? What type of glue are you using?
If using a conventional epoxy, my concern would be that during a hot session, the glue can soften and the barrel torque. It might not be visible but it will still torque. The glue goes rubbery. Are you indexing the barrel in the block or using a pin?
Considering using a block for my next cannon so would love your feedback and experiences.
I'm using a glued in only, barrel to block that is. Hole is bored oversize and O-ringed, filled with epoxy. Pinned? Not that I know of, I'll have to ask. Not a bad idea though, the trigger is the only safety "lug" if it breaks free when firing. images/icons/grin.gif I'll see what the epoxy is he uses for it.
The block will be bedded in epoxy and screwed down both, though it will still be removable from the stock.
This block was not split, just the bore in it opened up enough for the epoxy between them. I'll post a pic when it's done, shouldn't be too long now... I hope. Dave's milling some more recoil slots in the bottom too, although I don't think it's necessary, but he's set on doing it so I ain't argueing over it. images/icons/grin.gif
One thing I might point out is that the torque specs for a given screw/bolt size will stretch the bolt a given amount and this stretch is what keeps them from loosening from the claming force, so it's not a bad thing, only good, although it may not be as critical in some applications as in others.
I'm using a 10" aluminum block in the 30/338 Lapua Imp that's being done up now. It's being glued on vs. clamped on. It's being bedded on 4 or 6 pillars and the block acts as the recoil lug as well, the rear is flush with the reciever face with the action and barrel both freefloated.
The chamber is the hottest, and aluminum disapates heat a much, much faster rate than steel, so this is good reason to use it over steel IMHO.
Expansion ratios on cast iron cylinder blocks while using aluminum heads require some real serious considerations and preperation to retain gasket seal, not the case when using cast iron heads. This doesn't seem to be much an issue concerning barrel blocks, as many use them glued on or clamped with no problems I'm aware of.