Barrel blocks

[Doug Humbarger]

When you have the barrel in snadwiched in a barrel block with the action hanging in thin air (Palma) what size bolts are normaly use to tighten the block halves together?

 

[spclark]

It's going to depend on the design of the stock and barrel block you're dealing with.

I've seen some that are far longer and with many more fasteners on BR guns than the barrel clamp on my Mike Ross aluminum rifle stock. That uses 8 fairly small diameter socket-headed cap screws, I think 10-24 thread but I'd have to go pull one to be sure. The threads in the stock have steel inserts fitted to withstand the torque when tightened.

http://www.rossprecision.com/images/products/stock/Stock8.jpg

I use mine to shoot Palma with a Gilkes-Ross action, and with a barrel change can shoot 6BR, 260 Rem., or 6.5x284 too if I choose to. They all work great in that configuration.

The resulting clamping force is certainly sufficient to grip the barrel section tightly enough to prevent movement; it's effectively a barrel vise, built right into the stock.

 

[jlmurphy]

I built a barrel block rifle and used 10-1/4" cap screws on a 5" block, which is certainly overkill. I found the steel to steel contact around the block pulled too much heat from the barrel and eventually used an insulating gasket around the barrel. I also use it as a switch barrel, 6mmBR and .300 Win Mag.

 

[spclark]

That's an interesting evolutionary upgrade! What did you use to keep proper barrel tension while adding an insulating layer to inhibit heat transfer?

The G-R stock's barrel block is aluminum on the lower portion and is skeletonized to reduce surface area while the upper component is solid steel. Between it and your rig, I'd have to guess the relative surface areas are vastly different; I've never noticed any adverse effect from heat transfer with my rifle.

 

[jlmurphy]

I found when I first started load development that the groups were walking as the barrel warmed up, it was a premium barrel and shouldn't have. I placed the assembled rifle on a heavy steel fabrication table and set dial indicators on the vertical and horizontal planes at the muzzle. I poured boiling water through the bore and watched the muzzle move about .010". I then held the barreled action in an action vice and repeated the drill, this time less than .001", the difference was the barrel block. I then tried a copper heat sink sleeve thinking that the bottom was pulling the heat away faster than the top, but it was even worse. Finally, I tried an asbestos type gasket material of about .050" instead of the copper, and this time no movement when heated. I have since found, through searches, that many rail guns use epoxy sleeves to secure the barrel. An added benefit is the reduction of transmitted vibration. The scope is mounted on the block cap, the gasket material is hard enough that after it takes the first compression there is no movement, I have swapped the barrel about a dozen times, eventually I will replace the gasket.

 

[Doug Humbarger]

"Asbestos type gasket material of about .050"

What keeps the barrel from sliding in the blocks from recoil since there is no metal to metal contact? Is there a shoulder on the barrel that butts up against the blocks?

 

[spclark]

That would be akin to a recoil lug on a traditionally mounted action. Jmurphy indicates friction alone between his barrels and the gasket material is sufficient to resist movement under recoil, I assume in a manner similar to composition brake pads used with disc brakes. Developed friction may be greater with the gasket material in place than with direct metal-to-metal contact.

His barrel block is larger by far than that on my Gilkes-Ross stock, which also features a 1" dia. bore design. That all my barrels are profiled to a 1" section in front of their mounting threads, there's no room for me to try any thickness gasket material greater than maybe .004" in full contact.

Narrower strips might work, but the reduced contact area I'm afraid would not resist movement.

 

[TonyR]

Any experiences with gluing the barrel into the block instead of clamping?