doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com gap between barrel flats and water table?

why is there usually a gap between the barrel flats and watertable?

thanks!

The gap is there so when the gun is starting to wear the barrels can be pulled down a touch more and action will remain tight.That is the way it is for a rotary bolt locked A H Fox. Bobby

Marc, the gap is there to allow the action to flex upon firing and not cause undue stress to the barrels and lockup. If there was no gap and everything locked tightly the forces released in firing would soon jerk the action apart. So, in a way, the gap is somewhat a shock absorber. Unfortunately many guns that are put back on face today do not leave the gap and the lifespan of the job is much shorter than what it originally was. Clear as mud?

The action seems "massive" but will still flex under the forces of firing. A tight fit leaves it no where to go. If it has no where to go, the bending forces are going to be transferred to the locking system and that is a very bad thing.

Perhaps some of you have seen the demonstration where a railroad rail is equipped with a strain gage and a short lever to twist said rail. A child usually has no trouble bending the rail enough to make a strain meter register. Force moves metal. The only question is, "How much?"

DDA

so if a gun has no gap does it shoot loose quicker (if so, how much quicker) or do you risk cracking the action at the action flat/standing breech angle?

what is the remedy?

build up the barrel lug slightly to move barrels back a touch.

When properly fitted there should be a few thousands between the barrel flats and the bar in the area about midway along the bar. Less so as it gets towards the hinge pin/knuckle and just about none right at the corner where the bar meets the standing breech. There should be none, zero, nada between the breech face and the barrels. The afore mentioned gap allows the bar to flex on firing. Think spring. Super important. Reduces shock to the whole locking mechanism. If some fool has removed this gap then put it back by removing metal from the barrel flats, not the bar. Remember, just a few thousands. If the tool you intend using is anything other than some emory cloth and a piece of wood then you are doing it wrong.
nial

[quote=Marc Stokeld]so if a gun has no gap does it shoot loose quicker (if so, how much quicker) or do you risk cracking the action at the action flat/standing breech angle?

what is the remedy?[/quote

It will depend on the gun ,how much gap is needed and the condition/reason the gap has gone . There is no one size fits all answer other than some re-joining will probably be needed. This may involve new joint pins or welding up the hook or it could be as simple as filing a couple of thousands off the flats of the barrel and or action as has been the case with some new O/Us that have not been freed off correctly and are hard on the bite because the barrel wings are hard down on to the action .

Here are examples of the gap, and how the barrel flats make more and more contact with the table as the bolting wears.

I bought both of these Foxes virtually unfired. I've documented nearly 38,000 rounds through the 16ga and the toplever has just moved just past center; note that it grabs a .203mm (.008") gauge snuggly, but I can pull it out without much effort.



Note the shiny spots near the junction of table and breech...wear at the hinge has increased enough in the last 5,000 or so rounds, that the barrel flats now hammer on the table under recoil. Still plenty of life, perhaps another 10,000 rounds or so, before a rebuild is necessary.



This 12ga Fox has digested a little over 60,000 rounds. The gap is similar and hasn't changed, but note the more extensive contact of flats and table. It's the "spring" in the action that allows the gap to exist at rest but be overcome under recoil. It's still safe to shoot, but it's beating itself to death and is due for a rebuild before the next Bo-Whoop Challenge.

Mike,Your great pictures show it all. Bobby