doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com On face but barrels not tight to frame at lockup

For Bushveld:

Although the copy of the page above is a bit "cloudy", the arrow pointing to the action/barrel flats in figure 2 reads .002" to .004" clearance between the flats of the barrel and the action body at this point. This is a statement from the famous Birmingham gunmaker Robert "Bob" Turner. He further notes that the clearance between the circle of the lumps and the draw of the action is .0005" to .00015".

The clearance is for shotguns, not double rifles. Twice as much clearance between the barrel/actions flats and rubbing between circle and draw for double rifles.

Stephen Howell

I am trying to figure out how the headspace on wonko perrazi is maintained if barrel isn't fitted to action

I looked at the two Perazzi guns I currently have, a MX8 and a DC12. Both have blued actions and have been shot a lot so it is easy to see where the bbls bear on the action due to blue wear. Both were bought new, are still tight on the face w/ the top lever well to the right & have never had any adjustment on the bbl to action fit since leaving the factory.


On the MX 8 the back of the top barrel bears on the face of the action from about the 9 to the 3 o'clock position & there is no indication of the monoblock bearing at all on the flats that is visible from the blue wear.

On the DC 12 SxS both barrels bear from approximately the 8 o' clock to the 4 o'clock position including the rib between the bbls & approximately .200" of the front edge of monoblock is bearing on the action flats.


As mc posted, I don't see how you can keep the hook tight against the hinge pin (for long) unless the back of the bbls are bearing against the action face.

In one of the Purdey videos, the barrel fitter talks about that joint as being gas tight at the breechface.
If I recall the video correctly, he stoned it in.

Stoning is the last phase, after filing, when fitting a set of barrels. The ideal is 100% contact between the barrel breech faces and the action breech. But, that is virtually impossible. The higher the percentage of contact, determined by smoking in, the better. There are very few men in America that are capable of doing this job right, IMO.

Gough Thomas had written (cannot remember if it was in a book or ST article) of a way to prove action flexing and the need to make room for it by relieving the contact between between barrel and action flats. It involved the use of a small lump of plasteline (play dough in American I think) on the flats and closing the gun. Open and measure the diameter of the flattened plasteline. Now load and fire and remeasure. The plasteline dot grows in diameter after firing, proving that it has been subjected to further deformation due to the flexing of the action bar.

That is a neat experiment but there is no need to go that far. Close any SXS and slide a thin paper, cellophane or feeler gauge between barrels and action flats. That should convince that there is a gap there.

One mechanical phenomenon rarely, if ever, discussed in barrel fit is the Poisson effect. It concerns the behavior of thick wall cylinders (walls thicker than 1/10 of the diameter). Under pressure such a cylinder shortens and expands radially. Presumably that happens to the chamber end of barrels under pressure and this is followed by an equally fast recovery. This process must involve some considerable slamming of chamber ends against the breech face and the hook on the cross pin, and all this is in addition to the flexing of the action bar.

Simply holding the barreled action to a strong light source will reveal the tapering gap without the need for paper or other "devices". A .004" gap at the rear, with strong light behind it, looks big enough to throw a dead chicken through. An exaggeration, certainly, but it does look bigger than it measures, IMO.

So I checked four of the Perazzis, one MX8, two Mirages, and a MT6, and a 682 Beretta. All wearing their original factory fitted barrels. On every one the barrel shoulders (barrel flats) solidly engaged top of the action walls (action flats). The 682 has a replaceable block in the barrel shoulder at the breech end to accommodate wear. Those blocks as well solidly engaged the top of the action walls.

Someone best be getting those two manufacturers informed about how to do things the proper way.

The thinnest feeler gauge that I have is 0.001" and the action of my GR3 will not close if that is between the flats at the breech. It will also capture a human hair. What a POS. Looks like Beretta can't fit a SxS either.

I appreciate all of your comments about the fitting stuff. Gotta tell ya that I'm pretty disappointed in the quality of the factory work on my guns. Not even going to check the others, they're certainly just as crap.