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Installing barrels
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Member Posts: 168,427 ✭
What insures threaded barrels are turned and tight with the sights where they belong?
Maybe I am missing something.
Maybe I am missing something.
Comments
The amount taken off the shoulder determines that......
Or it depends on what rifle you are talking about...
On the FN-FAL and L1A1 different size locking shoulders are used
What is a locking shoulder guys?
The amount taken off the shoulder determines that.....
What is a locking shoulder guys?
What the barrel tightens up against. Most barrels tighten up against the front of the receiver, some (like Mausers, for example) tighten up against the inner ring.
If you know the number of degrees the sight is off when the barrel is tight, and the thread pitch of the barrel, you can calculate the amount of material that needs to be removed from the barrels seating surface.
IE a 10 TPI thread moves 0.100 per 360^ rotation (1"/ pitch = distance / turn). .1"/360^= 0.0028" (0.0027777... if you want to be fussy) per degree. To move the sights 10^ you would need to remove either .028" or .072" depending on which direction the sight needs to move. The chamber may need to be re-cut, depending on what the original headspace was at.
What [e]nsures threaded barrels are turned and tight with the sights where they belong?
A competent gunsmith. [;)]
OK, answer has been given already. It depends on the exact model of gun you're talking about.
With some guns, the barrel is installed FIRST, THEN the location for the sight is determined, the sight dovetail cut and the sight installed. That's the conceptually easiest way to do it.
With others, you need to remove material from where the barrel mates with the gun (ie the "shoulder") to alter how far the barrel screws into place, and thereby control the absolute orientation of the barrel (and sight).
Needless to say, you do need to know what you're doing here and have the proper tools to remove precise amounts of metal.
Again, depending on the gun and what was done, once the barrel is installed you may need to re-cut the chamber to re-headspace the gun. For a revolver, you might need to recut the forcing cone.
With some gun designs (eg FAL) the shoulder that controls the barrel seating depth itself can be removed and changed, potentially making this operation a little easier.
The last barrel I installed that had sights was an 03A3. The new replacement barrel was timed perfectly and all I had to do was tighten it till the front sight was 90* to the bottom of the action.
As for the rest, it goes pretty much like Tailgunner says, and there ae several ways you can index the sights, and make headspace. It all depends on the gunsmith, and how much experience/knowledge they have. For those who build tack driving rifles everyday, it is like second nature to them, kinda like putting a nut on a bolt.
Best
?
It's a good exercise for learning the relationship but you'll learn to do it by eye in business. You can guesstimate the number of degrees and hopefully be just a tad under on you estimate then make a tiny correction to come to TDC. But I'll have 5 of these done before you can accurately measure the correct number of degrees and then do the math.
Always be sure to make both shoulders (action and barrel tenon) parallel and perpendicular. Any irregularities on either face will result in faulty measurements and inaccuracy of the finished product.
Be sure that all surfaces are clean before test assembly or final assembly as tiny chips and dirt will affect fit and timing. There is nothing more disheartening than doing the final assembly only to find that there must have been a small irregularity (dirt, chip) involved in the last fitting and the timing is too far past TDC.
The last check is for headspace and the correction for it. Be sure to NOT go too deep as this will result in a setback and re-timing...
Best.