One modern adaption of the multi-screw breech is a British airgun (can't remember which one, but I saw a video) that uses 6 setscrews arranged in two groups of three, front and back.... Each group is at 120 degrees (one on top, others on lower sides, IIRC), allowing the barrel to be "steered" to align with the optical zero of the scope (at your intended zero).... Obviously the breech fit is intentionally SLOPPY to allow for that.... Apparently it works extremely well....
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
Yup ...have a link to that one at home...can't recall the name right now.
Milbro Matise is the one we were thinking of Bob.
It's all over the board Al.
Walther has 3 at 9, 12 and 3 oclock
Steyr has 3 across the 12 oclock position
FWB has 6 in rows of three at 3 and 9 oclock
I think they need that rigidity to ensure the barrel doesn't touch the tube it floats inside.
I do like that idea Bob of arranging 2 rows at at 120deg. Set into a shallow radius groove that would be rock solid. Then completely float the remainder of the barrel.
Sean
A bit of a problem sealing the transfer port, unless it seals against the barrel itself (still custom lenght required).... I was wondering about using a fairly close barrel fit at the back of the breech (behind the transfer port) with virtually no movement.... O-rings either side of the port to seal the barrel to the breech.... Then the rear row of setscrews just in front of the front O-ring.... The front row of setscrews would be as far forward as possible to allow "aiming" the barrel.... The breech would be oversize from just ahead of the front O-ring to the front....
You would back out the rear row of screws, aim the barrel with the front row of screws.... it would be rotating on the rear of the barrel where it fits snug in the breech and the O-rings.... When you get the alignment right, then you progressively tighten the rear row of setscrews for ridigity....
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
I just did some quick trig to get an idea of what the impact of a single set screw screw could be.
If side a is 0.001" (this is the clearance between the breech socket and the tenon
And side b is 1.25" (the length of the breech socket
And it's held together by a single grub screw which provides a pivot
Then the side a magnified to 100 yards becomes 2.88 inches
However in reality they are much looser than 0.001. In fact I have 0.006" of shims stuffed in one
That 0.006 becomes 17.25" at 100 yds
Holy cow
Sean
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