Mk I sight swinging on the leaf

[bow]

Good evening. problem occurred today at the range : while shooting i felt something wrong..Good groups enough, but these groups were shifting from left to right and viceversa and high to low ( and viceversa).. I rembered i substituted oringinal mk III canadian rear sight that is a mk2 pattern, with a sort of mkI rear sight i took from a No.5 jungle carabine. Why? Beacause it has fine vertical adjustment..
Slide swing left to tight in a adiagonal pattern under light fingers pressure. Probably this is the cause of groups' stringing. How could i fix it?

Teflon between leaf and slide... a new backsight...? Saturday i have my first 2013 competition so i have not the time for the shipment of the new backsight..

Information

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[Simon P]

The problem may be the fore-end bedding.

Sembra che hai un problema con il letto fore-end

[Peter Laidler]

To be honest Bow, the slight movement between the solid axis block type Canadian Mk3 (and 4) type backsight slide and leaf shouldn't be noticeable(?) on the target. However, if you have a UK made Mk3 or 4 backsight fitted, then these sights require a SPACER, pin axis backsight to be fitted too. Without this, the sight can and will move from left to right and vice verca.

As for the horizontal error, we need more info but I'm sure you'd have said if it was the catch that was defective. BUT as I said, the slack between the slide and the leaf doesn't usually notice on the target.

No5 rifle backsight is not calibrated for the No4 rifle barrel trajectory or harmonics

[bow]

if you have a UK made Mk3 or 4 backsight fitted, then these sights require a SPACER, pin axis backsight to be fitted too. Without this, the sight can and will move from left to right and vice verca.

http://www.euroarms.net/EFD/manuali/...RE-IT-1948.pdf
TAB. B shows nomenclature of backsight, what letter identifies the spacer we are speacking about?

To give an idea the clearence i have here i nedd a thickness of two paper leafs used for computer press.

[Peter Laidler]

Item number 10 is the spacer that you must have

[bow]

I haven't it... But the paly i detected takes place between the leaf ( items number 1) and the slide ( items number 6). One edge of the slide goes higher and the other goes down for about 0.21 mm

[Thunderbox]

I haven't it... But the paly i detected takes place between the leaf ( items number 1) and the slide ( items number 6). One edge of the slide goes higher and the other goes down for about 0.21 mm

As Peter says, the normal movement in sight components will not make any difference at the target.

If you have good groups, but they move around the target, then the rifle has some sort of bedding problem. I would guess that maybe:

1. The front handguard is moving - and obstructing the movement of the barrel by touching the foresight protector;

2. There is something in the barrel channel which is causing the barrel to stick. Sometimes "moving groups" are the result of a lump of cosmoline in the barrel channel: when the rifle is cold it shoots in one place, but then as the barrel gets hot, the cosmoline melts - and the barrel moves its point of impact somewhere else.

[bow]

Just finished to check bedding. All thing seems to be in good order: fore-end wrist contact, equal bearing on draws ( recently patched) , around main screw and under the reinforce. main screw is screwed with 5 turns as always, collar length checked.

The only thing different from past fitting is muzzle bearing: some days ago i've machined away 2 mm circa of wood in order to try canadian center bedding. What a mess!! So i decided to restore military bedding. To restore it , i used asilicone, very hard, used in odontoiatry: it's 95 Shore A of hardness. Barrel requires 10 pound to be lifted. Probably this pundage in too high??

[Thunderbox]

Barrel requires 10 pound to be lifted. Probably this pundage in too high??

Far too high. You are probably getting some strange barrel vibrations as a result.

Try about half - 5 lbs. Many No4s work well with just a light pressure.

[bow]

Thanks!