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-   -   Oh fudge... (loose front sight on 7-4) (https://www.rimfirecentral.com/forums/showthread.php?t=370845)

Kevin6q 12-23-2010 08:30 PM

Oh fudge... (loose front sight on 7-4)
 
In reality I let loose the grand-daddy of 'em all. A word I'd heard my father say almost every day of my life.

In keeping with the shooting sports at Christmas I've started this with some interpretation of Ralphie in the movie "Christmas Story".

The northeast racing season starts next week with a NorAm Cup race combined with the Junior Worlds Team trials held in Jericho, VT at Camp Ethan Allen Training Site. The best 17-20 year old biathletes from around the US will be in attendance racing for a slot on the US Team and competing in Novoe Meastro, Czech Republic in mid January. The race organizers allow duffers like me to compete with the other FOGs who show up with the only thing on the line is a little pride and bragging rights.

Back to the Oh fudge....

I have a 50 meter range at the house but not enough snow to ski and wanted to work through some range procedures before racing. Shooting with skis on is very different and I was having issues with my groups moving around and the paper targets used for zeroing looked more like I had used a shotgun rather than a .22. The home range is not idea for shooting with skis on until there is a lot of snow so I figured I'd head the 90 minutes north to attend a practice session with my biathlon club.

Part of the testing was also putting on a new blinder to test it before sending some off to Europe where they are used by athletes on the World Cup. I was testing a new layup on the composite blinder. When I picked up the rifle something moved and I figured the bedding bolts were loose. Checked them and they were fine. I placed my thumb onto the barrel and pushed it a bit and it too felt solid but the nasty feeling of something loose was still there.

I started checking the rear sight. Okay, the butt plate, cheek comb, mag holder, handstop, carry harness. All okay. I figured I was imagining the feeling so I started going through the mounting and dismounting to see how the blinder folded up on my back and popped into shape when the rifle came off my back. I lift the rifle off my back by hooking my thumb under the barrel weights attached to the front sight and felt a definite, click. Upon examination I discovered the front sight mount is loose and wobbled around.

Here is the spot in the story where the Oh fudge came forth. I had no idea how the front sight is held onto the barrel. Was it press fit? I sure hope not. I remembered how there is nothing on a Russian rifle that has no purpose and there is a hole on the underside of the globe where the spring that keeps the sight cover in place is visible. I always thought this was an oil hole for lubing the spring. Just maybe it was the access hole for some kind of set screw that keeps the sights in place. Taking of the snow cover required grinding off the end of the pin which acts as a hinge and also runs through the plunger inside the spring. A 4d nail pushed it right out and looking down into the hole I saw a slot. Inserting a screwdriver and giving it a twist had the sight held firmly into place. I figured zero would take a few more rounds when I got to the range. I used the 4d nail as a replacement for the pin I ground off. The head was large enough and I just bent over the nail and cut it off. Works fine.

Turns out the extra training day was earlier than I arrived so I missed it and have no idea how off my zero is. I'll just spend tomorrow morning at home re-zeroing and try to squeeze off a few round while on my skis and hope for the best next week. On the up-side, I had a blast skiing around on wonderfully groomed snow. My kids were with me and we spend almost two hours chasing each other around.

If anyone was wondering how to remove the front sight its held in place by a single set screw hidden by the spring..

aom22 12-24-2010 09:31 AM

BI 7-4 Front Sight ... Held In-Postion By Screw
 
Here are a few pictures of the front sight on the BI 7-4 used by Kevin6q.

Biathlon Sport & Biathlon Rifles
Quote:

Originally Posted by Kevin6q (Post 3231875)
... and there is a hole on the underside of the globe where the spring that keeps the sight cover in place is visible.
http://i84.photobucket.com/albums/k2...verRotated.jpg
I always thought this was an oil hole for lubing the spring.

Just maybe it was the access hole for some kind of set screw that keeps the sights in place.

Taking off the snow cover required grinding off the end of the pin which acts as a hinge
and also runs through the plunger inside the spring.

A 4d nail pushed it right out and looking down into the hole I saw a slot.

Inserting a screwdriver and giving it a twist had the sight held firmly into place.
http://i84.photobucket.com/albums/k2...ghtcloseup.jpg
If anyone was wondering how to remove the front sight its held in place
by a single set screw hidden by the spring.


aom22 12-24-2010 10:22 AM

STICKY: Front Sight Screw
 
Kevin6q ... I STICKIED the information about the front sight screw.
Definitely good info to know - aom22. :bthumb:

Quote:

Originally Posted by aom22 (Post 2484353)
Sticky: Rimfire Tactical Precision Match Competition and BI-7-4 Tactical Rifles
Oh fudge... (loose front sight on 7-4)



Kevin6q 12-24-2010 10:49 AM

Thanks.
 
Had I not been in a paniced rush to get the sights back into place and into the truck to head north I'd have taken photos of the operation. I'll have a chance to shoot in a few hours and I'll report how far off the zero is or if the ball end of the setscrew put the sights back into the original position. Hopefully the tight front sight will have the groups back to a smaller shotgun pattern. It (the loose front sight) would have been a good post race find and built in excuse for bad shooting. I'll have to find a new one.

midwest swiss 12-24-2010 12:29 PM

Here is where the set screw is for my CM-2 frnt. sight.
http://i28.photobucket.com/albums/c2...100_4906-1.jpg

aom22 12-24-2010 01:08 PM

CM-2 Front Sight Set-Screw Access
 
Quote:

Originally Posted by midwest swiss (Post 3232884)
Here is where the set screw is for my CM-2 frnt. sight.

Swiss ... I STICKIED your post.
Quote:

Originally Posted by aom22 (Post 2238115)


Kevin6q 12-27-2010 08:23 PM

re-zeroing after tightening the set screw
 
After digging out of the snow today I was able to see how much the front sight had moved after re-tightening the set screw holding it in place. It was getting dark and the wind had subsided a tad so it was just cold (9F) and minimal wind chill and I was motivated by tomorrow being the first race of the season.

I broke 5 shots and had a decent group 4" to the right of the X so I dialed in a 12 clicks of left and sent another 5 rounds. This time the group was a click or two right and a click high. After making the changes I decided to shoot the metal target and see what I had. Dropped 4 of 5 prone so it must be decent. I had my skis on and unloaded the remaining 40 rounds offhand and felt okay shooting with skis under me.


I was pleased the group only moved 4" and came right back in. Not a bad thing either as I usually only move the sights a few ckicks and noe I can add wear to a new thread section.

aom22 12-28-2010 04:39 AM

Front Sight ... ONE Screw
 
I'm surprised that only one screw and not even a set-screw is holding
the front sight in-place.
Considering the rough and tumble action of biathlon, I would think
a more substantial means of securing the front sight would be employed.

Such as, duel or triple set-screws.
Or, pinning the front sight base in-place.

Kevin6q 12-30-2010 02:39 PM

I asked around and a few athletes believed there is also some epoxy or other adhesive to help hold things in place.

aom22 12-30-2010 07:46 PM

BI 7-2 ... CM-2: Similar Manufacturing Methods
 
I had forgotten that the BI series rifles have their barrels press-fit
and epoxied into place.
It is logical that a similar process would be extended to the front sight assembly.
Quote:

Originally Posted by aom22 (Post 1763963)
Biathlon 7-4, 7-3 and 7-2 barrels are press fit with a bonding agent (engineering grade epoxy).
They are not pinned.

This thread will explain:

dumb question BB mag owners .. Convert .22Mag to .17 HMR -Safe? - Barrel: Press/Bond


The BI 7-2 and CM-2 share manufacturing methodology.
Quote:

Originally Posted by Eastside Ptarmigan (Post 3032401)
I have a new CM-2 as opposed to the older vostock or ural models.
I believe the barrel is pressed in and secured with engineering grade epoxy as is the front sight

Kevin, thanks for the memory jog.


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