OzFclass

First post here, so hopefully I'm not breaking any rules asking this question.
I've recently got a license again and got into some target shooting after about 30years away from rifles.

Long story, but I've ended up with 3 old Omarks. An older one with a DAxxx s/n that has an adapter and been rebarreled in 6BR, and the other 2 are stock standard later model SDN/SDO s/n ones in 7.62/308W
My intention is to participate in F-class with the 6BR, and TR with one of the others, see which discipline I prefer and go from there.

The 6BR shoots accurately, but has very heavy trigger. I don't have a pull gauge but it feels about twice as heavy as the 308's (which feel similar to each other).
Interesting thing is that if I take the bolt from either of the 308's and put it in the 6BR, then the trigger weight and feel is much improved - pretty much the same as the 308's.
My conclusion from that is there's nothing wrong with the trigger itself on the 6BR - but something isn't happy with its bolt.

I've looked closely at the where the trigger touches on the firing pin, and the only noticeable difference between the 6BR bolt and the others is that the angle seems to slope more away from the bolt face.
IE the 308's have a steeper angle closer to 90deg. There's bugger all in it, and I can only see the difference by touching the 2 bolts together with those faces back to back and holding them up to the light.

I've no experience with trigger geometries, but wondering if that increased slope would cause the heavy trigger and may need some gunsmith loving - or maybe its completely unrelated and more likely to just be in need a strip and clean of the bolt assembly (which hasn't been done).

Any thoughts?

Steve

Hi Steve. From memory there were two different triggers on Omarks, an early and a late version. The early one (which was more durable) had an angle of about 45degrees on both the cocking piece on the rear of the bolt and the top of the corresponding part of the trigger. The later setup had a 90 degree angle on both the cocking piece and the trigger. The main difference in the two was the way the trigger operated which dictated the reason for different angles. Bolts will physically swap between the two but the timing and operation of the triggers changes and suffers. Square cocking pieces with square triggers and angled cocking pieces with angled triggers is the go. Hopefully Barry Davies (Davies Triggers) chimes in with a bit more technical info to help out. Regards Malcolm.

Thanks Malcolm.
The 3 bolts I've got all look exactly the same (aside from the 6BR one having a longer handle fitted).
Here's a photo - 6BR one that I'm having issues with is on the left



Steve

Hi Steve. Just check the trigger units on all three. The bolts are all early type but you may have an action with a later trigger unit fitted. Check the mating part of the triggers to see if one has a right angled piece where the cocking piece on the bolt contacts it. Even if they all match up (all angled or all square) there are still a lot of issues with Omarks regarding bolt fit and timing due to adaptors being fitted and mismatching of bolts and actions. New barrels being fitted can throw out the relationship of trigger unit and bolt position causing changes to the bolt timing and trigger engagement positions. Maybe get someone in the club familiar with Omarks to have a look or see a gunsmith that has worked on Omarks to have a look. Regards Malcolm.

Trigger units all look the same. Same matching angle where they contact the cocking piece.
I removed the firing pin assembly from the 6BR and one of the 308's hoping to swap them between the 2 bolts, but unfortunately the 6BR has a smaller diameter pin and the bolthead has been plugged and drilled to suit. So I can't just straight swap them as the 308 firing pin won't fit through the hole in the 6BR bolt head.
What I HAVE found though, is that there seems to be some binding in the 6BR firing pin assembly where the cocking sleeve slides in the bolt plug. I'll strip it down tomorrow and see what's causing that.

Steve

Most of the trigger let off pressure comes from the firing pin spring.
Way back somebody made a heavier spring for the omark due to a constant problem with misfires. This worked ok and solved the misfire problem but also introduced more downward load into the trigger resulting in a heavier let off pressure. Couldbe one of the bolts has this spring fitted.
Other problem with the omark trigger was the pressure adjusting spring. To make it work properly it had to be wound up resulting in a too heavy let off pressure.
A lighter spring could be fitted but that introduced a problem with sear return and sometimes the firing pin would not cock or sear engagement varied giving variations in let off pressure.
The square cocking piece and pivoting the sear at the rear solved the problem to some degree but the whole design is still somewhat agricultural for what is needed in today's target rifle..
Barry

Thanks Barry - I appreciate the background info.
I think you may be on the money with the heavier firing pin spring suggestion.
I stripped down the troublesome 6BR firing pin assembly along with one of the 308 ones, and used the smaller diameter 6BR firing pin with everything else from the 308 one.
While I don't have a practical way of measuring the spring force, the 308 spring did seem to be easier to compress by hand.

Assembled it back into the 6BR bolt and success!! I've now got a much nicer trigger
Putting the remaining parts together for the second firing pin assembly and fitting it back into the 308, and it still feels OK (albeit possibly a fraction heavier than it was to begin with).

Unfortunately I still don't know exactly what the issue was as swapping out a bunch of parts is pretty poor troubleshooting practice. But the goal was to sort out the 6BR trigger and I've done that - along with gaining a bit more knowledge.
Will see how it goes at the range tomorrow....

Steve

Just reporting back that all went well at the range. The trigger was very nice to use and definitely made it easier to shoot than it has been previously.
Thanks all

Steve