MK-3 Accuracy

[hawkeyepdx]

All,

I picked up a 18" SST MK-3 with 4x12 Nikon Monarch back in December and have been fighting problems ever since.  I was having the FTE/FTF issues everyone seems to be having along with it shooting 3"+ 5-shot groups, so I sent it back to the factory.  They said they adjusted the factory gas block, and sent it back.  I added a Magpul MOE rifle stock, spring, and buffer to it.  I ran 50 rounds through it yesterday with the best 5-shot group being 3.125".  The recoil and FTE/FTF seemed to be rectified.  I was using American Eagle 150gr and Fusion 150 gr.

I shot a 0.875" 5-shot group with my Tikka .270 (and Fusion 150gr) yesterday also just to prove to myself I'm not a crap shot.  When I came home, I switched my scopes so I can make sure its not the Nikon Monarch.  I also have a JP adjustable gas block on the way before I hit the range again.  Could overgassing premature unlock the bolt affecting accuracy?

I want to be able to use this for western elk/deer hunting, but I won't feel comfortable with long shots with a 3+ MOA rifle.  What should I expect for groups?  Are people getting under 1 MOA?

Thanks!

[98Z5V]

Could overgassing premature unlock the bolt affecting accuracy?

Yes, it could.  However, if it's overgassed enough to attempt premature unlock, it's going to affect your brass.  Look for extractor marks on the rims, or bent rims.

[edgecrusher]

Have you tried any other ammo? Maybe something heavier, say , 168 gr GMM? What's the twist on your barrel ?

[hawkeyepdx]

I haven't tried any other ammo.  Its "shoot what you can get ahold of" here in SW Washington.  The twist is 1:10.

What should the extractor marks on the rim look like?  And how bent is bent?

[edgecrusher]

Can you do me a favor, check to see how tight your barrel nut is, and I would say if that is okay, try some heavier pills, when you can...

[98Z5V]

Any bend to the rim on the brass at all - that's not good.  You'll almost always be able to spot some extractor marks on brass, but it certainly should not be chewed up or gouged, man. 

[BayouBob]

Some folks have gotten outstanding accuracy with their MK 3's.  Mine shoots right at an inch with Federal Gold Medal Match 168 gr. Sierra Matchkings.  It took trying a couple of dozen loads before I finally found a hunting load that stays close to an inch.  I settled on 165 gr. Sierra Gameking hollow points as the most accurate bullets out of my rifle.

[hawkeyepdx]

Thanks for the help.  The barrel nut is as tight as it can be without taking the proper tools to it.  The casings don't look all messed up either.  I'll order some heavier bullets, try my other scope on it, put the adjustable gas block on and see what happens.

If anyone else has some good groups, your input is appreciated!

[hawkeyepdx]

All,

I wanted to update this post with my findings.  I finally got some heavier bullets and went to the range.

I switched scopes with my .270 and the scope was fine.  I also installed a wilson combat adjustable gas block.  The results were instantly better with 168gr, 175gr, and 178gr, with the 168gr shooting a 0.875 3-shot group.  I didn't have a 150gr bullets left, so I couldn't completely figure out the problem.  I'll shoot some when I can get any and update this post.

My gut feeling is the gas was the problem though.  I had the gas block as closed as it would go and it locked the bolt back a couple of times.  I have it opened about 1/2 turn and had no problems.  Casings were in a nice neat pile at 3:00 instead of 1:00.

I am now hopeful that this gun will work out now!  My advice to anyone purchasing an mk3 would be to plan on an adjustable gas block from the getgo (something wilson combat puts on at the factory!).  Thanks for all the help and I'll post on the 150gr accuracy.