Yugo M48 used to stay zeroed, aggravating range day!

[Shrinkmd]

I was shooting my Yugo M48 today, and cold barrel was 4-5 inches high, at top right edge of target (standard letter size sheet). It had been shooting ok and was zeroed last time, but the last few times I've shot it, same problem.

Equipment: Yugo M48BO, shooting 1955 Yugo surplus, S&K scout mount with Leupold 2.5x scope. Otherwise stock. I have been shooting this gun for years with same ammo, and although it has needed a little adjustment between range sessions, this is ridiculous.

It was bizarre, I had it dialed in, final, grouping in the center at 100. Went to change targets, talking with some other people, and the gun cooled down. And then went right back to shooting high, even off the edge of the paper, although more centered.

Any ideas on what could be wrong? Same crate of surplus, so that shouldn't matter this much. Could it be the (lack of) bedding, cosmoline seepage, scope going bad, my poor shooting? Or is 1200 rounds or so of surplus 8mm too much for the scope/mount/rings and likely need to retighten or remount everything?

It's the days like today that make you want to go back to shooting tin cans with a 22

 

[kwg020]

Same ammo or different ammo? Different ammo can be loaded with different powders and it will affect POI. In one of my rifles the slower powder always his about 2 inches lower and 1/2 inch to the left or right.
kwg

 

[Shrinkmd]

All the same ammo, 1955's finest!

 

[fireman 9731]

Snugging up your mount and rings would be the absolute first thing I would check.

 

[WardenWolf]

A lot of the old surplus ammo is going bad. I recommend trying PPU and see the results you get.

 

[Llama Bob]

So is it one cold bore flier every time the gun cools down, and then it's accurate? Or is it now generally inaccurate?

 

[Shrinkmd]

The gun was consistently shooting it's usual 3-4 inch groups with surplus, but way up and off to the right. After fiddling with the scope and shooting a nice group (well 3 inches or so, but hey, it's surplus) that was centered, I let it cool down.

When I started shooting again, everything was centered, but high, even off the top of the piece of paper, onto the next target above it. I wonder if the scope went bad? It is a Leupold, couple years old now, lots of rounds through it.

 

[Slamfire]

I was shooting my Yugo M48 today, and cold barrel was 4-5 inches high, at top right edge of target (standard letter size sheet). It had been shooting ok and was zeroed last time, but the last few times I've shot it, same problem.

The Mauser action is intolerant of poor bedding and these Yugo's went through a rebuild process that ignored action to stock bedding. Radical changes in zero, and strange shaped groups are characteristics of poor bedding. I bedded every Yugo I own, in two cases the accuracy improved and the groups became round. Zero changed so expect that. One rifle, the barrel was 0.328" in diameter, though the barrel was absolutely new, and the bullets I had were 0.323". It would stay on an 8" X 11" piece of paper at 100 yards.

I recommend bedding the action, with these Mauser service rifles, route out a little wood and pour in the epoxy. No need to pillar bed. I used Johnson paste wax as a release. Read up on bedding these things as the barrel to barrel channel bedding is important.

Now surplus ammunition, military ammunition will shoot through bricks, houses, etc, but it was never meant to be target ammunition. If it was shooting 4 MOA with military ammunition that is all you can expect, even with a target rifle.

 

[Llama Bob]

It might be bedding, but I wouldn't go narrower than "something's moving" to explain the problem right now, because the truth is we have no idea what. I would start by replacing the scope with a known good one and tightening every screw in sight (bases, rings, action screws, etc.) to torque spec. Then shoot again and try to zero the rifle and see what you get.

 

[WelshShooter]

Good suggestions on the rings and bases, these would be the first things I would check. Might be worthwhile checking out the action screws too, if these are loose then accuracy could change.

 

[ofitg]

Dang it...... I was thinking about buying a S&K scout mount for a Yugo Mauser, but now I want to wait and see how this thread turns out.