Winchester loading migraines

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Bushbum4.0

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I've been trying to load up something accurate for hunting season in my model 70 fwt. It's a .308, bbl cut down to 18".
I've put together several different loads, and I shot a 1/2" group at 100 with 43.2gr imr4895, but loaded up a batch and it was all over. Some groups 2", one group half an inch. Scope mounts are tight, rings torqued correctly, scope is in good shape. What the heck is going on with this stupid thing??
 
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Lefty D!ck has some sound suggestions.

Did the groups open up as the gun got hot? Those pencil barrels are great to carry, but usually get scorching hot after only a few rounds and groups sometimes go to hell on them as they heat up.


Mark
 
Assuming the condition of the rifle and scope mounts are fine what were the groups on either side of the charge weight you chose like? Was the load developed before cutting down the barrel? What were atmos when you shot your groups with the consistent 1/2”
 
Bushbum4.0 said:
I've been trying to load up something accurate for hunting season in my model 70 fwt. It's a .308, bbl cut down to 18".
I've put together several different loads, and I shot a 1/2" group at 100 with 43.2gr imr4835, but loaded up a batch and it was all over. Some groups 2", one group half an inch. Scope mounts are tight, rings torqued correctly, scope is in good shape. What the heck is going on with this stupid thing??
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This is when a chrono can help show if it's the load or the gun. Cheers
 
Bushbum4.0 said:
I've been trying to load up something accurate for hunting season in my model 70 fwt. It's a .308, bbl cut down to 18".
I've put together several different loads, and I shot a 1/2" group at 100 with 43.2gr imr4835, but loaded up a batch and it was all over. Some groups 2", one group half an inch. Scope mounts are tight, rings torqued correctly, scope is in good shape. What the heck is going on with this stupid thing??
Click to expand...
One, 3 shot, 1/2" group is statistically meaningless.

Now that you've fired more rounds, you have discovered the actual potential of that load, and it's not great.
 
Ok so I shot 3 shot groups, up and down in powder charge .5 gr at a time, until I shot a 1/2 group. Groups were all over, but saw the 1/2 and settled on it. Load up a dozen at that charge, 43.2 imr 4895.

Shoot those dozen 3 at a time and it's like 1.5, 1.75, 1/2, 1.25.

I've never had anything like this. It's always been load till you find the sweet spot, then when you reproduce that load it's consistent.

Oh and when I switch back to the factory load it likes, fed blue box 180s, it groups less than an inch.
 
Bushbum4.0 said:
Ok so I shot 3 shot groups, up and down in powder charge .5 gr at a time, until I shot a 1/2 group. Groups were all over, but saw the 1/2 and settled on it. Load up a dozen at that charge, 43.2 imr 4895.

Shoot those dozen 3 at a time and it's like 1.5, 1.75, 1/2, 1.25.

I've never had anything like this. It's always been load till you find the sweet spot, then when you reproduce that load it's consistent.

Oh and when I switch back to the factory load it likes, fed blue box 180s, it groups less than an inch.
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As jas been mentioned, one three shot group is meaningless, it could be a fluke, and your follow up shooting is indicating that this was the case.
 
I’ve been having a similar issue with a REM 783 in 450 Bushmaster and think I got it finally figured out
The barrel gets hot quick on it and I discovered that it wasn’t quite free floated properly
Sliding a 20 dollars bill up the barrel revealed a tight ish spot so I removed the stock and sanded the barrel channel a bit to make it free floated properly
I’ve shot a few groups and have seen a noticeable improvement in my grouping
I’m still playing with loads but at least my groups are not all over the place anymore
Maybe you have the same problem, not sure if a model 70 is free floated or not
I think on my rifle that as the barrel heated up the stock was introducing a pressure point on the barrel which was throwing the accuracy off
 
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