POI moving

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swampdonkey338

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I have an issue with my POI changing. For example last time at the range my first two were within .5MOA and my next three .5 MOA but four inches lower, then the next shot is back up four inches high within 1.2 MOA of my first two.
Winchester 70 sporter - 338 WM - Leupold Vari-II 3x9x50 (bought in 1987 new)
Glass bed the stock at the lug and tang, barrel is floating no pillars
Room in front of the lug and below, about 1/16 inch
Stock Screw tightened - first front, then rear and the magazine screw snug
Scope sent to Okatoks for a check up
Gun checked by gun smith ie crown, scope, etc
Cleaned every 50 or so rounds, remove all the copper
Replaced the rings with the most expensive
Lapped the rings, checked the screws twice
Reload – IMR 4350 with the 225 Accubond @ 2900 ft/sec (Chrony)
Sometimes signs of high pressure
Weigh each load, neck size, trim to spec, no crimp
Muzzle brake – custom

When I hold the gun at the range I have the bags on the stock (not barrel) and hold on to the front of the stock.

I’m starting to think it could be the load is too heavy creating a lot of barrel jump off the rest (it does have a little). I’m waiting for it to warm up a bit to try some lighter loads ( 1 and 2 grains less ).

I was wondering if anyone has experienced anything like this or have any other ideas short of $600 obo?:confused:

Thank you in advance
 
Hi

Good to hear you are worrying about this. I think it's a *lot* more important than group size.

Is the rifle newly bedded? If so it may take a couple of shots to get everything to fully seat. Your front screw may pull things away from the bedding and then the shots move it back.

Loosen up the rear screw a half turn and see if that helps. Also check to see just what hits the bedding first. Hopefully it's the recoil lug.

Your list mentions everything except the scope mounts. That may just be a typo. There is no guarantee that mounts match the rifle they are screwed down on. Bedding compound can help things there.

Bob
 
Bob
I had P&D install new rings & mounts and do the lapping and reinstall the scope. The bedding was done 9 months ago.

I would think the bedding is right up against the recoil lug. I have tried to feel for the contact and it does appear to contact before the other components of the gun hit the stock. But is does raise the question?

The hole for the screw through the bedding behind the lug is the same size as the stock holes.
 
If it's a late production model 70 it might be the barrel. Q/A was damn near non existent the last few years out of New haven.

I think the rule of thumb on a model 70 is front screw as tight as it will go and back screw just finger tight.

Have you owned this gun since 1987 and only now this has started?
 
Might recoil be an issue? I can only shoot big boomers for so long before the problem is me, a 225 gr bullet at 2900 is going to be punchy. As for a muzzle brake, I can't shoot them at all the blast is just too much for me.
 
swampdonkey338 said:
Bob
I had P&D install new rings & mounts and do the lapping and reinstall the scope. The bedding was done 9 months ago.

I would think the bedding is right up against the recoil lug. I have tried to feel for the contact and it does appear to contact before the other components of the gun hit the stock. But is does raise the question?

The hole for the screw through the bedding behind the lug is the same size as the stock holes.
Click to expand...

Hi

Messy way to check for clearance under recoil that does not always work:

Put a bit of grease between the tang and the bedding in the stock. Clean things up good and head out to the range. If the rifle is coming back in the stock, it will drive the grease out of the gap.

Next issue:

If the front screw is the first thing to "hit" that's not a good thing. You should be able to slide the proverbial dollar bill behind the screw with strong pressure pushing the barrel back into the stock.

There can be nasty problems like the barrel, but I'd eliminate the easy to fix stuff first ....

Bob
 
Maybe try a Caldwell Lead Sled? Also try 2-shot group, then completely cool, then another 2-shot. Has this rifle ever shot consistent for you?
 
Double check you can run a playing card 'tween barrel and stock, even a little binding can cause this. It happened on my BRNO, very frustrating.
 
Bob, I'm not sure what you mean by "You should be able to slide the proverbial dollar bill behind the screw with strong pressure pushing the barrel back into the stock. " The grease is a good idea at the tang that I will try.

The barrel is free floating all the way back to the chamber. The stock is beddded about 1.25 inches ahead of the lug under the chamber.

To answer the question, did it just start? I'm not totally sure. In the past I was guilty of only shooting a 1/2 box off a year and getting so so groups. But I do remember having to move the scope between some years. Last year I started to reload to practice with the goal of improving my shooting skills. During the load development , I would always clean between outings and would always get the first one or two flyers at the range. Also i was more interested in accuracy / groupings then consistent POI. Since that time i have not shot alot but i would say about 300 reloads.

Attached, hopefully, are the last targets.



reynolds338mag


reynolds338mag
 
Go buy a box of factories and see if it still does it. That will take your reloading out of the mix.


I had a M70 Classic Compact in 308 wich did the exact thing that you mention. I had beded the action front /rear of the action like normal but only beded under the rear most portion of the tang (the part that sits on top of the stock). That was the problem, I rebeded the tang, including the lug that sits down in the stock that the rear screw goes into, relived it a bit in the very back so the stock would not crack and the problem went away.
 
swampdonkey338 said:
I have an issue with my POI changing. For example last time at the range my first two were within .5MOA and my next three .5 MOA but four inches lower, then the next shot is back up four inches high within 1.2 MOA of my first two.
Winchester 70 sporter - 338 WM - Leupold Vari-II 3x9x50 (bought in 1987 new)
Glass bed the stock at the lug and tang, barrel is floating no pillars
Room in front of the lug and below, about 1/16 inch
Stock Screw tightened - first front, then rear and the magazine screw snug
Scope sent to Okatoks for a check up
Gun checked by gun smith ie crown, scope, etc
Cleaned every 50 or so rounds, remove all the copper
Replaced the rings with the most expensive
Lapped the rings, checked the screws twice
Reload – IMR 4350 with the 225 Accubond @ 2900 ft/sec (Chrony)
Sometimes signs of high pressure
Weigh each load, neck size, trim to spec, no crimp
Muzzle brake – custom

When I hold the gun at the range I have the bags on the stock (not barrel) and hold on to the front of the stock.

I’m starting to think it could be the load is too heavy creating a lot of barrel jump off the rest (it does have a little). I’m waiting for it to warm up a bit to try some lighter loads ( 1 and 2 grains less ).

I was wondering if anyone has experienced anything like this or have any other ideas short of $600 obo?:confused:

Thank you in advance
Click to expand...

Max load don't always give the best results, most times as much as two to three grains lower gives the best accuracy. A different weight and brand of bullet and a lesser powder charge will often cure any poi problems. Some guns are very fussy with powder and bullet selection.Some are high maintenance and some will swallow whatever you feed'em.:D
 
I don;t have the Nosler book handy, but Hornady lists 68.5 grs of h4350 as max for 2800 fps. You may be way over SAAMI pressure and it doing all sorts of funky stuff. If you are a guy who shot 10 rounds a year and are now trying to get good at shooting by practising with full whack 338 loads you aren't helping yourself. Next time you go to the range bring yourother guns, starting with a 22 and see how good your groups are with other rifles. Another thing to try is get someone else to shoot the gun for you that you know is a really good shot.

I've had a few rifles that gave me fits trying to get good groups, I tried all sots of different loads without success then had guys shoot them and get good groups. In a couple of cases the gun got into my head, and I moved around alot when shooting etc.
 
If all the usual suspects pass muster, your barrel is a stress case and you'll either have to learn where the first shot goes or rebarrel it, ouch! Or sell it to your brother in law.
 
...sometimes signs of high pressure! This doesn't equate to accuracy.

Also, what do your velocity shot strings look like? It's winter and it's cold. Cold ammo and cold gun won't shoot at the same point of impact as everything warms up and you continue shooting. This is especially true on large powder capacity magnums.
 
swampdonkey338 said:
Bob, I'm not sure what you mean by "You should be able to slide the proverbial dollar bill behind the screw with strong pressure pushing the barrel back into the stock. "
Click to expand...

Hi

The hole that the front screw passes through in the stock should be a bit large. There should be enough room that the sides of the screw do not contact the walls of the hole. That should be true even when the barrel is pushed back into the stock. The same thing applies to the rear screw, but it's not normally tight enough to be a problem.

Essentially the screw pulls the receiver down into the stock and keeps it there. The screw bends easily, so you want the fore and aft motion to be transmitted to the recoil lug rather than the screw.

A couple of thousandths is all the clearance you need. Hogging the hole out by a quarter of an inch is not necessary or desired.

Something else to try:

Some rifles shoot better with the first inch or so of the barrel bedded. I certainly would give a shim (like a piece of paper) a try before I gave up on the whole thing.

So many things to try!

Bob
 
Bob
You should be able to slide the proverbial dollar bill behind the screw with strong pressure pushing the barrel back into the stock
I have drilled the holes out a bit to ensure the screws are not taking the recoil. Plus when I screw the stock down I apply pressure on the barrel towards the butt to help ensure the lug is against the block in the stock.

Some rifles shoot better with the first inch or so of the barrel bedded.
This is something I will try!

Woodsman
what do your velocity shot strings look like?
I just borrowed a chrony for a day but have since got one for Xmas. I will be checking.

Cold ammo and cold gun won't shoot at the same point of impact as everything warms up and you continue shooting.
It hasn’t indicated to be more problematic with temp.

Martinbns
Another thing to try is get someone else to shoot the gun for you that you know is a really good shot.
That hurts! but I will do this.

I don’t have the Nosler book handy, but Hornady lists 68.5 grs of h4350 as max for 2800 fps.
My nosler book has max 71.5 of the IMR4350 for the 225 g. which is what I have loaded

Next time you go to the range bring your other guns, starting with a 22 and see how good your groups are with other rifles.
I have done this quite a bit with the 22 and an old 303.

Gibbs505
When I read this, my first thought was that the scope is gone. Have you tried a different scope?
I had Okotoks check it out and the guys at WS did the boresighting and knocked the scope around to see if it moved and they thought it was fine. I do not own another scope that would take the recoil.

Republic
Go buy a box of factories and see if it still does it. That will take your reloading out of the mix.
I will do this.

I had bedded the action front /rear of the action like normal but only beded under the rear most portion of the tang (the part that sits on top of the stock).
I will try this.

Thanks guys, I really appreciate the help.:)
 
If you sometimes have physical signs of high pressure, the load it too hot for your rifle. I don't understand why you would continue to shoot a load like that.
 
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