Dad's BSA 303 no1 Mk3 groups but point of impact moves between range sessions

[Doekster]

Good day to all fellow members.

After the members have helped me so much on the issues I had with my .270, I am knocking on the door of all the 303 fundi's once again.

My dad have the following hunting setup:

• 303 no1 mk3 BSA rifle,
• ATI synthetic stock fitted with a frontend barrel ring.
• The stock is fully bedded, so there is no free floating of the barrel.
• SA hunters TITAN 3-9 x 40 scope.
• Load data - 39.5gr S335 PMP cases(sorted according to internal volume), pmp magnum primers, 174gr PMP SP bullets +/- 2450fps (groups under 25mm at 100m on ave)

The issue we have with this rifle is that we have no problem getting the rifle zero in, but after getting it zero'ed in on one range session and testing to see if the zero held during transport to and from the range, the point of impact moved from where it wat set the previous range session. We live 25km from the range and there are no bad roads.

No adjustments to the scope is made between range sessions, and when we zero the rifle the scope tracks true on the adjustments we make on the range. (So to my knowledge it should not be the scope as it is behaving as it should?) We have also made sure all the screws are set tight and nothing can move.

The groups are fairly consistent under an inch at 100m with no "flyers", so I doubt that the problem can be with the barrel...?

The only thing that I can think of that may cause an issue is the fully bedded stock, but then again why do the rifle shoot consistant groups?

For me this is a very weird becuase we have tested everything that we could think of, but then again the experts may have came across something like this before.

I will appreciate any inputs on this.

Kind regards

[GVC86]

Thought of paralax issues?
Are you able to get consistent cheek weld or is the scope too high?
Might also be a scope issue.

Anyway this is where I would start with the fault finding process.

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[Stu_Han]

Hi.

One possibility, worth checking.
If memory serves, your scope mounting is bolted to the side of the 303 action. Check that the mount is correctly torqued to the action. I have heard of a couple of occasions where this has resulted in a scope zero moving.

Hope you come right.


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[opalsasquatch]

Is it possible the stock is warping between trips due to humidity/temperature change? If the wood isn't stable the full length bedding could be pushing the barrel around


"Shuuuuuuussssshhhhh.

You can't post stuff like that, too many heads will explode."
Hillbillyreefer

[Doekster]

Hi.

One possibility, worth checking.
If memory serves, your scope mounting is bolted to the side of the 303 action. Check that the mount is correctly torqued to the action. I have heard of a couple of occasions where this has resulted in a scope zero moving.

Hope you come right.


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Hi Stu_Han thanks for the input, we will double check the scope mounting this weekend.

[LoopSoosStroop]

How many shots do you shoot per group? If you are zero-ing based on a three shot group, it wont help you much. Shoot a ten shot group and see what it says.

You also don't mention how much the POI shifts between sessions?

[Doekster]

Thought of paralax issues?
Are you able to get consistent cheek weld or is the scope too high?
Might also be a scope issue.

Anyway this is where I would start with the fault finding process.

Sent from my SM-G610F using Tapatalk

Hi GVC86, We tested the scope on my uncle's 308 and it worked like it should.

As far as the cheek weld and the scope height goes, it has never felt uncomfortable looking through the scope. The cheek rests nicely onto the stock when looking through the scope. Because of the front lens only being 40mm we managed to get the lowest scope mounts for the rail, so the scope does not sit as high as it does normally.

I will take some pictures this weekend and show you.

"Paralax issue" On this particular scope what will cause a paralax issue? I am asking this because being a "simple" scope the only place one can adjust on this scope is the eye relief. Could it be that there is a better eye relief setting, then we just need to adjust accordingly?

[Doekster]

How many shots do you shoot per group? If you are zero-ing based on a three shot group, it wont help you much. Shoot a ten shot group and see what it says.

You also don't mention how much the POI shifts between sessions?

Hi LoopSoosStroop

We only shoot 3 shots at most, but you have a valid point here. We will shoot 10 shots without adjusting the scope and see what it says.

The POI shifts by almost 3-4 inches at 100m sometimes.

[GVC86]

Hi GVC86, We tested the scope on my uncle's 308 and it worked like it should.

As far as the cheek weld and the scope height goes, it has never felt uncomfortable looking through the scope. The cheek rests nicely onto the stock when looking through the scope. Because of the front lens only being 40mm we managed to get the lowest scope mounts for the rail, so the scope does not sit as high as it does normally.

I will take some pictures this weekend and show you.

"Paralax issue" On this particular scope what will cause a paralax issue? I am asking this because being a "simple" scope the only place one can adjust on this scope is the eye relief. Could it be that there is a better eye relief setting, then we just need to adjust accordingly?

There will always be paralax issue on any scope. The higher end scope have paralax adjustment to dail this issue out. Usually fixed power or low magnification scopes are set to be paralax free at 100 or 150m.

The issue comes in when you do not line up and get precisely the same cheek weld as the previous range session, this might cause the shifting of poi between sessions and possibly between shooters as well. Also the cheek weld will be different between shooting positions which could also cause this poi shift.

Hope this makes sense?

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[Doekster]

Is it possible the stock is warping between trips due to humidity/temperature change? If the wood isn't stable the full length bedding could be pushing the barrel around


"Shuuuuuuussssshhhhh.

You can't post stuff like that, too many heads will explode."
Hillbillyreefer

Good day opalsasquatch

The stock is an ATI synthetic stock, can humidity/temerature change still influence this?