Point of impact after shortening the barrel.

**treeman** · 18-09-2021, 20:54

I have shot 7 mm of my .270 Win rifles chamber throat area away, and can no longer shoot 130 gr bullets - I switched to 150 gr but notice that they have of recent also started to show wider grouping than 5 years ago.

I have now had the chamber re-cut and will collect the rifle on Tuesday, Wednesday.

I have a large number of loaded cartridges for this rifle, and really do not feel like pulling and reloading

I mentioned this to my Gunsmith and he assured me that the grouping will remain the same, but the POI may shift.
I do not argue with my Gunsmith, but I just know this is not the case, you know like OBT etc.
Orrrr ?
Is this another Treeman moment again?

**pre 64** · 19-09-2021, 08:25

Treeman...you have shortened the barrel but not in the conventional manner. Normally when shortening the barrel we talk of lopping off a couple of inches from the muzzle end and re-crowning.
You are re-cutting your chamber....the barrel becoming shorter is just an obvious result of this procedure.

If you look at accuracy or the way a rifle shoots then a few factors need to be taken into consideration.
. Relationship between barrelled action and the stock with barrel taper moving rearwards....has changed
.Barrel lengh,vibrations.......have changed.
.Chamber dimensions......have changed
.Head space ref.point......has changed
.concentricity , as in relationship between new chamber and barrel....has changed.
.torque or tightness of barrel into action and action into stock....has changed

While all these changes will [should be] in spec , this has now become a completely different rifle and should be treated as such with load development.
Of course...you may be lucky...but be carefull.

**Bonedoc** · 19-09-2021, 08:27

Can't talk from experience, but the few millimeters change to the barrel will equate to about 0.1gr of propellant is you look at OBT. More likely that you will need to adjust setting depth as the free bore of the new chamber will be shorter than before.

Sent from my SM-G973F using Tapatalk

**treeman** · 19-09-2021, 08:44

Originally Posted by Bonedoc

Can't talk from experience, but the few millimeters change to the barrel will equate to about 0.1gr of propellant is you look at OBT. More likely that you will need to adjust setting depth as the free bore of the new chamber will be shorter than before.

Sent from my SM-G973F using Tapatalk

********************
Be a lot more than a few mm, likely 15/20 mm, throat was visually gone for 7 mm.
Free bore will be what it is cut too ?
.....................or not ?

**treeman** · 19-09-2021, 08:45

dam !!!!!!!!!!!!!!!!!!!!!! - surely this will change my bedding now ?

**Bonedoc** · 19-09-2021, 08:54

Free bore(or lead, or throat) is the few millimetres in front of the chamber where the reamer has removed the lands. If you had 7mm "freebore" from barrel wear, the gunsmith could have shortened by as little as 7mm to get to "fresh" lands.

Change to the bedding will depend on how far forward your action and barrel were bedded. If it was only on the parallel part of barrel, then it should still be good. Otherwise you might need to redo the bedding on the barrel part only.

I would measure the max TPL of the new chamber with whatever bullet you are using. If it allows your current tpl without jamming into the lands, shoot and see what groups you get. If it's too long, just adjust seater and shorten loaded bullets, shoot and see.

Sent from my SM-G973F using Tapatalk

**driepootx** · 19-09-2021, 08:56

O doom and gloom. Shoot the rifle once you get it back and then only will you be able to see if the old reloads will work. How hot are they loaded?

**AK-Gunner** · 19-09-2021, 10:06

Originally Posted by treeman

Is this another Treeman moment again?

Yes, it's called 'pointless overthinking'.

**414gates** · 19-09-2021, 10:40

Originally Posted by treeman

dam !!!!!!!!!!!!!!!!!!!!!! - surely this will change my bedding now ?

If the rifle was full length bedded, it will need to be re-done.

If it was free floated, not.

For precision loads, treat the rifle as new.

For accuracy with the already loaded ammo, there will be an improvement, after you fix the bedding.

Will POI change ? Nobody can tell you for sure.