POI shift after adjusting headspace

[Nomad47]

I installed a new bolt face on my Savage PTA today. Then I checked headspace and brass that chambered easily was now a little snug. So I backed off the barrel a little, I would say no more than .002".
Then I went out to check 100 yard zero and it was 4.5" left of previous 100 yard zero. What would cause this? Barrel not perfectly straight?

 

[savagedasher]

No barrel is perfectly straight. All good gun smiths time their barrels. Good Shooting Larry

 

[Ggmac]

Just curious , did you remove your scope while changing headspace ? Did you take the barreled action out of the stock ? If you did these things there are many more possibilities !

 

[Ggmac]

I forgot , if your headspace decreased , that means your new bolt head is thicker ( for lack of a better word ) right ? If thats the case your firing pin protrusion changed also , maybe not much , but if you were marginal before this could also be the culprit , but I seriously doubt it , you never know.

 

[Larryh128]

I agree with savagedasher, no barrel is completely straight. I would definitely use a go guage to set the headspace. A little extra can do some wierd things.

 

[Lapua40X]

Is there any info here that helps?

http://www.switchbarrel.com/BOLTHEAD.htm

 

[Ggmac]

I dont mean to step on any toes , please explain how I can time a prethreaded and chambered barrel and still have correct headspace ?
In order to time a barrel , would require you to thread the barrel , determine at what point you want your barrel , witness mark it , remove ,chamber , than install , and final chamber ,at you desired timed position . What am I missing . 2+ years of trade school , 6 years of apprentice , 25 + years of strictly bolt rifles . Please I dont mean this the way its sounding , has something changed .
I once remember someone asking for a negative space adapter .
Gary

 

[savagedasher]

You do it just like any bolt gun with the action in your hand. You and I both know that. I have a problem spending the money on a barrel and not having it timed to the action.
Good Shooting Larry

 

[Nomad47]

Just curious , did you remove your scope while changing headspace ? Did you take the barreled action out of the stock ? If you did these things there are many more possibilities !

Yes, scope but not base was removed. And the barreled action was removed from the stock. I'm used to removing stock and scope and having POI remain within 1 MOA. But I guess in this case things were different.
The barrel in question was chambered by a very competent gunsmith. Also, after more thought, barrel straightness would not be the issue. Changing headspace by .002" on a Savage involves rotating the barrel 1/25th of a turn or 14 degrees.

 

[BigDMT]

Just curious , did you remove your scope while changing headspace ? Did you take the barreled action out of the stock ? If you did these things there are many more possibilities !

That's exactly what I was thinking. Either scope or stock. Most likely scope. It's pretty rare that a scope will re-zero itself perfectly after being removed. Plus Savage rifles are pretty sensitive to action screw Torque levels

 

[BigDMT]

And it's not just "changing a bolt face and headspacing". I guarantee the new bolt face's recoil lugs contact area is different on the receiver. The recoil lugs could be out of square or not making contact the same as the last bolt face, etc.

After all those changes, I think you are actually pretty lucky that POI shift was your only problem. Could have been worse...Could have had to develop a new load...

 

[Nomad47]

I measured lug and bolt face recess on both bolt faces before making the switch and saw no difference between the two. So I was a little surprised to see the headspace change.
Anyway, after moving my scope 4.5 MOA, everything is back to normal. I guess I'm just plain lucky.

 

[Nomad47]

Just curious , did you remove your scope while changing headspace ? Did you take the barreled action out of the stock ? If you did these things there are many more possibilities !

That's exactly what I was thinking. Either scope or stock. Most likely scope. It's pretty rare that a scope will re-zero itself perfectly after being removed. Plus Savage rifles are pretty sensitive to action screw Torque levels

Thanks for the info, Big. I have my action screw torque values recorded and returned them to their original values after making the headspace adjustment. They are 20, 30, and 40 in/lbs, starting at the trigger guard. BTW, all screws get torqued to 20, then the front two to 30, then the front screw to 40.

 

[BigDMT]

Just curious , did you remove your scope while changing headspace ? Did you take the barreled action out of the stock ? If you did these things there are many more possibilities !

That's exactly what I was thinking. Either scope or stock. Most likely scope. It's pretty rare that a scope will re-zero itself perfectly after being removed. Plus Savage rifles are pretty sensitive to action screw Torque levels

Thanks for the info, Big. I have my action screw torque values recorded and returned them to their original values after making the headspace adjustment. They are 20, 30, and 40 in/lbs, starting at the trigger guard. BTW, all screws get torqued to 20, then the front two to 30, then the front screw to 40.

Sounds like you know your Savage very well As long as she still shoots well, should be good to go.

 

[Nomad47]

Thanks, BigD. I have two Savages and four barrels that get swapped a couple times per year. But I wish I knew them better. I made a mistake a couple months ago. I cut a notch out of my action wrench so that I wouldn't have to remove my scope base when swapping barrels. But I didn't realize the front base screw ran into the barrel threads until I had scored the barrel threads a little. Lesson learned - the hard way.

 

[Ggmac]

Thanks nomad , Ive been doing this for almost 30 years now , Im new this computer stuff , but not to barrel chambering / threading .
In order to to adjust headspace you 1- rotate barrel 2- face receiver 3- cut lugs ,receiver or bolt 4- surface grind recoil lug .
Almost all barrel installs , on guns that use a barrel nut , its a no brainer to just rotate the barrel . After all thats the reason Savage , mossberg , marlin , and I think the new REmington and ruger have barrel nuts .
The 20 TPI = 1 revolution of barrel = .050 1/16 rev = .003125 . 1/16 revolution =aprx. 22.5 deg. Its early and havent had my coffee yet so my math mite be a little off .
Glad your are back to POA .

 

[Nomad47]

Thanks, Ggmac. As I said, I turned the barrel out no more than .002" and since a .001" headspace change equals 1/50th of a turn, then .002" would equal 1/25th of a turn or 14.4 degrees. For the barrel not being straight to cause the POI shift of 4.5", then a 90 degree turn of the barrel would cause a 18" shift in POI to the left AND a 18" shift in POI down (if my math is correct). I sure don't see that happening. And that would have to be from the barrel starting out pointing straight up.

 

[chevytruck_83]

its possible. I had to return my Savage because it was something like 48" low at 100. they deatermined that the barrel was banana shaped.