Tikka action headspace changed

[id_jon]

Have a tikka T3 action that seems to have changed headspace. Used to not close on No-go gauge, now it will close on a field gauge, multiple barrels/bolts that all headspace fine on other actions. Is it possible that I messed it up by torqueing barrels on too tight? Can it be fixed safely? Anyone else had this happen before?

 

[AM3]

Does it still not close on the No-Go? Field gauge isn't what I would be checking headspace off of.

 

[mxgsfmdpx]

Is it possible that I messed it up by torqueing barrels on too tight?

Very unlikely.

 

[Lawnboi]

Has the barrel been on and off multiple times?

 

[id_jon]

Does it still not close on the No-Go? Field gauge isn't what I would be checking headspace off of.

Closes on the no-go, that's why I got the field gauge since the field is the longest.

 

[id_jon]

Has the barrel been on and off multiple times?

Yes. Checked multiple barrels that previously headspaced on this action in the past and now do not.

 

[id_jon]

Very unlikely.

Any other ideas for why it would change?

 

[Macintosh]

for those who have more of a clue in these things, is this sort of change likely to be the result of wear on the locking lugs? Do you have another tikka action…and if so can you swap bolts and barrels together to isolate whether its the action itself, or the bolt, or both in combination?

 

[pods8 (Rugged Stitching)]

Is there anti seize or such built up on the face of the action (or barrel shoulder) preventing it from screwing down as far?

 

[waspocrew]

No clue why you’d be seeing that change now. What sort of torque values were you using to set your barrels?

 

[SDHNTR]

Stretched out threads? So that the original torque setting doesn’t headspace to the same place as the same torque setting now.

 

[mxgsfmdpx]

Any other ideas for why it would change?

I would think the opposite would be more likely. Too loose not fully threaded in?

Not sure without looking sorry.

 

[id_jon]

for those who have more of a clue in these things, is this sort of change likely to be the result of wear on the locking lugs? Do you have another tikka action…and if so can you swap bolts and barrels together to isolate whether its the action itself, or the bolt, or both in combination?

I have another action that I checked all barrels and bolts against.

Is there anti seize or such built up on the face of the action (or barrel shoulder) preventing it from screwing down as far?

Action face and barrel shoulders are all clean

No clue why you’d be seeing that change now. What sort of torque values were you using to set you barrels?

120ish

 

[id_jon]

Stretched out threads? So that the original torque setting doesn’t headspace to the same place as the same torque setting now.

Maybe? I've checked hand tight as well as 100+lbs

 

[TaperPin]

It sounds like the locking lugs have set back into the receiver a bit. If you google “locking lug set back” or “lug abutment setback” there will be similar stories, although many will be older military receivers. If the receiver or bolt was extra soft and loads fired were normal pressures, that would be bad and hard to fix. If you’ve had some spicy reloads, that’s probably the culprit and luckily, using normal-pressure loads will prevent it from happening again. Fat cases like PRC or SAUM cartridges would produce more bolt thrust than standard cases - odds are you have one of those and not a 223 if that is the problem.

The fix is simple - cutting the barrel shoulder back the amount headspace needs to be reduced, and eliminating high pressure loads.

 

[id_jon]

It sounds like the locking lugs have set back into the receiver a bit. If you google “locking lug set back” or “lug abutment setback” there will be similar stories, although many will be older military receivers. If the receiver or bolt was extra soft and loads fired were normal pressures, that would be bad and hard to fix. If you’ve had some spicy reloads, that’s probably the culprit and luckily, using normal-pressure loads will prevent it from happening again. Fat cases like PRC or SAUM cartridges would produce more bolt thrust than standard cases - odds are you have one of those and not a 223 if that is the problem.

The fix is simple - cutting the barrel shoulder back the amount headspace needs to be reduced, and eliminating high pressure loads.

All have been 6/6.5cm and nothing over book max, though that could still be over 65k psi I guess

 

[Castle Rock]

Sounds like something is in the interface stopping the barrel from screwing in fully

 

[Wapiti1]

There are only 3 possibilities, two could be in combination.

1. The barrel isn't threading fully into the receiver. At anything over 50 ftlbs torque, this seems unlikely. However, cleaning the action threads and locking lugs with carbon remover, and scrubbing is a worthwhile task. Get it squeaky clean. Same with the barrel threads.

Also take the scope mount off the ring and make sure no screws are binding it, same with action screw.

Wear on the threads of the barrel or action only mean it won't time the same, but the shoulder to breech dimension doesn't change. By "time", I mean the lettering on the outside is rotated more due to loose threads.

2. The bolt lugs, either on the bolt head or abutments in the action are worn, displaced, etc. i.e. not in the same spot as prior. Possible, but rare in modern actions. Even ones with tens of thousands of rounds show tiny amounts of wear. One final possibility is the action had a burr or machining feature on one of the abutments and it has finally worn off, or battered flat. Inspect the locking abutments. Was the bolt lapped into the lugs?

Combo of the two above.

3. Lastly, it wasn't right before, and still isn't now. I've seen a few goofs where a no-go gauge got swapped for a go gauge and the headspace was long.

Since you said you checked with a field gauge, that is concerning. They are way long. Are the gauges all the same brand? This matters. Forster can be different than Manson, or Clymer, or JGS, PTG, etc. I have seen more than a few rifles not work with one or the other gauge.

I'll also throw out one bonus possibility. You swapped the bolt with another rifle by accident.

Jeremy

 

[TaperPin]

All have been 6/6.5cm and nothing over book max, though that could still be over 65k psi I guess

It’s a weird thing for sure.

In the rifles that have lug setback I’ve heard that you can see and feel where the lugs have pressed into the receiver and left indents.

Do you still have the original no-go? If not, it could be it wasn’t the correct no-go for a creed and headspace has always been a little long. A 243/308 no-go would look very similar, but if I remember right is a little longer.

 

[id_jon]

CLymer no-go, 1.547", Forster field, 1.549"
Fired brass measures 1.564" @ .375 datum, my no-go measures 1.5645 @ .375
This rifle has my only black tikka bolt, so it's very distinct.
Some of the barrels are pre-fits, but it is also not headspacing on a barrel that was chambered/fitted by a reputable gunsmith to this action, with this bolt.

Planning to have him look at it, but wondered if anyone had any thoughts while I wait for him to have time.