The extractor plays a crucial role in determining the amount of resistance that causes the bolt head to remain in the extended position when the bolt is retracted from the battery position (and subsequently removed from the action). It is not at all uncommon to find that the resistance is insufficient, resulting in a bolt head that: 1) Will be prone to jamming in the bolt guides, causing very stiff bolt operation;2) With the bolt withdrawn from the receiver, will snap into the retracted position with the slightest bump; or 3) Will fail to remain in the extended position at all when the bolt is removed from the receiver. The cure for this problem may be to adjust the amount of arc in the extractor.
Increasing the amount of arc in the extractor increases the force of the extractor tail bearing on the bolt head, thereby increasing the resistance to bolt head retraction. Excessive arc will result in stiff operation of the bolt due to the unnecessarily large forces necessary to cause the extractor to cam out of the axial detent slots in the after end of the bolt body. Insufficient arc will also result in stiff operation but for an entirely different reason. In the first case, excessive extractor arc will cause the extractor tail to bear on the bolt head with undue force. In the latter case, insufficient extractor arc will allow the mainspring to act on the bolt head, causing it to begin to rotate and retract into the bolt body. With the bolt head semi-rotated, the locking lugs will drag in the bolt guides.
Altering the amount of arc in the extractor should be attempted only after the extractor tail has been examined for wear. A worn extractor can be dressed with a small file or a stone to achieve a more crisp profile although removing too much metal may lead to accelerated wear in the future. Nevertheless, if the profile of the extractor tail has become rounded, increasing the amount of extractor arc will only result in stiff bolt operation and further accelerate wear on the extractor tail. See the procedure for examining the extractor tail.
Having examined the extractor tail and confirmed that it is of the correct profile, the amount of arc in the extractor may be adjusted.
1) Disassemble the bolt.
2) Lay the extractor on a stiff steel rule (or other suitable hard, stiff surface) with the concave side down and the extractor claw overhanging the edge of the rule. In other words, the claw should not be contacting the rule; only the tail of the extractor and the point where the extractor necks down to 1/4" width should be in contact with the rule.
3) Using a set of calipers, measure from the rectangular hump on the back side of the extractor (typically this is where you'll find the letters K or R) to the back side of the rule. Write this down as dimension "A".
4) Now measure the thickness of the rule. Write this down as dimension "B".
5) Subtract "B" from "A". The result, "C", is a proxy for the curvature of the extractor. Write it down.
6) Now clamp the extractor in a small vise. Don't clamp on the extractor claw. Clamp the vise on the thicker portion of the stem, just behind the claw where it measures 1/4" wide.
7) Lightly tap the free (tail) end of the extractor with a small hammer.
8) Remove the extractor from the vise and re-measure the amount of curvature (i.e., repeat steps 2 through 5). The reason for taking before and after measurements is to verify that the arc is being altered. Without the measurements it is impossible to tell if anything is being accomplished.
9) Reassemble the bolt and extend the bolt head. The amount of arc is sufficient if the bolt head remains extended and does not snap back into the retracted position when lightly tapped. If the bolt head snaps back, go back to step 2.
The extractor I have here as I write this measures .178" and the bolt I took it out of operates quite nicely.