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View Full Version : firing pin travel,protrusion and bolt timing



canuck
09-30-2015, 03:04 AM
Firing pin travel and protrusion....I often see these things mentioned but I haven't seen an explanation on how to adjust these parameters( ie. on a Remington 700).Also, does the trigger affect these parameters?
Another rookie question I have is....what exactly is meant by "bolt timing" and how do you adjust it?
Is there a book or something that covers this subject?
Thanks

Boyd Allen
09-30-2015, 01:03 PM
There are no adjustments for these parameters on a Remington 700.

When the firing pin falls during dry firing, its forward motion is stopped by the front of the shoulder that contains the front of the spring hits the inside of the bolt. In this position, the firing pin will be protruding from the bolt face. The amount that it sticks out is the firing pin protrusion. It is built in and is unlikely to have a value that causes a problem.

Firing pin fall may be seen and measured by observing the relation of the back of the cocking piece to the shroud. By measuring how far the cocking piece is above the back of the shroud when the action is cocked, and adding to that how far into the shroud it is after dry firing you will arrive at the total firing pin fall. When a cartridge is fired, the primer stops the pin, so the fall is interrupted before it reaches full extension.

There is no evidence that I am aware of that points to an advantage from changing either of these parameters on a Remington 700 or any of their clones.

Small variations in trigger construction will effect fall, but not so much as to affect accuracy.

canuck
10-01-2015, 02:32 AM
thank you for the explanation....

Boyd Allen
10-01-2015, 09:52 AM
It seems that I got in a hurry and overlooked the subject of timing in my previous answer. In a bolt action timing is about having things happen as they should as the bolt is manipulated, not too soon or too late, relative to each other, and where they are in relation to each other when it is closed. Ideally, as the bolt is closed, it will not have to be pulled forward by the closing cams that are generally built into the leading edges of the lug abutments (surfaces that the back of the lugs bear against when the bolt is closed) to complete cocking. This would be described as cock on close, and increases the effort required to close the bolt. Also it is desirable that the firing pin will not drop any (in reality a very slight amount will not be noticed, or be a problem) as the cocking piece comes off of the top of the cocking cam at the rear of the bolt (the V shaped notch at the back of the bolt body that is parallel to the bolt on one side) and is caught by the trigger, holding it in cocked position. This transition of the firing pin load from cam to trigger is known as the hand off. There is also the matter of how the bolt handle is placed on the bolt. It should be such that the cocking piece is in the correct relation to the cocking cam notch when the bolt is closed, not touching in the fired position, and the lugs should be in their proper place on their seats when the bolt is closed. Although it may not strictly be called timing, the bolt handle needs to be properly positioned for and aft on the bolt so that it does not bind as it is closed, and so that it is not so far back that the extraction cam operation (root of the bolt handle against angled surface at the top rear of the rear bridge of the action) does not have a full range of pull. Bolt position may have to be corrected as a part of an action being blueprinted, to compensate for the effects of material being taken off of lug abutments and the rear of lugs, the combination of which will cause the bolt to be farther to the rear in the action body when closed and cocked. I have undoubtedly overlooked a detail or two in this, but hopefully someone will correct and complete my answer if that is required.

Boyd Allen
10-01-2015, 09:56 AM
It seems that I got in a hurry and overlooked the subject of timing in my previous answer. In a bolt action timing is about having things happen as they should as the bolt is manipulated, not too soon or too late, relative to each other, and where they are in relation to each other when it is closed. Ideally, as the bolt is closed, it will not have to be pulled forward by the closing cams that are generally built into the leading edges of the lug abutments (surfaces that the back of the lugs bear against when the bolt is closed) to complete cocking. This would be described as cock on close, and increases the effort required to close the bolt. Also it is desirable that the firing pin will not drop any (in reality a very slight amount will not be noticed, or be a problem) as the cocking piece comes off of the top of the cocking cam at the rear of the bolt (the V shaped notch at the back of the bolt body that is parallel to the bolt on one side) and is caught by the trigger, holding it in cocked position. This transition of the firing pin load from cam to trigger is known as the hand off. There is also the matter of how the bolt handle is placed on the bolt. It should be such that the cocking piece is in the correct relation to the cocking cam notch when the bolt is closed, not touching in the fired position, and the lugs should be in their proper place on their seats when the bolt is closed. Although it may not strictly be called timing, the bolt handle needs to be properly positioned for and aft on the bolt so that it does not bind as it is closed, and so that it is not so far back that the extraction cam operation (root of the bolt handle against angled surface at the top rear of the rear bridge of the action) does not have a full range of pull. Bolt position may have to be corrected as a part of an action being blueprinted, to compensate for the effects of material being taken off of lug abutments and the rear of lugs, the combination of which will cause the bolt to be farther to the rear in the action body when closed and cocked. I have undoubtedly overlooked a detail or two in this, but hopefully someone will correct and complete my answer if that is required.

Added later: On a 700, hand off is generally adjusted by modifying the cocking piece.