I've noticed that when I run full pressure loads in my gun I don't get good primary extraction. When I lift the handle on a fired round to eject it the caming action on the lugs ends before the bolt handle and the cocking ramp on the action engage each other. Shouldn't these be simultaneous? The bolt handle ramp meets the action ramp near the base, like it should, but it just seems to do it after the lugs have finished moving the case and cause me to pop the case out with the cocking ramp only.
Gunsmithing Extraction/Timing question
- Thread starter jsthntn247
- Start date
Are you saying the bolt stops rotating before the bolt cam surface engages the action cam surface?
The primary extraction cam, which I think is what you're calling the cocking ramp, can't be touched by the bolt handle until the action lugs disengage, otherwise they'll jam against each other. The lugs on the bolt are square to the action in most actions, which is what holds everything together when you fire. The bolt can't move back at all until the lugs clear, then the primary extraction surfaces hit each other and force the bolt back a small amount.
The cocking ramp is the angled surface on the bottom rear of the bolt.
Edited to add: there is a camming surface in the front of the action as well, but it's only used for getting the case into battery, not extraction.
The cocking ramp is the angled surface on the bottom rear of the bolt.
Edited to add: there is a camming surface in the front of the action as well, but it's only used for getting the case into battery, not extraction.
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I believe what you show in the video is as the cocking piece rides up the cocking ramp and when it hits its peak before rolling over into the detent it can sit there on the little flat on the bolt in a neutral position. Most Remingtons (if not modified) can be made to do that and perfectly normal. The ramp and detent can be modified to smooth cocking and for the most part eliminate it if you wanted.
When extracting stuck cases what you describe is normal as well (if I understand your description correctly). As Red described there is a bit of no mans land between the locking ramps and the extraction cam if not it would bind. If a case is stuck there will be some rotation without rearward movement after the lugs are out of battery but before the extraction cam picks up.
When extracting stuck cases what you describe is normal as well (if I understand your description correctly). As Red described there is a bit of no mans land between the locking ramps and the extraction cam if not it would bind. If a case is stuck there will be some rotation without rearward movement after the lugs are out of battery but before the extraction cam picks up.
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First, there appears to be a bit of a disconnect on the vocabulary so trying to sort this out is a bit challenged. That said, we'll start with fundamentals so we understand each other.
Basically this is what you have:
Fire control timing: We first must determine exactly what you have.
Close the bolt on an empty chamber and dry fire the action. Now lift the bolt, you have one of the following:
1. Cock on open only (meaning that when you rotate the bolt completely out of battery the striker and striker spring are as compressed as they are ever going to be. You verify this by then closing the bolt and watching the cocking indicator inside the shroud very carefully. As you rotate back down you'll feel the bolt "take off" and become essentially effortless to close. As this happens the cocking indicator will move forward (towards the breech) ever so slightly. Then you'll feel some resistance build as you continue to rotate all the way down into battery. But as this resistance builds, it levels off and the cocking piece does NOT move with the remaining rotation left in the handle. Basically, the cocking piece is pulled to the rear all its ever going to be as you lift the handle.) Actions like Nesika and others with a benchrest heritage are often designed to operate this way. The perception being that bolt manipulation is a bit smoother resulting in (hopefully) less disturbance in the bags. It also goes a long way towards making super light weight bench rest triggers less susceptible to slam firing as the loading placed on the transfer bar is much less "abrupt" than the operating principle described next.
2. Partial cock on open and partial cock on close (meaning that as you rotate the bolt out of battery the striker and striker spring are compressed. Then as you rotate back into battery the cocking piece on the striker purchases against the sear prior to the lugs being past the clearance ramps of the receiver. The bolt lugs "climb these ramps" as the bolt body rotates and consequently continues to move forward until the lugs of the bolt moves past the clearance ramps of the receiver and begin to transition and purchase the flat lug abutments. This forward motion effectively compresses the striker/striker spring a bit more as they are held back by the transfer bar on the trigger. This is how actions like the M700, M70, and a number of others are designed to operate. -On a side note. Actions made from materials like chromoly and 400 series stainless tolerate this loading well. Actions made from materials like precipitating hardening stainless's (17-4, 15-5, etc) are usually a bit more prone to lug galling because its more challenging to heat treat them to a level that resists the rubbing going on. A good rule of thumb is to have a minimum of 5 points of differential hardness between the bolt and the action. Seven is even better.
-On YET another side note this cocking operating principle is why actions like the M700 can be a bit cranky when attempting to go super light on triggers like the Jewel. The cocking piece can cause the transfer bar to "bounce" the sear and consequently trip the mechanism; resulting in a slam fire. Careful modification of the fire control (basically converting it to a Cock on open only) will greatly reduce this problem.
K, that covers The fire control, now onto primary extraction.
The clearance ramps at the front of the receiver ring where the horizontal raceways transition into helical ramps that again transition to the lug abutments are only acting as a cam to ensure the cartridge is fully loaded into the chamber on closing. If everything is correct it (ammunition is right, etc) it does little more than ensure the extractor pops over the rim, overcomes spring pressure from a plunger style ejector, and puts a bullet into/against the lands when applicable.
On a partial cock open/close style action the clearance ramps serve an additional purpose. They do all the above as well as compress the striker spring. (a bit redundant as I already covered this)
Ok, that concludes getting the bolt closed on the chamber. Now you pull the trigger and it goes "bang".
Onto extraction:
The ramps up front are just along for the ride at this point. The primary extraction cam at the back of the rear bridge is now tasked with yanking the bolt to the rear as you rotate out of battery. Simultaneous to this the cocking ramp in the bolt is compressing the striker and striker spring assembly. The job of the primary extraction cam is to get the case out of the chamber. How much primary extraction you have depends on how the action is designed. Some have more than others. Defiance actions have quite a bit when compared to many. More isn't necessarily better however. The helical surfaces need to be machined correctly as they are serving as a bearing. Spreading load over a broader surface is generally a good thing as reduces the amount of perceived effort to snatch a case out of the action. So, the point to take here is a large bearing surface is usually a good thing. A number of actions do this well and Defiance does a really good job at it. The most radical design I've seen is the BAT that uses a little roller bearing. This is pretty cool, but I fear the pin took a beating as it was quite small.
Regardless, all well designed 90 degree turn bolt actions use some variant of the primary extraction cam feature.
Last, some diagnostics:
IF your rotating the bolt out of battery and your feeling a distinct "tick" as the case comes out I'd encourage you to review your loading procedure carefully AND ensure the headspace of the chamber is within proper specifications. Assuming headspace is correct and the chamber isn't blown out of proportion due to poor machine work, it's likely your pressures are elevated.
That "tick" is the cam having to literally "pop" the brass from the chamber because the head/web area is swelling due to pressures outside of what the cartridge is designed for. Flat primers along with cratering, ejector marks, and burnishing on the case webs are all tell tale signs of things being too hot. (although big chambers and excessive HS will also cause the case to swell abnormally)
Hopefully somewhere in this you found what your looking for. I know these kinds of responses get long winded, but the simple fact is this stuff can't be answered in two little sentences. As simple as a bolt action is, there's a number of important things happening in concert. To avoid misdiagnosis its important to understand the operating principles at work.
Hope this helps.
C.
Basically this is what you have:
Fire control timing: We first must determine exactly what you have.
Close the bolt on an empty chamber and dry fire the action. Now lift the bolt, you have one of the following:
1. Cock on open only (meaning that when you rotate the bolt completely out of battery the striker and striker spring are as compressed as they are ever going to be. You verify this by then closing the bolt and watching the cocking indicator inside the shroud very carefully. As you rotate back down you'll feel the bolt "take off" and become essentially effortless to close. As this happens the cocking indicator will move forward (towards the breech) ever so slightly. Then you'll feel some resistance build as you continue to rotate all the way down into battery. But as this resistance builds, it levels off and the cocking piece does NOT move with the remaining rotation left in the handle. Basically, the cocking piece is pulled to the rear all its ever going to be as you lift the handle.) Actions like Nesika and others with a benchrest heritage are often designed to operate this way. The perception being that bolt manipulation is a bit smoother resulting in (hopefully) less disturbance in the bags. It also goes a long way towards making super light weight bench rest triggers less susceptible to slam firing as the loading placed on the transfer bar is much less "abrupt" than the operating principle described next.
2. Partial cock on open and partial cock on close (meaning that as you rotate the bolt out of battery the striker and striker spring are compressed. Then as you rotate back into battery the cocking piece on the striker purchases against the sear prior to the lugs being past the clearance ramps of the receiver. The bolt lugs "climb these ramps" as the bolt body rotates and consequently continues to move forward until the lugs of the bolt moves past the clearance ramps of the receiver and begin to transition and purchase the flat lug abutments. This forward motion effectively compresses the striker/striker spring a bit more as they are held back by the transfer bar on the trigger. This is how actions like the M700, M70, and a number of others are designed to operate. -On a side note. Actions made from materials like chromoly and 400 series stainless tolerate this loading well. Actions made from materials like precipitating hardening stainless's (17-4, 15-5, etc) are usually a bit more prone to lug galling because its more challenging to heat treat them to a level that resists the rubbing going on. A good rule of thumb is to have a minimum of 5 points of differential hardness between the bolt and the action. Seven is even better.
-On YET another side note this cocking operating principle is why actions like the M700 can be a bit cranky when attempting to go super light on triggers like the Jewel. The cocking piece can cause the transfer bar to "bounce" the sear and consequently trip the mechanism; resulting in a slam fire. Careful modification of the fire control (basically converting it to a Cock on open only) will greatly reduce this problem.
K, that covers The fire control, now onto primary extraction.
The clearance ramps at the front of the receiver ring where the horizontal raceways transition into helical ramps that again transition to the lug abutments are only acting as a cam to ensure the cartridge is fully loaded into the chamber on closing. If everything is correct it (ammunition is right, etc) it does little more than ensure the extractor pops over the rim, overcomes spring pressure from a plunger style ejector, and puts a bullet into/against the lands when applicable.
On a partial cock open/close style action the clearance ramps serve an additional purpose. They do all the above as well as compress the striker spring. (a bit redundant as I already covered this)
Ok, that concludes getting the bolt closed on the chamber. Now you pull the trigger and it goes "bang".
Onto extraction:
The ramps up front are just along for the ride at this point. The primary extraction cam at the back of the rear bridge is now tasked with yanking the bolt to the rear as you rotate out of battery. Simultaneous to this the cocking ramp in the bolt is compressing the striker and striker spring assembly. The job of the primary extraction cam is to get the case out of the chamber. How much primary extraction you have depends on how the action is designed. Some have more than others. Defiance actions have quite a bit when compared to many. More isn't necessarily better however. The helical surfaces need to be machined correctly as they are serving as a bearing. Spreading load over a broader surface is generally a good thing as reduces the amount of perceived effort to snatch a case out of the action. So, the point to take here is a large bearing surface is usually a good thing. A number of actions do this well and Defiance does a really good job at it. The most radical design I've seen is the BAT that uses a little roller bearing. This is pretty cool, but I fear the pin took a beating as it was quite small.
Regardless, all well designed 90 degree turn bolt actions use some variant of the primary extraction cam feature.
Last, some diagnostics:
IF your rotating the bolt out of battery and your feeling a distinct "tick" as the case comes out I'd encourage you to review your loading procedure carefully AND ensure the headspace of the chamber is within proper specifications. Assuming headspace is correct and the chamber isn't blown out of proportion due to poor machine work, it's likely your pressures are elevated.
That "tick" is the cam having to literally "pop" the brass from the chamber because the head/web area is swelling due to pressures outside of what the cartridge is designed for. Flat primers along with cratering, ejector marks, and burnishing on the case webs are all tell tale signs of things being too hot. (although big chambers and excessive HS will also cause the case to swell abnormally)
Hopefully somewhere in this you found what your looking for. I know these kinds of responses get long winded, but the simple fact is this stuff can't be answered in two little sentences. As simple as a bolt action is, there's a number of important things happening in concert. To avoid misdiagnosis its important to understand the operating principles at work.
Hope this helps.
C.
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