Lapping the Bolt
- Thread starter gillamboy
- Start date
A lot of the new factory firearms need little or no lapping. With the new CNC equipment being used today, everything is fairly square.
I's easy to check if you need to lap the lugs.
Bolt must be fully assembled to get the spring pressure to help make this job much easier.
Take a felt pen and and completely blacken the surfaces of the contact areas on the locking lugs (rear area).
Then insert the bolt back into the rifle and close and open the bolt a couple of times and remove the bolt.
Inspect the blackened areas on the lugs. They should have about 70% of the blackening rubbed off their surfaces.
If they don't, add some coarse valve grinding compound (available at Cdn Tire or automotive supply store) to the lug with the MOST BLACKNING RUBBED OFF.
Reinsert the bolt and work the bolt handle up and down 20-30 times.
Remove the bolt, clean the grinding compound from the receiver and the lug.
Reblacken both lugs again and reinsert the bolt and check the amount rubbed off the lugs again.
Repeat the process until both lugs have approximately 70% contact, as illustrated by the rub marks on the blackening.
I's easy to check if you need to lap the lugs.
Bolt must be fully assembled to get the spring pressure to help make this job much easier.
Take a felt pen and and completely blacken the surfaces of the contact areas on the locking lugs (rear area).
Then insert the bolt back into the rifle and close and open the bolt a couple of times and remove the bolt.
Inspect the blackened areas on the lugs. They should have about 70% of the blackening rubbed off their surfaces.
If they don't, add some coarse valve grinding compound (available at Cdn Tire or automotive supply store) to the lug with the MOST BLACKNING RUBBED OFF.
Reinsert the bolt and work the bolt handle up and down 20-30 times.
Remove the bolt, clean the grinding compound from the receiver and the lug.
Reblacken both lugs again and reinsert the bolt and check the amount rubbed off the lugs again.
Repeat the process until both lugs have approximately 70% contact, as illustrated by the rub marks on the blackening.
Republic of Alberta
CGN Ultra frequent flyer
- Location
- ,location, location
Lapping the lugs increases the head space. You had better know what you are doing, it's not for the average guy to do in the basement.
I wouldn't do it. You can lap but it isn't a pure process where the guaranteed result is that you improve geometry. When you lap on an iron lap, the lap itself has been surfaced, and it is softer so that it holds the grit, and doesn't change rapidly due to the rubbing together of parts. But here is a process where we don't know what is wrong with the surfaces and we only partly control their relative hardness. A normal bolt action does not hold the bolt body in proper alignment during the process, and other areas of the bolt that may need truing up do not get lapped, like the bolt face.
If this is a really high performance rifle then it probably is worth breaking down and machining the surfaces if it doesn't perform up to expectations. If it's a normal rifle, then I think you can improve accuracy with simple stuff like better shooting, bedding, and load development.
I suppose if you have a serious rifle that you would be willing to invest in should it need a complete rebuild, then you could always try the lapping since any damage could be undone during machining, and who knows you might lap in a home run.
Theoretically you could lap so much that you might change headspace. I imagine people get bored long before that. You also need to get all the grinding compound out after the work is done and flush out all the grit, or it will keep wearing the parts until it is all broken down.
If this is a really high performance rifle then it probably is worth breaking down and machining the surfaces if it doesn't perform up to expectations. If it's a normal rifle, then I think you can improve accuracy with simple stuff like better shooting, bedding, and load development.
I suppose if you have a serious rifle that you would be willing to invest in should it need a complete rebuild, then you could always try the lapping since any damage could be undone during machining, and who knows you might lap in a home run.
Theoretically you could lap so much that you might change headspace. I imagine people get bored long before that. You also need to get all the grinding compound out after the work is done and flush out all the grit, or it will keep wearing the parts until it is all broken down.
handy to do if you are going to go through the entire process such as first truing the action and then lapping the bolt face and then the lugs.
If you are going to build on a mil surplus M98 or other similar action it would be a good idea to ensure that you are truing things up. Then of course you need to nail the new chamber to proper headspace as well as to ensure that it is true to the bore and everything should come out quite nicely.
If you are going to build on a mil surplus M98 or other similar action it would be a good idea to ensure that you are truing things up. Then of course you need to nail the new chamber to proper headspace as well as to ensure that it is true to the bore and everything should come out quite nicely.
Here is one method. The barrel is removed from the receiver. An iron lapping tool is used on a mandrel to lap the receiver lug seats. The bolt lugs are then lapped to the receiver using a tool that threads into the receiver, applying pressure directly backwards, so that the lugs are lapped evenly. This isn't the same as "blueprinting" an action, but the locking shoulders will be lapped true to the boltway, and the lugs to the locking shoulders. It does nothing to align the receiver axis with the bore. Non-embedding lapping compound should be used, and it is important to remove all traces of compound when the job is complete.
Lapping can increase headspace, relative to the barrel that was installed prior to lapping. If the barrel is fitted afterwards, there will be no headspace issue. It may be necessary to refit a factory barrel after lapping, to insure correct minimum headspace.
Be careful lapping in the lugs on a '98 Mauser. The receiver and bolt are surface hardened. If the action has been subject to wear and tear previously, and then lapping removes more metal, the carburized layer may be removed.
Lapping can increase headspace, relative to the barrel that was installed prior to lapping. If the barrel is fitted afterwards, there will be no headspace issue. It may be necessary to refit a factory barrel after lapping, to insure correct minimum headspace.
Be careful lapping in the lugs on a '98 Mauser. The receiver and bolt are surface hardened. If the action has been subject to wear and tear previously, and then lapping removes more metal, the carburized layer may be removed.
If you're not going to pull the barel and adjust for the headspace change, don't bother. - dan
