I have a finnish nagant that I have chpped the barrel and going into a new stock with pillars, muzzle brake etc. got the target crown down. I was curious about squaring the bolt face and what tools are needed and just how difficult it would be. I have a mill/lathe and a full size lathe but I have zero experience with the practice.
whats needed to square bolt face
- Thread starter skizzums
- Start date
Dixie Gunsmithing
Moderator Emeritus
You have to have a mandrel that will fit inside the receiver, and it needs to be able to fit with no play, and be locked to the receiver. You mount the mandrel in your lathe, as it is in line with the center line of the receiver, so when you make a facing cut at the receiver's front, it will square the receiver to the center line.
Agreed with Dixie for the most part.Thats about trueing the receiver face ,and that may be the foundation the barrel rests on...unless like a military Mauser barrel,the barrel has no shoulder.I do not know your particular rifle.
In any case,the critical surface the barrel tightens against should be square to the threads so when the barrel tightens there is a good,evenly loaded 360 deg foundation for the barrel.
That's all good,but realize its done with the barrel out,and you have removed steel,so your front sight will not be indexed any more and your headspace has shortened.Bummer.
And your bolt face may not be square to the bore,which was your question.
I'm not trying to rain on your parade,you are thinking right!!I'm trying to let you know there is a lot to what you want to do.
The receiver threads are likely cut in a different operation than the receiver bolt bore.They likely are not perfectly co-axial.Some blueprint jobs involve re-chasing the receiver threads co-axial to the bore.That is not easy.
Then there are the surfaces the locking lugs rest on in battery.Worn? set back?
Careful with the idea "lapping lugs".What are you lapping to?It helps if these surfaces are flat and true...and parallel to the receiver face.They are rather tricky to get in to face,with a facing boring head or rotary table,and realize they may be pack hardened.
That flat established,I prefer a threaded bushing with a spring loaded plunger screwed into the receiver to put a central,even load on the boltface to check lug bearing.Sharpie marker on the bolt lug faces tells the story.
I save some time using high spot technique and stones to lower the hi spots on the bolt lugs till I get good bearing,then just a finish lap.Use the center load plunger on the bolt face for lap pressure.Grabbing the bolt handle is an off center load.Not so good.
OK,all that done!! Now you would be ready to square the bolt face .
One way,A threaded bushing that screws in like a barrel shank with a precise hole in the center to guide a lap,,if only a little steel needs to come off.(Several ways to do this,a sinker EDM would be great!!A careful mill setup can work,but,low tech,lapping through a bushing is one way)
Of course,all this changes the headspace,so you may need to set the barrel back a thread,re-index the front sight straight up,and recut the chamber.If the barrel has any extractor cuts,those will need rework...
If you want education,go for it!!If you want a tack driver,consider the sows ear/silk purse story.A Winchester/Savage/Remington etc maybe?
Or,let it be what it is and shoot it!!
In any case,the critical surface the barrel tightens against should be square to the threads so when the barrel tightens there is a good,evenly loaded 360 deg foundation for the barrel.
That's all good,but realize its done with the barrel out,and you have removed steel,so your front sight will not be indexed any more and your headspace has shortened.Bummer.
And your bolt face may not be square to the bore,which was your question.
I'm not trying to rain on your parade,you are thinking right!!I'm trying to let you know there is a lot to what you want to do.
The receiver threads are likely cut in a different operation than the receiver bolt bore.They likely are not perfectly co-axial.Some blueprint jobs involve re-chasing the receiver threads co-axial to the bore.That is not easy.
Then there are the surfaces the locking lugs rest on in battery.Worn? set back?
Careful with the idea "lapping lugs".What are you lapping to?It helps if these surfaces are flat and true...and parallel to the receiver face.They are rather tricky to get in to face,with a facing boring head or rotary table,and realize they may be pack hardened.
That flat established,I prefer a threaded bushing with a spring loaded plunger screwed into the receiver to put a central,even load on the boltface to check lug bearing.Sharpie marker on the bolt lug faces tells the story.
I save some time using high spot technique and stones to lower the hi spots on the bolt lugs till I get good bearing,then just a finish lap.Use the center load plunger on the bolt face for lap pressure.Grabbing the bolt handle is an off center load.Not so good.
OK,all that done!! Now you would be ready to square the bolt face .
One way,A threaded bushing that screws in like a barrel shank with a precise hole in the center to guide a lap,,if only a little steel needs to come off.(Several ways to do this,a sinker EDM would be great!!A careful mill setup can work,but,low tech,lapping through a bushing is one way)
Of course,all this changes the headspace,so you may need to set the barrel back a thread,re-index the front sight straight up,and recut the chamber.If the barrel has any extractor cuts,those will need rework...
If you want education,go for it!!If you want a tack driver,consider the sows ear/silk purse story.A Winchester/Savage/Remington etc maybe?
Or,let it be what it is and shoot it!!
Last edited:
Dixie Gunsmithing
Moderator Emeritus
It took me a while to dig these links back up, but view both parts 1 and 2 for what you're needing to do. This is on a Remington 700, but its basically the same for all of them.
Part 1:
https://www.youtube.com/watch?v=pGn9qWJIM9M
Part 2:
https://www.youtube.com/watch?v=UmMSeBAGV0M
Part 1:
https://www.youtube.com/watch?v=pGn9qWJIM9M
Part 2:
https://www.youtube.com/watch?v=UmMSeBAGV0M
The Mosin-Nagant has a floating bolthead, not unlike modern Savages...I think Mosin and Nagant were ahead of their time 
To true the boltface to the centerline of the action on something like this I suspect you'd need to use a tool similar to this one, for the Savage:
http://www.midwayusa.com/product/795229/ptg-bolt-face-lapping-tool-savage-110
Natch, it would need to be made as you're not going to find one anywhere.
Once I move in Feb and can set up a gunsmithing lathe I'm planning on doing a top-to-bottom Mosin blueprint and re-barrel, both as a learning/practice experience (more fun than the usual Mauser to learn on!) and to see the practical effect.
I've seen 700 bolts fixed in an arbor, indicated, then the back of the lugs cut square to the body on the lathe, and the boltface squared with a homemade cutter with a notch that fits under the extractor- but that's a different animal.
So, you can't do it without removing the barrel (again, because it's a floating bolthead) and it would be of dubious value IMO without trueing the rest of the bolt, receiver and barrel anyway. Blueprinting should be a complete package for best results.
To true the boltface to the centerline of the action on something like this I suspect you'd need to use a tool similar to this one, for the Savage:
http://www.midwayusa.com/product/795229/ptg-bolt-face-lapping-tool-savage-110
Natch, it would need to be made as you're not going to find one anywhere.
Once I move in Feb and can set up a gunsmithing lathe I'm planning on doing a top-to-bottom Mosin blueprint and re-barrel, both as a learning/practice experience (more fun than the usual Mauser to learn on!) and to see the practical effect.
I've seen 700 bolts fixed in an arbor, indicated, then the back of the lugs cut square to the body on the lathe, and the boltface squared with a homemade cutter with a notch that fits under the extractor- but that's a different animal.
So, you can't do it without removing the barrel (again, because it's a floating bolthead) and it would be of dubious value IMO without trueing the rest of the bolt, receiver and barrel anyway. Blueprinting should be a complete package for best results.
Squaring is best done relative to the barrel tenon threads. Their axis is rarely aligned with the bolt way axis nor square with the receiver face.
Square the receiver face up to the tenon thread axis with it threaded onto a jig turned on centers first.
Then strip the bolt to lap its lugs to full contact with the receiver.
Thread a bolt facing jig in the receiver to square up a closed bolt face. Brownells sells them.
This is the best way and it keeps the tenon threads' size the same. If they're rethreaded larger, then the old barrel cannot be used.
Square the receiver face up to the tenon thread axis with it threaded onto a jig turned on centers first.
Then strip the bolt to lap its lugs to full contact with the receiver.
Thread a bolt facing jig in the receiver to square up a closed bolt face. Brownells sells them.
This is the best way and it keeps the tenon threads' size the same. If they're rethreaded larger, then the old barrel cannot be used.
We (as students at TSJC) put the bolt into a LA Bounty jig that was then mounted in a four jaw chuck. After dialing it in, we then used a dremel (mounted on carriage) to face the bolt face.
Here's a link to the LA Bounty jig.
http://www.brownells.com/gunsmith-tools-supplies/rifle-tools/action-bolt-trueing-tools/bolt-fixture-prod7789.aspx
BTW, when I trued my lugs for action blueprinting, I used a regular cutting bit. Bolt was placed into a 4 jaw chuck and dialed in. My instructor is returning to reteach the two week course this summer. Bring a Rem 700 action if you take it. First three days will be spent on making the tools. Then the other seven days will be working on the action and barrel. Buy a pre-contoured barrel (one size over since you can turn it down later and make the exterior more concentric to the bore).
Here's a link to the LA Bounty jig.
http://www.brownells.com/gunsmith-tools-supplies/rifle-tools/action-bolt-trueing-tools/bolt-fixture-prod7789.aspx
BTW, when I trued my lugs for action blueprinting, I used a regular cutting bit. Bolt was placed into a 4 jaw chuck and dialed in. My instructor is returning to reteach the two week course this summer. Bring a Rem 700 action if you take it. First three days will be spent on making the tools. Then the other seven days will be working on the action and barrel. Buy a pre-contoured barrel (one size over since you can turn it down later and make the exterior more concentric to the bore).
no, I don't think I will do it. I have no desire to try to remove the barrel anyways. I thought it might be a good idea since the bolts get changed around so much during the lives of nagants, but since it will never be a 1000 yard rifle or a benchrest comp gun, I doubt it is warranted
also, is there any real vale being a rimmed cartridge? does the boltface even contact the chamber?
also, is there any real vale being a rimmed cartridge? does the boltface even contact the chamber?
The bolt face does not contact the chamber, it pushes the base of the cartridge into the chamber.
The real reason to square the bolt face is so that brass is truer when you go to reload it, not slightly out of true. Accuracy with virgin brass will be the same between a blueprinted action and one with an out of true bolt face. But on the first reload your accuracy will drop about a quarter minute, in my experience, with an out of true bolt face. Even with a Savage and their floating bolt face.
I wouldn't bother on a Mosin.
Jimro
The real reason to square the bolt face is so that brass is truer when you go to reload it, not slightly out of true. Accuracy with virgin brass will be the same between a blueprinted action and one with an out of true bolt face. But on the first reload your accuracy will drop about a quarter minute, in my experience, with an out of true bolt face. Even with a Savage and their floating bolt face.
I wouldn't bother on a Mosin.
Jimro
Dixie Gunsmithing
Moderator Emeritus
The thing about squaring a bolt face, is it still may not be square to the bore and chamber, unless everything has been aligned to the centerline of the bore, which requires blueprinting. The bolt face could be square to the bolt from the factory, and may still be square to it later, but is it square to the centerline of the bore and chamber?
If you notice in those videos, how the barrel threads was canted off center, and had to be straightened up, which required over-sized threads to be cut on the barrel and in the receiver to center it up. So, you might square the bolt face, and it still not help one bit.
One might make a cutter that could revolve in the chamber, and be rotated by hand at the muzzle. You could close the bolt, and advance the cutter against the bolt face, and by having a close fit in the chamber, it would square the face with the bores centerline. However, I don't know how well that would work with a rimmed or tapered cartridge.
If you notice in those videos, how the barrel threads was canted off center, and had to be straightened up, which required over-sized threads to be cut on the barrel and in the receiver to center it up. So, you might square the bolt face, and it still not help one bit.
One might make a cutter that could revolve in the chamber, and be rotated by hand at the muzzle. You could close the bolt, and advance the cutter against the bolt face, and by having a close fit in the chamber, it would square the face with the bores centerline. However, I don't know how well that would work with a rimmed or tapered cartridge.
I plan to buy another mosin next year and build it from a bare receiver and up. New bbl etc, I think I will wait till then to play with the internals to that extent. Thanks for the good information and giving me a better understanding of the practice. I honestly think this mosin will be sub MOA when its finished in two weeks, and if that's the case, I will be elated as is. Thansagain
If the receiver face is first squared up to the tenon thread axis, then the bolt face squared up to the same axis, a small amount of bolt axis misalignment to the tenon thread and chamber axis isn't a problem. Win 70 receivers have a little bit of this but they still enable bullets to be shot as accurate as high dollar precision actions with everything in perfect alignment.
If a barrel is fit to a receiver whose face isn't square to the tenon thread axis, it'll start walking shots away from point of aim as it beats up.
If a barrel is fit to a receiver whose face isn't square to the tenon thread axis, it'll start walking shots away from point of aim as it beats up.