Mosin Nagant Bolt Head measurment

seanc · May 28, 2013, 10:56 PM

I need a favor, please: can I get some measurements of the bolt head for Mosin Nagants? The measurement I need is the from the bolt face to the bottom of the bolt head through the guide channel.

On my rifle with a good chamber, a 91/30, I get a measurement of 1.4775".
On my 1st rifle, an M44, I get a measurement of 1.4725".

I don't have chamber guides but I may get a set if it comes back that the issue here is just the bolt head. I really like my M44, but I know it has excessive head space and I'm hoping all I have to do is swap that bolt head. If I use the bolt head from my 91/30, I can easily chamber a round and the action is still very smooth (much better than my 91/30), though I haven't yet fired the M44 this way.

Thanks in advance,
Sean

tobnpr · May 29, 2013, 09:36 AM

There is no definitive measurement. There probably was back when they were manufactured... I suppose if there were a "new" one somewhere you could get the number- but I don't know of any way to prove that. I'm would guess that most if not all of the parts these days come from decommissioned rifles that were parted out.

Swapping bolt heads is a common way to address a headspace issue- I needed to do it with my very first MN. Fortunately, I have a milsurp supplier a half hour from me and I could pick through until I could find one that worked.

Otherwise, it's unfortunately hit and miss- and they're not cheap these days.

The excessive headspace on the 44 could very well be from worn lug recesses- for which there's obviously no fix.. perhaps a "like new" bolthead with almost no wear would get it in the safe zone.

seanc · May 29, 2013, 12:12 PM

Understood. And I assume I probably made things worse when I did such a good job cleaning the corrosion off the bolt when I first got it. Again, I'm hoping to hear others bolt heads are longer so there's hope when/if I order that I'll likely get something that will make a difference for me.

Gunplummer · May 29, 2013, 02:26 PM

I made a bolt head for a Russian when I put a 30-40 barrel on it. Take two parallels, or two level blocks and set the back of the bolt lugs on them. Take another block that is flat and set a depth mike on it (Or use a drop indicator) and measure down to the face of the bolt. Take another bolt head and do the same. Subtract the difference and that is the difference in headspace between the two bolts. The total length of the bolt head really has nothing to do with the headspace. Besides that, any rimmed cartridge chamber is generally on the large size for military ammo. Who knows where the bolt head was made? There should be an ordinance stamp on it, but it could have been made in Albania for assembly into a rifle in a Russian factory.

tobnpr · May 29, 2013, 03:58 PM

Since the 54R headspaces off the rim, the chamber is irrelevant as relates to headspace...

Take the bolt from your "good" 91/30, and run it in the carbine.

If a no-go (or field, whichever you're using) still shows excessive headspace, the lug races in the receiver are worn out- no fix for that...it's a wall hanger.

The biggest cause of excessive headspace in rifles- in general- is worn lug races, not chamber erosion...

It's metal on metal, for thousands and thousands of rounds being chambered. Get a bit of grit/dirt in there, and it's like an abrasive compound.

seanc · May 29, 2013, 05:03 PM

I have a no-go gauge on the way.

Anyone measure their bolt head yet?

P.S. tobnpr --> nice stocks! I was checking out Boyds, but I think I like yours better, especially the walnut.

tobnpr · May 30, 2013, 09:22 AM

Thanks.
I found a new supplier for Walnut, big outfit that supplies blanks for large firearms manufacturers like Remington. I'm able to pass along the savings

On your measurements...

EDIT: I didn't see Gunplummer's post above. I duplicated the info he already provided...

I just re-read how you were doing this, it's not going to be relevant for headspace.

Remember, the Mosin-Nagant has a floating bolthead like a Savage. The length of the bolthead from boltface to bottom is irrelevant. It's the distance from the boltface, to the back of the locking lugs- the bearing portion- that determines the headspace.

I checked a couple of mine.
#1.. Total length back of lug to top of rim: .637.
Subtract rim to boltface: (.059)
Back of lug to boltface: .578

#2.. Total: .639
Less: (.062)
Back of lug to boltface: .577

It's important to catch the rim of the bolthead at the very edge- or the calipers will angle and increase the measurement.

Gunplummer · May 30, 2013, 02:35 PM

Bout time you get with the program. Forget the rim and measure to the bolt face off a block set up as I described earlier. The less areas you add and subtract from, the more accurate the reading. The locking recesses always wear out before the chamber does ? What nonsense. I have seen them get set-back from bad heat-treating and excessive loads, but not wear.

tobnpr · May 30, 2013, 07:26 PM

Quote:

The locking recesses always wear out before the chamber does ? What nonsense.

Nonsense?? I don't think so. This post pretty much sums it up.
For you to stipulate that bolt lugs and races don't wear, is what's nonsense.

And in the case of the 54R that headspaces off the rim, chamber wear is IRRELEVANT.

Quote:

A lot of people confuse throat erosion with headspace wear. Barrels wear out from throat erosion caused by the hot gases from the fired cartridge. This wear occurs at the end of the casing as the bullet is forced out by the expanding gases. Headspace is measured at the shoulder of the cartridge, about 1/2" to the rear of where the hot gases escape. There are no hot gases in this area and the only stress on the shoulder of the barrel is when the soft brass case expands against it. This wear is so minimal that once the barrel is reamed for proper headspace when new, it seldom changes enough to measure. Wear to the area where the bolt lugs rotate against the receiver is what causes headspace to increase.

Quote:

The wear points...
which affect headspace in the M1 (or any locked-breech rifle) are the rear faces of the locking lugs of the bolt and the corresponding supporting surfaces in the receiver. Both of these are subject to mechanical wear (and about equally so, since they are of similar size and their bearing surfaces are intentionally sized to match), and both can be deformed by excessive stress. In service, with good and consistent ammunition, the usual cause of dimensional changes in these parts is abrasion caused by continued use under field conditions of dust and dirt. Both parts are gauged in rebuild, and, if found to be within the specified tolerances, and not otherwise obviously damaged, are judged suitable for re-use. While the chamber of the barrel can be deformed by excessive pressures, it is not normally worn out-of-tolerance by abrasion of the shoulder against which the cartridge case headspaces, and is commonly replaced because of normal erosion in the throat due to long use and/or muzzle damage - though corrosion of the bore due to neglect can cause the barrel to be condemned.

seanc · May 30, 2013, 09:48 PM

This is the measurement I was wanting:

Not from the rim, but from the bolt face to the bottom of the bolt head through the guide channel.

tobnpr · May 31, 2013, 09:25 AM

You're still missing the point...
That measurement is irrelevant to headspace.
When the bolt is in battery, the back end of the bolthead is floating in space- it is not bearing on anything.

Only the back face of the locking lugs, which bears on the races in the cut in the receiver, is what determines your "length".

Gunplummer · May 31, 2013, 10:08 AM

I suppose it would appear that the body of a chamber has nothing to do with the rim, but not so. I have made rimmed case reamers and I think I know a little more about this than you do. If the chamber area is on the high to begin with, and a lot of rounds are run through it, the result will be the same as if you have bad headspace. This area may not be considered "Headspace" in a book but has the same result, bulged and split cases. The Soviets were notorious for sloppy dimensions during WWII. Some loose spec guns were intentional for ease of extraction and some of it was because of the steel cased ammo could support more pressure. I had a very early hex receiver rifle that would not even chamber some steel cased ammo. I have had lever actions that REALLY failed the headspace gauge and the extracted brass was fine. The chamber was close enough to the brass to actually make it function as a rimless cartridge. There is a lot more to headspace than what is written in the book. I had a lot of guys bring me 8MM Mausers that they used a headspace gauge on and it failed. Nothing wrong with the gun, different specs.

On the M-1 article: How many fired steel cased ammo?

seanc · June 3, 2013, 04:21 PM

OK, I got a set of gauges today (go-no go) and both rifles are good. The reason I assumed my M44 had excessive head space is that I sometimes have trouble ejecting brass cartridges from it. I have no issues with steel cased ammo, regardless if it's copper washed or lacquered (I prefer the copper washed). I've shot this rifle both hot and cold and had no issues with steel, even with some heavily lacquered Polish rounds. However, with brass, once it gets hot, I sometimes have to force the ejection. The ejected brass looks good and I box the stuck rounds separately so I don't reload them. -- As I'm typing this, I'm wondering if I'm causing this sticky bolt by shooting steel cartridges 1st, then brass? <-- I guess that's the question now.

Gunplummer & tobnpr
I think I understand what you're saying about the difference in headspace between the two bolts and the total length of the bolt head really has nothing to do with the headspace. What difference does the total length of the bolt head+bolt body make? At least in regards to rimmed cartridges.

Thanks again,
Sean

tobnpr · June 4, 2013, 11:15 AM

Rimmed, or not rimmed, doesn't matter. The location of the boltface is set by the locking lugs, not any other portion of the bolt.

Headspace is defined as the distance from the cartridge datum line, to the boltface. In the case of a rimmed cartridge, it's from the back of the chamber where the rim hits. In a non-rimmed cartridge, it's where the shoulder hits the chamber wall. Both are the forward "stop" points for the case.

Gunplummer · June 4, 2013, 11:31 AM

"Force the ejection", or do you mean force the bolt open? Check your primers. Usually if you have to force the bolt open on a bolt action rifle the primer is welding around the firing pin. Might have the pin protrusion off. Or could be laquer build up in the chamber. Scrub it out good. I had a very early hex receiver rifle that had a very tight chamber and steel cased ammo started to screw it up. It was some of the first copper washed ammo coming into the country. The burrs left on the case rims were so bad it started to chew up the face of the chamber where the rim contacted. Anything is possible when you have multiple countries producing something.

May 29, 2013, 02:26 PM	#4
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	I made a bolt head for a Russian when I put a 30-40 barrel on it. Take two parallels, or two level blocks and set the back of the bolt lugs on them. Take another block that is flat and set a depth mike on it (Or use a drop indicator) and measure down to the face of the bolt. Take another bolt head and do the same. Subtract the difference and that is the difference in headspace between the two bolts. The total length of the bolt head really has nothing to do with the headspace. Besides that, any rimmed cartridge chamber is generally on the large size for military ammo. Who knows where the bolt head was made? There should be an ordinance stamp on it, but it could have been made in Albania for assembly into a rifle in a Russian factory. Last edited by Gunplummer; May 29, 2013 at 03:05 PM.

May 29, 2013, 05:03 PM	#6
seanc Senior Member Join Date: December 28, 1998 Posts: 591	I have a no-go gauge on the way. Anyone measure their bolt head yet? P.S. tobnpr --> nice stocks! I was checking out Boyds, but I think I like yours better, especially the walnut. Last edited by seanc; May 29, 2013 at 05:11 PM.

May 30, 2013, 09:22 AM	#7
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	Thanks. I found a new supplier for Walnut, big outfit that supplies blanks for large firearms manufacturers like Remington. I'm able to pass along the savings On your measurements... EDIT: I didn't see Gunplummer's post above. I duplicated the info he already provided... I just re-read how you were doing this, it's not going to be relevant for headspace. Remember, the Mosin-Nagant has a floating bolthead like a Savage. The length of the bolthead from boltface to bottom is irrelevant. It's the distance from the boltface, to the back of the locking lugs- the bearing portion- that determines the headspace. I checked a couple of mine. #1.. Total length back of lug to top of rim: .637. Subtract rim to boltface: (.059) Back of lug to boltface: .578 #2.. Total: .639 Less: (.062) Back of lug to boltface: .577 It's important to catch the rim of the bolthead at the very edge- or the calipers will angle and increase the measurement. Last edited by tobnpr; May 30, 2013 at 02:42 PM.

May 30, 2013, 02:35 PM	#8
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	Bout time you get with the program. Forget the rim and measure to the bolt face off a block set up as I described earlier. The less areas you add and subtract from, the more accurate the reading. The locking recesses always wear out before the chamber does ? What nonsense. I have seen them get set-back from bad heat-treating and excessive loads, but not wear. Last edited by Gunplummer; May 30, 2013 at 02:46 PM.

May 30, 2013, 09:48 PM	#10
seanc Senior Member Join Date: December 28, 1998 Posts: 591	This is the measurement I was wanting: Not from the rim, but from the bolt face to the bottom of the bolt head through the guide channel. Last edited by seanc; May 30, 2013 at 09:54 PM.

May 28, 2013, 10:56 PM	#1
seanc Senior Member Join Date: December 28, 1998 Posts: 591	Mosin Nagant Bolt Head measurment I need a favor, please: can I get some measurements of the bolt head for Mosin Nagants? The measurement I need is the from the bolt face to the bottom of the bolt head through the guide channel. On my rifle with a good chamber, a 91/30, I get a measurement of 1.4775". On my 1st rifle, an M44, I get a measurement of 1.4725". I don't have chamber guides but I may get a set if it comes back that the issue here is just the bolt head. I really like my M44, but I know it has excessive head space and I'm hoping all I have to do is swap that bolt head. If I use the bolt head from my 91/30, I can easily chamber a round and the action is still very smooth (much better than my 91/30), though I haven't yet fired the M44 this way. Thanks in advance, Sean

May 29, 2013, 09:36 AM	#2
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	There is no definitive measurement. There probably was back when they were manufactured... I suppose if there were a "new" one somewhere you could get the number- but I don't know of any way to prove that. I'm would guess that most if not all of the parts these days come from decommissioned rifles that were parted out. Swapping bolt heads is a common way to address a headspace issue- I needed to do it with my very first MN. Fortunately, I have a milsurp supplier a half hour from me and I could pick through until I could find one that worked. Otherwise, it's unfortunately hit and miss- and they're not cheap these days. The excessive headspace on the 44 could very well be from worn lug recesses- for which there's obviously no fix.. perhaps a "like new" bolthead with almost no wear would get it in the safe zone.

May 29, 2013, 12:12 PM	#3
seanc Senior Member Join Date: December 28, 1998 Posts: 591	Understood. And I assume I probably made things worse when I did such a good job cleaning the corrosion off the bolt when I first got it. Again, I'm hoping to hear others bolt heads are longer so there's hope when/if I order that I'll likely get something that will make a difference for me.

May 29, 2013, 03:58 PM	#5
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	Since the 54R headspaces off the rim, the chamber is irrelevant as relates to headspace... Take the bolt from your "good" 91/30, and run it in the carbine. If a no-go (or field, whichever you're using) still shows excessive headspace, the lug races in the receiver are worn out- no fix for that...it's a wall hanger. The biggest cause of excessive headspace in rifles- in general- is worn lug races, not chamber erosion... It's metal on metal, for thousands and thousands of rounds being chambered. Get a bit of grit/dirt in there, and it's like an abrasive compound.

May 31, 2013, 09:25 AM	#11
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	You're still missing the point... That measurement is irrelevant to headspace. When the bolt is in battery, the back end of the bolthead is floating in space- it is not bearing on anything. Only the back face of the locking lugs, which bears on the races in the cut in the receiver, is what determines your "length".

May 31, 2013, 10:08 AM	#12
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	I suppose it would appear that the body of a chamber has nothing to do with the rim, but not so. I have made rimmed case reamers and I think I know a little more about this than you do. If the chamber area is on the high to begin with, and a lot of rounds are run through it, the result will be the same as if you have bad headspace. This area may not be considered "Headspace" in a book but has the same result, bulged and split cases. The Soviets were notorious for sloppy dimensions during WWII. Some loose spec guns were intentional for ease of extraction and some of it was because of the steel cased ammo could support more pressure. I had a very early hex receiver rifle that would not even chamber some steel cased ammo. I have had lever actions that REALLY failed the headspace gauge and the extracted brass was fine. The chamber was close enough to the brass to actually make it function as a rimless cartridge. There is a lot more to headspace than what is written in the book. I had a lot of guys bring me 8MM Mausers that they used a headspace gauge on and it failed. Nothing wrong with the gun, different specs. On the M-1 article: How many fired steel cased ammo? Last edited by Gunplummer; May 31, 2013 at 10:20 AM.

June 3, 2013, 04:21 PM	#13
seanc Senior Member Join Date: December 28, 1998 Posts: 591	OK, I got a set of gauges today (go-no go) and both rifles are good. The reason I assumed my M44 had excessive head space is that I sometimes have trouble ejecting brass cartridges from it. I have no issues with steel cased ammo, regardless if it's copper washed or lacquered (I prefer the copper washed). I've shot this rifle both hot and cold and had no issues with steel, even with some heavily lacquered Polish rounds. However, with brass, once it gets hot, I sometimes have to force the ejection. The ejected brass looks good and I box the stuck rounds separately so I don't reload them. -- As I'm typing this, I'm wondering if I'm causing this sticky bolt by shooting steel cartridges 1st, then brass? <-- I guess that's the question now. Gunplummer & tobnpr I think I understand what you're saying about the difference in headspace between the two bolts and the total length of the bolt head really has nothing to do with the headspace. What difference does the total length of the bolt head+bolt body make? At least in regards to rimmed cartridges. Thanks again, Sean

June 4, 2013, 11:15 AM	#14
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	Rimmed, or not rimmed, doesn't matter. The location of the boltface is set by the locking lugs, not any other portion of the bolt. Headspace is defined as the distance from the cartridge datum line, to the boltface. In the case of a rimmed cartridge, it's from the back of the chamber where the rim hits. In a non-rimmed cartridge, it's where the shoulder hits the chamber wall. Both are the forward "stop" points for the case.

June 4, 2013, 11:31 AM	#15
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	"Force the ejection", or do you mean force the bolt open? Check your primers. Usually if you have to force the bolt open on a bolt action rifle the primer is welding around the firing pin. Might have the pin protrusion off. Or could be laquer build up in the chamber. Scrub it out good. I had a very early hex receiver rifle that had a very tight chamber and steel cased ammo started to screw it up. It was some of the first copper washed ammo coming into the country. The burrs left on the case rims were so bad it started to chew up the face of the chamber where the rim contacted. Anything is possible when you have multiple countries producing something.