mannlicher schoenauer hard bolt lift?????

R

RoyB

Member
I have a 1908 Mannlicher Schoenauer in 8X56MS that after firing a very mild load experiences extremely difficult bolt lift once the bolt handle has reached 1/2 way of its lift.

DSC_2346-vi.jpg


There was concern that some of these Mannlicher Schoenauer rifles had undersized bores and this might be causing a pressure situation. Although the case exhibited zero signs of pressure, I performed a cerrosafe cast of the barrel and measured a proper bore diameter.

So.........Last night I completely disassembled the bolt.

With no cartridge in the chamber the bolt will easily open. No resistance what so ever. These rifles exhibit a relatively hard bolt lift without anything in the chamber, so removing the firing pin and cocking piece removes all extra resistance to bolt lift.

Using the bolt without the firing pin or the cocking piece I inserted a piece of fired brass. I experienced extreme hard bolt lift once the bolt handle was raised to 1/2 its upward movement.

I full length sized this brass and although the resistance was lessened, it was still very difficult to move the bolt handle past the half way mark.

I measured this piece of brass and confirmed that all dimensions are under the spec I found on the internet for 8X56MS cartridge.
But to be sure I ground a few thou off the rim.....no improvement.

I then ground a few thou off the base of the cartridge....no improvement.

I them took the resized case and cut it 1/2" above the base and using this stub I inserted it into the bolt and pushed the bolt home. I wanted to be sure the resistance was not due to the extractor or the ejector......Bolt opened easily. So the issue is somewhere north of the first 1/2" of the brass.

I then took a piece of once fired brass and in the lathe removed one thou from the middle third of the case. Voila! The bolt handle moved easily!

I then smoked a piece of once fired brass to see if I could observe where it was hitting. The smoked case showed contact with the brass over it's whole length.

My conclusion is that I have a "banana" shaped chamber or an "oval" shaped chamber. Although I can't confirm either of these theories with the measuring equipment I have at my disposal.

I've had this happen with a few rifles in the past. Usually egg shaped chamber resulting from poor chambering jobs (not of my doing) with short cartridges (6BR and 6PPC).
My solution has always been a Cerrosafe cast of the chamber and using the casting attached to a long brass rod with grinding compound and an electric drill to polish the chamber round.

Unless anyone has something else they think I'm missing, I'm moving forward with this process.
Comments and suggestions welcome...........
Thanks

DSC_2618-vi.jpg

This photo shows the test brass. As you can see on the "smoked" piece, there is extra contact on the middle portion. The piece to the far right shows the turned down rim and the ground base. I also filed some brass off the shoulder to see if this might be the sticking point. And finally the turned center section.

DSC_2619-vi.jpg

The machining on this 1908 bolt is nothing short of amazing!

DSC_2620-vi.jpg

The bolt without the firing pin or cocking piece
 
I would cast the chamber with Cerrosafe and measure it before doing anything. A simple micrometer will do. I have never ground a chamber with a casting but I can't imagine that would be a good thing to do. Have you new brass to try?
 
There is no "new brass" for the 8X56 MS. The only option is to form and trim from 8X57 Mauser. The problem with a "banana" shaped chamber and a chamber cast is that as you push the cast out, it changes shape. I'm not sure this will show me anything, but I'll try it anyways.

Thanks for the suggestion.
 
Read about Cerrosafe... it shrinks just after it is poured and is easily removed... then it will grow back to size as it 'cures'... the chamber will not 'distort' or damage it on removal unless you leave it in too long.

I don't understand how a banana shaped chamber could be made to start with... I can see someone aggressively polishing a 'jugged' chamber... one that is slightly larger in the middle...

Does the extraction problem occur with new fully sized brass?
 
Last edited by a moderator:
Does the extraction problem occur with new fully sized brass?
Click to expand...

Yes, simply resize a piece of brass, insert, and bolt lift is hard.

I drilled and taped the end of a piece of sized brass, threaded the end of a piece of 1/4" drill rod, attached it to the brass. Chucked it up in a drill, applied a bit of 800 grit grinding compound and had at it.

It seems to be much better. The bolt can now be opened with a piece of resized brass. But we won't know if this resolved the issue completely until I fire the rifle again.
 
RoyB said:
Yes, simply resize a piece of brass, insert, and bolt lift is hard.
Click to expand...

That tells me there is probably something wrong with the cartridge... it is not correctly sized... ?

Who made your 8X56MS dies?
 
Redding made the dies...........

Dennis, you could be correct.

I did sime very fine polishing last night with a piece of resized brass threaded onto a piece of 1/4" drill rod. I then turned a bushing to fit into the bolt raceway. Electric drill and some 800 grit grinding compound and I polished the chamber. At first the brass was so tight the drill would stall. After a 1/2 minute or so, it was progressing much smoother. I then cleaned everything up and observed much easier bolt lift. I need to fire the rifle to confirm.

BTW, I used the term "banana", I should have said "hour-glass" shaped as this describes the chamber better. I've seen this in a couple of 6BR and 6PPC chambers over the years. I believe it happens if the reaming set up isn't proper and the chamber reamer does a bit of wobbling............
 
Probably the chamber is "jugged" (swollen in the center - opposite of hour glass) - that appears to be the problem judging from the scratches on the brass. You are doing the right thing - lapping out the rear of the chamber so that the brass can be extracted. Jugged chambers are usually a result of excess pressure, but could also be a chamber polishing defect caused by rust removal, etc. If the effect is small, removing some material at the rear of the chamber should make things right enough for a hunting gun. Brass life will be shortened.

Scott
 
Good example of bore compression from shoulder being overtightened probably to get barrel index for sights correct. Measure bolt face forward and see where it (tight spot) falls on the action or barrel. Polishing chamber is the correction.
BV
 
Brian Voelker said:
Good example of bore compression from shoulder being overtightened probably to get barrel index for sights correct. Measure bolt face forward and see where it (tight spot) falls on the action or barrel. Polishing chamber is the correction.
BV
Click to expand...

Brian, could you please expand on this "good example of bore compression???" :)

I'm guessing you meant to say "chamber compression?"

As I see it the problem (probably jugging) lies right where this supposed constriction would occur.


Scott, care to explain why "brass life will be shortened?"



(BTW I think you're right. I too believe the chamber to be swelled or 'jugged' and that the proper fix is to open up the rear of the chamber.)


al
 
Al
I consider the hole in the barrel as the bore. Thread major diameter is 1"x12tpi v on those guns. Most Mauser set ups had back of barrel touching action collar and custom set up was to hit back collar and shoulder for tight fit. Now if you cut a groove at thread and shoulder junction for thread clearance at action face the minor diameter at that point is around .925 and the cartridge diameter is about .450 in that area leaving metal in that area of .250 thickness (.925-.450=.500 divided by 2). With high load at that area (shoulder/action face) and thin area of metal it is stretched and when it stretches the bore gets smaller. Compression may not be the proper term as that implies a force pushing in. In layman terms if you took a rubber hose and pulled both ends the hole gets smaller. Edit There may be some compression from the V threads also as the closest threads to the joint would be pressing in. Square thread would eliminate that theoretically.end Edit
I first encountered this in 22 rim fire guns as the shoulder is normally in the rifling area ahead of the chamber and you could feel this with a slug if you checked and sometimes it would go away when you loosened the barrel if it did not take a set.
I suppose a good proof load may eliminate his problem also but I would not recommend it.
BV
 
Last edited by a moderator:
Brian,

Great explanation! And I bet you are correct on what happened to my rifle. I'm going to make up some lead slugs and "slug the chamber" to look for tight and lose spots. With a tapered cartridge case, this will be difficult, but worth a try.

Thanks for the input.............
 
Thank you Brian, I agree, good explanation.

Can't say I agree with it but a fine description of your contention.

I will say this though, if Brian's right then the scrubbed section should measure parallel or even reverse taper, visible with a set of calipers,

al
 
Al,

I made a somewhat offhand comment about the brass. If the chamber is enlarged from lapping and resizing is done full lengththe brass will be worked more - I assume this would shorten the life, however I have no first hand experience with this cartridge. By just neck sizing for the new chamber shape there might not be any significant brass problems.

I have not seen a tightening of bore/chamber diameters from "stretching", but a 60 degree barrel thread will compress the bore - the more torque, the greater the compression. This is a straight vector component and the values are quite high on a fine thread- one of the reasons I don't like high barrel torques. I have seen this many times and sometimes clean up the compression effects by re-reaming while the action is in place (sacriledge) or by lapping.

scott
 
I have seen this many times and sometimes clean up the compression effects by re-reaming while the action is in place (sacriledge) or by lapping.
Click to expand...

If I had access to a reamer in 8X56MS, I'd attempt this. A tricky proceedure to not effect headspace.
 
Ck the leading 'edge' of the extractor blade to see if it is digging into the brass in the extractor groove. If this is the prob. it shows up about half bolt lift. Emery paper fixed mine. Mine had been 'up chambered' to 8x57Mauser before I got it and provided all sorts of nightmare fantasies. Did and considered most of what you have. I think the 1/2" case stub probably doesn't offer enough resistance/ drag in the chamber and turns IF it is the extractor that engages and binds. I think the normal chamber drag on the case gives the point of the extractor enough purchase to dig into the brass so it makes it seem the case is sticking for what ever reason. I putzed with this prob. off and on for a couple yrs until I took it all apart one more time and as Sherlock Holmes advises-" ... what ever remains after you have eliminated the impossible, however improbable, Must be the truth." Good Luck.
 
Last edited by a moderator:
Radar,

I think you are on to something. I can't wait to get home from work and look into this possibility. It sounds very plausible.

thanks
 
You must log in or register to reply here.
Back
Top