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Condensed from a longer thread.

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Dutchman
Moderator - Swedish Military Firearms Forum
Posted - 08/11/2007 : 02:40:23 AM
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How would trying a bolt in another rifle reveal lug setback, which is a primary cause of excessive headspace?

This fellow's problem needs professional attention. It can't be diagnosed with the bolt and rifle separated, IMO. He needs a competent gunsmith. If the receiver is stretched he needs a new receiver, not a new bolt. If it has lug setback he needs a new receiver. We don't know if this rifle has been subjected to hotrod loads by a young lad with no respect for loading manual limits.

We need to be cautious about diagnosing such problems in a forum like this. The rifle's owner doesn't have the qualifications to say why the rifle has excessive headspace, nor can he even state as fact that it has excessive headspace until it has a gauge dropped in the chamber by someone familiar with the procedure. Second guessing something like this because it seems the logical conclusion violates acceptable and prudent protocal. This forum won't be used to disseminate erroneous or bogus information or methodology... such as checking headspace with scotch tape or aluminum foil on the back end of a cartridge. Let us leave that kind of Bubba'speak for other forums that have no standards.

As Mike442 says, a field gauge is around $20. That's the first thing to do.. but it needs to be done by a qualified individual, not a novice. How many times have we heard of someone forcing the bolt closed on a gauge "just a little bit"? Its a precision tool and it requires some level of skill and experience to manipulate correctly.

30calron -- you need a gunsmith, not a collector's forum. Pay heed to the advise you've received in this thread. Act on that advise or don't, but I won't allow slipshod advise or practice to be passed on via this forum and that's what I see developing here.

http://www.brownells.com is where the gauges may be purchased. I haven't read anything in this thread that "leaves no doubt" as to what the problem might be. You seem fixated on swapping bolts until the problem goes away. That's not going to happen. Your rifle, most likely, has either lug setback or the receiver is stretched. Any problem with the bolt that's caused it to change dimensionally would indicate some horrendous pressure exerted upon it and would render the rifle wholly unsafe for further use. Consider this the worst end of "what might be".

Your comment about the bolt being re-stamped is meaningless. It was standard practice in Sweden to recycle parts including bolt parts and many times we've seen sloppy restamping. You haven't shown us this bolt or the markings so you'll have to pardon us if we discount what you assume. Given the possibility that this bolt is correct to your rifle we then must ascertain why its stretching brass, as you say, and the first thing to do is check the headspace with a gauge.

You've not given us spent cartridge length and web diameter, before and after firing. You've not told us how many times the case has been fired. You've not told us what brand of cases this happens to, which have you tried? You've not told us if this occurs with all cases fired in this rifle. How many cases have you fired that have stretched? How long have you owned this rifle? How many rounds have you put through it?

Post photos of the bolt numbers, all of them. We'll tell you if we think its been done in Sweden or elsewhere, if possible. Even the firing pin number... especially the firing pin number. Also the bolt knob where the number is and show us the crown stamp on the bolt knob. This are the areas that will tell us if the bolt is correct to your rifle and will add a lot of flavor to the stew.

Dutchman



BobVZ
Posted - 08/12/2007 : 10:41:23 AM
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What type of ammo are you firing - factory or reloads? If you are reloading, your dies(depending on brand)may be adjusted so they are pushing the shoulder back too far. I have also encounter some PMC factory ammo that was undersized(base to shoulder)and had brittle brass that gave the appearance of a headspace problem.

What is the case head diameter? Swedish Mauser ammo has a case head that is .480 in diameter compared to .470 for .30-06 and other Mauser calibers. You could be firing undersized brass and you are getting a swelling of the brass that forms a ridge around the case head. I have 6.5 brass that measures from .472 to .480. The undersize stuff is American made(Winchester). When you say "evidence of severe stretching" do you mean a ridge as I described or a bright ring and possible hairline crack?
Photo's would help.

Often you can detect lug setback by removing the firing mechanism and cycling the bolt slowly while pulling back hard on the bolt handle. If there has been setback, metal from the lug seat will have extruded into the ejector slot and around the edges of the lugs causing you to feel a "bump" when you unlock the bolt. A headspace gauge may not reveal this since it may stop bolt rotation before it reaches the setback area. Also, this condition would make it difficult to open the bolt after firing. In any event, unless you know how to use headspace gauges, I'd take this one to a gunsmith.



BobVZ
Posted - 08/12/2007 : 5:53:01 PM
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(...) lug setback. It is a very common reason for excessive headspace in milsurps and just because someone doesn't mention it in their post, it doesn't mean its not there. The other posters were correct in bringing it up as a possibility. Before using a headspace gauge it is important to know if it is present because it can give false readings.

It is also important to determine if 30calron even knows what case stretching looks like. He may be confusing it with case head swelling from undersize brass. We don't know. He only showed 3 posts and may be new to the hobby and inexperienced.

There are many reasons for headspace problems(or what appears to be) besides the three you mention. The only true test is for an experienced individual to check headspace with proper gauges....once you know you are dealing with flat surfaces on the lugs and their abuttments.


Dutchman
Posted - 08/12/2007 : 7:12:15 PM
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I promise this will be the last time I'll waste my time with a newbie asking a techical question. Why bother asking a question if you're not going to participate in the discussion by filling in the empty spaces you left out in the first place?

For the benefit of others: Cartridge cases don't only stretch because of excessive headspace. Every time you fire a piece of cartridge brass it stretches "some". How much depends on the individual rifle's chamber. If you reload a single cartridge case 5 times, 10 times or somewhere inbetween, at some point its going to stretch to the point that you have an incipient head separation (incipient = partial). In worst cases the head completely separates from the upper portion of the cartridge case.

http://www.exteriorballistics.com/reloadbasics/caseinspect.cfm

Many newbies misinterpret the "ring" showing expansion as stretching and therefore mistake it as indicating excessive headspace. Some rifles have oversize chambers to the point that the web of the cartridge will expand more than you'd like. It doesn't mean it has excessive headspace. This is why there was nothing ~obvious~ in this thread indicating excessive headspace.

If you're interested in learning more.. but there's some slight differences between rimless and rimmed cartridges as far headspace indications.
http://www3.sympatico.ca/shooters/FvsPvsN.htm

Wish the photos were better..
http://jeffersonian.name/reload-r.html

Varmint Al is always good for any question. Check out the case expansion animation down the page.
http://www.varmintal.com/a243z.htm

You could almost forget any other page about case head expansion and just study Varmint Al's page for the next 5 years. Its very indepth.

Dutchman



MP78
Posted - 08/13/2007 : 8:56:48 PM
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It's true that lug set back is one cause of excessive headspace but this is accompanied by harder than normal to real hard bolt lift. This is because the bolt has to force the expanded case back into the chamber slightly for the bolt lugs to jump out of the little indentions made in the rear of the bolt lug raceway in the receiver. A soft receiver or firing hot ammo is most likely the cause of this. If 30calron found it harder to open the bolt after firing it compared to just chambering a round and then ejecting it he most likely would have mentioned that.

Mike442 told him to buy a field guage and check his headspace. What type of field guage. SAAMI specs are different than what the Swede's used. Buying a SAAMI field guage really won't tell him anything even if he knew how to basically use one which I doubt.

Bobvz, If you push the neck back too far, are shooting brass that isn't annealed properly or reloading too light a charge you should also see sooting of the cartridge along with the other pressure signs. It's true if the back of the lugs have been flattened that would also cause the headspace to be out.

It's very difficult to explain, to a novice, what he may be experienceing. After all there are complete books written on the subject and it's almost impossable to explain it in a forum like this. Not enough information can be just as bad as not understanding the info being put out. That's what I liked about Dutchman's response compaired to the others...Jim


Mike442
Posted - 08/14/2007 : 01:17:55 AM
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It is true that the Swedish chamber specs are not the same as the SAAMI specs. That's why a Swedish Mauser will sometimes close on a SAAMI spec gauge and not on a Swedish spec gauge. So if it doesn't close on the SAAMI spec "field" gauge, then you know for sure it won't close on the Swedish spec "field" gauge. Also, the whole purpose of checking headspace is to determine how well the cartridge case of the ammo being used fits up to the chamber. If your shooting SAMMI spec ammo, then the headspace should be checked with SAAMI spec gauges. Don't mix apples with oranges. The following site goes into the comparison of the Swedish gauges to the SAAMI gauges.

http://www.rebooty.com/~dutchman/headspace.html

If you covert the Swedish metric size gauges to English units and compare them to the SAAMI spec gauges, you will see that the SAAMI spec gauges are slightly shorter than the Swedish gauges.

Lug setback could still be a part of the problem since the original post did not state one way or the other on this. The answer can not be any more accurate than the information given. Sometimes things that are not stated can be more important than the ones that are. Especially when dealing with a novice who doesn't know what is important and what isn't. Just because it wasn't mentioned, doesn't mean it didn't happen, at least to some degree. Some setback can be present without excessively hard bolt lift, given the springback of the specific brass used and the camming action of the bolt. Excessive bolt lift is indicative of the more extreame cases of lug setback.

The bottom line is there hasn't been enough information given for anyone to state with any degree of certainty what the problem is. The suggestions given above are only a few starting points of investigation.
 
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