Need some knowledge here???

[qajaq59]

I have a Marlin 30AS in 30-30 that was made in 1983, but got very little use until about 2 years ago. It has had a habit of misfiring, but only maybe 2% of the time. I had already had the hammer spring and the firing pin replaced, but it still did it. The other day I took it to a gun smith to check the head space, and according to the book it should fall between .010 and .015.

Unfortunately it came in at .019 which he thinks is likely why it misfires. My question is, "If I have him turn the barrel in one thread is it always necessary to rebore as well?" Or do you think I'd get away with just turning the barrel in?

Thanks

[Big Dave]

:brokenimaMyself, If you reload try just neck sizing your cases instead of full length sizing. Cases fired in the chamber will have the shoulder set forward to the chamber dimension and if you do not push it back to minimum they should work just fine. All you need to do is re set your sizing die maybe a half turn higher in the press. After several loadings if you start to have cases that chamber hard you may have to set the die down a little at a time untill you resize the case to fit freely but still not push the shoulder back far enough to again cause misfires. The 30-30 is a pretty low pressure cartridge and neck sizing is all you need most of the time.
Cartridges should be marked and used only in ths rifle as they may not chamber easily in guns with proper headspace

[Jon K]

When you cut and turn the barrel back 1 turn you will have to rechamber to set headspace. 1 turn is way more than the .004-.009" you're looking to take up.

Do it right and set up with tight headspace tolerance.

Jon

[Dutchman]

I have a Marlin 30AS in 30-30 that was made in 1983, but got very little use until about 2 years ago. It has had a habit of misfiring, but only maybe 2% of the time. I had already had the hammer spring and the firing pin replaced, but it still did it. The other day I took it to a gun smith to check the head space, and according to the book it should fall between .010 and .015.

Unfortunately it came in at .019 which he thinks is likely why it misfires. My question is, "If I have him turn the barrel in one thread is it always necessary to rebore as well?" Or do you think I'd get away with just turning the barrel in?

Thanks


There's a couple things here that don't sound right.

First, headspace with a rimmed cartridge equals the thickness of the rim plus X for tolerance and free function. Did you witness this gunsmith inserting a headspace gauge into the chamber?

Headspace gauges do not measure anything. They gauge. It either *is* or it *isn't*.

Marlins are not cheap junkie rifles. There are Marlins still firing after 100 years without having the headspace adjusted. Why would your Marlin require the barrel be set back to correct headspace? Could it possibly be this "gunsmith" is looking to add some $$$ to his weekly take? It kinda sounds like it.

I would check firing pin protrusion. A firing pin that isn't long enough, for whatever reason, would fail to indent the primer sufficiently to setoff the primer. Check the cavity in the bolt body for debris that may be keeping the firing pin from fully extending from the bolt face. Not likely but you need to check all the possibilities before allowing a gunsmith to reach into your pocket over some dubious .004".

The hair on your head (if you have any left) measure .002" to .0035". This is not going to keep a rifle in otherwise good order from firing. IMO.

A good illustration though I'm not real happy with using primer protrusion added to rim thickness to determine "headspace".
http://www.castbullet.com/misc/hspace.htm

Over the years I've seen a lot from those who use scotch tape on the cartridge face or otherwise shim a cartridge to "check" headspace. There's a right way and a wrong way to check headspace. This is the wrong way. It means very little but you'll hear all manner of justification for doing it, including indignant responses. In some cases with rimmed cartridges you can do a remedial check that should lead to a more competent check but using shims and a cartridge case are only cursory at best. How much does scotch tape compress under load? How much load compresses scotch tape or aluminum can material, invariably beer can material?. A headspace gauge is a "standard". A fixed and known factor in an equation. It does not vary. When you introduce variables you create errors from the git-go.

I also heard one story about a "gunsmith" (term used loosely) where the rifle owner witnessed this act: the gunsmith stuck his little finger in the chamber and pronounced the headspace "ok".

How does a gunsmith check headspace on a rifle where he has no gauge?

Answer: he doesn't, he can't. But an unethical SOB will lie and cheat all the live long day if it means $$$ from your pocket into his.

There are some cartridges where headspace gauges aren't available. The 7.65x53 Mauser cartridge is one. And there are cartridges where U.S. headspace gauges are of little to no value due to differences in dimensions. The 6.5x55 Swedish is one of those. I have a relatively rare 4 gauge set of Swedish military headspace gauges so I've been down this road with 6.5x55.

You ask if the barrel is turned in 1 thread will you have to re-bore. You don't rebore, you rechamber. And yes, you would have to rechamber the rifle to set the headspace.

The simple explanation: If a barrel has a pitch of 10 threads per inch. You clock the barrel one turn. That means the linear advancement is .100". If you have 20 threads per inch the linear advancement is .050" (20 x .050"= 1.00"). If you have 50 thread per inch the linear advancement is .020". Its just pure math.

Normally, there are 3 gauges used. "Go" is the minimum allowable headspace. Its the rim thickness + .00A". This gauges is mostly used in chambering barrels.

"No-go" is an intermediate gauge that's actually an arbitrary measurement but we accept no-go as being the maximum distance for handloaders where brass isn't over-worked. Rifles that do not close on a no-go are said to "pass".

"Field" gauge is the maximum allowable length. It is rim thickness + .00B". Rifles that close the bolt on a field gauges are said to "fail".

There is no degree of bolt closure. It either *is* or it *isn't*. There is no "almost", there is no "half closed", there is no "closed with some force". You never ever use any kind of force on a headspace gauge... but we know a nimrod has spoken when we hear of it.

The Forster field-reject gauge is .070". Where is this .019" number coming from? What does it mean? What do these numbers .010" to .015" mean? They're not headspace gauge measurements.
Go gauge is .063" and no-go is .067".

This means safe headspace for .30-30 WCF is between .063" and .070".

.010" .015" .019" these are the numbers of a beer can gunsmith.



Unfortunately it came in at .019 which he thinks is likely why it misfires.

A competent gunsmith should also be a forensic examiner. Until he finds the cause of excessive headspace he should not be making alterations to a firearm in order to fix something where he has no idea of the causation. "Likely" is a word that means "I don't know". Find a new gunsmith and determine his professional training before you hand him your rifle and your money.


Dutch

[qajaq59]

Thanks Guys, I guess I'll try the neck sizing first before I spend the money for the other. And Jon thanks for your info too. I didn't quite understand that a full turn of the barrel would be far in excess of what was needed. I shoot 'em fairly decent, but I'm out of my league when it comes to fixing them.

[qajaq59]

Dutchman, I sent you an e-mail.

[Big Dave]

Been doing a little review on headspace. P.O. Ackley in his Handbook for Shooters and Reloaders, Copyright 1962, Publishers Press, Salt Lake City, has an excellent discussion of the subject where he states that headspace for rimmed or belted cases is .006 inches MAXIMUM from closed bolt face to face of fully seated cartridge. He continues that standard rim thickness is .063 to.067 so maximum headspace for a 30-30 chamber is .069. (minimum rim thickness plus .006)
From this then a steel disk the diameter of a 30-30 cartridge rim and .067,(maximum rim thickness) in thickness should chamber and a similar disk of .070 thickness should not.
Headspace on rimless cases is a whole different ball game involving location of a theoretical datum plane at a specific diameter on the case shoulder, construction of which is difficult without access to a good cylindrical grinder and an optical comparator or better still a tool makers microscope.
So I think neck sizing fired cases is still the easiest option.
Do have to wonder where your " gunsmith " came up with his .010 .015 .019 numbers.

[Dutchman]

Been doing a little review on headspace. P.O. Ackley in his Handbook for Shooters and Reloaders, Copyright 1962,.....


First off, neither P.O.Ackley nor his 1962 book are the final authority on headspace in 2009 in the U.S. The final word is from S.A.A.M.I. or Sporting Arms and Ammunition Manufacturers' Institute. They are the body who sets the standards for headspace along with pretty much everything else connected with civilian ammunition in the U.S. And S.A.A.M.I. disagrees with your presented opinion via P.O.Ackley circa 1962.




He continues that standard rim thickness is .063 to.067 so maximum headspace for a 30-30 chamber is .069. (minimum rim thickness plus .006)

:groner:

.067" + .006" = .073"

As a minor tutorial on machineshop math, you would not use a minimum number plus a tolerance to conclude a maximum dimension. You would use the maximum number plus the tolerance which would equal the overall allowable dimension. Your math is off by .004" and in that .004" lies the dividing line between "yes" and "no" on the issue of headspace for .30-30 WCF, according to this discussion (which is hypothetical).




From this then a steel disk the diameter of a 30-30 cartridge rim and 067,(maximum rim thickness) in thickness should chamber and a similar disk of .070 thickness should not.

Your math error is magnified now by your using the incorrect numbers in your equations. If a customer brings his Marlin to your gunshop for a headspace check and his bolt closes on a .070" gauge you're going to tell him... incorrectly.. that his rifle has excessive headspace, when, in fact, it does not.

You'll then advise your customer that his rifle needs to have the headspace "adjusted" or "regulated" by turning the barrel back one rotation of the thread and rechambered, thereby correcting the headspace. For this you'll charge your soon-to-be-ex-customer $200.

Since you're using your own shop-made headspace gauge made using your math calculations you'll argue till the cows come home that his rifle is now within "specs" and, as you wave your hand over his rifle, you declare his "problem" solved.

But when Mr.Gun Owner tries chambering some cartridges he finds the bolt won't close. Agast he phones you to proclaim this new problem that his rifle won't chamber ammunition.

Well, blah blah blah and on and on.

This entire exercise presents a repeated dilemma for gun owners. The "expert" gunsmith who's prideful ego tell's him daily that his shop-made headspace gauges, or his learned opinion, are every bit as good as those dang costly Clymer or Forster gauges. In other words, "we don't need no stinkin' standards.....".

Conclusions based on archaic, outdated information, bad math or incorrect procedures, are pretty much worthless as a comparative standard. This is why we have S.A.A.M.I. In some areas of life we'd prefer some things conform to a set standard. Like no woman can have vanity breasts larger than her cranial cavity divided by 2 and multiplied by the length of the broken bow strings of the violinist who plays ragtime down at the pizza parlor on saturday night. :violin:


The strange thing is.. your presentation included tolerances when you stated ".063 to .067".... but your ignored those numbers in your mathematical equations.

(we'd call that a "mistake"....) :veryconfu

But in making that mistake you afforded me the opportunity to continue with this discussion in a more meaningful way exactly because you made a mistake. People can be so fearful of making mistakes.. or having their mistake pointed out to them.. that they'll go so far as to deny the mistake ever occurred or they'll try and side-step the mistake.

hey Gomer what's the headspace on that ol' Mowzin-Hagant rifle?

ah...er.... two Budwiser cans and a flap from my chewin' tobaccy. :redneck:


http://www.clymertool.com/headspac/index.html

http://www.redman.com

http://www.violinist.com/wiki/violin-strings/

http://tinyurl.com/l8j6s9

Dutch

[Big Dave]

Dutch,
Carefully reread my previous posting and recheck your math.
If as Ackley says max headspace is .006 this must be measured from a minimum thickness rim, .063 for a maximum dimension of .069 and minimum must still allow a maximum thickness rim to chamber. From numbers used I will stand by my calculation.
If you have current SAMMI specs please specify.
Also for rimmed or belted cases a carefully made set of shop gages are functional. As I also said datum plane gages for rimless bottleneck cases are another thing entirely.
In any case I would certainly reccomend using current specifications.

[qajaq59]

A good illustration though I'm not real happy with using primer protrusion added to rim thickness to determine "headspace".
http://www.castbullet.com/misc/hspace.htm The method illustrated on that page is essentially where the local smith came up with the .019. Except instead of pushing a primer in he used some plasic gage.
However, I'll get my hands on a real headspace gauge and use that.

Thanks, I appreciate the help.

[sharpshooter3040]

Something else that will affect the head space on a Marlin is the locking bolt relationship with the breech bolt. A quick test is to take a fired -resized cartridge, chamber it and close the bolt and lever. With the hammer in full cock position push the back end of the breech bolt with your thumb.......did it move forward ? and how much. This is fixable, but caused by forcing the bolt closed for what ever reason and of course normal wear.




Doug

[Trailblazer]

I have heard that Marlin offers different thickness locking bolts to correct headspace problems. It still needs to be fitted by a gunsmith but may be cheaper than remachining the barrel.

[TAWILDCATT]

turning the barrel in will reset it for further work.but will any thing else be changed.not having a marlin to check will the dovetails on the barrel need to be reset?check the firing pin protrusion.and look at how deep it makes a mark.I used to have a 73 win and it was original it never failed to fire and that was in 1956,bought it for $5 from a gunshop in AL on way home in 1945.:coffee: