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Old December 23, 2012, 03:24 PM   #1
mordis
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M1 Garand barrel chamber and headspacing question.

Hi. I have a not so simple question, that i would like to know.

Im currently going through the process to be able to order from the CMP. I plan on purchasing a Stripped reciever to put togther my own shooter. I plan on putting on a Criterion Gi Chrome lined barrel. It says that all barrels are .010 short chambered and should be finish chambered by a gunsmith.

My question is, how does a gunsmith finish chamber a chrome lined barrel with out destroying the chromelining?

I know that the m1 does not historicly have a chrome lining, and fought in WW2 with out it. The advantages of chrome lining out weight the cons for me.

So gunsmiths, when i get my barrel, how do you finish the chamber?
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Old December 23, 2012, 03:57 PM   #2
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The chrome is removed only where the finishing reamer removes metal for minimum headspace (that is if you want minimum headspace). The rest of the barrel is untouched. BTW, .010" doesn't sound like much but when it comes to chambering that's a lot of material to be removed.
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Old December 23, 2012, 05:22 PM   #3
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So can normal gunsmithing tools finish the job?? Does the removal of material in the chamber reduce the protection the barrel has from the chrome lining??
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Old December 23, 2012, 09:15 PM   #4
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Certainly a normal finishing reamer is used.

It will only remove that which needs to be removed for the chamber. As for the remainder of the barrel (with the lands and grooves), that will be untouched.
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Old December 23, 2012, 09:40 PM   #5
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Well... you're ordering a chrome lined barrel, and the first thing you're wanting to do is compromise the chrome lining?

I think you need to step back and consider that your headspace is composed of the relation between the depth of the chamber, the mounting of the barrel on the receiver, then the receiver and the bolt fit-up. Before you get ahead of yourself in this project, you need headspace gages to see just how close your bolt is to closing.

If you have a chrome lined chamber/bore that is very close to allowing your bolt to close on a "go" gage, you could lap the bolt lugs onto the receiver to gain a few thousandths of headspace without touching the chrome in the front of the chamber. If you put a reamer into the chamber, it should be of the type of reamer that doesn't touch the throat. If you compromise the chrome in the throat, you might as well not have bought a chrome lined barrel.

For short-chambered Garand/M14/M1A barrels, a pull-through reamer is typically used and the bolt is allowed to close (gently) on the reamer from the rear, then you rotate the reamer using the drive rod from the muzzle. Clean the chamber/barrel, insert the go gage, check the headspace and repeat as necessary. Never turn a reamer backwards.

Chrome lined chambers typically require carbide reamers or tooling. Chrome is pretty hard - hard enough that it prevents use of HSS tooling.

Personally, I have no use for chrome lined barrels.
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Old December 24, 2012, 12:36 PM   #6
mordis
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Why would they even make short chambered chrome lined barrels to begin with, if the act of finish chambering will destroy the integrity of the lining...

God it may be simpler to just get a normal barrel and deal with it shooting out faster. Edit to clarify, while i dont intend to abuse it, i intend to shot it alot. WHich is why i am wanting chrome lined. Every rifle my Father in law has, that is not chrome lined, only lasts about 2000 shots before its useless. His Remington 700 in 7mmRem Magnum is testament to that. I want to avoid that situation.

Last edited by mordis; December 24, 2012 at 12:44 PM.
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Old December 24, 2012, 01:47 PM   #7
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Chrome Brl

I got to go with Mordis on this. I don't see the need for chrome. I can't think of a top notch barrel maker that offers chrome lined match barrels. The idea of lapping the reciever and bolt face ruins the reciever for you next barrel. If you are not shooting competition you most likely never shoot out a barrel.
Big Mag's and high performance loads eat up Brls. My 300 Win Mag has noticable wear at 1 at 1000 rounds. A 06 and 308 in a Garand for casual shooting shoud be good for 10K rounds

Last edited by Howard31; December 24, 2012 at 01:53 PM.
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Old December 24, 2012, 01:53 PM   #8
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Barrels last according to how hot the ammunition they're shooting is loaded and how hot the barrel gets. The net:net is that over the entire lifetime of the barrel, perhaps bullets are travelling in the bore for all of 2+ seconds. That's the lifetime of a typical barrel.

For rifles like the Garand, which were fed a steady diet of ammunition that isn't all that hot (as .30-06 loads go), the GI barrels lasted quite a while. My copy of Hatcher's "Book of the Garand" is packed up right now, but I seem to recall a War Dep't test cited therein where the barrels were good for 7,000 rounds (plus or minus) for the WWII spec barrels. I'll try to find that book and look up the barrel life tests they ran. The Hatcher book on the Garand is quite interesting and for Garand fans, I'd recommend at least trying to find it in a library and having a read through it.

Rifles that are set up in high pressure rounds (like your Father's 7mm RemMag) and are loaded at the maximum end of the range start seeing throat erosion anywhere from 1,200 to 2,000 rounds - and your estimate of 2,000 rounds is right in the range where a 7mm RM might well see throat erosion. Some cartridges are notorious for burning up barrels - like the .264 WinMag. 1,200 rounds was typical. The .284 Winchester - again, notorious for short, 1,200 round barrel lifespans. Some cartridges have barrel lifetimes in the 10's of thousands of rounds - eg, the .22LR. A .30-06 loaded to M2 ball ammo specs should see lifetimes in excess of what you're seeing in 7mm RemMag. If you hot-rock the -06, then sure, you're going to see throat erosion more quickly.

Do you need a *new* barrel at this point on a rifle like a Rem700 or other bolt gun? Maybe not. You can ask a gunsmith to "set the barrel back" by one turn. This means the tenon is cut back, the chamber is set deeper (by the length of one turn of barrel tenon pitch) and this deeper chambering set-forward usually eliminates the erosion in the throat area. The problem usually becomes that there is a pretty large gap opened up between the barrel and the stock that looks like crap, but the barrel will shoot reasonably well for awhile.

For chambering a short-cut barrel with chrome lining, it might be possible to leave the throat alone and just move the headspace datum forward by using a reamer that has no cutting edges in the neck & throat area - ie, it cuts only in the body of the case and the front of the shoulder area.

On a rifle like the Garand, M1A/M14 etc, you've got a much more complicated barrel installation issue, due to the gas system and the fittings attached to the barrel for the gas system. Setting the barrel back by a turn isn't an easy option.

Chrome lining of barrels is done to make them resistant to both less than ideal maintenance in high moisture environments and rapid rates of fire (eg, military operations in such garden spots as swamps, and full auto weapons). For civilian use... unless you're looking for a low-maint weapon, why bother? Stainless would handle most everything a civilian would want for lower maintenance, and it doesn't create issues for your gunsmith. Most chrome plating eats HSS tools for breakfast, and most of us 'smiths are using lots of HSS tooling - because carbide is more expensive to buy, it's more brittle and it's difficult to sharpen in a typical gunsmith's shop. Why do they create a chrome lined barrel for a Garand? I honestly don't know. I guess it's solving some perceived problem - or it's selling well to people who want one. When I say I have no use for a chrome lined barrel, I'm being quite serious - I don't load my ammo to the max pressure end of the spectrum, I don't go in for rapid fire that heats up barrels and on most of my rifles, I might well set a barrel that was shooting well back a turn and extend the life.

Chrome lining acquired a rep for reduced accuracy due to the earlier chrome plating jobs being inconsistent in thickness in the bore. Recent chrome plating in bores is pretty consistent when done well. Still, it's no longer the best solution to the problems it was trying to solve. There are other barrel treatments that have been explored for the same purposes as chrome lining - stellite liners (eg, in the M2 machine guns) and nitriding of the barrels after all machining is done (all chambering, threading, etc), which has been recently explored by some of the benchrest guys with good results. These nitriding treatments have received some very favorable reviews and results in both barrel life and ease of cleaning - but the tooling to cut through the nitrided layer (if you ever wanted to do something with the barrel after nitriding) is very expensive - and most smiths would probably give it a miss.
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Old December 24, 2012, 02:56 PM   #9
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Thanks for the heads up. With regards to my father in laws rifle as its sitting right now more than 25percent of the rifling is gone. Of course he was loading 150 grain bullets aproaching 3500fps. Kinda hot.

I'll look into the barrel nitrididing. Do you know of anyone doing the treatment, or what kind of nitriding is used?(salt bath,ect)
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Old December 24, 2012, 03:08 PM   #10
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I would check with Mr Criterion before I flew off on a tangent.

Their site says:
"•Available chrome-lined with finished chamber (STD/G.I. contour only)"

I would guess there will be some amount of luck involved on the headspace thing, but they won't be guessing. Call 'em up.
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Old December 24, 2012, 04:16 PM   #11
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There's about 0.004" to 0.005+" difference between the minimum chamber headspace for a go gage and the point just before the bolt closes on a no-go gage.

So there's room to work.

And as I indicated above, there's more than one way to arrive at the proper headspace. The headspace issue is widely misunderstood by many shooters. At the very crux of the issue, headspace is just the distance from the datum for the cartridge in question to the bolt face. For the .30-06 and similar non-magnum, bottlenecked cartridges, the datum is a point on the shoulder. For a belted magnum, the datum is on the front of the belt. For a rimmed cartridge (eg, .30-30), the datum is on the front of the rim, etc.

Nitriding: The nitriding processes I've seen used on barrels have been salt baths.

Last edited by wyop; December 24, 2012 at 04:22 PM.
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Old December 24, 2012, 04:27 PM   #12
mordis
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I have a email into Criterion barrels. Ill report back what they say, but i dont expect a email back till after the hollidays.

If it is a easier route, ill just get a normal barrel and have it fitted by a gunsmith then send it out to http://www.trutecind.com/ This is who i have found on the net that does Salt bath nitriding. I just hope they do gun barrels.
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Old December 24, 2012, 05:45 PM   #13
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False alarm

There is only one .30-06 M1 Garand and only one .308 M1 Garand Criterion barrel offered at the CMP store. They are made from 4140 alloy CHROME/MOLY steel, meaning there is about 1% chromium and 0.2% molybdenum in the steel alloy. It is not chrome-lined. I have two of them and can verify that for you.

If you want to buy a chrome-lined Criterion barrel, it will have to come from some other source than the CMP and it will be fully chambered to a middling chamber length value.
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Old December 24, 2012, 06:52 PM   #14
mordis
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Thanks, i didnt notice that. I think that im going to foregoe the chrome plating in lue of other methods.

I was wondering about other nitride finish i have found. A company that sells electroless boron Nitride plating kits. I wonder if that would be good for a rifle barrel. Any thoughts on that guys?
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Old December 24, 2012, 07:09 PM   #15
mordis
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Hmm i dont think that will work either apon further research. It is also a plating system and would not work either.

Hmm...
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Old December 24, 2012, 09:50 PM   #16
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This won't be something you can easily do outside a well equipped shop. Here's a bit of marketing lit about the process:

http://www.met-sol.com/assets/Indust...C_Brochure.pdf

As you can see from the pictures on the second page, the layer that results (ie, "the case" as we'd call it if you think of this as just a high-tech case hardening) is quite thin.
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Old December 25, 2012, 10:07 AM   #17
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From what I have been reading the sbn treatment thin tho it may be, is quite tough. I am hearing reports of bench rest guys getting 5000 rounds or more from there treated barrels.

I see what your saying about plating my own barrel tho. While I could do the plating I could not do the machining to remove the extra material from the bore/chamber before plating.

All this so I can shoot a few thousand more rounds before I have to change barrels.
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Old December 25, 2012, 10:09 AM   #18
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Hard chromium is tough as well as hard. It is plated onto an oversize bore so that the plate thickness doesn't constrict the rifling. I don't know if nitriding is tough or not? It's hard, but it may be too brittle for the pressures and temperatures near the throat, promoting premature surface cracking. I just don't know, but I wouldn't just assume it's a good idea until I checked with a metallurgist about it.
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Old December 25, 2012, 10:25 AM   #19
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Well as I said some guys on long range hunting.org are reporting good results as well as on the various bench rest sites. To be sure tho I have put in emails to a few different metal treatment places so I can get opinions.
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Old December 25, 2012, 11:39 AM   #20
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It may be fine, then. It's just outside my personal experience.
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Old December 25, 2012, 12:42 PM   #21
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Nitriding is tough and hard as hell.

Ask any gunsmith that's put a tool to it without being warned. Make sure there are no women or children present to hear the answer to your question.
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