.30-40 AI questions

[AviatorTroy]

Now I know there has been other threads on this, but I thought Id start my own.

I'm just finishing up some work on a sporterized Siamese Mauser in .30-40 that a family member gave me that was half finished. I checked headspace and it seemed safe, and worked up a few dozen handloads and gave it a try. The results were that it looks like someone did a really poor chambering job and although it shoots OK, if you can imagine this there is a significant ring around the case about halfway up the sidewall, like there is a scratch in the chamber all the way around at that point. Sorry, Im not home so no pictures. I'm thinking this is probably purely cosmetic, but it does bother me.

What I was thinking...

Run a chambering reamer for 30-40 AI in there and that would push the case wall out in the chamber enough to remove the horrible toolmarks that currently reside inside.

I only want to do this if I don't have to remove the barrel and set it back, as I just did a bunch of work including bluing the receiver and barrel and I'd like to try not to screw that up as much as possible.

Also any ideas on where I can get such a reamer? Would I only need the finishing reamer? This appears to be a WWII vintage 2 groove springfield barrel, for what it's worth. ( I know, I know, not much! )

OK gents, ideas?

[swheeler]

http://www.4-dproducts.com/display.php?group=Rifle+Calibers

[johnly]

I just happen to have a 30-40 AI reamer in my collection. Drop me PM if you want to borrow it.

John

[No_1]

Great project!
Here are my 2 Siamese Mausers. The top one is a very much like the one you discribed, built as a sporter with a 2 groove barrel that has a "ring" in the chamber that leaves a unsightly mark on the brass. The finish when I got it was poor so I had it parkerized. They bottom one is in 45-70 and was a gift from my dad that is perfect in every way. The wood is sweet and the metal finish is flawless. Both have been fitted with Timney triggers, mercury tubes and Pachmayr Decelerator pads. I would love to see pictures of yours.

Robert

http://i129.photobucket.com/albums/p206/no_one_photos/SIAMESE%20MAUSERS/DSC01129.jpg
http://i129.photobucket.com/albums/p206/no_one_photos/SIAMESE%20MAUSERS/DSC01130.jpg
http://i129.photobucket.com/albums/p206/no_one_photos/SIAMESE%20MAUSERS/DSC01131.jpg
http://i129.photobucket.com/albums/p206/no_one_photos/SIAMESE%20MAUSERS/DSC01132.jpg

[Willbird]

There is not a thing wrong with a 2 groove springfield barrel :-).

Bill

[Mk42gunner]

Just wondering, but could the ring in the chamber be were the .30-06 shoulder was if the barrel wasn't set back far enough?


Robert

[Multigunner]

A problem with modern production .30-40 and .303 cases is the rims are usually thinner than they should be, usually .059 when they should be .064.
If headspace is at the .068 maximum which is based on the original case specs then you have .009 head gap which with the thin walls of commercial cases leads to the annular ringing just above the web. The ring shows as a bright ring on the outside but is due to the brss being stretched thin on the inside. This can cause case seperations after a few firings.

I have an old .30-40 case in my collection that has a .063 rim, and literature from the 60's gives even higher numbers for rim thickness of other brands.
At one time Krag cases were used to make .303 cases because the thicker rim made up for loose headspace of the SMLE.

Original US Government specs put the nominal rim thickness of the .30-40 at .060 but the civilian specs list it at .064. Military cases being intended to make allowance for dirt for reliable feeding, while civilian cases were intended for reloading and top grade accuracy.

If theres no annular ring, then its likely the chamber can be polished without causing looseness.
A well polished chamberwall increases case life in any case.

[No_1]

I am not sure about that question. In my case the ring only covers about 1/3 of the chamber.

Robert


Just wondering, but could the ring in the chamber be were the .30-06 shoulder was if the barrel wasn't set back far enough?


Robert

[Multigunner]

I am not sure about that question. In my case the ring only covers about 1/3 of the chamber.

Robert

Sounds like loose headspace, or excessive headgap due to thin rims.

When theres too much play in a chamber and the cartridge body has much taper the case rests at the bottom of the chamber. When fired it will expand more at the upper side than anywhere else so the mark only goes about 1/3 the way around.
Due to the body taper the effect is the same as a loose chamber.

I'd mike the cases you are using. Besides thin rims the cases are often smaller in diameter than they should be.
You may have to set the barrel back one thread and rechamber using the minimum size reamer for these chambers.

Finding a brand of case that mikes closer to the maximum acceptable size may cure the situation.

A trick used by .303 reloaders when dealing with oversized SMLE chambers and loose headspace is to center the case on first firing with a thin strip of paper wrapped above the rim. Cigarette paper or plumbers silicone tape.
This is also used by owners of Jap 7.7 rifles rechambered to .30/06, to center the 06 case in the loose chamber caused by the original jap case diameter being larger.
The best method of rechambering was to set the barrel back a few threads first.

A temporary spacer for the rim can be made from fishing line. It holds the case back against the breechface for fire forming, after that the case if neck sized only will headspace on the shoulder same as a rimless case.

[scrapcan]

in the case of the original poster, he could have a ring due to reammer chatter or galling due to not cleaning the reamer, being it is half way up the case. can you tell if it is a transition in chamber or a groove/scratch?

[AviatorTroy]

Sorry guys, Ive been out of town so not much time to look at this project lately, but thanks for all your thoughts. Ill try to get some pictures of the project as well as the cases that we are talking about here. I really don't think its a headspace problem, ill look at it very carefully again but of course with a rimmed case there's not alot to go wrong there as long as the bolt face is relieved the correct amount for the particular rim thickness. (which I think someone else pointed out to look at as well)

I'm still thinking about the AI reamer, because I would most likely just neck size the cases which would save me from buying seperate dies, not to mention improved accuracy, case life, etc.

Wait, found a pic, lets see if I can figure out how to post it.......
http://i254.photobucket.com/albums/hh100/aviatortroy/-1-1.jpg

[AviatorTroy]

A few other observations..

Yes, with a bent wire I can feel a circular scratch around the inside of the chamber. That's what makes me think somewhere along the line probably 40 or 50 years ago, a bubba somewhere ran a bad reamer in there or no oil or allowed tool chatter to occour. Which keeps bringing me back to the thought that the AI chamber has a straighter wall and a longer reach to the shoulder and that would "clean up" the bad spot in the chamber we have right now. Ill try to get a pic of the cases but i just sized them all.

By the way, I have to say Im pretty shocked at the potentially decent accuracy. With no load development at ALL, I have maybe shot 50 rounds through this rifle so far. A few were 168 gr FMJBT, the rest were Lee's C309-170-F, all loads were over Harris's recommended 16 gr. of 2400. Both loads gave me about two to 2 1/2 inch groups. Not sure what I was expecting, but not too bad. I suspect there's a lot of room for improvement there as well.

[sailor]

I would put money on the chance that the original chamber was not cut off far enough up to clean up. It is a hard thing to judge. It happened to a friend of mine. I chambered his barrel and thought I had gaulled it. But he just did not shorten the barrel enough to start, wanting as long a barrel as he could get.
I put a two-groove barrel on a High-wall in .30-40, just for fun. I found I could not get match accuracy no matter what I did with cast lead bullets. Finally an old timer loaned me his 311291 molds and groups dropped to 1". The old timers knew that the long bore-riding nose and short driving band was the only design that would perform in the two groove springfield. By the way, if you slug that barrel you may find the bore is more like .302 than .300. This was my experience, and I had to make a die to "bump up" the nose of the bullet to bore diameter.

[madsenshooter]

Multigunner, those are some very astute observations that many are not aware of. There are a lot of different reamers available for the 30/40 AI, about the most improved is that made by ptg. It cuts a .447 shoulder that is moved forward, can't find it at the moment or I'd tell you how far forward. Ironically, I've been buying PRVI .303 British to make 30/40 from and it's thicker at the base then commercial 30/40. I'd be hesitant to use the 30/40AI in an original Krag barrel, I've seen one cross sectioned and those sight screw holes come awfully close to the bore. I thought I'd like to have a Siamese Mauser, but not in the original caliber, I don't need another caliber to load for, but since I'm already doing 30/40....Actually I thought of using the Siamese for a 6mm/30-40AI I'm building, but opted to use a Krag action I have instead.

Yes, you can use just the finish reamer, as a matter of fact since your chamber neck is already cut, you could get a removable pilot reamer in something smaller, 257Krag AI, etc, and just run it in using a 30 caliber pilot, to cut the body of the chamber. As long as you have the proper headspace on the rim, moving the shoulder forward and outward to get rid of those marks should work fine, I'm using my reamer at the moment, or I'd loan it, maybe. http://ammoguide.com/?catid=383

[madsenshooter]

Multigunner, to illustrate the truth of some of your observations, today I received a set of very old Krag headspace gauges that I got off ebay. The go gauge is .064" thick, the no-go is .0675". Yet we know modern Krag brass' rim is only .060 max. I don't think they use those dimensions anymore for the go and no go, I know a field gauge is .070 A friend of mine lapped the locking lug on a new Krag bolt body to just that, and you could certainly see that his cases were stretching near the point of seperation. Not long ago on the Krag forum there was a fellow who said his go gauge wouldn't go, but a cartridge would chamber. He must've had an old gauge like mine.

[AviatorTroy]

I have seen this in my .303 brass, but not my Krag brass. Some older .303 brass has rims that are way thicker than the newer stuff I've seen...

[madsenshooter]

I was just reading some about that on milsurps.com, the .303 had a max headspace dimension of .074 at one time, and American cases have much thinner rims, usually around .058. The PRVI cases I recently got were right at .060. Rim thickness of Krag cases is not easy to measure, the bevel on the rim keeps you from getting a purchase on the base proper. I have a wide footed sheet micrometer, and it just barely gets there. Troy, if you can wait a couple weeks, I have a PTG 6mm/30-40 AI reamer and a 30 caliber pilot, you're not very far away and I could loan it. Do you have a reamer handle?

[AviatorTroy]

I have a lathe. Also, I have plenty of time, since I'm going to be out of town for work most of February and March, I wont have too much time to play with it anyway. Thanks for your generous offer by the way!