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Hello all,
I'm working on building my first M1A rifle and I need some advice. I have a Krieger Heavy profile SS 1/10 short chambered barrel in my little hands and I'm having trouble making a couple decisions and need some guidance please. I plan to set the headspace to safely fire 308 and 7.62 X 51 ammo.

Where I'm having difficulty is:
-Should I use a standard 308 Finnish reamer or should I use a 308 match reamer?
-Should I polish the Chamber after reaming with 0000 steel wool or will the Finnish reamer set the desired smoothness for the chamber?
-I have a Clymer finnish reamer and on the instructions it said to remove chips by running a piece of carbide along the face of the flutes, being careful to avoid rolling over the cutting edge. What did they mean by this and where can I get a carbide? Were they talking about a carbide drill bit? Sorry if I sound lost.

My goal is to have a rifle that will last me a very long time, that's safe to shoot, and be able to have the accuracy I can learn to use. To take advantage of using the benefits of Match ammo down the line. Mind you, I've got a long way to go before I get to shoot as well as half of everyone here, but it's something I'd like to work on!

This question came up when I dropped off the barrel to a local gunsmith to adjust the barrel's shoulder so it can hand index properly ( I don't have access to a lathe). He asked "What kind of reamer are you using? You may as well use a match reamer since you're going this far."

I've been doing a lot of research here, and I'm almost to the point of information overload ha ha ha. I know there's many other things I can do to tweak my rig later but chambering a barrel is from what I understand a one time deal per barrel. I'm fully aware of the risk I'm taking by doing this myself and many have warned me of ending up with an expensive paper weight. This is something that I've always wanted to do and now I have my chance. Thanks so much for your help! GI1
 

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Those chambers have been polished dom. Just finish ream and call it a day. Dom I'll call you later I have to get ready to go to the airport
 

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For the 'carbide', probably a used lathe cutting bit such as a 'brazed carbide bit', or a 'carbide insert' would work.
The gunsmith or a local machine shop would probably have something free or cheap.

Anything done to the barrel shoulder should be in conjunction with screwing the barrel into the receiver.
Basically so that the flat under the rear sight is parallel with the front sight base.
Finish reaming for headspace would be done with the barrel installed & properly indexed.

Jay Kosta
Endwell NY USA
 

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Hello all,
I'm working on building my first M1A rifle and I need some advice. I have a Krieger Heavy profile SS 1/10 short chambered barrel in my little hands and I'm having trouble making a couple decisions and need some guidance please. I plan to set the headspace to safely fire 308 and 7.62 X 51 ammo.

Our Guru, Gus Fisher, as you probably know by now, suggest between 1.632 and 1.633 for both cartridges
Where I'm having difficulty is:
-Should I use a standard 308 Finnish reamer or should I use a 308 match reamer?

It is my understanding that the only difference between the two, is the Match reamer changes the bottleneck angle very slightly from standard finish reamer. Unless you are going with complete match weapon only, which mil-surp rifle is not, take 82nds advice and stick with just a finish reamer.-Should I polish the Chamber after reaming with 0000 steel wool or will the Finnish reamer set the desired smoothness for the chamber?

I believe all chambers should be polished....carefully ! I had to send one back to SAI for polishing, it had no failures, it just looked rough, since coming back, it is a real accurate shooter.-I have a Clymer finnish reamer and on the instructions it said to remove chips by running a piece of carbide along the face of the flutes, being careful to avoid rolling over the cutting edge. What did they mean by this and where can I get a carbide? Were they talking about a carbide drill bit? Sorry if I sound lost.

When chamber reaming, you must keep oil or some positive lubrication medium going to it while cutting, to flush out cut material from between the cutter and chamber, otherwise it will score it deeply and cause problems with chamber and possibly extractions later, not to mention trouble cleaning it because of the deep scratches in it. The carbide they refer to I believe is a carbide knife, in the business they are called knives and not bits, it can be any carbide tool that can be used for this purpose that will fit as directed without hitting cutting edges, in other words, the proper size. Any large equipment supply or welding house will have carbide toolsMy goal is to have a rifle that will last me a very long time, that's safe to shoot, and be able to have the accuracy I can learn to use. To take advantage of using the benefits of Match ammo down the line. Mind you, I've got a long way to go before I get to shoot as well as half of everyone here, but it's something I'd like to work on!

You will be shooting MOA off the bench before you know it !This question came up when I dropped off the barrel to a local gunsmith to adjust the barrel's shoulder so it can hand index properly ( I don't have access to a lathe). He asked "What kind of reamer are you using? You may as well use a match reamer since you're going this far."

He just asked this to see if you knew what you were doing.
Some unscrupulous smiths will overcharge once they have determined you are clueless, so go armed with this knowledge...No offense and I am not saying he is like that, just that they exist out there.
I've been doing a lot of research here, and I'm almost to the point of information overload ha ha ha. I know there's many other things I can do to tweak my rig later but chambering a barrel is from what I understand a one time deal per barrel. I'm fully aware of the risk I'm taking by doing this myself and many have warned me of ending up with an expensive paper weight. This is something that I've always wanted to do and now I have my chance. Thanks so much for your help! GI1
Good luck, and get with 82nd as offered, he will walk you through it.
 

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Discussion Starter · #5 ·
Warren! good to hear from you. Calling me may be hard due to the time difference and I can't have a phone with me at work due to the nature of security but we'll find a way to talk.

Thanks for the tips guys. I also dropped off my reciever with the barrel and explained in great detail how I wanted the barrel to hand index to the receiver.

Looks like I'm going to look around for a carbide insert now. How often do you need to clean off the reamer with the carbide? Does metal accumilate that fast on the reamer? I'll only be cutting maybe 10 thousands of an inch.

Jay, I have a hand reamer so I won't be able to have the barrel matted up to the reciever for reaming. Is a pull through reamer better than a hand reamer?

Ripsaw, I planned on setting the headspace to 1.635 due to the 308 field headspace being 1.638 and 7.62x51 go headspace is 1.6355. I've been doing much research on this and it sounds like 1.635 would be optimal for both, or is that too much for 308 that it will affect accuracy?
 

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Finish Reaming Krieger

While a gun smith can finish ream your barrel on a lathe the job can be accomplished with a pull through type reamer. The barrel only needs to have the chamber deepened to the final head space. This involves removing material from the shoulder only. Whether you use a match reamer or a standard .308 Win. reamer won't make a lot of difference. I use match reamers myself. Carbide reamers are expensive and not made by some reamer manufacturers. A HSS reamer will work fine.
I'd recommend you have a professional do the job. It's no fun to screw up a $500 barrel and adjustments to fit a commercial receiver can be difficult for an inexperienced builder.
 

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I rebarreled my own Springfield M1A with a Barnett barrel many years ago. It turned out pretty well. At the time, I was quite willing to buy tools to learn, so I ended up with a regular reamer, another reamer driven by a tap wrench from the muzzle, and a third for a Palma match chamber. These days I would have left off the commercial reamer because I believe it cuts the throat too long. I would first run the Palma reamer to make sure the chamber has a proper throat and finish with the one driven from the muzzle. I believe this is safe because I don't ever plan on using any round nose bullets in this caliber. I prefer not to have the bullet too far off the rifling in a loaded round.

On my gun, I believe headspace is between 1.630 and 1.631 inch. I believe I tested this with a Go headspace gauge and shim stock of some kind but it was a long time ago and I don't remember all the specifics. Be careful with shim stock though. I have collected brass from about 20-30 M1A and M14s of various makes. Not one so far has had the bolt face square with the chamber, so depending on how you use shims, you may get different readings.

Check out the cartridge headspace specs for .308 and 7.62. I believe that although the chambers may be long in 7.62, the cartridges are not.

- Ivan.
 

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I rebarreled my own Springfield M1A with a Barnett barrel many years ago. It turned out pretty well. At the time, I was quite willing to buy tools to learn, so I ended up with a regular reamer, another reamer driven by a tap wrench from the muzzle, and a third for a Palma match chamber. These days I would have left off the commercial reamer because I believe it cuts the throat too long. I would first run the Palma reamer to make sure the chamber has a proper throat and finish with the one driven from the muzzle. I believe this is safe because I don't ever plan on using any round nose bullets in this caliber. I prefer not to have the bullet too far off the rifling in a loaded round.

On my gun, I believe headspace is between 1.630 and 1.631 inch. I believe I tested this with a Go headspace gauge and shim stock of some kind but it was a long time ago and I don't remember all the specifics. Be careful with shim stock though. I have collected brass from about 20-30 M1A and M14s of various makes. Not one so far has had the bolt face square with the chamber, so depending on how you use shims, you may get different readings.

Check out the cartridge headspace specs for .308 and 7.62. I believe that although the chambers may be long in 7.62, the cartridges are not.

- Ivan.
Please share with us the method you used to determine the bolt faces were not square to the chambers ?

I have recently seen several with extraction problems, so this relates.
 

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Hi Ripsaw,

Take the spent cases, hold them by the rim using Lee's old trim tool and spin them in a drill. The wobble is VERY noticeable for stuff from M14 / M1A guns. Doing the same thing with cases from other guns such as the M1 Garand or Remington 700 doesn't show the same effect that I have noticed.

This is a consistent effect though the degree varies between guns. The bolt is located via the two locking lugs and the back end of the bolt against the underside of the top of the receiver. You know the case alignment from the extractor marks on the case. The back end of the bolt goes too high.

Not sure what can be done other than squaring off the bolt face but then firing pin portrusion and headspace are affected.

Most of this effect is eliminated via resizing the case when reloading.

- Ivan.
 

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Hi Ripsaw,

Take the spent cases, hold them by the rim using Lee's old trim tool and spin them in a drill. The wobble is VERY noticeable for stuff from M14 / M1A guns. Doing the same thing with cases from other guns such as the M1 Garand or Remington 700 doesn't show the same effect that I have noticed.

This is a consistent effect though the degree varies between guns. The bolt is located via the two locking lugs and the back end of the bolt against the underside of the top of the receiver. You know the case alignment from the extractor marks on the case. The back end of the bolt goes too high.

Not sure what can be done other than squaring off the bolt face but then firing pin portrusion and headspace are affected.

Most of this effect is eliminated via resizing the case when reloading.

- Ivan.

Thank you. I figured it was along those lines. I too have noticed this issue among many spent cartridges during trimming. The height, and center position, of the receiver bridge 60 degree arc, bolt saddle, would seem to be the only viable solution for correction to the bolt face position, and the continuity of the lugs on the bolt and receiver.
The variance in the firing pin protrusion of Min. .044.......Max.
..060 would be an interesting solution also and should have enough play to take a lot of the out of square from the equation, although surface hardness cut through would be an issue if taken too far. This coupled with adjustments to the bridge should help, but one thing I have long considered is the relationship of the right bolt lug and it's contact on the receiver in the battery position. This static position being affected by the amount of slip allowed in the left lug, toward the downward position, by perhaps a weakened op rod spring, loose bolt roller, worn helix cut in the op rod, dimensionally incorrect bolt, and the horrendous action exerted on the casehead during extraction, all lead to making these adjustment, very difficult to master.
The bolt could be more square than we know, and the case head being torqued upon extraction to the right only, and then being allowed to further expand in that one direction of extraction only, might cause a large percentile of the problem also. As we know, the case is still expanding during extraction with this design and cyclic rate, and the ejector is exerting force on the case mouth end of the cartridge to the left, from the right side of the chamber inside, before it clears the chamber. A small amount of bending force could also be imparted there while the soft brass is hot and being jerked right by the extractor, and left by the ejector.
It would be interesting to have a dual extraction system on a bolt with the ejector at the position that would flip the case straight upward and out, just to see if these problems persisted, or were caused by the extraction design.

I guess we could turn the spindle valve to the off position till brass cooled, then eject and compare to see if extraction is the main cause, or bolt squareness to the chamber. Not scientific, but might tell us something.

Once these adjustments were attained though, one should have an extra accurate rifle to shoot.
 

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Hi Ripsaw,

This discussion is gonna get WAY off topic, so I hope if anyone is offended, they speak up. As we know, to some extent EVERYTHING is related.

I believe one way the angle of the bolt can be altered is to put a couple large Allen screws through the receiver under where the clip holds in the rear sight parts. They could be used to adjust how far up the back end of the receiver goes. The change in angle isn't much, but I don't know if the bump when going into battery would cause problems.

I have a gun that still has an operational gas cutoff because the Front Band and Gas Cylinder were brazed or welded instead of screwed together. I fired the gun with the gas system off and still had the same bent cases.

I am not sure I agree with you that it is a given that the case is still expanding during extraction. I believe that SOMETIMES it is and sometimes it is not (at least on a stock gun). I used a RCBS Precision Mic to check the "Headspace" of the fired cases and got numbers that varied quite a bit. (The RCBS Precision Mic presumes a square boltface, so it doesn't measure cases from these guns very well for actual headspace.)

To cure the problem of residual pressure during extraction, I shortened the back end of the gas piston according to a Marine manual I found. The idea is to increase the dwell time so that the op rod doesn't begin to cam open the bolt until the bullet is gone. The op rod should still stop against the gas piston and not the bolt roller. To test this, put in a max length case (or a Go gauge and a small piece of paper as a shim and close the bolt. When the bolt is closed, make sure that unscrewing the gas plug allows the op rod to go forward a bit.

After I did this, the spent cases didn't vary significantly according to the RCBS Precision Mic.

There should not be very much movement of the bolt downwards because the next round or the mag follower is holding it up. I remember that shooting without a magazine in place tossed rounds all over the place. The strength of the op rod spring should not affect things because the op rod should not be bottoming out on the bolt's roller.

- Ivan.
 

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Thank you for your impressions Ivan. You are correct in stating that the mic is not measuring the cases very well for actual headspace, and I believe the reason their numbers vary is because it is in fact still expanding upon extraction.


The idea of changing the dwell timing by working the piston or gas plug is not a new one as you know, but the bullet fired in a standard 22" barrel is in fact , 17-23 feet downrange, depending on your load, in a standard rifle, before anything in the gas system ever moves. Although a sonic wave of air in front of the bullet, caused by ignition of the powder and mass of the bullet speeding forward, has emparted energy to the wave, it has not enough time or energy to actuate the gas piston, only to fill the void and gas chamber area.

So adjusting the dwell would seem to me, to be a fix for repeatability only, to affect accuracy.
 

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You can trash a barrel in a heartbeat on a lathe. I know!
For the ending I would go by hand so you can "feel" if you get a trapped chip.
A piloted reamer, pull through HSS works fine.
Some Smiths, like myself, don't mind at times of people watch and ask questions while I work. Some do. like when there trying to make a living at it. With this said, he may let you be an attendance when it is being done.
P.S. slip him a $20.00 tip if he does.

Edward5759
 

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I best read the question,
What they are saying "remove chips by running a piece of carbide along the face of the flutes" is if some of the steel sticks to the reamer cutting edge. Sort of like drilling aluminum and it builds up on the end of the bit. I clean the reamer with ATF and a soft brush and then keep them in a tygon tube.
No matter how hard you try barrels have "soft spots".
These soft spots will tend to butter to the reamer. Newer barrels don't have this so much anymore.
Edward5759
 

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Hi Ripsaw,

Perhaps I am not understanding you but I see a contradiction in your comments:

If the case is still expanding upon extraction, that means that there is still pressure in the barrel. The only way there is pressure still in the barrel is if the bullet is still in the barrel as well. The bullet has perhaps another 8 inches to go (No I have not measured it) and the op rod only has perhaps 1/4 inch to move before unlocking. Pressure at the gas port is sposta be between 8,000 and 12,000 psi, so there is quite a lot of force working to accelerate the piston and op rod.

The accuracy improvement with shortening the piston wasn't much but it was definitely noticeable over the long run. I would guess around 1/4 inch to 1/8 inch for 5 shot groups. When I was done, this gun was shooting a lot of 5/8 inch 5 shot groups with average groups between 5/8 and 3/4 inch. Perhaps the gun was better, but the operator wasn't.

The reductions in measurements with the RCBS Precision Mic were not imaginary. The important thing is that they became much more consistent. I can't think of any other explanation besides unlocking later without pressure in the barrel.

- Ivan.
 

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Discussion Starter · #17 ·
I best read the question,
What they are saying "remove chips by running a piece of carbide along the face of the flutes" is if some of the steel sticks to the reamer cutting edge. Sort of like drilling aluminum and it builds up on the end of the bit. I clean the reamer with ATF and a soft brush and then keep them in a tygon tube.
No matter how hard you try barrels have "soft spots".
These soft spots will tend to butter to the reamer. Newer barrels don't have this so much anymore.
Edward5759
Thanks! I didn't have any problems with any chips of metal on the cutting surfaces of my reamer luckily but I'll definitly keep this information in mind for my next build. Every 15 turns I cleaned the flutes with a clean terry cloth and paintbrush just so in case if there was some steel shavings stuck there the terry cloth would snag on it.
 

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Make sure when you start reaming that when you pull the reamer out to check headspace absolutely clean the reamer of all metal shavings before reaming again. I've seen people use paper towels or I prefer brake cleaner which blasts it off. Make sure to re lube the reamer and start again.

If you don't the metal shavings will score grooves into the shoulder of the chamber. Don't ask me how I know that!!!!!
 

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This is what happens if you don't clean the reamer. For the record, these are not cases that I fired. These came in a bag that someone gave me. I did however have a chamber that looked like that but not as severe.

 

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Hi Ripsaw,

Perhaps I am not understanding you but I see a contradiction in your comments:

If the case is still expanding upon extraction, that means that there is still pressure in the barrel. The only way there is pressure still in the barrel is if the bullet is still in the barrel as well. The bullet has perhaps another 8 inches to go (No I have not measured it) and the op rod only has perhaps 1/4 inch to move before unlocking. Pressure at the gas port is sposta be between 8,000 and 12,000 psi, so there is quite a lot of force working to accelerate the piston and op rod.

The accuracy improvement with shortening the piston wasn't much but it was definitely noticeable over the long run. I would guess around 1/4 inch to 1/8 inch for 5 shot groups. When I was done, this gun was shooting a lot of 5/8 inch 5 shot groups with average groups between 5/8 and 3/4 inch. Perhaps the gun was better, but the operator wasn't.

The reductions in measurements with the RCBS Precision Mic were not imaginary. The important thing is that they became much more consistent. I can't think of any other explanation besides unlocking later without pressure in the barrel.

- Ivan.

If Yellow Thunder will permit, and please forgive that as threads have the tendency to wander, and morph, we are still talking about chambers here.

I can see where it would seem to be a contradiction, but I was thinking not only of pressure causing the expansion, but heat as well, coupled with the fact that the cartridge is tapered. The initial compression against the chamber wall causing the swelling, and the extraction process pulling it back an ever so scant amount, with some residual pressure in the bore still, after the bullet is gone, ....this evidenced by the expulsion of gases through the venting port in the bottom of the gas cylinder, and the blast coming out of the flash suppressor spline cuts through slow motion photography, all at the instant of unlocking. Would leave enough of residual pressure and heat to impart more swelling and deformation of the cartridge upon breaking it out of battery. As the taper opens up away from the chamber wall in micro seconds, the brass must go somewhere. To prove this to your self, go to the bench with a ball cap on, pull the brim down tight over your eyebrows, leaving a bit of your forehead exposed. Make sure your skin is clean. Then fire twenty rounds with irons, take a wet ,white handkerchief or washcloth, and wipe the left side of your forehead. There will unburned powder residue, and nitrates all over the cloth. Do it with 100 rounds and wipe, and you will really be able to tell how much pressure and gases get out the back. The small hole that is the bore, and the small splines of the suppressor cannot evacuate the bore fast enough, there will be residual pressure and heat in the rifle when the bullet is gone. That's why it's called a suppressor, it suppresses the flash and to do so, it must suppress the exiting of the gases around the tail of the bullet ....this helps to disrupt it less in it's initial flight stabilization. The gas cannot get out quick enough to "not" have an effect on the cartridge. Physics supports this as pertains to the robust qualities of brass up against the gases and heat during the extraction process.
 
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