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Barreling receivers.

This is a discussion on Barreling receivers. within the Gus Fisher forums, part of the Gun Professionals category; Folks, discussion with manufacturers and reps of receivers at Camp Perry gave me the idea for this thread. They, I and others have seen some ...


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Old August 28th, 2010, 01:22 PM   #1
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Barreling receivers.

Folks, discussion with manufacturers and reps of receivers at Camp Perry gave me the idea for this thread. They, I and others have seen some pretty nasty things done to receivers and barrels by those who don't understand what they are doing or those who use something other than the proper tools.

There are a WHOLE lot of people barreling AR 15 receivers today and that includes many hobbyists. One doesn't really need to be a gunsmith or machinist to barrel up an AR and we often tell that to Police and LE personnel we teach in the Armalite Police Armorers' Course. The reason it can be done is because it is rather easy to "pre-set" headspace on these rifles as the bolt to barrel extension fit is factory pre-set. I know a good number of people who have assembled a lot of AR's and they have never had to adjust or chamber headspace in any rifle.

The next rifle many hobbyists work on is the M1 Garand. G.I. Garand receivers were held to extremely tight tolerances over the entire course of their production, no matter which of the four makers made them. Lapping bolts on Garands is usually not necessary and/or it can be a waste of time. The receiver and bolt lugs were held to such tight tolerances, you almost never have to lap a Garand bolt. You DO have to have a chamber reamer to rebarrel Garands, though, as the length of the bolts vary a lot over the years of production. Even with the pull type chamber reamers, you have to be careful not to cut the headspace too deep, though. The nice thing is you usually don't have to have a lathe to barrel most Garands and that makes it more hobbyist friendly. The fact the receiver itself is made to such precise tolerances ensures this and gives a little "goof" room in case some folks get a little to heavy handed with the receivers.

M1 Carbine Receivers are a little more difficult to barrel. The thing you have to ensure is you absolutely have an action wrench that properly fits the receiver so you don't crack/crush the edge that holds the recoil spring and guide and more importantly the early receivers that are milled away for the tube that holds the spring and guide. I've seen a good number of the early receivers that were cracked due to improper fitting tools. I barreled quite a few carbine receivers using a standard headspace reamer for years, but I finally broke down and bought a pull through reamer and it is very nice to use and saves a good bit of time. I have seen more Carbine receivers messed up than Garand receivers, though, from the misuse of improper tools and/or folks who didn't know what they were doing.

Barreling a REAL G.I. M14 receiver with G.I. barrels is downright easy when you have the proper tools. This is because the receivers were held to such high tolerance standards. You almost never had to lap the bolts. The distance from the area the bolt lugs seat in the receiver to the front of the receiver was extremely accurate. That's how they could use a chrome lined barrel and no chambering reamers. You also almost never had to worry about fitting any part to the receiver (except maybe a little filing on some cartridge clip guides) and that was/is a real great thing. Again, this came from the extremely tight tolerances of the receiver. Further, they could make thousands of stocks to a standard pattern and they all fit because the receivers were held to such high standards. Unfortunately for civilian use, the M14 receiver was full auto capable, so we will never see a plethora of them on the open market like a Garand.

Then we get into commercial semi auto M14 receivers that historically have not been nearly so precise or held to such tight tolerances all over the receivers. That is the reason a G.I. stock may or may not fit and why it is so difficult to impossible for a wood or other stock to fit even most of the receivers. Commercial receivers may have the distance from the front to back of the receiver legs off so that you either have to file a G.I. stock liner to fit or have to glass bed short receiver legs into the stock liner so there is no front to back movement of the receiver in the stock.

Commercial receivers also have not been NEARLY as precise as G.I. receivers in the distance from the bolt lug area in the receiver to the front of the receiver. That's why we have to resort to bolt lapping to get enough headspace on some G.I. barrels and with other G.I. barrels, you can't use them without having the headspace cut with a carbide cutter. When the front of the receiver is shorter than spec., that can also mean the end of the barrel sticks back too far into the receiver. That can cause all kinds of problems with bolts rubbing or binding that were never found with G.I. receivers. Gene Barnett once told me that he had to buy a SAIinc. receiver about every 6 months to see how they changed this distance and make his barrels to fit by the serial number ranges. He finally had to give up and leave the shoulders long on his barrels so they could be fitted to any receiver - no matter how long or short this distance was. Of course, that sometimes requires the use of a lathe to cut the barrel shoulder as needed. This is definitely outside the home hobbyist's abilities for the most part.

OK, this is getting long, so will go on to Part II in the next post.

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Old August 28th, 2010, 06:38 PM   #2
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Gus How about some pics of barrels when they are hand tight from inside the reciver so that we novicess can see what you call 6:30, 7:00 oclock ect? I know pics are additional trouble, but as they say One picture = one thousand words.

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Old August 28th, 2010, 09:05 PM   #3
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I would like to post pictures, but I don't even have a computer capable camera let alone the knowledge to post pictures. Sorry.

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Old August 28th, 2010, 09:16 PM   #4
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Cool

Thanks, great post Gus, I am anxiously awaiting the continuation. I am wanting to build my own soon but not ready yet tool-wise.

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Old August 28th, 2010, 09:58 PM   #5
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Leadbug,

I hope you aren't too disappointed, but the intention of this thread is not meant as a "how to" on barreling receivers. Actually, I'm hoping to persuade most folks OUT of trying to barrel receivers themselves; by informing them of the type of tools needed, the costs and just SOME of the problems you will run into. Unless one has a background in some type of gunsmithing and/or machining, this is not something the average home hobbyist should attempt. This is something one really needs a personal instructor or mentor in person to teach them how to do it.

When I was the Instructor of OJT's (apprentices) at the Rifle Team Equipment Repair Shop at Quantico, my OJT's first went through about four months in the machine shop and then out to me to teach them how to build a NM M14. It took about 3 1/2 weeks for them to build their first three rifles with me there to instruct and supervise every little thing they did and that included each individual cut they made when they cleaned up the glass bedding. It took the better part of two to three days for me to teach them how to barrel and cut headspace on their rifles and that was with some of the most intricate and supremely expensive tools and gages made.

It is impossible to teach one the "feel" of how to do many of these things without having an instructor right there beside you. I also can't think of every problem you will run across, even though I've run into what seems like too many of them.

The intent of this thread is more to give the home hobbyist an idea of how it is done and how to check a receiver when considering purchasing of one. Then my most sincere recommendation is to have it done by someone who knows how to do it. After the barrel is correctly installed and headspaced, then a standard rifle can be built by a home hobbyist.

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Old August 29th, 2010, 07:18 AM   #6
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Have to agree 100% Gus! Having the right tools and someone looking over your shoulder is half the battle. When I twisted on my first barrel I had a gunsmith standing right there for that matter he was there at every step. I must say it was a two day evolution. On another note the next one I built I finished up in about four hours solo. It was a winderful feeling, one that I am sure you have had thousands of times. I have three more of my own to go and hope to get to one of them real soon so I can do a show and tell sort of post. Considering I have five actions to put together I figured it would be more econmical to buy the tools and I am glad I did. There is one more tool I would like to add to the box and that is a hand knurling tool. At this point it's not nessasary because every op rod guide I have fits tight but I'm a tool freak and ya never know! Thanks for your post and advice!

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Old August 29th, 2010, 09:48 AM   #7
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Gus, as much as I would love to, I know there is way too much I do not know to do this extremely soon. The whole process sounds like what I do (neon glass tubebender) where you just can't do (well) without an apprenticeship and lots of practice.

These posts do inspire me though, because they really help me understand the "mysterious" nature of it. So many of my questions have been answered here about building, but I would not want it heard through the grapevine that ol leadbug blew himself up doing something stupid! I figure it is a good idea to start collecting the necessary tools/guages.

I just really appreciate reading all of the wonderful information that all the experienced builders share here because usually with such information, many are very secretive.

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Old August 29th, 2010, 11:27 AM   #8
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Part II

OK, well maybe it is time for a bit of historical information next. When I first began building NM M14's, the only NM barrels we had were the exact same contour as issue barrels, but of course they were not chrome lined and they were chosen and stamped "NM" from air gage readings. Still, those barrels were not nearly as good as most any NM barrel today.

The first step we did was air gage all our NM barrels and record the readings from the throat, about halfway down the bore and the muzzle. The very best barrels were selected and put aside for THE Marine Corps Rifle Team and we used all the others for Division Match and Post and Station NM rifles. The BIG Team barrels had to vary no more than .0003" (that's three ten thousandths of an inch) between any two of the three readings for BOTH the lands and the grooves measured at those points. They also preferred a barrel that was straight or better still had a taper from larger at the breech to smaller at the muzzle. I wish I could tell you that we had done extensive tests and found these standards from true scientific examination. Honestly, it was a little bit from tests and probably more by what everyone in all the "accurate barrel disciplines" believed and still believe what makes a better barrel. Today's NM barrels often vary less than .0001" along these measurements and that's why they shoot so much more accurately. BTW, the "vaunted" M1903 barrels that were star gaged were not really found to shoot any better than other barrels. However, the Star gage only read in increments of .001".

For some reason, I just happened to have a knack for doing air gaging. I don't know if it was because I was stubborn on getting everything set up correctly and doing it as uniformly as possible and/or if there was a certain amount of luck involved. I also talked to the gages as I set them up and sometimes went back and checked things when things didn't "feel" right. As such, I was chosen to do a lot more air gaging than a lot of other Armorers. The same knack or luck had me doing a lot more barreling of receivers than many others.

In 1973, we used a number of tools that almost no one can use today to barrel receivers. It began with a special vise that was bolted to the bench and the only thing we did was use it to loosen the standard issue barrels. The two vise jaws inside precisely fit the breech of those barrels. We had HUGE wrenches with rectangular cuts that fit the receivers. Just picking those wrenches up and using them gave you a great work out. The weight of them gave good inertia when pulling the G.I. barrels out. Then we slightly greased the threads of the NM barrel and hand tightened them down into the receiver. As best I recall, the issue NM barrels ran about 25 to 35 degrees off from top dead center when hand tightened. Then the receivers were placed in a reworked M1 Garand Barreling Machine that had a pointer and scale to show you ABOUT where the barrel would line up TDC. I say "about" as the person who taught me made me line up the pointer on the line and then when the barrel so often did not line up at TDC, we had to take the barrel off, run the barrel shoulder back and try again. We didn't argue with our Instructors in those days, but when I was doing it, I "snuck up" on the line and tested it for TDC and then took it up a little more at a time until it was at TDC. Of course, that meant I almost never had to pull the barrel, lengthen the barrel shoulder and try again. That made things much faster for me when barreling and that's why I was often chosen to do "mass barrelings." For example, in one three day period I averaged more than 25 barrels a day properly aligned.

After the barrel came out of the barreling machine, we pushed a precision gage over the muzzle and placed the gage on a precision ground block of granite. We tested the bottom of the gage against the bottom of the front of the receiver that was also placed on the precision ground granite block. You pressed down on the receiver with one hand and then pressed down on both sides of the precision gage at front to see if there was any "wiggle" that showed the barrel was off TDC. When there was no wiggle, it was considered TDC. I was told these procedures came from 5th Echelon Arsenals, but I can't name the Arsenal/Arsenals we got the information from. I strongly suspect it was Rock Island Arsenal, but I can't prove that.

When we first mounted the first 10 NM "Heavy" barrels right before we went to Camp Perry in 1975, we could not use the barreling machine as the barrels were too big to go in it. We probably could have eventually modified the machine for it, but we didn't have time as we built those first 10 rifles (along with five of them that had our first rear lugs) in four days from stripping Depot Rebuilt Rifles to function/test firing. Four of us Armorers and one Machinist were involved in the project. I don't want anyone to think I was any kind of "mastermind" on this project. I was the Junior Armorer and mostly did the "Grunt Work" of routing stocks, mixing glass, basic clean up and filing the glass, etc., etc.

Looking back, I still chuckle about the arguments we got into on how we were going to barrel those receivers with the heavy barrels. Well, the two senior armorers and the machinist argued, anyway. Grin. Now, of course they had used a pneumatic press to barrel bolt action rifles many times and that was what we used. Our Machinist made us a set of vice blocks for the then "new" heavy barrels that went into the pneumatic vise. I'm pretty sure we still used the precision gage block we used on standard barrels to align them, but even that eventually changed. Well, I wish I could tell you exactly came up with the idea to do it differently and to our thinking, more accurately, but I don't believe I knew even then all those years ago. It may have been GySgt Scott Walker, but I'm not sure.

Well, I seem to be running low on space, so will add more in the next post.

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Old August 31st, 2010, 11:08 AM   #9
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Part III

I was sent off on independent duty for four years and when I came back, many things about barreling had changed in the shop and some of them not so good.

They came up with a specially modified flash suppressor FS with a precision ground plate they welded on top and used that to align barrels. That seemed OK for a while, but some of us noticed it wasn't making the barrels line up quite as close to TDC as possible or needed. I think the Team Armorers first came up with using the FS that was actually going to be put on the barrel as the way to align the barrel. That made more sense as there would be a tiny amount of difference due to manufacturing tolerances of the FS's. We used angle finders that were scaled by one degree measurements on top of the FS.

Now, the place where some of them REALLY screwed up on aligning the barrel to the receiver was one of two things.

Some of the guys were using the flat surface on top the barrel ring at the front of the receiver to align the barrel. That raised my eyebrows when they first told me. So I went and grabbed a bunch of those real, G.I. receivers and demonstrated to them how they were NOT precision made surfaces. Had to call Picatinney Arsenal and verify that with them before I got them to quit using that surface. However, they also confirmed the correct surface to use to align the barrel and that was the flat cut out on the receiver for the rear sight base. We made up some precision ground blocks that fit into the surface and got the angle finder above the ears on the receiver. What that did was effectively ensure the rear sight adjustments would go straight up and down and side to side with the front sight on the flash suppressor aligned at TDC. If the front sight post was not TDC, then the adjustments would be at an angle going up and down and side to side. The more off TDC, the worse the angle of adjustment would be. The further off straight up and down sight adjustments, the worse off the shooter would be in trying to figure out how to move his/her sights to center the shot impacts.

The other thing we got into quite a few and sometimes heated discussions, was whether or not to use only ONE angle finder to check the alignment at the front and back. Some of the guys were using two angle finders, one on the front and a second on the back. The problem with using two is they are not calibrated to each other. Man, that took some discussions and proof on barrels before we stopped using two angle finders and just moved one of them back and forth between the front and back.

I have been asked many times if there was ever a problem with the op rod and other parts out of alignment due to aligning the barrel this way and my answer is a resounding NO as long as one is using G.I. or G.I. spec parts. There is plenty of tolerance “slop” in the system for everything to function correctly when aligning the barrel this way.

OK, this is going long, so I guess I should cover some necessary tools in the next post.

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Old August 31st, 2010, 05:34 PM   #10
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Thank you Gus - very interesting read!

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Old September 7th, 2010, 06:57 AM   #11
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Keep it coming Gus. I finally had a chance to read this post but am waiting for more.

By the way, how does one "roll back" the barrel shoulder?

I have minimal experience with machining, so I await enlightenment.

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Old September 8th, 2010, 11:16 AM   #12
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Quote:
Originally Posted by tonyben View Post

By the way, how does one "roll back" the barrel shoulder?

I have minimal experience with machining, so I await enlightenment.
In a tool rest (the part of the lathe that usually holds a cutting tool) you have a tool with a hardened wheel that is rolled/pressed into the shoulder of the barrel. That forces metal backwards and gives you enough metal so the shoulder can be torqued in place against the receiver.

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Old September 8th, 2010, 01:05 PM   #13
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Thanks. I kind of figured it was something like that.

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Old December 26th, 2010, 07:24 AM   #14
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Gus,
One time, years ago, I talked with Gene Barnett about fitting barrels and when I mentioned cutting the barrel shoulder, he cautioned me not to do it because he said it was too easy to go to far and that you might need something special in a tool to be able to get to the shoulder. His solution was to "work the barrel in" with the wrench, by repeatedly torquing it and then loosening it until one could crush the barrel shoulder enough to reach correct alignment without too much torque required all at once. I didn't take his advice, knowing well that he had more experience, but I do quite a bit of machining at work, so I wasn't too worried about going too far, and I didn't. I hadn't ever installed a barrel before on anything, either. This was an installation on an Armscorp M14 Receiver. I'm not sure if I'd try that method which he mentioned, since I have access to a lathe anytime I want. I went against his advice knowing what the risk was, and I accepted it.

Danny

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Old December 26th, 2010, 01:26 PM   #15
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Gene told me years ago he had to buy a new receiver from SAinc. about every six months to try to keep up with how they changed the finished length of the barrel ring in the receiver. Then he finally went with a long shoulder.

I am not a machinist, but watching Gene turn down barrels years ago flat out scared the Bejesus out of me how fast he did it. That was his experience with doing it and his machines, though.

I have turned a very few of Gene's barrel shoulders down over the years and it will work, if one is careful. The barrels were just too far out to work them in the way Gene described. I don't blame Gene, as it was the receiver/s that were too far out of spec. I would much rather have too much shoulder than too little shoulder any day.

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