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Discussion Starter #1
I have been looking at the barrel band in a new light, and from all the post and experience on the front end, and gas cylinder assembly, and with unitizations, I think I might have found a new area of concern here.

How I noticed this was during some ongoing work with barrel assemblies for my collection, and happened to notice that a couple of the barrel bands were different in dimensions. Upon closer inspection, I found two were commercial as evidenced by their thickness and other things, which I will not mention here. Suffice it say that there are at least 5 differences from these to G.I., not counting finish. Hard to believe isn't it, on such a simple part.

The area of concern, and probably G.I. too, is the inside diameter of the barrel hole and the width. A circle is a circle is a circle, not so, I have learned. Some seem to be a bit oblong or egg shaped at the side to side as compared to the top and bottom. A bit wider horizontally than height. Unitizing might help take care of this better than shims, but shimming will only stop for and aft movement. After so many rounds have been fired, the left and right play could come into the equation, however imperceptible to the shooter, whichever method is used. Even though it is unitized, that just means the entire gas system will move side to side. The grooves for the splines having any play at all, will cancel out a good bit of your unitizing efforts at complete success. You may wiggle your gas cylinder every now and then, and be unable to feel or see this small amount of movement.

The gas lock will only stop it so long and for a given amount of rounds till the shims mash down and let go. Most likely a lot of rounds, I would not venture a guess. I suspect it would be directly related to heat and rate of fire also.

I also checked the boss, or barrel band stop ledge, ( I don't know what it's called technically) and they show several small imperfections from machining, and past weak cleaning regimens, with dust ,dirt, carbon and moisture build up, leaving residue and spotty rust or light pitting. Backing the gas system off more often and cleaning under this area would help. These should be worked down to bright and shiny, smooth finish to mate with the band, and reblued or similar parkerizing. Same thing inside the opposite surface of the band.

Looking at the amount of space on the sides of the band, as compared to the space at top and bottom, leaves only one conclusion to me. When the splines get movement, the gas system will to, thereby leading to problems with exact repeatability due to the barrel band banging the barrel as it whips around. I am thinking what might happen if the barrel band was machined out wider and exact, all the way around any given barrel, and a shim made of something like hard mycarta was inserted like a gasket between the barrel and band, capturing it tight, and buffering all movement. These could be replaceable as needed.

I'm thinking about 3/16" thick all around, and a bit sticking inside to the rear, in the barrel band that can be also used to hold the handguard up to the top of the band and off the barrel, cancelling out need for silicone and like products for modifications, and rattle or sloppy loose, controlled handguards.

Thoughts or ideas welcome,....as always, chasing the X's.
 

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"Death From Above"
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What barrels were you using? Were you using nos gas cylinders? I have not run into this problem on any of the builds I have done, probably because of the barrels I use they are over built to say the least. I found nos gi gas cylinders go on snug and the ones from the reset person in the southwest need to be hammered on. Very tight! All the holes I have seen are round and gas cylinder shoulder a ok. If they are gi there is only so much one can expect considering there previous use. Fill me in because I'm clueless when it comes to barrels other than what you know I already use.
 

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Barrel Bands

Barrel bands may vary somewhat and still be acceptable. Mil Specs call for a thickness of .0630" + '0015" to - .0035". I have found hole to be out of round in some commercially produced bands and some GI bands. I suspect that GI bands may become out of round in the barrel hole due to wear or the impact of recoil forces.

This isn't much of a concern in standard issue type rifles, and shouldn't be a concern in unitized gas sytems found on match rifles. Loose barrel bands always effect accuracy in unmodified rifles so that is a given.

Normally unitized gas systems will have their barrel band holes reamed larger. This is mostly to provide clearance in poorly assembled units so they don't bind on the barrel. When alignment is correct, there isn't a problem.

Rotaional movement of the gas cylinder assembly on the barrel also is detrimental to accuracy. Splineways should be peened if movement is found.

In my opinion, shimming the gas system is not necessary when the gas system has been unitized. Not everyone agrees with this, but it prevents binding when the barrel heats up and that can effect accuracy.
 

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Art Luppino has addressed this elsewhere. I am with Ted as well. You can unitize using one of the various methods,( or combinations of methods), or you can shim. Some folks do both. Simply out, when you shim, you are correcting the alignment of the gas ports in the barrel and the gas cylinder as well as overall stiffening/tightening the gas cylinder to provide a uniform movement during firing and recoil. When you unitize, you are actually going a couple of steps beyond to insure the variables of the ferrule, ferrule contact and gas cylinder band all move in concert and do not obstruct the ports. That is why you normally unitize AFTER you have bedded. The situation you describe is fairly common but is of lesser concern though. You have to have a degree of movement or you create undesirable counter movement or harmonics.
 

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I have definately experienced different size and thickness of front bands. My commercials are the thinest but out of 4 usgi's I get 2 different thicknesses. I don't use shims on my unitized gas cylinder and have excellent accuracy and no looseness. If I were shooting with a gas system that was not unitized then I would consider some sort of gasket for the situation that ripsaw mentioned. I have often had suspicions that there was side to side or up and down movement in the area of the front band and shims.
 

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Front Bands

This small part is, or could be called the Heart of the Accurate M1A. Ted has provided the correct material as always, read it a couple of times before you make any decisions.

There are two acceptable methods to address the FB, Unitize or two parts independent of one another held together in a firm position by adding Shims. Both are excellent methods, two methods to produce accuracy, it is a matter of choice.

The real important issue is between the FB and the stock ferrule rather you use shims or do not use shims.. This relationship can and does determine an accurate M1A, Everything else about the rifle can be correct but a poorly located FB to stock ferule will prevent the results we all desire.

Understanding this relationship and how to fit these two surfaces together under load is the Key to accuracy given the above material. Art
 

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Discussion Starter #7
You have to have a degree of movement or you create undesirable counter movement or harmonics.
That is what I was wondering Ripper, if I came across a loose gas cylinder, and peened it to tighten it up, then opened up the hole in the band and shimmed it, then...would it be a detriment to accuracy because of the counter movement or dampening of natural barrel harmonics.

Thank you all gentlemen for your comments, and for the measurements Ted.

This statement "prevents binding when the barrel heats up and that can effect accuracy." I happen to agree with. It seems to me that it would be the same as putting a flash suppressor on so tight that it affected the barrel.


The barrels are all USGI Warren, and two of the five are NOS.
The gas cylinders are used except two are NOS G.I.
 

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That is why you normally unitize AFTER you have bedded.
+1. Slight clearance in the front band openings for the barrel and gas cyl is necessary to achieve optimum vertical alignment to the stock ferrule, which, itself, may be less than perfectly hung on the front of the stock. You want up-down, not diagonal. Locate or relocate the parts as needed to achieve that; mark or stake to index, then unitize. Old screwed & glued lends itself to precise drilling & fitting.
 

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So how tight should the fit be between the front band and the stock ferrule? Shouldnt this be addressed when bedding occures? What would be a good way of testing this draw pressure? Would it be much of an issue rip with the heavy barrels and the double lugged receiver. I did not think any draw pressure would be desired I thought one would want to free float the barrel. Any thoughts?
 

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Discussion Starter #10
So how tight should the fit be between the front band and the stock ferrule?

I have heard of success with ranges between 4-8 pounds of draw, and success from 16-20 pounds of draw. I think it varies from action to action, and the accuracy varies from barrel to barrel based on each individual set-up and draw pressure. For instance, a super match heavy might benefit greatly from a draw of 5 pounds, where a standard G.I. profile might benefit from 12 pounds. These are just random examples, and each shooter will have to find their own special combination for each rifle.Shouldnt this be addressed when bedding occures?

Absolutely, if not, you will have to bed all over again.
What would be a good way of testing this draw pressure?

I'm sure others all do it differently, and I don't propose to know or say my way is the best, but some squeeze and release and watch for amount of play, and have a feel for it, to know when it is too much or just right. Then test firing will be the only tell. Then others like myself will use a produce scale and a clamp. I use a quick grip with rubber jaws. Now, this is all before bedding, to find out my perfect combination and accuracy rating. Then when I find it, I incorporate this amount of draw during the bedding process. If the bedding is built up too much and I loose or gain pressure, I sometimes must anneal the barrel band lip and reset it to regain my desired draw, or surface bedding down some in places. Hence the idea of another way to adjust by using the inside diameter of the barrel band. A way to make adjustments quickly and precisely with shims of varying thicknesses and even varying hardnesses. Would it be much of an issue rip with the heavy barrels and the double lugged receiver.

I really don't know since I have fooled with them very little, and have learned alot from Ted and his assessments of them and postings, but would think that the draw does have some effect, however small, but the adjustable screw pillar type helps I'm sure. Probably the barrel band relationship to the ferrel would be the biggest variable. Perhaps pick your chosen stock and action combo, and sit down in the recliner watching TV at night with your lapping compound, and mate the two together till they are slick, or use Art's method for radius mating.
I did not think any draw pressure would be desired I thought one would want to free float the barrel. Any thoughts?

Well, to each his own, and yes, a free floated M14 would be good if possible, but the only way is to throw the barrel band away. If you have one on the rifle, there will be some draw pressure, if not just sitting still, for sure when its fired and starts whipping around, but I have done experiments with lashing barrels down, and gotten good results with accuracy, and I have done several with different varying degrees of draw on other guys rifles, with positive results.

Not long ago I posted about one of my rifles that has the op rod guide bottomed out on the stock, and most all will tell you to gain clearance there, I believe the word was, be able to slide a dollar bill under it and saw back and forth freely. Mine shoots excellent like that and is definately not free float. When the wood gets beaten down and accuracy wanes, I will fix it.

I think the trade off is in the amount of forces exerted by the barrel band in fighting the opposite whip. In other words, the round is fired and the barrel starts to rise, the op rod guide comes up off the stock for an instant, the barrel band has it captured and the lip stops the upward travel of the barrel and it has nowhere to go but back down, "Except" side to side because of the varying degree of gaps around the barrel band to barrel relationship. Now your have the star shaped whip occuring, again, hence my idea of modifications in this area.

Perhaps a longer and all encompassing lip on the barrel band that forms a perfect U shape, and locks all the way around the ferrel would be of interest, it is to me. You could have a set screw on each side of it and dog it down, then grind the bottom of the op rod guide off and hog out the stock, so there is no contact during firing. For all practical purposes, it would be free floated except the one capture point at the barrel band. Same concept as a Sage EBR stock and the accuracy improvement is documented, except they use the op rod guide as a terminal point to lash it down, why not both guide location and barrel band, unless the vibrational forces begin to conflict. So since we cannot use the op rod guide area, why not the barrel band area for lashing or capture point ?

You can try the same experiment as I did if you would like to see. It is really simple. I cut a wood block for a shim and placed it under the gas cylinder between it and the stock, so it couldn't go down under force, then I took a regular hose clamp like for radiator hose, and clamped it around the barrel with the handguard removed, on the receiver side of the barrel band and under the barrel band lip. Then another clamp in front of the barrel band and under the lip, in essence, keeping the barrel from rising under pressure.

First go shoot ten rounds without it, then go shoot ten rounds with it like this. That is lashed and captured, is what I call it, you might be surprised at the effect. The repeatability should be there if your receiver is properly bedded and/or secure.

I believe all accuracy issues, with a properly bedded rifle and a good barrel, can be located forward from the barrel band on out to the muzzle. If you want to make it the best it can be, talk Gene into making undersized groves on the match barrels for the gas cylinder splines, then lap those in by hand till you have less than .001 inch clearance from every surface, bottom ,left and right spline contact areas.

The word match comes from the perfect mating of two things together, or meaning two things exactly alike. I think up north, the carpenters call it marrying two boards together. I have heard people say they had to beat their gas cylinders on and think they got themselves a nice tight set-up and is match conditioned. So whats to say that the front or back was just tight, and the other end or middle is moving all around under fire ? With a unitized system, that means any movement in the gas cylinder is translated to everything, including the barrel band and ferrel contact.

Any movement at all is reason for concern when talking about accuracy, anywhere. Same thing for the flash suppressor and its mating surfaces. For true match conditioning, there is no end to it, you should have an undersized gas cylinder bore and lap your oversized match piston to it.

When I can quit finding areas that need or could be improved on, with this rifle, I either will have succeeded , or gotten bored and moved on to the next thing, or area of interest to me.

 
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