[GDavis]

I did not want to steal the other guy’s thread, so I am asking this in a separate post.

I apologize for perhaps my ignorance, for I know there have seen many threads on “front band tension” but I still an unclear.

I have absolutely NO front band movement between the front band and the stock ferrule. No matter how I press (pressing upper band and lower hand guard together at the stock ferrule), there is no movement at all; the two are ROCK SOLID tight against each other. Again, ABSOLUTELY no movement up or down or side to side.

I have shimmed the gas cylinder so the front band has no movement on the gas cylinder, but the top of the stock ferrule sits against the lower bends of the stock ferrule (where the ends are bent to hold the upper hand guard in). There just is no place for there to be ANY movement, so that is where my confusion lies.

Reading posts (and http://m14tfl.com/upload/showthread.php?t=54400), it seems I should have pressure where if I squeeze the upper band and the stock ferrule together, there should be some movement with pressure. I must be missing something here, for the front band does not seem to have any gap within it where movement of the stock ferrule is possible. If I shim the stock channel, I’m not sure it that will really do anything.

In the link it says "Place a stand off spacer in the barrel channel midpoint between the rod guide and end of cyl." . I’m not real clear on what a "stand off spacer is (or what it would be made out of). I'm also not clear on how to do that, because I sure don’t want anything rubbing against the operating rod as it moves. It seems any shim would need to go under where the OP operating guide rod is, or under the gas cylinder itself, but not between the two. If so, what material would you recommend to shim?

Where do I have a hole in my head? (Please don't say all over :O) )

 

[High Hat]

Don't feel bad GDavis, damned if I understand this matter yet!

 

[Rocket6R]

How is your fit between the upper handguard and the stock? Is there space between them or are they sort of clamped together?

I have proper tension on two of my M1A rifles. However, I have a USGI handguard on my third M1A. The USGI handguard has different dimensions then than the SAI handguard. Anyway, on this third M1A it appears that the ferrule and stock are frozen together. This is because of the dimensions between the stock and the USGI handguard.

Thanks, Paul

 

[bd111]

Reads like you may be needing to relieve the inside of the stock and ferrule to clear the gas cylinder and/or relief trim the handguard to clear the stock. Think about when you've seen Garands where the stock ferrule was rubbing the op rod or the rear handguard and stock were mashed against each other. Reads like you're dealing with basically the same undesired conditions.

 

[GDavis]

It is in a USGI synthetic stock right now, but I have the same situation with a USGI birch and an USGI E2 stock. The upper hand guard does not touch the lower stock at any part. Also, there is fore and aft movement of the upper hand guard. The upper hand guard/forearm fits looser in the front band while the bottom area (stock ferrule) fits tight.

It just seems that the front lower stock ferrule sits snug in the front band, squeezed between the lower band lip (lower area) and the bent “tabs” (on each side) that holds the upper foreend in the barrel band. The bottom “half” where the stock ferrule is fitted into, is tight. I just don't see how pressure down on the front band against the lower stock CAN move anywhere.

Tomorrow I will try to get some pictures up.

Thanks for all the replies

 

[TheTinMan]

You wouldn't have been "stealing the other guy's thread"... I'm still confused about what the right amount of tension is between the front band and the stock ferrule. I also didn't understand the standoff spacer concept at all. Is that part of the glass bedding process?

 

[artkat2]

Temporary spacer

"Place a stand off spacer in the barrel channel midpoint between the rod guide and end of cyl."

These guys are a lot sharper than I am (Art, Gus, Ted & a lot of others), but what I'm reading is that the "stand off spacer" is a temporary object used to flex the barrel so that the front band and GC get "drawn" into the correct position by tightening the GC lock. Or the same process to know what GC shims to use etc...

That's how I read it, but like I said sometimes I'm a genius, sometimes I'm sharp as a marble!

Either way, I'd sure like to hear the real thing!

Andy

 

[copterdoc]

When I place my SAI barreled action, in a USGI stock, and don't latch the trigger group down, I don't have any front band tension, and there is a gap under the heel of the receiver. It's not a huge gap. Maybe 0.060".

When I latch the trigger group in, the gap goes away, and I get all the front band tension anybody would ever want.

I can't tell you how many times others on this forum have said that you shouldn't have a gap under the heel of the receiver, when the action is resting in the stock.

They say that you should break out a dremel tool, and grind away at something, until the gap goes away.

I think they are full of crap!

I think the rifle was designed to work this way, and they are screwing up, by grinding the stock.

 

[copterdoc]

BTW, this same rifle shoots 2" groups, at 100 yards, off the bench, with Lithuanian GGG ball ammo. (It really loves that stuff.)

It sits in a walnut E2 stock, has a standard USGI chrome lined SAK barrel, non-unitized gas cylinder, and no gas cylinder shims.

The trigger has been worked to 4.5#, but it does have a little creep. It's my "perfect" Walter Mitty rifle.

 

[TheTinMan]

My apologies to the OP if this appears to be a hijacking of the thread he started. Seems like it's on point to me, but I could be wrong...

I was in the "Why in the world should there be a gap under the rear portion of the receiver" crew until reading a couple of glass-bedding tutorials. Apparently you want the portion of the receiver aft of the "legs" to float above the stock.

Experiments over the weekend to use shims to create some front band tension with my floppy SAI stock seem to confirmed this. Here's my theory (and that's all it is):

The stock ferrule contacts the front band. Between the front band and the receiver, the barrel should not touch the stock (or handguard) at all. The outside ledges of the receiver and the "legs" are the key contact points between the receiver and the stock. After all, that's where the metal stock liner is for wooden stocks, right? The trigger group clamps down immediately behind the receiver legs. In effect, the receiver-stock contact point forward of the trigger group serves as a fulcrum to put pressure on the front band / stock ferrule contact point when the trigger group is locked in place and pulling downward on the rear of the receiver. If there's no gap between the stock and the rear portion of the receiver, the pressure created by closing the trigger group can't put additional pressure on the front band//stock ferrule.

When I put shims under the receiver rails just forward of the legs, I reduced the amount of slop in the front band. However, the receiver was pushing down harder on the stock aft of the receiver legs than it had been before. With a little judicious filing on the stock, I created a tiny gap under the rear portion of the receiver. That reduced the slop at the front band some more. Not enough to make me entirely happy, but I don't think I'll ever be entirely happy with this wet noodle of a stock.

Does my theory make sense to anyone else?

 

[M1AallTheWay]

...It just seems that the front lower stock ferrule sits snug in the front band, squeezed between the lower band lip (lower area) and the bent “tabs” (on each side) that holds the upper foreend in the barrel band. The bottom “half” where the stock ferrule is fitted into, is tight. I just don't see how pressure down on the front band against the lower stock CAN move anywhere...

On a good day, there isn't a lot of room between the tabs on the front band and the top ends of the ferrule's "U" they sit near. Indeed, one of the steps in unitizing the gas cylinder is to bend those tabs up and that moves them up and away from the ferrule, providing more room for ferrule/front band lip movement. You're correct in thinking that until there's clearance, the rest of the discussion is moot. In comparing three front bands, two USGI and one SAI, I noticed two things. First, the tabs all seemed bent just a little differently and sometimes with the two sides different, and that could eat up what little clearance there is. Second, the lip is sometimes horizontal and sometimes angled slightly down. On the latter, it acts as a kind of ramp, so the closer the ferrule is to the back face of the front band, the further up the ramp it is, and thus higher and closer to the tabs. It's also possible that the ferrules are at the long end of their tolerance, but with three stocks acting the same way, I'd look at the front band first. (I vaguely remember Gus Fisher commenting that the holes for the barrel and GC aren't always exactly where they should be either.)

Also, it's possible that you do have tension there but without clearance to allow movement, the only way to infer it is that locking up the trigger guard pulls the heel down on the stock with some reluctance.

...The trigger group clamps down immediately behind the receiver legs. In effect, the receiver-stock contact point forward of the trigger group serves as a fulcrum to put pressure on the front band / stock ferrule contact point when the trigger group is locked in place and pulling downward on the rear of the receiver. If there's no gap between the stock and the rear portion of the receiver, the pressure created by closing the trigger group can't put additional pressure on the front band//stock ferrule...

I've described this as a kind of see-saw, with your shims the fulcrum and the barrel moving up in front (and taking the front band lip/ferrule contact point with it) as the heel is pulled down in back by the trigger group, but your description is the way it works. If the heel is already down, the see-saw doesn't work, so the shims raise the heel, giving the see-saw room to rock.

 

[GDavis]

The TinMan,

On point and no need to apologize because you are not hijacking the thread I started. It is good to know I am not alone after reading everything I can. I do recommend you shim your front band to gas cylinder, or better yet, unitize it. I figured I’d shim first, and it is now rock solid. I’ll see how it does.

Your description did help, for while there is no way I can have movement between the front band and the stock ferrule, I guess the trick is to get the barrel action raised up a bit so that a stock must be “slightly (ever so slightly) bent when everything is locked down. Not bent so you can actually see it, but so there is pressure. Perhaps I have been too locked into “that if you press the front band and the stock ferrule together, you should see and feel movement with pressure applied”.

But, as you mentioned, I can see shims in the receiver area to accomplish this, but not in the underside of the stock channel (unless it is directly under the OP rod guide, or, the gas cylinder). Any where else may rub the OP rod as it cycles.

 

[TheTinMan]

GDavis - I think that the "stand off spacer" Art wrote about in that post you linked to at the start of this thread is solely for the purpose of properly centering the front band on the stock ferrule. IOW it provides an even more pointed, and higher, fulcrum for the barrel/receiver to rotate on when you are fitting a shimmed front band. The idea is that you can accentuate the rotation and pressure of the stock ferrule on the front band, forcing the front band to center itself on the stock ferrule. Then you tighten the gas lock to keep the front band in that position relative to the stock ferrule. I say "center" although the stock ferrule and/or the front band may not be perfect but this procedure ensures that they are lined up for the best possible fit of your actual components and rifle.

The standoff spacer is NOT left in the rifle after this procedure to locate the front band properly.

P.S. I still don't know how to determine whether or not you have the ideal amount of tension between the front band and the stock ferrule but am making progress...

 

[GDavis]

Thank you my friend, that makes sense!

 

[ripsaw]

I apologize for perhaps my ignorance, for I know there have seen many threads on “front band tension” but I still an unclear.

I have absolutely NO front band movement between the front band and the stock ferrule. No matter how I press (pressing upper band and lower hand guard together at the stock ferrule), there is no movement at all; the two are ROCK SOLID tight against each other. Again, ABSOLUTELY no movement up or down or side to side.

There just is no place for there to be ANY movement, so that is where my confusion lies.

Reading posts (and http://m14tfl.com/upload/showthread.php?t=54400), it seems I should have pressure where if I squeeze the upper band and the stock ferrule together, there should be some movement with pressure. I must be missing something here, for the front band does not seem to have any gap within it where movement of the stock ferrule is possible. If I shim the stock channel, I’m not sure it that will really do anything.

Where do I have a hole in my head? (Please don't say all over :O) )

Lets begin at the end: Three in the front and one on each side.

You did not say what type rifle you have SAI ? And you did not say what type stock you have? wood? fiberglass ? synthetic ?

I suspect that your barrel band is commercial and is out of spec, to not exhibit a small gap between it and the stock ferrel. That, or.... either/and, your stock is dimensionally incorrect as well. I recently came across a Boyd's national match stock that I am repairing for Arcticdog, that is dimensionally incorrect as well, but his is in the area of the location of the ferrel tab mounting area. The wood was milled out too high at the level line on top the stock where the handguard runs. The front ferrel should be level with the top of the stock on both sides, his is sticking up a full 3/32". He had sent it to be repaired by a friend, and the gentleman had hulled out the inside, as in a normal national match modification, to keep the gas cylinder from contacting the stock and ferrel. When finished enough for clearance, the stock ferrel wood tab was paper thin at the bottom. After comparing his to the NM SA I have, I found the differences.
Now I must build up under the bottom on the outside and take enough off the top to get the ferrel wood tab even with the top of the stock when the ferrel is in its final installation location.

One of my SAI rifles only has a small gap on the left and a larger one on the right, and since reading your post, I noticed some scratches on the left where it is hitting during recoil. I will file the barrel band down to clearance it some more, and cold blue it. That, or anneal it, and bend the handguard ears up some more to clear it. You can also do the same to the lip at the bottom of the ferrel, but bending it down to allow a gap to form between the ferrel and band. This in turn will allow you to shim up like Art suggest, as it gives you room to work with.

Check your stock up front and make sure the top of the ferrel is level with the stock, and not sticking up.

Check your op rod guide and make sure it is not sitting, and touching, in the bottom of the stock, you will see marks from this hitting during recoil. This is another good location to temporarily shim as you incorporate draw pressure into your rifle, then work your way back to the forward receiver bevels, legs, and heel fitting.

Check the front of the receiver at the bevel locations, forward of the bolt stop, and opposite side for good, shiny, and even contact, of your receiver.

Copterdoc brings up a good point about the heel of the receiver contact, but, when he made his statement, it wasn't absolutely clear saying "at rest", whether or not that meant, locked in by the trigger group. When locked in by the TG, a crack is undesireable for me at the heel. The more contact, the more stable, although, this contact must be the right amount of pressure. It shouldn't take a cheater pipe to bend the trigger guard down and latch it.

If there is no gap at the bottom of the receiver legs, between them and the stock liner, you will be able to do nothing with the front receiver beveled edges for adjustment, period. There will be no fulcrum effect either, to work with for draw pressure. You will have to build up under the front of the receiver on each side, so that when locked back down, the receiver legs and the heel, contact correctly and with the right amount of pressure.

This is very difficult to explain how this symphony should work together, but is much easier to show someone in person. I hope I didn't just confuse you more, and that some of this will help.

 

[GDavis]

Ripsaw AND M1Aallthe way---Wow, great info.

The gun is an early SAI (1982 I believe (serial 0224##)). I have several stocks for it. It is in a USGI synthetic stock now, but I have two USGI (one birch and one birch E2) and the one that came on the rifle (I admit the original SAI has not been in that for years and I need to check it). Stock ferrules (well-synthetic stock does not have a metal one) are all even with the top of the lower “hang guard/stock” on all.

I’m starting to get this all clear in my head (thanks to everyone). I am still unclear on why if the stock ferrule is tight in the front band, logged between the front band tabs on the top (that hold the upper hand guard on), and the bottom of the front band, why it would be good to have any gap. I understand why upward pressure may be good, but I would think it would be better not have any gap where you can feel it. This is what I think I have. I realize (if I'm careful!) I can bend the "tabs" so that there is some gap, but want to be sure there is a reason before I do so. I know if I break a tab I can just get anotther (being sure it is USGI) front band.

Also, if all this is about so the ferrule returns to the same position in the front band after each shot, why did they not build in a groove in the front band and a ridge in the stock ferrule so that the two would be locked together?

 

[M1AallTheWay]

...Also, if all this is about so the ferrule returns to the same position in the front band after each shot, why did they not build in a groove in the front band and a ridge in the stock ferrule so that the two would be locked together?

Well, actually they do, it's just kind of wide. The tension we're talking about serves at least a couple of purposes. When you shoot, the barrel will whip around (these high speed videos make the point well). Especially in rapid or automatic fire, the barrel is still in motion at the next shot, which screws up accuracy, so the tension on the barrel tames the movement. Secondly, because of the stuff hanging off the barrel, it can't truly be floated like a bolt gun or gas impingement AR. The curve of the front band lip and the curve of the ferrule match, and with that tension applied, the two curves are pulled together since when they align, the tension is at a minimum. IF the receiver is secured in the stock by bedding or a very tight fit, neither will move relative to the other, so the ferrule end of the stock always presents the same position for the front band lip (and the barrel attached to it) to return to, and it's the tension which provides the encouragement to do that.

 

[GDavis]

Understood, and makes sense.

But- I still question that there has to be a gap so when you press the front band and the lower stock together, you feel the pressure and see some movement. Would not a tight fit of the stock ferrule and the front band do the same thing (dampen any vibrations)(assuming there is upward pressure)?

Since all of my stocks are the same way, I'm going to mess with the tabs on the front band holding the upper handguard in place. If I bend them upward, then I might be able to get a little gap. I just want to be sure it's needed before I do anything.

I know if I break it a tab I can get a new front band. Luckily, I have a castle nut pliers from my shimming the gas cyl and front band!

And please don't ask me how it shoots now- I'm WAY beyond that (meaning it does not matter)-- it's now a quest to get this right :O)

 

[M1AallTheWay]

Understood, and makes sense.

But- I still question that there has to be a gap so when you press the front band and the lower stock together, you feel the pressure and see some movement. Would not a tight fit of the stock ferrule and the front band do the same thing (dampen any vibrations)(assuming there is upward pressure)?...

The gap is there because the barrel is going to whip regardless and this way it has some breathing room. More important, the curve of the front band lip means that if the barrel is to move sideways during its whipping, it's got to follow that curve, thereby temporarily increasing the tension (if the stock and its ferrule stay put, as the ferrule rides up the curved side of the lip, the barrel is bent slightly down [the stock will likely bend up a bit too, but either way, the tension increases]). That self-centering couldn't work if the parts were locked together. And a side benefit is that by squeezing, you can feel the tension if there's room to squeeze.

BTW, what I think Art was describing was a way to allow the barrel to establish its rest position and then let the front band adjust itself to that before locking the front band and the GC together. The self-centering works best if there's no sideways tension caused by a misalignment of the ferrule and front band lip when both are at rest without interference from the other.

 

[ripsaw]

Ripsaw AND M1Aallthe way---Wow, great info.

Also, if all this is about so the ferrule returns to the same position in the front band after each shot, why did they not build in a groove in the front band and a ridge in the stock ferrule so that the two would be locked together?

This is a good question, and shows you are thinking real well about it.

I am now working on a modified barrel band that is a full U shape and goes all the way up to the top of the ferrel on both sides, making a cradle of sorts.

Although they will not be service rifle legal unless we can get the CMP and NRA and others to change their rules. But as for bench shooting, or military applications, it should be the best for accuracy.

M1A's is correct, trying to shoot this rifle without some give, up front between these two parts, would most likely split the wood , given enough time, or dent the parts up like where mine is banging against each other... Like trying to tame an untameable Lion.