Another Front Band Question

4137 Views 41 Replies 13 Participants Last post by M1AallTheWay, Jan 26, 2011

Discussion Starter · Jan 23, 2011

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) )

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bunsen27

· #28 · Jan 25, 2011

(raises hand) I'm still confused.GI3

I have a standard SIA circa 1994 in a SIA synthetic stock. I have 1/16 in clearance all around the sides of the stock ferule and front band except at the front band lower lip. I have shimmed the gas cylinder to the front band so that the gas cylinder lock is snug at 5:30 and can be thumb tightened to 6:00. Grasping the top of the barrel and squeezing on the bottom portion of the stock yields about 1/16in of movement with minimal pressure (thumb and index finger) until it contacts the upper potion of the front band. The hand guard is not touching the stock until I squeeze up on it. The trigger group in this stock locks up extremely tight (it's a bugger to cam over and lock) and there is no gap at the heel of the receiver even with the trigger group unlocked.

I have been trying to improve the 2.5MOA groups the gun is shooting by installing a Sadlak NM guide rod and gas piston. I've gather from reading this thread and others that one issue may be the fit in the stock. I've relieved the stock somewhat in the front where the gas cylinder was rubbing. Any help or suggestions would be greatly appreciated. I can post pictures of specific areas if that would help. Thanks.

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bunsen27

· #31 · Jan 25, 2011

M1AallTheWay said:
One simple way to check for that tight fit is to grasp the GC with your fingers, with your palm resting on the stock and ferrule. While watching the heel as it rests on the stock (focus on wood grain or paint imperfections), push the ferrule area sideways with your palm. If the fit of the receiver in the stock is not tight, you'll likely see the heel move over the stock. That's what bedding is intended to eliminate.

Thanks for the feedback. What would the status of the TG be for this test? Locked in or just cammed over?

As I mentioned previously the TG on this rifle locks up extremely tight so I'd be surprised if the heel was able to move with the TG locked in. However, I've been wrong before.

I'll check it when I get home this evening and I will try to post some photos to go along with my questions.

My reason for originally posting is that "I think" I don't have enough tension on the front band/stock ferule. I did read the entire thread on shimming with the metal flashing, but am uncertain if that is an option with the already tight locking TG.

Ultimately I am going to put this rifle in a JAE G2 stock, but until I save up all those pennies I'll continue to tinker and learn about this platform.

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bunsen27

· #41 · Jan 26, 2011

M1AallTheWay said:
The test would be done with the TG locked up. (BTW, an easier way to lock up is to use something like this to pull the heel down on the stock before you close the trigger guard.) The basic idea is to prevent the receiver from rotating sideways in the stock, even a little bit. Unless it's rear or double lugged, the only parts of the receiver that are in contact with the inside surface of the stock are the outer faces of the receiver legs and the section just forward of the legs. If the fit there isn't extremely tight, a small amount of rotation is possible (which is what the test of movement of the heel over the stock is designed to disclose). And if there's a little rotation at the receiver, imagine how much displacement there is way down at the end of the stock/barrel contact point (front band lip/ferrule). The tension intended to guide the barrel back to it's rest point on the ferrule would be guiding it to a different place every time, not a good thing.

Even if the heel is really tight against the top of the stock, if there's some slop between the legs or the section forward and the stock, you can still get a bit of sideways movement there and a lot at the ferrule.

Using shims to raise the heel even further off the stock would make locking up even harder or maybe impossible. But using the "L" shaped shims just inside the stock would tighten the fit without tightening the lockup. In any case, thinking of that tension as part of the "see-saw" motion has the ferrule end of the stock being pulled down (creating tension) as the back end of the stock is pulled up to meet the heel. Since that's what's happening to you, I bet you've got the tension, just not the clearance so it can be demonstrated or operational.

I think the light bulb just lit over my head reading your explanation and re-reading the shimming thread. I may even have comprehension. Thanks for the detailed explanation.

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