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Discussion Starter · #1 ·
If you have not read Gus's contribution on the Dwell issue take a look, this is one of his best. Thank you Gus.

I think it is now safe to state, the bolt does not begin to rotate before the bullet leaves the barrel. That's good news. There is still the issue of other parts moving however.

The piston does have movement to the best of my knowledge. If the piston moves to the rear any GIVEN amount, so does the rod, the spring has compression and the spring guide is further under load. This small rod movement may have some effect on the receiver.

The more movement that can be eliminated the better the chance of accuracy. That is a fair statement, given what we know about accuracy.

At this point, the data indicates the piston movement can be slowed down. The question is, how much before function becomes an issue. I have gone too far all ready, so I will back up my efforts a little at a time and perhaps the correct combination will result in success.

Any measure of success is a worth while venture in my camp, for those that have rifles that group, 5 shots, in the 2 to 3 inch range any improvement would be welcome. I have one of those rifles, so off to the range tomorrow for another go.

All the test are with loads using 168's close to the 2550 fps vel. Other loads may result in different results. Art
 

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Hi Art and thanks for all your r&don this subject. Can I ask a question without sounding like a newb? Would one of the adjustable gas plugs do the trick to bleed off gas? If you turn it all the way down to the point that it just operates the action would tuis still be to much gas?
 

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Hi Art and thanks for all your r&don this subject. Can I ask a question without sounding like a newb? Would one of the adjustable gas plugs do the trick to bleed off gas? If you turn it all the way down to the point that it just operates the action would tuis still be to much gas?
Don't mean to answer for Art, just throwing my two cents in. Using an adjustable plug would slow down dwell time up to rather dramatically. However, you still have that hole going out of the plug into the open air. That's not a problem for civilian use, but for military or police use, I would prefer not to have a hole that would allow "junk" to get into the Gas System.
 

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Discussion Starter · #5 ·
Hi Art and thanks for all your r&don this subject. Can I ask a question without sounding like a newb? Would one of the adjustable gas plugs do the trick to bleed off gas? If you turn it all the way down to the point that it just operates the action would tuis still be to much gas?

That's a good question.. The bleed off method just does not sound like it addresses the same issue. I'm speculating, but the bleed off begins too late, maybe during. either way this does not sound to me like it has much to do with introducing less gas initially. Less gas would also bleed off. I have never heard of the vented plugs contributing any thing other than allowing heavy bullets or heavy loads to be fired without damage to the rifle, MAYBE.... I fooled around with making vented plugs years ago to no contribution to accuracy.

Dwell time is a term we should all be on the same page when discussing it. My definition as it applies to the M1A : Control the induction of gas into the cylinder to allow the bullet to exit the barrel before the piston begins rearward movement.

It is important to remember the force of gas entering the piston has in itself, a strong downward force. This force causes a similar action at the muzzle since it is all one unitized system... The AK 47 has a pronounced downward movement that can be seen from the side...
M1A shooters will have to live with this.

Any reduction in early piston movement will reduce movement in the rifle. That is my contention regarding the entire issue. Others may feel differently or just don't give a squat.

If nothing else, I feel these kinds of discussions on the Forum are the essence of why we have it. It requires people just like yourself to question and offer alternatives to advance a common interest, There are not many of us, keep involved. Art
 

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I'm not a gunsmith nor do I have a lot of experience working on non-functioning, or malfunctioning M1A's.

I have bought a Schuster adjustable gas plug for my M1 Garand, and I like it. I've not really done a lot of shooting without it (I put it in and it works and I don't want to "mess with it") in my "shooter" rifle but the rifle is a good shooter. A good enough shooter I've had folks ask me if it has a "match" barrel on it (and I mean experienced shooters, not just folks at the range).

It takes a certain amount of gas pressure to operate an M1 or M1A. Some may be a little smoother/slicker than others and operate slightly easier but I doubt I could measure/feel a difference when fired so can we rule out such differences?

The adjustable gas plugs, especially the Schuster since it can be adjusted "infinitely" rather than by removing/installing different sized ports/bleed holes, allow you to "tune" the rifle's gas system. You can "tune" it to allow the use of heavier bullets and slower burning powders that might otherwise result in pressures above the normal and safe gas system pressures for the rifle. The instructions that came with it said it might also result in your being able to set the system up so that an increase in accuracy is realized. How would it do that? Maybe by bleeding off excess gas pressure over and above what it takes to actually work the rifle? If the bleeding takes place immediately then it may take slightly longer for the piston to begin to move (if microseconds are important then bleeding off gas that would normally build up faster may slow it down).

My only reason for getting one was to play with heavy bullets and IMR4350 powder (which I haven't done yet) based on resluts I saw in M1A many years ago (in which I broke the op rod twice).

Ideally, a system needs to operate within a certain pressure range, but not begin to operate (if its operation is detrimental to accuracy) until after the bullet has left the barrel.

I really believe one of the keys to accuracy is consistency. Watching the videos of the barrel flexing when the rifle is fired just amazes me and makes me believe in more that if you can get all that moving, whipping, vibrating, etc. to repeat consistently you'll have greater accuracy.
 

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...Dwell time is a term we should all be on the same page when discussing it. My definition as it applies to the M1A : Control the induction of gas into the cylinder to allow the bullet to exit the barrel before the piston begins rearward movement...
I'm sure I'm just stating the obvious but another way to do that it to shorten the barrel, such as on the Scout. You also get less barrel whip, judging by the high speed videos. And watching the one with the full size barrel at double size and advancing it by hand frame by frame, as the gas just begins to exit the flash suppressor, the op rod seems to move up before it starts moving back (and, no, it doesn't seem to be just the result of recoil).
 

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Art,

I have to politely disagree about bleeding off the gas not being associated with dwell time.

I'm not sure which gas law pertains, but when the size of the container you are trying to fill with gas is increased (and the gas pressure coming into the container remains basically constant) the longer it will take to fill the container. That's why a gas plug with a larger inside hole will take longer to fill and thus increase dwell time.

Now when you open the hole to the outside atmosphere, as in a vented gas plug, the gas pressure has to try to fill up both the inside of the piston and gas plug - but it is also trying to fill up the outside atmosphere. It won't fill up the outside atmosphere as fast as the inside because the hole going outside is smaller. Still, that will slow down the piston moving as you have less gas pressure that is operating on the piston. Hence, slower dwell time.

Best Regards, Gus
 

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Discussion Starter · #9 ·
I like disagreements.

Gus, I agree with the first paragraph, larger requiring more gas.

The second paragraph has me somewhere else. Filling the cylinder up with a hole in one end takes more gas and longer to fill, if it ever fills. But does this combination keep the piston from moving?

The difference between your position and mine is: The vented plug will take longer to fill the space, I am suggesting it would be more valuable to control the gas flow before it gets into the cylinder.

Maybe the results are the same, I don't know. I do know accuracy was not improved using vented plugs.

Are you having a White Xmas in VA. Pull up one of the big dogs and stay warm... ? art
 

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Gus, I agree with the first paragraph, larger requiring more gas.

The second paragraph has me somewhere else. Filling the cylinder up with a hole in one end takes more gas and longer to fill, if it ever fills. But does this combination keep the piston from moving?
OK, now I think I understand. Don't know if it would stop the piston from moving at all, but a large enough hole will not allow enough gas to fuction the rifle as the piston would not receive enough gas pressure in that case. Any hole size up to the size where the rifle barely functions will slow down the time it takes to fill the gas chamber and start the piston moving with the larger the size slowing down the time it takes to fill the piston, though. That would mean the dwell time is more as the size of hole is increased. Of course, we are talking microseconds.........

The difference between your position and mine is: The vented plug will take longer to fill the space, I am suggesting it would be more valuable to control the gas flow before it gets into the cylinder.
It may and I'm not sure about that without extensive testing. I think it could be better. So let me say, "I just don't know."

Well, come to think of it, maybe so indeed. We used to order our barrels with no gas port drilled. Then we centered the hole in the gas port by drilling through the spindle valve hole to mark the hole. Then we used smaller diameter drill bits to drill the gas port. Number 48 was the smallest size the rifles were pretty much sure to function properly. So you probably are onto something there.

Maybe the results are the same, I don't know. I do know accuracy was not improved using vented plugs.
I personally have never used them as I stick to Mil Spec ammo. I've had some customers say they did not experience a loss in accuracy BUT the rifles were being used for hunting loads and I don't believe they really tested and measured the group sizes. Might definitely need a different piston to get them to shoot well with the adjustable plug. Again, I don't know for sure.

Are you having a White Xmas in VA. Pull up one of the big dogs and stay warm... ? art
That's a nice way of saying we have snow up to our rear ends. Especially for Virginia. Grin. We have about 14 yo 16 inches on the ground right now. Largest amount of snow since 1908. I stocked the house on Friday and have not tried to leave yet. Don't need to get anything and don't have anyplace I have to go, so I'm staying put. There are too many idiots out there driving foolishly and the numbers of fender bender accident have been rather amazing, even for folks who don't know how to drive in snow.

No problems with heat, though if there were, I have three 55 lb Collie girls who would love to snuggle in bed with Daddy, if needed. I can officially make it a "Three Dog Night" anytime I need to. Grin.

Thanks for asking.
 

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Just how far is the bullet down the bore before things get moving?? I don't need too know excatly just a Idea where?

I have 1 of the old Schuster bored and vented plug with a 1/64th hole in the end for a larger expansion chamber 58%, the bores hole is apprx .40in wide X 1.5in deep. On average 2600psi less pressure on the op-rod reducing bolt wear and movement. That's the claim from Schuster.

I have tried this plug on the range and while it did little for the accuracy of the rifle the op-rod did feel like it started to run later durring recoil the amount of recoil was the same, I also have a grooved piston that makes the op-rod feel like its pushed to the rear and not slapped to the rear felt recoil in/out of battery is less noticable. Trying too compare the plug vrs the grooved piston is hard but they are very differnt I hope this helps. The grooved one shoots the smaller groups and the rifle feels softer so that's the one that stays in the rifle.

I measured a used/spare piston I have and its .497 thick the hole is .318 wide X 1.556 deep before the tail, I was thinking about making the bigger hole .4 and going 1.5 deep, while its not the same as 58% of the Schuster plug it is a increase none the less, mabe add a groove as well sort of a combo/hybrid piston.
 

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Discussion Starter · #12 ·
Bullet , how far

Hey Phil, Excluding the recoil and possible effects, the bullet is somewhere past the barrel gas port, but according to all I can find out, it is still in the barrel to some degree. Is that vague enough?

It is for this reason I am trying to find a method to have the bullet gone before any movement occurs much like the Garand, or close to it..

Arizona 28 Neb, 14 .....Art
 

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Grand and M-14

Art,
From what I have read about the development of the M-14 they moved the hole back because it didn't make that much different in dwell timing because of the different gas systems. Also have you played much with just turning off the gas system and shoot a few groups and then turn it on and shoot a couple more groups. There was also a time when they put a pencil on the front site of a Grand and it caused a big difference in POI. When you turn off the gas system the POI changes but the groups stays consistent. All I can say is keep thinking and playing because that is what brings advancement. The information is from the book The M1 Grand To The M-14 by Stevens
 

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I have been following this as all of this is fun to wrap your head around.

In gas operated rifles, there are two ways to reduce the effect of the gas entering the system without changing the port size.
1) vent off the energy that is not needed......or
2) increase the volume requiring more time in miliseconds to do the same work.
The work required to overcome the op-rod spring, friction, move the mass of moving parts, then store this energy and use it to reset the system is required, and it wasn't easy to get to this point. Since every rifle is different, slight variations in the amount of energy needed leaves some room in standard parts to be tinkered with, or redisigned. This tinkering resulted in the domination of the AR in service rifle, and may keep the M14/M1A competitve in the future. It is a nobel cause.
The Idea that there is a pressure wave ahead of the bullet as the static air column is forced down the barrel is an interesting phenomenon. This may explain why just increasing the volume of the gas system doesn't have the same tuning effects as the same technique in the Garand, as this energy is preloading the system above atmospheric pressure before the projectile gets to the gas port.
What if we use this energy to hold everything still with another chamber, and port working in the other direction ? Could we seal off the working port with the piston but still allow enough venting to get it started at a later time ?
It may be possible to use this in combination with other dwell increasing measures to do just what Art is talking about. That is keep everything from moving untill it can no longer effect the accuracy of recurring shots.
I'm with you Art. This is effective brainstorming.
 

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Discussion Starter · #16 ·
Interested parties, READ THIS.

Fick USMC has provided us with a valuable piece of information, please take a moment and read his well thought out message....

"The pressure wave ahead of the porjectile {bullet** pre loads the system......

Fick USMC is on to it, good stuff.. Art
 

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Fick USMC has provided us with a valuable piece of information, please take a moment and read his well thought out message....

"The pressure wave ahead of the porjectile {bullet** pre loads the system......

Fick USMC is on to it, good stuff.. Art
Never thought about that much and yes it is very interesting. I am not at all sure how much it preloads the system, though, as the piston doesn't start moving until the bullet is very near the muzzle. This last from actual XRay high speed photography of the M14 system.
 

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No doubt the bullet moves some air. Resistance to movement results in pressure increases. The barrel has a small amount of air in it and large vent hole (the muzzle). Air (and lots of other stuff) uses the path of least resistance and while the path to the muzzle is large and straight the path to the gas cylinder is small and has a 90 degree turn in it. Firing a cartridge with no bullet in it will not operate the gas system (that's why I got me a handy dandy blank firing attachment) because with no bullet between muzzle and the gas port the pressure follows the path of lease resistance right out the end of the muzzle.

I wonder if anyone has ever measured the increase in pressure in front of the bullet?
 

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No one has speculated that this column of air does any work of moving anything, but only that some value of pressure is added to the gas system from this phenomenon. If the gas port is open to this pressure, it is safe to say that some portion of this air does act to fill the volume that we increased in the gas system. The closer this port is to the end of the barrel should reduce this effect. This is why it is a non issue with Garands, and possibly a benefit to how they operate.
If we are trying to increase dwell in the M14 by increasing the gas system volume, this phenomenon may decrease the effectiveness of this effort as it preloads it with non working pressure ahead of the bullet. This effectivly giving the gas system a head start no matter what the volume is.
A super long plug with the abilty to adjust from standard volume out to a very large volume could be rigged up. It could also have telemetry to plot a pressure time curve on a graf. We could then give a value to all pressures working and non working.

I am unemployed. My mind has nothing else to do . LOL
 

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Pressure is like electricity it tends to go toward the path of least resistance. Having said that nature will always try fo fill a void. If the pressure in the barrel preceeding the bullet is above the atmospheric pressure that is in the cylinder some of that pressure will find it's way into the cylinder until they equilize, thus "preload" is possible. Now my head hurts.
 
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