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Discussion Starter · #1 ·
Following all the responses generated from this Post has been fun, I've learned many things, most of them about the proper rifle position when shooting off the bench.. Bamban, send pictures, please

The other part of this discussion about Dwell time and after effects on the bullet from the gas are also interesting. i have to admit, I know little about gas effects on the bullet once it leaves the muzzle, but I do know something about the atmosphere that occupies the space in the barrel in front of the bullet. We called this moving atmosphere "The Cursor Wave", that was an in house term..

This contained atmosphere is pushed forward rapidly as the bullet advances down the bore, some of that atmosphere transfers into the gas Cylinder, more than you would suspect and with more force than you would expect.. This force starts things moving, and the bullet is still in the bore, this may surprise some you, but enough movement to start things happening in the rearward movement of the piston, and since it is under some pressure from the Opt Rod, everything behind it is affected in order... This is where a longer Dwell helps things go more smoothly.

The longer Dwell time keeps the bolt from moving sooner than Short Dwell time, more like a bolt rifle, and that is what we want, we being the Bench Shooter, maybe some of you real shooters also....

Back to the early piston movement cause by the atmosphere being forced into the Cylinder {Cursor Wave This unwanted early movement can be, to some extent, curbed by adding a modification to the gas Cylinder. This Modification provides a means to relieve some of the atmosphere that lives in the gas cylinder.. yes, there is space inside the cylinder, that atmosphere has to go somewhere also when things get hot and moving very fast..\

It all depends on how tight a Ten Shot Group you want.

Is any of this clear??? Art
 

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Art, as I recall the mod to the gas cylinder that you mention is a small (1/16"?) hole drilled near the back end of the cylinder. I have been meaning to try this mod, but it slipped my mind. Now that you've reminded me, I'm going to get 'er done!
 

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Does the groove in the national match piston have any role in offsetting this Cursor Wave? Does it influence dwell time? Or does it serve an unrelated purpose?
I did it to mine with a dremel, changes ejection pattern to 3 o'clock and they land about 6ft away. It could be altering the dwell time or it could just be reducing the physical force the piston applies to the op rod. Recoil does seem to be reduced a bit.

A hole drilled in the gas cylinder itself would probably do the same thing as would using a vented gas plug.
 

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Does the groove in the national match piston have any role in offsetting this Cursor Wave? Does it influence dwell time? Or does it serve an unrelated purpose?
I think the original purpose of the grooved piston was too vent pressure from the gas cylinder and piston so the op-rod was pushed too the rear not slammed, does it offset the Cursor Wave and influence dwell, sure anytime you enhance the ability too bleed off pressure faster or continually would be a accuracy enhancement provided the rifle still functioned. Now how measurable it is would be hard too prove or disprove. I know when I installed my grooved piston I wasn't thinking about "Cursor Wave" I wanted less/softer felt recoil and the barrel too stop thinking it was a springboard from the G/C venting on and off.


Art, as I recall the mod to the gas cylinder that you mention is a small (1/16"?) hole drilled near the back end of the cylinder. I have been meaning to try this mod, but it slipped my mind. Now that you've reminded me, I'm going to get 'er done!
Its done in the trapang groove, and I don't know of any accuracy claims with this mod. But I did mine and I just fired 80rds this last Sunday. I can tell you my piston is still clean, all the trash/carbon that's clings too the inside of the piston and that tell tail carbon burnt ring near the pistons hole gets blown out of the stocks weep hole, looks like I fired less than 20rds. The inside of the stock and the underside of the barrel is much-much cleaner.
 
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Discussion Starter · #12 ·
venting the Plug?

So would a vented Cylinder plug do the same as the small drilled hole?
No it does not do the same thing, at least not in the same direction. The drilled, or vented Plug relieves the gas/carbon and pressure at the front end of the cylinder,. The hole under discussion, in the rear of the cylinder, at the bottom of the cylinder, it is drilled into the Trapan grove... This hole{vent] allows the atmosphere and on rushing gas to vent out and down from the rear of the cylinder. This improves the removal of carbon build up in an area that is somewhat difficult to clean..

A clean cylinder will be more accurate than a dirty cylinder and Piston.. It is important that the Piston moves freely to function properly and a proper functioning Piston will aid accuracy.. Art
 

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Could you pull this mod of with a drill press and a vice or is that not going to be precise enough? I found the dimensions for the hole and the location from the back of the gas cylinder on another website and am wondering if it would be worth trying.... any thoughts?
 

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Could you pull this mod of with a drill press and a vice or is that not going to be precise enough? I found the dimensions for the hole and the location from the back of the gas cylinder on another website and am wondering if it would be worth trying.... any thoughts?
I did mine with a center punch and a sharp Tin coated drill bit in a hand drill using a vise, its so clean it looks like it was burnt thru with a laser.
 
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