Adjustable Gas Block?

[ricsmall]

Just curious- how does clamp vs set screw affect accuracy?

+1 on that

[Drifter]

Just curious- how does clamp vs set screw affect accuracy?

Here's a excerpt from by Robert Whitley (a very respected builder of precision uppers):

You want a gas block that does not impose pointed stress on the barrel. Clamp-on types that grab all the way around the barrel are excellent. The blocks that are pinned on with tapered pins that wedge against the barrel or the slip on type of block with set screws that push up from underneath (or directly on the barrel) can deform the bore inside of the barrel and can wreck the accuracy of an otherwise great barrel.

Link to source: http://bulletin.accurateshooter.com/...ffers-answers/

And from Mr. Whitley's website:

The best gas block for accuracy work is clearly the clamp-on type. It provides the least amount of stress on the barrel, while at the same time providing the best seal to contain all gas in the gas system. All our accuracy upper build ups are made with clamp-on gas blocks. In addition clamp-on gas blocks are also the easiest to install, adjust and remove so that the initial set up and any later servicing of the rifle or the gas system can be accomplished easily and quickly with no special tools.

Link to source: http://www.6mmar.com/Benchrest_AR.html

Coincidentally, Mr. Whitley designed a 6mm wildcat based on the Grendel case.

[txgunner00]

Interesting. Makes sense in theory but I don't know. Can little set screws really impart that much force to deflect a tube many times thicker than the diameter of the screws?

[Drifter]

Interesting. Makes sense in theory but I don't know. Can little set screws really impart that much force to deflect a tube many times thicker than the diameter of the screws?

It doesn't mean that an accurate weapon cannot be built using a gas block with set screws, but perhaps that the odds are a little better with a clamp-on style. That man's reputation is on the line with every upper that goes out the door (many of which are used in competition), so he likely tries to eliminate potential issues.

[Bwild97]

Interesting. Makes sense in theory but I don't know. Can little set screws really impart that much force to deflect a tube many times thicker than the diameter of the screws?

I think it could be possible in an ultra lite barrel, but not on a heavy or bull barrel. This could be the reason behind the AA barrel profile with a .906 dia. gas block land.

[Tailgate]

In addition to what has already been said...think of the barrel harmonics during a shot. Do you want the ripple or "bubble" to hit an object that is uniformly clamped around the barrel across the object's entire surface area...or do you want it to hit an object that is tightly secured at a single pin-point (2% of surface area?) with varying resistance around the remaining surface area? Why do you want a "free floated barrel?" It's because you don't want the harmonics being distorted by inconsistent surface tension on the barrel (the stock, the handguards, etc.).

As mentioned, doesn't mean you can't design a highly accurate gun with a set screw gas block...but your are more likely to do so with a clamping gas block.

I'm no expert, and in the past I have somewhat laughed about "harmonics" of a barrel. But there is plenty of scientific evidence around barrel harmonics. One day I had a mini-revelation when a mechanic friend was talking about this: Sometimes, the bass subwoofer in a car that is cranked up can negatively affect the way the engine of that vehicle runs (you know the ridiculously loud vehicles cruising down the street) due to certain frequencies in the music. Don't forget, musical notes are simply vibrations at certain frequencies. If it can affect a combustible engine simply with sound waves, think how much more a bullet traveling inside a vibrating barrel and exiting that barrel with a sound-barrier breaking pulse can affect the accuracy of that 150 grain projectile. I don't know if the one has anything to do with the other, but it made an impression on ME as far as harmonics are concerned.

[Tailgate]

Interesting. Makes sense in theory but I don't know. Can little set screws really impart that much force to deflect a tube many times thicker than the diameter of the screws?

Can a small willow tree branch barely touching the surface of a river change the ripple pattern of thousands of tons of moving water? Have you ever used a musical tuning fork? If you thump it to let it ring, if you touch the tiniest tip of a pin onto it, it will change the sound because the harmonic vibrations are being slightly diverted. Same thing if you have even a tiny chip or dent in the fork...that seemingly insignificant defect alters the uniform pattern of the vibration.

[txgunner00]

Hmmm...(scratching chin). Learn something every day.