Ruger SR 556 or Colt 6940 ?????

[synergy]

Good to know because I might be planning on an SBR in the near future.

it's more for the suppressor than the shorter barrel.

Short barrels tend to need MORE gas, but put a can on there and that changes dramatically.

An adjustable gas block might be the ticket, if your going shorty and thinking about a can. Pistons are an option too...but as you can tell, not without trade offs.

[d90king]

it's more for the suppressor than the shorter barrel.

Short barrels tend to need MORE gas, but put a can on there and that changes dramatically.

An adjustable gas block might be the ticket, if your going shorty and thinking about a can. Pistons are an option too...but as you can tell, not without trade offs.

Pretty sure that was the thoughts behind Noveskes switch block...

[mojo]

it's more for the suppressor than the shorter barrel.

Short barrels tend to need MORE gas, but put a can on there and that changes dramatically.

An adjustable gas block might be the ticket, if your going shorty and thinking about a can. Pistons are an option too...but as you can tell, not without trade offs.

I would definitely hope to have a can for it, so the adjustable gas block sounds like the way to go.

I will stop hijacking this thread

[Guns4Fun]

So what makes the piston better for SBR/suppressor over the DI?

I have a colt 6933 (11.5") with a can on it. I'm not sure if you shot it at the zrt shoot or not. I bought a gas buster charging handle for mine - it works wonders for keeping the gas out of your face. The other problem is that there is a great deal of carbon build up on the bolt - after shooting 500 or so rounds, you literally need to scrape it off. Since a piston upper does not put gas into the BCG it would run cleaner and you wouldn't end up with gas in your face.

Also, i have not noticed anuy excessive wear to the gun from shooting it suppressed. God only knows, i check it often - it's my baby.

[Legion_Prime]

it's more for the suppressor than the shorter barrel.

Short barrels tend to need MORE gas, but put a can on there and that changes dramatically.

An adjustable gas block might be the ticket, if your going shorty and thinking about a can. Pistons are an option too...but as you can tell, not without trade offs.

The can is still going to beat up an SBR even with the piston as it's still overgassing that system that normally uses a short sharp pulse to cycle. A variable gas block is going to do as much for extending the life of an SBR as a piston will.

I have a colt 6933 (11.5") with a can on it. I'm not sure if you shot it at the zrt shoot or not. I bought a gas buster charging handle for mine - it works wonders for keeping the gas out of your face. The other problem is that there is a great deal of carbon build up on the bolt - after shooting 500 or so rounds, you literally need to scrape it off. Since a piston upper does not put gas into the BCG it would run cleaner and you wouldn't end up with gas in your face.

Also, i have not noticed anuy excessive wear to the gun from shooting it suppressed. God only knows, i check it often - it's my baby.

There will be if you haven't noticed it yet. Here's a good timeline for parts replacement on a suppressed SBR.

Start out with a stock action spring and H Buffer.

1K replace extractor
At 1500/2K install an H2 Buffer and replace extractor

3K replace Complete Bolt
4K extractor, possibly heavy Duty Action Spring
depending on how the gas port looks, using a borescope.

At 5K I would replace the barrel and Hammer/Trigger springs and pins at a Min. and then you can go back to the H buffer and standard stock action spring.

Adjust as necessary to your own weapon and you should be running it for a good many years to come

[Guns4Fun]

There will be if you haven't noticed it yet. Here's a good timeline for parts replacement on a suppressed SBR.

Start out with a stock action spring and H Buffer.

1K replace extractor
At 1500/2K install an H2 Buffer and replace extractor

3K replace Complete Bolt
4K extractor, possibly heavy Duty Action Spring
depending on how the gas port looks, using a borescope.

At 5K I would replace the barrel and Hammer/Trigger springs and pins at a Min. and then you can go back to the H buffer and standard stock action spring.

Adjust as necessary to your own weapon and you should be running it for a good many years to come

Really? Where are you getting this info from? This has been my go to gun for the last 3 years. It has at least 3k rounds through it ( i don't count the rounds but i usually shoot 1k a year) and I have not had any problems or seen any excessive wear. The only time i've had any failures is when they were self induced, to practice clearing drills.

There is absolutly no excessive trigger / hammer pin wear and the only thing that is ever noticable is the carbon build up on the bolt but after cleaning everything is good as new.

I was going to wait until 5k to even think about replacing just the extractor spring / insert.

[Legion_Prime]

Really? Where are you getting this info from? This has been my go to gun for the last 3 years. It has at least 3k rounds through it ( i don't count the rounds but i usually shoot 1k a year) and I have not had any problems or seen any excessive wear. The only time i've had any failures is when they were self induced, to practice clearing drills.

There is absolutly no excessive trigger / hammer pin wear and the only thing that is ever noticable is the carbon build up on the bolt but after cleaning everything is good as new.

I was going to wait until 5k to even think about replacing just the extractor spring / insert.

1K rounds a year comes out to about 3 rounds a day. Most of the people I get my information from are .mil, PMC's or agency armorers. Shooting semi auto you can extend these round counts a good deal. However the intervals are not to replace when there is wear, but to do so before there is any wear. Today an SBR is a commodity, both in time (I think the wait time is up to 3-4 months now?) and money (Tax stamp plus engraving or premium on a factory SBR) and an aggressive PMCS schedule is not out of line. Unsuppressed firing will also extend these and separate buffers for suppressed and unsuppressed will also help reduce wear as a heavier buffer with a suppressor will help lower the cyclic rate and keep it from beating itself up as much. Like I said, there are many things that can affect this schedule which is for a hard run FA so use it as a guideline and adjust the round counts as appropriate.

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DI is Direct impengment which means that the gas is directed through a tube directely into the bolt. The carrier of the bolt acts as a cylinder and the back of the bolt acts like a piston. This built up gas will force the bolt carrier back which will cam the bolt counter clock wise with a pin conected to the bolt through the carrier. The piston design will either force the carrier back through several push rods that tap the carrier back or the carrier and op rod are one piece and as they travel back under gas pressure (or tapped or nocked back by a push rod) it will unlock by caming in the same why that direct impengment will. The benifits of direct impengment is a better balanced bolt because the pressure is equal to the center and is also lighter due to no op rod. If compared to gas system with several push rods it has fewer parts. You will find direct op rod bolts in M14's, Garands, and open bolt machine guns such as the M240, M249, and M60. You will find muliple rods contacting each other in a chain in the soviet designs. The down side the direct impengment is that you have to clean the bolt and carrier fairly often. Fortunatly it is mind numbingly easy to do so (it was designed to so). One more mention would be that the rifle was designed to be just that. A direct impengment rifle. The op rods and push rods when built sturdy ads alot of mass and the rifle was built stream lined. To built one that would be durable would completely change the rifle cosmeticly and would be a quit a bit heftyer gun. All the models that have been producted up to this point have worked but have not held up to the abuse of what a DI AR will take. The DI is not perfect, but why change a good thing. If you want a piston gas gun go by a M14, A fantastic gun in my opinion.

[adsstorm]

Just a heads up! A buffers sole purpose in life is to counter act a problem in AR's called carrier bounce. Being that the spring tension on the back of the buffer is the only thing keeping the bolt locked in the barrel extension when the carrier slams forward it has a tendancy to bounce back which happens in a split second. To counter act this the buffer has free floating weights inside that surge forward a split second after the full motion of the carrier has come forward and before it bounces back. So the differences in buffers will come in when your barrel is shorter, because shorter barrel means shorter gas tube and the shorter the gas tube the faster the cyclic rate of fire which in turn will change the timing of the carrier bounce. So word to the wise. Get the buffer that matches the barrel length. Their enginers at colt, FN, Knights that have full time jobs figuring this stuff out. Weather or not it has a can that creats back pressure is illrelivent. Once the bolt has opened the pressure is bleed off can or no can and the bullet passes the gas port hole at the same time peaking the pressure at the same time if you have a can or do not have a can. If you do not believe me throw a M4 buffer in a full length barrel AR and fire as fast as you can, auto if you can and see what happens. My bet is that the carrier will be out of battery when the hammer falls and it will hit the side of the carrier instead of the firing pin in the center of the carrier. giving you no BANG. NOTE: carrier bounce is mostly found in full auto burst, but can be replicated with quick semi fire.