Yes, I’m sure Stoner created the “GI proof” rifle in the hopes that soldiers would be kicking back, contemplating the nuances of the mechanics of its operation for decades to come.
One thing to check- Shoot your AR in the dark, if flames shoot out of the ejection port the spent case is being pulled out of the chamber while the bullet is still in the barrel and high pressure gases are exiting the chamber meaning the pressure is still high in the chamber, the case has not contracted from the chamber walls and at some point the extractor will fail due to excess stress from ripping the case out of the chamber. It doesn’t matter if the rifle is a DI or piston either can be over-gassed. If the carrier is moving while the bullet is in the bore it can effect accuracy.
No he designed the gun and it’s issued to GIs. Most people issued a gun have very little understanding of it’s operation and why it does what it does.
If you’re here to debate and discuss the design by all means do. If you’re here to be an ass your stay will be very short…last warning.
IMHO, stoner did NOT create a “GI PROOF” weapon. The AR15/M16 is much like the 1911. It is a great gun, but is not for everyone. A high IQ is needed in order to make this gun(s) run well.
C4
My entire reason for starting this thread was to ask the question, how do dedicated piston uppers deal with unlocking the bolt and extraction.
To my knowledge they just rip the bolt/shell out by brute force, where as a D.I. gun uses gas pressure to ease the unlocking of the bolt and provide dwell time to allow the case to cool for proper extraction.
What do piston systems like the HK416 employ to facilitate unlocking and extraction.
Has nothing to do with D.I. vs. Piston… this is a technical question
Both systems operate the same way, ie something is exerting force on the carrier. In a DI it’s the gas, in the op-rod design it’s the op-rod. Unlocking happens when the bolt carrier starts moving to the rear, and the cam pin follows the cam track in the carrier, thus rotating the bolt so that the lugs on the bolt does not align with the lugs in the barrel extention.
There is no forward movement of the bolt in either system.
Both systems incur wear on bolt lugs.
In my 4 years with the HK416 in service, I have not seen a single broken bolt lug…
There were some issues with the initial 416’s, with reports of bolt lug breakage after only 5000 rounds. That happened because HK used a dfferent metal and hardening process on the bolt. They switched back to the original process and metal, and now the bolts last a lot longer.
Well said Grant.
The M16Fow is certainly not GI proof. The system takes some knowledge to keep it running, thats why people who know the system will never have issues and the ones that dont will.
Some people think dry lubes are best for the M16 but if you know the system you will know it needs a good lube to run well.
Like Grant said, the M16 like the 1911 requires knowledge of the system to keep it running, and if you have that knowledge it will never give you troubles.
There is no way the expansion chamber will pressurize enough to start moving the carrier before the bullet can travel from gas port to muzzle. The distance from gas port to muzzle is shorter than it is from gas port to carrier. Also, if I remember correctly, the velocity of the supersonic gases drop to subsonic after passing through the gas port. In the race between bullet to muzzle and gas to expansion chamber, the bullet wins every time.
When you see flames coming out of the chamber, it’s for the same reason you see flames coming out of the muzzle. It’s the spent gases igniting as they mix with the oxygen in the atmosphere
The so called “piston” uppers actually work the same way as the Stoner system. Both use a piston and cylinder to turn the energy of the expanding gases into mechanical energy. The difference between the two systems is that the Stoner system eliminates the actuator rod and places the piston inline with the bolt & bore. The Stoner system may have a “softer” extraction as it’s expansion chamber (cylinder) has a larger volume. In either case, the bullet has long left the bore before the reciprocating mass has a chance to start moving
The bolt does not begin unlocking as soon as the carrier begins moving. The groove in the carrier which engages the bolt cam is straight for a short distance, then angles which delays the unlocking of the bolt
Arctic, your a bit off.
Don’t blame your armorer… they are constrained by the limit of education & most are lego assembling monkeys.
Look at where the piston is in the standard AR. In the middle of the bolt carrier. As gas goes through the key, into the chamber (within the carrier) it pushes in all directions.
- The bolt will be pushed forward and the carrier rearward… gas venting out the side holes in the carrier as the gas rings pass.
- as the carrier is pushed rearward the cam path unlocks the bolt, aligns it with openings in barrel extension
- momentum is keeping the carrier moving rearward.
The difference was very clear with early hk416’s which dug chunks out of the inlet, for the cam pin, in the upper receiver.
BTW the 416 can more correctly be referred to as a gas tappet, not oprod. Ala the G36 some of your countrymen use
There will be forces pushing forward against the piston/bolt, but not great enough to cause the bolt to move within the barrel extension.
1- The resistance to pushing the bolt forward is much greater than the resistance to moving the carrier rearward.
2- A round in the chamber usually fits snugly enough to take up any slack there may be between the bolt and barrel extension, even before firing.
3- The expanded case will keep the pressure in the expansion chamber from moving the bolt forward. During firing, the case is pushed rearward against the bolt face and expands to stick to the chamber walls. The case should have shrunk by the time the gases enter the expansion chamber, but the case has expanded to fill the chamber. The only way the bolt can be moved forward is to crush the brass.
4- While the pressure in the entire system is dropping because the bullet has uncorked it, pressure in the carrier is still less than the pressure in the chamber and bore.
The gases in the expansion chamber cannot move the bolt forward in the barrel extension
The bolt does not begin unlocking as soon as the carrier begins moving. The groove in the carrier which engages the bolt cam is straight for a short distance, then angles which delays the unlocking of the bolt
Yeah, I know, poor wording on my part perhaps. I didn’t mean that unlocking starts when the carrier moves to the rear, I was trying to say that it was a result of the cam pin following the cam track, and the resulting rotation of both cam pin and bolt. If that makes sense…I suck at english firearms nomenclature…sorry…
@dano5326:
We still have cam pin recess wear marks, if that is what you are talking about in regards to inlet:
Don’t blame your armorer… they are constrained by the limit of education & most are lego assembling monkeys.
Well, this guy is actually quite experienced, having been in the business for over 30 years, with several armorer courses from various manufacturers (FN, HK, Colt Canada/Diemaco, Glock). He does know his stuff.
Look at where the piston is in the standard AR. In the middle of the bolt carrier. As gas goes through the key, into the chamber (within the carrier) it pushes in all directions.
- The bolt will be pushed forward and the carrier rearward… gas venting out the side holes in the carrier as the gas rings pass.
- as the carrier is pushed rearward the cam path unlocks the bolt, aligns it with openings in barrel extension
- momentum is keeping the carrier moving rearward.
Yeah, I understand the physical differences between the two systems. I just don’t see where the bolt can go. I can see the gas inside the carrier making sure that the bolt stays forward during unlocking, but the same thing can be said about the firing pin spring on th HK bolt.
Gotcha. No apologies needed
Yeah, I understand the physical differences between the two systems. I just don’t see where the bolt can go. I can see the gas inside the carrier making sure that the bolt stays forward during unlocking, but the same thing can be said about the firing pin spring on th HK bolt.
The bolt is held in place mechanically by the locking lugs during unlocking. It’s also held in position within the carrier mechanically by the bolt cam. If anything holds the bolt in the forward most position in the carrier during extraction, it’s inertia
^ That in a nutshell.
Another difference that I have not seen mentioned so far is that of reduced dwell time with a piston upper.
With a conventional DI system the gas enters the gas tube as the bullet passes the gas port, then has to travel all the way back the gas tube, enter the carrier and pressurize it before any carrier movement and extraction takes place.
This dwell allows the obturated case to shrink away from the chamber walls.
With a piston upper, as soon as the gas enters the gas port it can pressurize the small chamber and start the rearward piston movement immediately, which starts carrier movement and extraction pretty much right then. Obturation of the case may still be going on, which means the case is still gripping the chamber walls. Hence the extractor ripping through the rim, or just breaking.
Of course this is exacerbated when you have a 16" barrel and shorty gas system.
I’m guessing you are assuming the 15,000 psi gas behind the bullet moves at the same speed as the bullet which when passing by the port in the 7" location is apx 2400fps? You may want to do a little more research on that.
Ok are the flaming gases coming out of the muzzle high pressure or do you think they flow out all mellow like? If they shoot out of the ejection port that would say there’s a little pressure behind them.
If you look at a pressure curve from a P. or PT system the 58,000 psi pressure is only while the bullet is in the first few inches by the time it passes the gas port it’s 12-15000 psi and then around 8000 psi when the bullet exits depending on the caliber, powder and barrel length. after the bullet exits the pressure in the barrel drops to 0 very quick, there shouldn’t be any pressure in the case so the walls of the case contract and allow it to be pulled from the chamber.
With a piston upper, as soon as the gas enters the gas port it can pressurize the small chamber and start the rearward piston movement immediately, which starts carrier movement and extraction pretty much right then. Obturation of the case may still be going on, which means the case is still gripping the chamber walls. Hence the extractor ripping through the rim, or just breaking.
Yeah, you would think that they didn’t test this, huh? :rolleyes:
that’s going to depend on the volume of that expansion chamber. you can’t assume it’s less than the volume of the gas tube and chamber inside the carrier, unless you know that it is.
Exactly. On a DI AR as the gas enters the carrier key and the carrier the bolt receives forward pressure and the carrier rearward pressure as the carriers chamber fills with gas (at the same time since the bolt is the forward end of this chamber and the carrier is the rear of this chamber). When the chamber can no longer contain anymore the carrier moves rearward and this causes the bolt to unlock due to the track in the carrier (bolt connected to the carrier via cam pin) follows this track. By this time the chamber pressure has dropped so much that the empty case easily follows and stays attached to the bolt via the extractor. As the bolt reaches fully unlocked the gas rings pass by the two ports on the right side of the carrier and the gas is vented outside those ports.
One of the reasons for the H (3.8oz) and heavier CAR length buffers are to help delay the carrier from defeating the buffer and spring as soon as it would with a CAR (3.0oz) buffer, a heavier weight buffer is harder to defeat (simple physics). The CAR length gas guns are trying the move the bolt rearward faster than a longer rifle gas system does due to the shorter length and reduced gas system capacity. Because of the shorter gas system length the internal chamber pressure on the fired casing on a CAR gas gun is higher than it is on a mid length or rifle gas length gun, thus why the heavier buffers and stronger extractors help. Some of this can be controlled via the gas port in the barrel size. But it’s still a timing issue, the system has to have enough gas to fill the gas system fast enough before the bullet leaves the barrel (dwell time). The stronger extraction devices (stronger extractor springs and O-rings) help keep the empty on the bolt due to this higher pressure on the empty case.
The velocity of the ejecta is faster than that of the bullet once it uncorks. In the formula to figure the free recoil of a rifle is a constant (if I recall correctly) is 4750 fps. However, the gas port reduces the flow of the gas increasing the time needed to pressurize the expansion chamber and get the carrier moving.
In order for the rifle to extract the spent case before the bullet clears the barrel, it would have to do so in fraction of a millisecond a that’s all the time it takes the bullet to travel from gas port to muzzle
Let me add that until the bullet uncorks the gases in the bore are only traveling as fast as the bullet.
Robb, I’m pretty certain that the expansion chamber reaches operating pressures after the bullet uncorks. I believe the pressure and density of the residual gas is what the rifle is operating on