Why is there still a forward assist on AR's?

[Caveman Jim]

OK, say you went to an auto parts store to buy a radiator hose. You told the clerk what car you had and he takes you to the radiator hose display and shows you four options of hoses that would fit your car. One of those hoses comes in packaging that includes a roll of duct tape and the store clerk recommends that you buy that one, because it's very popular. You ask: "What's the duct tape for?". He says: "Well when these hoses first came out, they had a real problem with leaks, so the manufacturer just started adding duct tape to patch the leaks rather than re-engineer the hose design. But these hoses come with really cool integrated hose clamps and water temp gauges that are molded into the outside surface of the rubber. So most people don't mind buying this hose that leaks like a sieve brand new, if it comes with duct tape."



It kind of goes without saying that having the FA isn't going to make it less reliable. It was put on the AR as a band-aid fix to the gun's combat-proven habit of letting soldiers down. The point of this thread is not to shrug shoulders at something we've all gotten used to, but to question why it's still there after so many years of opportunity to fix the core problem that led to the need for a band-aid.

If ya want to have an AR without a FA then get one. Why compare it to an automobile part, IT AIN"T!!!!

 

[metrotps]

"We still use the direct impingement gas system, which BTW the French were the first ones to use this kind of a system (first experimented on in 1901, adopted in the MAS-49/1949) before Stoner designed the AR-10/15. Just some insight since I've heard people refer to the AR systems 'DI' gas system as being the 'first ever', when in actuality it is just a more refined version of something that had been tried decades before."
Just a side note: The Swedish AG42 designed in 1941 used this system and the Egyptian Hakim and Rasheed also. designed by the Swedish engineer Erik Eklund, who based it on his previous Hakim Rifle (8 x 57 mm Mauser cartridge), which was itself a slightly modified version of the Swedish AG-42 Ljungman rifle (6.5 x 55 mm Swedish cartridge).

 

[erudne]

Back in da Day I had the choice between an M-16, a Tommy Gun, a SMLE Mk IV, and a M-2 carbine
I chose the carbine.
The M-16, even with it's chromed bolt carrier/chamber would have been my last choice. The non-reciprocating charging handle is the only Sin Stoner committed but then he was a Navy puke, not a soldier. Stoner never repeated that mistake

 

[usagi]

the ljungman design is excellent. the hakim is a very soft shooting 7.92x57mm rifle.

 

[erudne]

the ljungman design is excellent. the hakim is a very soft shooting 7.92x57mm rifle.

I used one for a few months in the 1980's, good design but heavy

 

[Jammer Six]

The forward assist was not added as a result of combat.

The forward assist was added because every weapon accepted for general issue up until that time had had a way to force a round to chamber, and the M16 did not.

Good book: The Black Rifle

 

[erudne]

I'd stay w/ M-1 carbine if there was a bubblegum-load of ammo available
Audie Murphy chose it as his anti-sniper rifle and he kicked ***: 10 for 1

 

[Rix]

I've used the forward assist on at least two of my ar15s.

 

[Rix]

I used one for a few months in the 1980's, good design but heavy

Really heavy. I love it regardless.

 

[Ownerus]

The M16 is not direct gas impingement in the sense that the Llungmann AG42, Hakim, and Rashid are. Those rifles have a simple cup on the face of the bolt carrier that engages the end of the gas tube an the gas simply blows the cup and attached bolt carrier off the tube. The M16 pipes the gas into the bolt carrier where it expands in the chamber between the bolt and bolt carrier and sends the bolt carrier rearward. Unlike a conventional gas piston system a la M1 Garand/AK47 etc., virtually all the forces exerted on the bolt and carrier are coaxial with the barrel so there's almost no bending moment applied to the barrel while the bullet is still in transit. There's a reason the system can produce such excellent accuracy. As with all designs, it's a series of trade-offs. Accuracy and weight and simplicity given priority in this system as I see it. Is it the correct trade-off? A matter of opinion I suppose. Not a bad trade-off overall IMO.

The Llungmann is an interesting rifle but would not be even my third choice in a fight.

 

[usagi]

I thought the bolt didn't even start to unlock until the bullet was already well out of the barrel AND the pressures had subsided enough to be safe?

Unlocking the bolt while the bore is still under tens of thousands of PSI would result in a really bad day for the shooter.

 

[Ownerus]

Correct. The BOLT doesn't unlock until after. However the gas piston starts moving as soon as the bullet passes the gas port. The op rod/bolt carrier (depending on action type) moves a distance before beginning the unlocking process. It's during this travel time of the op rod/gas piston that the bullet departs and the pressure drops. The motion imparted to those components then carries the action the rest of the way open.

 

[simon99]

The question is, why is there still a forward assist? No why was one designed.....

Easy answer - money.

Think of how many AR lowers have been built with an FA.....nuff said.

 

[Ownerus]

There are two differing design philosophies with regard to dealing with dirt. Keep it out or make it really easy to clean. The M1 Garand is an example of the latter. Drop it in the mud and you can yank the trigger group off, remove the stock and quickly shake most of the junk out. The AR is an example of the "keep it out" philosophy. A dust cover over the ejection port, and especially no slot for a bolt handle to travel through which would create an opening that could allow junk into the works. The cocking handle on the AR can't reciprocate with the bolt without endangering your face so it's pull but not push. So, without the FA, there no fast way to deal with a dented round, bit of dirt, etc.

I've had both with and without. I would choose to include it on a new rifle. Sorta like a seat belt. Totally useless until something goes wrong.

 

[usagi]

Correct. The BOLT doesn't unlock until after. However the gas piston starts moving as soon as the bullet passes the gas port. The op rod/bolt carrier (depending on action type) moves a distance before beginning the unlocking process. It's during this travel time of the op rod/gas piston that the bullet departs and the pressure drops. The motion imparted to those components then carries the action the rest of the way open.

if you look at where the gas is tapped in an m1 garand you'll see why i believe it is rather unlikely that the op rod gets a chance to move before the bullet has well exited the barrel.

 

[Ownerus]

It won't move very far in that time but it WILL move. The op rod on an M1 will start to move as soon as there is sufficient gas pressure on the gas piston to overcome the spring preload. What could possibly cause it to wait until after the bullet has left and pressure is subsiding? Likewise other gas operated rifles that have the gas port further from the muzzle. The parts start to move while the bullet is still in the barrel. The delay before unlocking is due to the lost motion between the op rod or bolt carrier and the bolt, not because the pertinent parts can ignore the gas pressure sent through the gas port for the appropriate amount of time.

 

[usagi]

<broken link removed>

"There is a common belief that the external piston operated systems are less accurate than the Stoner internal piston system because the operating parts start moving while the bullet is still in the bore. This is not true: Army Ordnance tests conducted in the 1960s revealed that the bullet is 25 feet out of the bore of the M1 and 15 feet out of the bore of the M14 before any operating part begins to move."

 

[Ownerus]

Got a link to the actual army test? A second hand report of the test does not convince me that the laws of physics don't apply in rifles. I strongly suspect the report says the BOLT doesn't move until then. Think about it. What would cause the op rod to sit immobile for a period of time while tremendous force is applied to it? If NOTHING moves until the bullet is well out of the barrel, why did the Russians need to cut chamber flutes in the SVT40 to float the case so it wouldn't tear the head off in extraction? How did the gas pressure know to stay there longer than on an M14 which has a similarly located gas port but doesn't need a fluted chamber? Ain't buying it. Show me the actual report.

 

[Medic!]

I'm thinking about all the countries that used FN FAL's and G3/HK91 type rifles. They have no method of forward assist. My HK91 also S#it's where it eats. Not with DGI. But the roller delayed bolt with the flutes in the chamber blow gas and powder right out it's chamber/mouth, And into the action. It's the dirtiest gun to clean! Yet people think HK's are perfect [Some people also think HK sucks and they hate you]. I much prefer my Belgian FAL.
And I prefer my Sig 556 or even my Deawoo to my AR's. I still like AR's. But they better have the dam forward assist!
And for the record. My ARMY issue M-16's never jammed on me. Of course I grew up on a farm with guns, and knew how to run one. You know what I mean? There is always that kid from the inner city, that was just learning guns. Those guys found fault with everything they could not get to work! And that was most things in general! And guns in particular! They were also most likely to end up on the expectant list.

 

[Trailboss]

Just did a calculation of the lag time between the bullet passing the gas valve on my Sig556 and the bullet leaving the barrel based on the speed of a 55 grain 5.56 round.

3240 Feet per second
38,880 Inches per second
0.00002572 Seconds per inch of travel
0.02572016 Milliseconds per inch of travel
4 Inches between gas port and end of barrel
0.102880658 Milliseconds expended between gas port and end of barrel

So there is approximately one tenth of a millisecond of time between when the bullet passes the gas port and the bullet leaving the end of the barrel. I wonder how much time it takes the gas to enter the gas port and the piston chamber and to reach sufficient pressure so that the piston can be driven back? If it takes one tenth of a millisecond or more for this gas to piston process, the bullet has already left the barrel and will be unaffected by the piston stroke.