Another shorty M14, short stroking...

[M14Doctor]

Does it do this with every magazine?
Does your piston appear to have vacuum pressure?
Has the mag release roll pin broken and collapsed
Is your oprod guide overly loose
Does your gas cylinder port align with barrel port?
Many things can cause this and often it's a simple thing

If I understand the problem correctly, the first few rounds in the mag fire fine and then the last couple rounds the issue arises
Do I have this right?
And is it the same no matter what mag?
Have you installed a match oprod spring guide?

As per my earlier comment on stock dimension , distance from top of stock receiver bearing surface at heel to top of trigger pads at rear of trigger is 1.703" -.010"
Forward trigger pads should have 10 degree bevel and be same distance from receiver plane to maintain receiver/trigger parallelism.

 

[Xman]

Have you tried that technique of looking for binding by removing the oprod spring, and tilting the rifle muzzle down and up to see if the weight of the oprod and bolt are enough to have it smoothly travel back and forth by gravity, without any binding? Hammer needs to be cocked to avoid that interferance.

I tried the gravity test after you posted this. The answer is no. I took the the op rod spring guide and spring out, put the trigger assembly back in, cocked the hammer but when I let the bold and op rod slide backward on their own, the bolt binds on the face of the hammer. It will go all the way to the back with the smallest of pressure from my hand but, on its own, no. The hammer is spring loaded up a bit, enough to be in the way of the bolt as it travels rearward.

Yours slides back without any help if you take the spring out?

 

[Xman]

I don't want to sound like a ####, but with everything else apparently having been tested, the only two things I can think of is that you either haven't indexed your gas piston correctly or the gas port is obstructed somehow? I know they're both longshots, but I'll be damned if I can figure it out without the rifle in front of me otherwise...

Can you run a drill bit or a pin punch through the gas port into the barrel? Does the gas piston slide back - with its keyed shaft fully rearward - when you simply tilt the rifle backwards (minus oprod and spring, of course)?

What a conundrum...

-M

Not sure I understand how the gas piston could not be indexed correctly. It can only go in one way, right? Skinny part towards the back, with the flat part on the piston matching the flat part on the tube...Right?

Yes, I can put a 1/16 Allan Key all the way through the gas venting port, into the the barrel with the piston extended all the way to the back.

Yes, the piston slides back all the way when I tilt the rifle.

 

[Xman]

Does it do this with every magazine?
Does your piston appear to have vacuum pressure?
Has the mag release roll pin broken and collapsed
Is your oprod guide overly loose
Does your gas cylinder port align with barrel port?
Many things can cause this and often it's a simple thing

If I understand the problem correctly, the first few rounds in the mag fire fine and then the last couple rounds the issue arises
Do I have this right?
And is it the same no matter what mag?
Have you installed a match oprod spring guide?

The piston appears to have vacuum pressure. When the plug is in, if I tilt the rifle up, the piston will slide out the back of the cylinder but not as fast as it does if I take the gas plug off. Could it be a tighter fit between the inside of the cylinder and the piston? I think so.

The mag release roll pin is in good shape.

The op rod guide is tight and is indexed almost perfect to the gas cylinder. When the piston blows backward, it hits the op rod face almost center.

The cylinder ports align very well all the way from the outside of the gas cylinder through into the barrel.

The short stroking appears after the first two rounds after cleaning the rifle. After those initial first two full cycles, it won't cycle fully again until I clean it.

I've only tried two 20/5 magazines in it but these are the same magazines that worked flawlessly before the chop.

 

[Hungry]

Hmmmm

I'm really stumped!

 

[Lazerus2000]

I sanded and smoothed bolt, inside receiver where bolts slides along, the hammer face that interacts with the bold....still no joy.

The bolt to hammer surfaces are CRITICAL to safe functioning of the M14. They are also SURFACE HARDENED, to a very small depth. Too small a bolt diameter/cocking surface at the rear of the bolt, can cause hammer follow. Too much of an angle to the trigger group mounting can cause hammer follow. Too little clearance, or not enough angle, can cause increased hammer cocking resistance.
Sanding these critical surfaces on the hammer and the bolt is NOT an appropriate method of fixing this problem.

First of all,
IS THIS THE EXACT SAME STOCK YOU HAD THE RIFLE IN BEFORE IT WAS CHOPPED???
EXACTLY THE SAME STOCK???

Proper stock fit is CRITICAL to the proper functioning of the M14, and as mentioned in the FAQs/Stickies posted at the top of the battle rifle section, swapping stocks, or even painting a stock, can have an effect on safe functioning. Sanding/lowering the trigger group bedding surfaces can cause too much hammer interference with bolt travel. If the bolt/hammer are freshly cleaned and greased, and the action not fully settled into the stock then this might explain why, as the grease wears off, and the action settles, things get different.

Once agin,
is this exactly the same stock you had the rifle in BEFORE it was shortened??

PS: I do the op rod/bolt gravity tests WITHOUT the trigger group installed. I test the hammer cocking with the rifle completely assembled. Op rod sliding smoothness, and hammer cocking resistance, are two separate and independent events, and should be tested separately. And testing hammer cocking without the stock, is sort of like testing for head space with the ejector installed, and no ejector cut out on the head space gage ...
not relevant at all.

 

[Xman]

Wow, Lazerus, it sounds like this platform is really finicky. Not what I'd expected out of a battle rifle design that should function under somewhat adverse conditions.

Yes, the stock is exactly the same as before and so are the mags I tried so far. The only difference is the chopped barrel+vortex flash hider and a the gas system being unitized. Absolutely nothing else is different. I even used the exact same ammo, from the same batch. Federal, 150 gr. soft point. I had this rifle for about two years prior to this chop and gas system unitizing and I've taken it out many times. It was even very accurate. I was hitting the gong at 325 yards with iron sights, four times out five...

 

[Xman]

So, you guys are not going to believe this...

I decided to give it on last try before I'd send it to M14 Doctor for...medical attention. I cleaned it again, (and I have a confession to make here: I hadn't used the chamber brush that comes with the gun before, I had just cleaned the chamber with a rod, brush and pad and I thought I did a good job but maybe I hadn't.)

So I cleaned the crap out of the gun, including the chamber, re-greased the bolt lugs, bolt rear, bolt roller, pin tail, op rod track and camming space.

Then I cracked open a brand new crate of SA ammo and went to the range.

I loaded every single one of my seven 20/5 magazines (I wanted to see which one didn't perform) and went to town. I shot 100 rounds and didn't have a single failure to feed or extract, or anything. I pulled the trigger slowly, I pulled it as fast as I could, I changed mags and shoot right away, I let it cool off for a few and then changed mags...Everything I tried worked just fine.

I was also shooting really good groups. I was making a single large hole at 20 yards and 1MOA at 100 yards...

So, I am pretty happy. I don't know if it's the SA ammo or the extraordinary chamber cleaning that I performed and the hitch grease application but man, I got my friend back and she's a shorty now...a shorty that shoots like a dream again...

Very happy....Can you tell?...LOL....'k...I done now....

 

[M14Doctor]

Awesome news Xman
I allways get a lil nervous when a rifle I've touched has issues after the fact.
Referring back to one of my earlier comments.... It has to be something simple.... Chamber cleaning in general is an essential step in maintaining safe operation.****especially for reloaders and those using bolts/chambers tighter than 1.637 in headspace. Or nato +2thou and is imperative with rifles having .308 headspace in the 1.630 to 1.634 range.
Glad to hear your rifle is making you happy once again

 

[Lazerus2000]

glad to hear you are up and running.

My next guess was that if the gas assembly unitising was done by welding instead of bolts, that the gas assembly bore got warped, or some chrome lining got flaked off, and that was constricting the piston travel.

But you said, with gas plug installed the gas piston drops smoothly and slowly, which is the perfect combination. The piston should fit the bore tightly enough that there is actual vacum draw through the gas port in the barrel, which is why it drops slowly. And if the drop is smooth, with no hang ups, then the bore is not constricted,
so all is good.

Sounds like it wasn't the gas assembly after all.
[;{)

PS: how do you like the VLTOR stock???

 

[Doc M]

Not sure I understand how the gas piston could not be indexed correctly. It can only go in one way, right? Skinny part towards the back, with the flat part on the piston matching the flat part on the tube...Right?

Yes, I can put a 1/16 Allan Key all the way through the gas venting port, into the the barrel with the piston extended all the way to the back.

Yes, the piston slides back all the way when I tilt the rifle.

Yup, then I'm officially out of ideas!

However, seeing your latest post, it sounds like you've got it licked! Great news!!!

-M

 

[zxcvbn]

So, you guys are not going to believe this...

I decided to give it on last try before I'd send it to M14 Doctor for...medical attention. I cleaned it again, (and I have a confession to make here: I hadn't used the chamber brush that comes with the gun before, I had just cleaned the chamber with a rod, brush and pad and I thought I did a good job but maybe I hadn't.)

So I cleaned the crap out of the gun, including the chamber, re-greased the bolt lugs, bolt rear, bolt roller, pin tail, op rod track and camming space.

Then I cracked open a brand new crate of SA ammo and went to the range....

Hi Xman,
I have read that some SA ammo is corrosive. If you have been using SA ammo perhaps the gun became fouled (or worse) over time?

Maybe the longer term solution is to change ammo? Just a (newbie) thought

 

[M14Doctor]

glad to hear you are up and running.

My next guess was that if the gas assembly unitising was done by welding instead of bolts, that the gas assembly bore got warped, or some chrome lining got flaked off, and that was constricting the piston travel.

But you said, with gas plug installed the gas piston drops smoothly and slowly, which is the perfect combination. The piston should fit the bore tightly enough that there is actual vacum draw through the gas port in the barrel, which is why it drops slowly. And if the drop is smooth, with no hang ups, then the bore is not constricted,
so all is good.

Sounds like it wasn't the gas assembly after all.
[;{)

PS: how do you like the VLTOR stock???

A brass heat sink and heat paste(brownells) is used on every cylinder tig unitized in our shop.
Also I utilize a micro torch tig machine and the guy behind it has been seam welding stainless stel process piping for 30 years. He's the most sought after welder/fabricator in the entire lowermainland.
We have unitized 87 norinco, 23 usgi gas systems in the past year, NOT including unitizing done at clinics.
Not a single one has come back with warping or flaking.

 

[Xman]

So, I found out today that the most likely culprit for the drama I went through is the TZ 80 Israeli ammo that I was shooting. I made a whole separate post about it.

That explains why the first 3 rounds would fire and chamber but after that it short stroke. It`s very dirty ammo, the cases look rusted out and spotted and it`s either underpowered or very hot, depending on the lot you get. In my case it was under-performing, fouling up my gun big time and leaving so much lacquer and gunk in the chamber that the rounds were getting stuck.

Stay away from this ammo!