Tight Tapco Gas Piston fit

[theader]

I recently completed a L1A1 build using a Tapco Gas Piston as one of my 922r compliance parts. The piston head fits tightly into the gas block that I needed to lightly tap the piston head to get it to fit. The gas piston stays in the gas tube by itself without the gas plug in place and needs to be lightly tapped out to be removed. It shoots just fine with the gas regulator set at the 4 setting to cycle properly. The original non-compliant gas piston that came with the parts kit fits into the L1A1 just fine, no tapping. When I fit the Tapco gas piston into a metric gun, it fits smoothly. I’ve read that inch and metric gas pistons are very slightly different in length but are the piston head diameter’s suppose to be different too? Is the piston out of spec?

Thanks.

[elbo]

So, you have a part that works and you want to know how to change that. Correct?



top plug is inch - bottom is IMBEL, Israeli size is similar to the inch,
this shows the reason for, and difference in piston length.
Any plug will work in any block if you modify the lugs to suit. Which means for our purposes the pistons are the same diameter.

" Is the piston out of spec? "
Could be your gas block?

[garyd1961]

You shouldn't have to tap on the gas piston to install it. Tapco seems to have let some pistons out the door that are out of specs. I bought one from someone on here a while back that bought 4 and 1 was too big. I bought the oversized one, I thought I could custom fit it to my rifle. I used a drill and sandpaper to bring it down to size but I don't use it, instead I bought a new one and keep the old one as a spare.

[eyegun]

I've got a Tapco piston that was advertised as inch OR metric and it's just a little short in my inch gun (about 1.5mm). So, I'm back with the original piston

[garyd1961]

All of Tapco are a little short in inch rifles but they will work. If they were full length they wouldn't work in metrics. There are a lot of them in inch rifles now with no problems.

[theader]

Originally posted by elbo
So, you have a part that works and you want to know how to change that. Correct?



top plug is inch - bottom is IMBEL, Israeli size is similar to the inch,
this shows the reason for, and difference in piston length.
Any plug will work in any block if you modify the lugs to suit. Which means for our purposes the pistons are the same diameter.

" Is the piston out of spec? "
Could be your gas block?

Nope, just don't like the fact that I needed to tap the GP to get it into the gas block. Was wondering if other have experienced the same and what they did about it.

[theader]

Originally posted by garyd1961
[ I used a drill and sandpaper to bring it down to size [/B]

I think I'll do the same.

[jugrunner]

some of these guys can't read ...

I have had a couple of Crapco pistons that were slightly oversize in dia. ...

drill and emery cloth = quick fix

[brownknees]

Are you saying the head is tight when inserted head first (reversed) or that it's tight at the head when inserted normally (tail first)?

Just asking because if the "head is tight" when inserting normally where the head is the last thing in the hole you may have a pinched gas tube that is catching down inside & it just feels like the head is tight. If the metric it fits in doesn't have the pinch it would fit just fine giving you the symptoms you describe.

What does the head measure for diameter?

Check before filing would be my suggestion.

[nwobhm]

If it works, don't mess with it. Are you sure your gas tube is screwed in correctly?

[theader]

Originally posted by brownknees
Are you saying the head is tight when inserted head first (reversed) or that it's tight at the head when inserted normally (tail first)?

Just asking because if the "head is tight" when inserting normally where the head is the last thing in the hole you may have a pinched gas tube that is catching down inside & it just feels like the head is tight. If the metric it fits in doesn't have the pinch it would fit just fine giving you the symptoms you describe.

What does the head measure for diameter?

Check before filing would be my suggestion.

The GP head is tight going in both ways, tail first and head first.

I measured the head diameter with my crappy plastic micrometer and it looks like:

Original L1a1 GP between 0.42 and 0.43 call it 0.425
2nd L1A1 GP between 0.42 and 0.43 call it 0.425
Stg58 GP a shade under 0.43
Tapco GP a shade over 0.43

[elbo]

You'll likely have to change the gas setting afterward.

[GM4spd]

Originally posted by garyd1961
All of Tapco are a little short in inch rifles but they will work. If they were full length they wouldn't work in metrics. There are a lot of them in inch rifles now with no problems.

I agree--I was concerned when I noticed it was alittle short but it has
functioned fine in hundreds of rounds of shooting. Pete

[gunnut1]

The gas piston is supposed to be a "little short".

One possibility is that you screw the gas down too tight and it is pinched at the entrance. the gas tube should have some side side play. I would remove the gas tube and see if the piston is binding in the tube. and check it in the gas block with out the tube also. It should slide freely in the tube and not bind in the gas block.

[msnyder]

The gas piston should slide freely in the gas tube. I had a Tapco piston that would not slide freely. When the gas plug was removed the piston had to be knocked out with a punch from the receiver. The head measured .433" .
I replaced it with a Tapco piston that meaured .430" and it slides freely now.
The .433" piston slid freely in a metric gas tube so I didn't have to send it back. I measured about 20 original pistons and they all measured .429-.430". The inch pistons are slightly longer than metric but using a metric in an inch, as others have said, is not problematic.