Gas tube roll pin sheared?

exo

exo

Joined
Mar 3, 2009
Messages
7,697
Likes
2,408
Location
Hinterlands
Feedback: 106 / 0 / 0
Has anyone ever had this happen? My AR15 has been working fine since I assembled it. That is, until the last two outings. The second to last time I had it out, I started having ejection problems. OK, so I took a look at the extractor. The fit between the extractor and the bolt seemed fine, so I went ahead and just replaced the spring and plunger. The last time I had it out (today), I didn't have any ejection problems but I started having failures to feed. Same mags and ammo worked fine in my other AR, so I suspected it was short stroking. The gas rings seemed OK, but I went ahead and replaced them anyway. No improvement.

I just took my free float tube off, and damned if the gas tube wasn't sticking out about 1/10" past the end of the gas block. Turns out that the gas tube roll pin had sheared in half! Has anybody had that happen to them before? What would cause it? How do I keep it from happening again?

For reference, this is a 16" barrel with a carbine gas system.
 
I'll guess that the tube was a little misaligned and got slammed by the gas key, shoving it through the roll pin. That got it back in line, and since then it's been sliding around. Alternatively, I guess it could be a very over-sized port putting too much energy into the system. Finally, it could be just bad luck.
 
exodious said:
Remsport, stainless. I've had 3 (counting this one and my other AR, one I sold) of their barrels, and this is the first time I've seen anything like this.
Click to expand...

economist said:
I'll guess that the tube was a little misaligned and got slammed by the gas key, shoving it through the roll pin. That got it back in line, and since then it's been sliding around. Alternatively, I guess it could be a very over-sized port putting too much energy into the system. Finally, it could be just bad luck.
Click to expand...

My first guess was an oversized gas port, and the Remsport make does nothing to dissuade me of that opinion.

If the tube was misaligned, I'd think it would bend before it would shear the pin.
 
Well, this particular rifle is the first AR I assembled myself, so I'll grant that I could have screwed something up. When I put this back together I'm going to be re-checking everything. I don't think the tube was misaligned, but when I reinstall it I will definitely check on that.

What should the gas port diameter be, and what tool(s) do I need to accurately measure it?
 
Not having drilled a gas port myself, I really don't know what size is used. For a carbine I've seen sources that say the port should be about 0.063". Practically, the proof is in the function of the gun, and a good builder knows what size to use for their build.

For measuring, I would just use drill bits.

Brownells sells a port drilling jig that accepts size 42 and 49 bushings. That would imply 0.0935" or 0.073" for the bushing, and I suppose you could step down in bit size to 43 or 50 (0.089" or 0.070"). All of this is larger than 0.063", so that could be too small though I swear I've seen somewhere that is standard for an M4.
 
Last edited:
So, follow up here... you got me thinking about this, so I went ahead and took the gas block off. Some searching suggests that the gas port for this sort of barrel SHOULD be about 1/16". I can get a 3/32" drill bit into this port! I took the gas block off of my other AR with a Remsport barrel and it's the same story. WTF?
 
exodious said:
So, follow up here... you got me thinking about this, so I went ahead and took the gas block off. Some searching suggests that the gas port for this sort of barrel SHOULD be about 1/16". I can get a 3/32" drill bit into this port! I took the gas block off of my other AR with a Remsport barrel and it's the same story. WTF?
Click to expand...

That sounds way too big to me, but I'll defer to a gun builder on this. See my earlier post.
 
economist said:
That sounds way too big to me, but I'll defer to a gun builder on this. See my earlier post.
Click to expand...

I'm going to call Remsport tomorrow and see what is what. It sounds like the combination of a 16" barrel, carbine gas (already more violent, so to speak, than 14.5"/carbine or 16"/mid or 20"/rifle) AND an oversized gas port caused this breakage.

As for my other AR, also with a 16"/carbine and same sized gas port, it's running a gas piston from Osprey defense. Today is the first time I took it out, and it functioned flawlessly (however, so did this other AR until today). Osprey recommends a carbine buffer, but I figured I'd run an H buffer because I knew 16"/carbine wasn't exactly ideal. I'm wondering if I should try it again with an H2 buffer, would that help minimize the potential damage from this odd barrel configuration?

Another thing about the Osprey setup that -might- save it from this fate, is that it doesn't use a standard roll pin for securing the piston chamber to the gas block. It uses a solid groove pin.
 
exodious said:
I'm going to call Remsport tomorrow and see what is what. It sounds like the combination of a 16" barrel, carbine gas (already more violent, so to speak, than 14.5"/carbine or 16"/mid or 20"/rifle) AND an oversized gas port caused this breakage.

As for my other AR, also with a 16"/carbine and same sized gas port, it's running a gas piston from Osprey defense. Today is the first time I took it out, and it functioned flawlessly (however, so did this other AR until today). Osprey recommends a carbine buffer, but I figured I'd run an H buffer because I knew 16"/carbine wasn't exactly ideal. I'm wondering if I should try it again with an H2 buffer, would that help minimize the potential damage from this odd barrel configuration?

Another thing about the Osprey setup that -might- save it from this fate, is that it doesn't use a standard roll pin for securing the piston chamber to the gas block. It uses a solid groove pin.
Click to expand...

Interesting. Let us know what you find out.
 
I would just replace the pin (cheap enough), make sure that the tube is properly aligned and just shoot the gun.
 
Im no expert and I am going on memory from when I got the AR bug. The gas port should be larger for shorter barrels and decrease in size as the barrel gets longer(5.56) Trying to recal 14.5/16" barrels are .06ish on the low side? Im going to throw this out there
1. when installing the gas tube some how missed the roll pin to the rear ? this would cause the carrier to bang the gas tube forward into the pin ? look to see if there is any damage to gas tube at the carrier end.
2.roll pin was junk....did you install the roll pin and what source if so.
3. another issue maybe the gas tube it self, to short ?
Just throwing things out there. If remsport assembled your barrel I would let them handle it. As far as gas port size I would try and find what milspecs are on the gas port. Then ask remsport for their design reason.

Maybe your gas tube was to long and the carrier beat the roll pin to death, im currious is the tube or pin stronger ?
Do you see any damage to the gas tube ?
 
Last edited:
The gas tube doesn't appear to be damaged, and it is the ccorrect length for a carbine tube. The roll pin came with the tube. I do not know the manufacturer of either. I'm pretty sure that I would've spotted a half installed pin.

I'll call Remsport later today and see what's what.

As for the other AR, I've been reading about how the Osprey kit works. It is apparently a self metered / regulating design, so the oversized port may not be as big of a deal on that rifle.
 
mac1911 said:
is there any way you could have installed the gas tube short of the roll pin ?
Click to expand...

No, I had to drive out what remained of the pin, after pushing the tube back the 1/10" or so that it traveled forwards.

Edit: Also, had the gas tube been installed short of the roll pin (i.e. the pin got installed in empty space), the rifle never would have cycled. The port in the tube wouldn't have been anywhere near the port in the gas block.
 
Last edited:
Mac1911, gas ports should NOT be oversized on shorter barrels. The pressure in a carbine system is as high enough already.

IIRC, john oversizes his ports for "reliability", despite the fact that overgassed guns break more.
 
I think Economist was on to something. I would bet that the gas tube was a little too long, for where the shoulder was on the barrel and that particular BCG. It got shoved forward just a little, every time the bolt closed. It battered the cross pin until it broke.

I bet you can correct this with a little elbow grease and some abrasive paper. The tube needs to be ever so much shorter, or the key needs to be a little deeper.

B
 
Well, I just spoke to Remsport, and I believe this can be resolved to my satisfaction. Basically, John stands behind his products with a lifetime warranty, but he will let me return the barrel for a refund if that's what I want to do.
 
I don't think we are talking a lot of distance. I'm thinking it might be .010 ~.015 off. On the closing cycle, when the bolt is fully cammed over, the carrier has at least .100 more travel before the cam pin hits the back of the slot in the bolt carrier. This is done so that on the firing cycle, there is a little momentum built up in the carrier before it hits the cam pin, that starts the bolt rotating. The force of rotating through that camming cycle works better if carrier gets a little free run.

Take your bolt out and look at how much the bolt will still move in the carrier after it's cammed on the closing cycle.

B
 
bpm990d said:
I don't think we are talking a lot of distance. I'm thinking it might be .010 ~.015 off. On the closing cycle, when the bolt is fully cammed over, the carrier has at least .100 more travel before the cam pin hits the back of the slot in the bolt carrier. This is done so that on the firing cycle, there is a little momentum built up in the carrier before it hits the cam pin, that starts the bolt rotating. The force of rotating through that camming cycle works better if carrier gets a little free run.

Take your bolt out and look at how much the bolt will still move in the carrier after it's cammed on the closing cycle.

B
Click to expand...

This is the best answer yet. Another reason for the problem could be the port being drilled a little too far to the receiver side or the gas block being installed a little off in the same direction. I still think it's getting too much gas and I would replace the barrel, and that addresses all of these potential issues.
 
economist said:
This is the best answer yet. Another reason for the problem could be the port being drilled a little too far to the receiver side or the gas block being installed a little off in the same direction. I still think it's getting too much gas and I would replace the barrel, and that addresses all of these potential issues.
Click to expand...

I suppose anything is possible, I mean I never thought I'd see a sheared gas tube roll pin!

I am thinking that the gas block was aligned properly, though, because I used a jig to dimple the barrel for the low profile gas block, and then used the dimples to align the gas block itself.

Anyhow, I think I will be taking John up on his offer and returning this barrel for a refund. I'm thinking of getting a BCM barrel to replace it. Either I'll keep this as a 16" but go with a mid-length gas system, or I'll turn it into a 20".

Thanks for all the comments, folks.
 
was the gas block all the way against the barrel shoulder, i should be around 1/32 off. But I have seen oversized gas ports blow a hole in a gas block, so shearing a pin is not a surprise
 
Supermoto said:
was the gas block all the way against the barrel shoulder, i should be around 1/32 off. But I have seen oversized gas ports blow a hole in a gas block, so shearing a pin is not a surprise
Click to expand...

No it wasn't against the shoulder. I used this jig to drill the dimples for the gas block set screws. Based on that and the markings I see on the barrel (after I took the block off), the gas block was in the right place.
 
For anyone who is interested, I had emailed Osprey Defense to ask whether there would be any problems using their piston kit with a 16" carbine gas system barrel with a gas port as large as it is on Remsport barrels (~0.093").

Osprey's general manager responded to me that it would not be a problem.
 

Similar threads

Replacing Firing Pin Spring on Rem 700 Clone
Replies
4
Views
165
FalArAk
FalArAk
Gas tube position new PSA .300 Blk upper / Sig lower & BCG
Replies
12
Views
510
pastera
pastera
Pin and Weld Central Mass
Replies
2
Views
525
akma
A
Pin and Weld
2 3
Replies
68
Views
4K
drgrant
drgrant
Is my trigger installed correctly? (Pin walking)
Replies
12
Views
828
PappyM3
PappyM3
Back
Top Bottom