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Posted: 1/18/2006 11:48:13 AM EDT
I BELIVE THE GAS PORT SIZE IS 0.187 I NEED AND EXPERT RESPONSE THANKS
Link Posted: 1/18/2006 12:25:22 PM EDT
CAPS LOCK!!!!!

What exactly are you wanting, the gas port size?
On what length gas system?
I don't really know the answer, and I'm not sure how its a big deal, but you'll need to include more info for someone who does know what they are talking about. Randall is probably around here somewhere and I bet he knows.
Link Posted: 1/18/2006 4:37:32 PM EDT

Originally Posted By ZootTX:
CAPS LOCK!!!!!

What exactly are you wanting, the gas port size?
On what length gas system?
I don't really know the answer, and I'm not sure how its a big deal, but you'll need to include more info for someone who does know what they are talking about. Randall is probably around here somewhere and I bet he knows.



Gas hole size is my question thanks again ?
Link Posted: 1/19/2006 6:06:37 AM EDT
[Last Edit: 1/19/2006 6:07:58 AM EDT by FALARAK]

Originally Posted By COLT:
I BELIVE THE GAS PORT SIZE IS 0.187 I NEED AND EXPERT RESPONSE THANKS



Sorry, I guess all the experts are gone.

So you'll get my 2 cents.

1. Does search not work at all for non-team-members?

2. I dont know the "standard" gas port sizing for a 18" barrel.... especially since you didnt specify whether it is a carbine, midlength, or rifle length gas system.

However, I have never heard of a gas port that big. Biggest I have heard of is .120", and most are under .100.

I would bet you are thinking .087" which sounds right...

From a previous post:


From here: http://groups.msn.com/TheMarylandAR15ShootersSite/maintenacefaq.msnw

Relevant info below:

Barrel Lngth (in) Barrel Dia (in) Dist from Muz (in) Min Port Size (in) Max Port Size (in)
11.5 .625 3.850 .081 .089
11.5 .750 3.850 .086 .094
14.5 .625 8.375 .063 .078
14.5 .750 8.375 .070 .086
16 .625 8.375 .063 .078
16 .750 8.375 .070 . 086
20 .625 6.875 .086 .093
20 .750 6.875 .093 . 096
24 .825 N/A . 089 .089

Colt's gas port sizes are: [10.5" - .093] [11.5" - .081] [14.5" - .063] [16" - .063]





18" SPR's are typically built on the midlength gas system... but I cant imagine that having that much of an effect on gas port sizes. I would never cut one above .110, and would always start with the barrel makers recommendation.
Link Posted: 1/19/2006 8:09:20 AM EDT
THANKS
Link Posted: 1/19/2006 9:13:01 AM EDT
I recently built a "18, rifle length gas upper and had cycling problems in cold weather. Bigbore suggested I open the port some, which I did to about .108" runs like a clock now. I wouldn't be afraid to go up to .110 in this configuration. Mid gas most likely doesn't need that big of a port though.
Link Posted: 1/19/2006 12:54:17 PM EDT
My rifle lenght gas system 18" SPR has .098 port size and it works like a dream even a Finnish winter.
Link Posted: 1/22/2006 10:54:16 AM EDT
THANKS the cold weather was the issue when im up in the mountains in the winter i wanted make sure it ran !!
Link Posted: 1/22/2006 11:04:37 PM EDT
Link Posted: 1/23/2006 7:18:48 AM EDT
Thanks Randall.

Can you expound on the use of a drill bit vs a reamer for gas port sizing? i.e... the correct method to cut and/or open up a gas port? I have read about both.... but this is something I havent played with. I know when using a drill bit, you have very little control over variances in the size.... probably +-.002" if I were guessing.


And speaking of gas port sizing - we all know Wolf ammo is underpowered. I have a Bushmaster 20" govt profile rifle, with a Vltor carbine stock. It runs great, until it gets dirty. Once it gets dry and dirty, the Wolf/low power ammo wont cycle it.... it short strokes. But it runs great on any M193/M855 ammo. If I wanted to make a rifle run more reliably on cheaper/low power ammo... is simply opening up the gas port a bit the recommended solution?
Link Posted: 1/23/2006 8:32:00 AM EDT
[Last Edit: 1/23/2006 8:37:31 AM EDT by Randall_Rausch]
Link Posted: 1/23/2006 9:17:56 AM EDT
Randall, that is excellent advice. I learned the hard way, as usual.

I go to a specialty fastener/machining store to buy my gas port drill bits, or any other bits needed for hard metal (like those darn AMD-65 rear trunnions, or K-31 receivers). I specifically ask for the sharpest and toughest drill bit in the size I need, and costs several dollars. This is a small price for me to pay to get the job done right the first time. I have several complete drill bit sets, but I will not use them for specialty work like gas ports. A standard drill high-speed drill bit set is fine for household or automotive projects (non-critical). I drill using Kroil, slow bit speed, slow advance, and use several motions to complete the gas port; I don't drill it with one press down. I am not a fan of heating drill bits. If any burrs are present, I knock them off with either a patched jag or bronze brush. I have opened several gas ports, and never had a problem with this method.

Now, the first one I did for practice on a worn out barrel is another story...
Link Posted: 1/23/2006 10:56:55 AM EDT
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