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1/25/2018 7:38:29 AM
Posted: 12/19/2005 2:47:08 PM EST
I have installed a lightly used PRI flip up front sight/gasblock. I noticed the Rock River gas tube was a little sloppy going in and now I am having short cyling problems. Basically I would like to know is that common or is the gas block out of spec or shot. A couple spare regular front sight blocks I have the tube is snug in. PRI doesnt take a special tube do they? I have never read anything to that effect.

So if its the block, I am at a loss of what to do to fix it.
Link Posted: 12/19/2005 2:50:37 PM EST
The hole for the gas tube is one of the most precise specs for the rifle, very strict about being exact for a good seal. If the hole is wobbled out (not sure how it would happen) your best bet is buy a new sight, someone will say loctite or sealer... do you use the rifle for defense of life?

If you have the shop, you could make a sleeve and sleeve the hole, be a good evening project. Make it from SS and just tell everyone that it is an *improvement*

Link Posted: 12/19/2005 3:02:26 PM EST
[Last Edit: 12/19/2005 3:05:00 PM EST by bigbore]
Link Posted: 12/19/2005 3:12:54 PM EST
[Last Edit: 12/19/2005 3:19:25 PM EST by Onepoint]
Crud, I was afraid of that.
No its not one I defend myself with, but that isn't a reason to half ass it. So much for the good deal on a PRI. The gas block was the only used part, everything else was new.

ETA- Yeah I disassembled to check it, the carbon was centered around the hole from test fireing, I will try the Locktite and see what happens, can't do more than not work and make me replace it anyway.

Thanks for the advice.
Link Posted: 12/19/2005 3:32:46 PM EST
Link Posted: 12/19/2005 3:49:58 PM EST
[Last Edit: 12/19/2005 3:52:43 PM EST by Gunzilla]
Loctite will probably work, if it is not a *mission critical* piece what the hell, put a buck in a jar everytime you shoot it till it blows out (if it ever does) and then empty the jar and get a new one, and some other goodies!

A lot of shops get lazy and drill the hole rather than ream it, it is a number 15 I think that works, but not as good as reaming.

... oh, and welcome to the bigbore and Gunzilla show, don't forget to visit the gift shop on your way out!
Link Posted: 12/19/2005 5:21:24 PM EST
A show that belongs on Comedy Central...

Link Posted: 12/19/2005 5:23:09 PM EST
Heheh, your "gift shop" is going to break me.
Link Posted: 12/20/2005 5:14:47 AM EST
have you checked to see if you have it centered over the gas port correctly?
Link Posted: 12/20/2005 5:15:05 PM EST
Yep it wasn't exactly center, but the port had a carbon ring all arouund it so it wasn't blocking it off.

This is an 18" barrel with a rifle gas system and the hole appears to be about .093", that sound about right?
Link Posted: 12/20/2005 7:07:33 PM EST
[Last Edit: 12/20/2005 7:09:39 PM EST by bigbore]
Link Posted: 12/20/2005 7:29:12 PM EST
Flippin cold.

About 20 degrees or so with a little breeze.

So would you recomend opening it up to .10 or so? What would be the outsideport diameter for an 18" barrel?
Link Posted: 12/20/2005 7:31:29 PM EST
Link Posted: 12/20/2005 7:33:09 PM EST
[Last Edit: 12/20/2005 7:38:24 PM EST by tweeter]
i agree on the gas tube conclusion. PRI doesn't make cheap shiz, the metal on your $12 gas tube is probably a cheaper troubleshoot than a $100+ fronst sight/ gas block assembly.

give that a try first, gas tubes are easier to find anyway.

ETA: well, there's ADCO at it again, trying to fix everybody's problems... for free.

hope it works for you.
Link Posted: 12/20/2005 8:09:34 PM EST
Alrighty then, I opened it up to .108 and will try to get out tomorrow and see how it runs.

If nothing else and I screwed it up, you can sell me a new barrel.

To be fair to the PRI, when the pin is in, its solid and looks like the pin holds its down against the port in the block, it does blow by some, but the carbon marks were very minor. I compared my other uppers to this one and nothing really stood out. That led me to think maybe it was something else. When I got a chance to take another rifle out and swap parts I narrowed it down and confirmed it shortstroking and figured the gas block the culprit because of the slop.

I really appreciate the input from everyone, thanks. ( ADCO is A+)
Link Posted: 12/20/2005 8:23:59 PM EST

Originally Posted By bigbore:

Originally Posted By Onepoint:
About 20 degrees or so with a little breeze.

Theres the problem. Open it up to 105 or 106 and I bet it will work just fine.

Link Posted: 12/20/2005 8:52:10 PM EST
Link Posted: 12/21/2005 3:10:19 AM EST

Originally Posted By eklikwhoa:
have you checked to see if you have it centered over the gas port correctly?

Careful measuring led me to insure there was a 0.060 gap between the barrel shoulder and PRI front sight during final assembly. Otherwise, the gas port in the barrel and hole in the PRI would not be lined up perfectly. This probably varies depending on the tolerance of the individual parts.

It is IMPORTANT to know how much of a "gap" needs to be present, because at the range, the PRI's position will need adjusted again to center your iron sights group windage while at mechanical zero. If you have your feeler gauge with you, excellent results in minimum time can be obtained.

Unfortunately, obtaining a proper Elevation zero was impossible without installing a taller front sight post. Which yielded a piss poor sight picture compared to a correct HK style "circle with post half way up in the center".

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