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1/25/2018 7:38:29 AM
Posted: 6/14/2003 10:09:36 AM EST
I recently got the new 4 set screw version to mount on my Bushmaster barrel. After removal of the front sight and sliding on the PRI sight I noticed the front sight set screws holes dont mate up with the holes from the taper pins in the factory front sight. The set screws set lower than the factory taper pins did in relation to the barrel.

The set screws end in rounded nubs which "seem" to be getting into the hole which is too high just a tad and then pressing up against the edge of the barrel where the material is thin and covers the bottom edge of the hole. This prevents them from fully seating as far as they could if the holes lined up perfectly.

This "seems" to lock up fairly well even though the set screws dont go fully into the holes because they are not concentric. Is this going to be adequate to mount in this way or will I need to have the holes for the taper pins elongated down into an oval so the set screws can seat fully?

Also the left side does not srew in as far as the right side screws. I assume this is because the taper pin holes are smaller on the left side correct?

Am I required to use the gas tube pin that came with the PRI sight? Is it needed because the gas tube area is wider or something or is it just included as an extra nice thing to have?
Link Posted: 6/14/2003 11:17:40 AM EST
Devl, A friend of mine just installed the PRI on mine that has the cross bolts. He had to enlarge the old cross pin slots at the bottom of the barrel so they could lock in the old cross pin slots and thread into the other side. I would imagine that the same would have to be done with the set screw version. I don't know about the gas tube, I didn't see him do it and he gets to keep the old stuff for installing the new parts. So, I'm not sure what tube he used, If one was supplied, I would use that one. Hopefully this helps! Mark
Link Posted: 6/14/2003 2:00:53 PM EST
[Last Edit: 6/14/2003 2:01:05 PM EST by DevL]
I had the cross bolt version and sold it as it didnt fit and I would have had to modify the barrel for it to fit. MSTN assured me this would fit unlike the older version. Has anyone installed a PRI front sight on a barrel themselves that already had a front sight installed?
Link Posted: 6/14/2003 5:23:35 PM EST
I have the cross bolt version, I enlarged the hole with a round file with about the same diameter as the screw. I slowly worked on the holes until the screw just made it through.
Link Posted: 6/14/2003 6:06:13 PM EST
Well these holes with the set screws are the same size as my front sight holes just lower. MSTN no longer carries the cross bolt version and assured me this would fit no problem.
Link Posted: 6/14/2003 6:17:06 PM EST
[Last Edit: 6/14/2003 6:33:35 PM EST by Yojimbo]
I'm also planning to get a PRI flip up front sight in the near future. I recently posted asking about the pin hole specs on the "Optics and Sights" forum and I found out there were no specs! Troy replied and told me this was indeed true and that it's the same way with all the major AR manufacturers. The pin holes are drilled out as needed on each batch of barrels. This is news to me and it sounds crazy that no one has specified that pins must be x distance apart. I wonder how the we know the gas ports on the sights are in the correct place if there are no specs?[:\] This may be why you ran into trouble with fitting yout PRI sight. I called PRI and asked about this because I was concerned about getting a sight that I couldn't fit. They told me their flip sight with the clamp screws had the pin holes at 1 3/8" distance center to center. They said this was setup to match the Colt front sights they would be replacing. I measured the pin hole distance on my new CMMG/DPMS M4 upper and luckily it measures at exactly 1 3/8"! The PRI support person also told me they recommend using the clamp screw for combat rifles and set screws for match rifles. The reason being most match barrels have set screw style sights so that they can be adjusted for windage. According to the person I talked to at PRI they will be releasing a new model of the clamp screw (cross bolt)flip up sight in 3-4 weeks. It's suppose to have the screws a bit lower than the previous model so that no filing will be necessary to install them. How lowering the bolt locations will fix this is a mystery to me but that's what PRI said. It seems they often get a lot of calls about having to modify the barrel so the new model should make this a non-issue. BTW, if anyone can measure their clamp screw(cross bolt) PRI flip up sight I'd be interested to know if they are indeed 1 3/8" apart. I didn't know the PRI sight came with a gas tube. Is this tube different from the regular one?
Link Posted: 6/14/2003 9:01:17 PM EST
I've got the crossbolt version and it does indeed measure 1 3/8". -Cap'n
Link Posted: 6/15/2003 2:28:46 AM EST
Whta is the pRI web site address. I wanted to buy a PRIO front sight and I am now a tad confused on the the two type of set-ups. Do they explain it? Thanks
Link Posted: 6/15/2003 4:28:19 AM EST
Capn_Crunch, Thanks for measuring the pin holes! WSAR15, The PRI website is here - [url]http://www.pri-mounts.com/index2.htm[/url]
Link Posted: 6/15/2003 5:07:11 AM EST
[Last Edit: 6/15/2003 5:20:49 AM EST by WSAR15]
Thanks Yojimbo What is the difference between "clamp screws" and "opposing set screws"? - the photos seem the same. Given a choice, which is the better set-up and why?
Link Posted: 6/15/2003 10:17:59 AM EST
If you will reread my post I said GAS TUBE ROLL PIN not gas tube. This is in fact because the space for the gas tube is wider than factory. Some people use two gas tube pins one from each side for certain gas blocks if they lose the longer one provided with a different front sight or gas block. I do not know this is for a FACT for the PRI front sight but I know it is the case with other aftermarket sights and gas blocks. The problem with front sight pins is not the space apart. They (front sight pin holes) are all the same distance apart. The holes are not low enough on my barrel to mate with the set screws on the front sight. If PRI is going to make the bolt location lower it will not be touching the barrel at all, but connecting with friction only and while the shoulder the front sight rests on is more than enough to prevent the front sight from coming backward the only thing holding it from going forward will be friction. I dont know if they are infact coming out with a new version for replacement on factory barrels in a few weeks but I am a bit upset. By now one of the guys at MSTN is reading this thread. I sold the cross bolt version of the PRI front sight I had because it would not work without modification to my barrel and on the advice of MSTN bought this front sight instead. If there will be a new front sight that fits my requirements perfectly and this is a poor solution I feel that pushing a product because its on your shelf and saying something will fit when in fact its known not to is a VERY poor business practice. Its not something I expect from a company as professional as MSTN. I hope someone from MSTN can chime in and clarify all this.
Link Posted: 6/15/2003 3:53:34 PM EST
[Last Edit: 6/16/2003 9:10:48 AM EST by Yojimbo]
Devl, Thanks fir the clarification. BTW, not all front sight pin holes are in the same place. My pre-ban Eagle Arms upper has the front sight pin holes spaced 1 7/16" apart. It's not much difference but it's enough to make it PIA to install a sight with pin holes set at 1 3/8" apart! [;)]
Link Posted: 6/16/2003 7:47:02 AM EST
Link Posted: 6/16/2003 9:00:54 AM EST
Anyone install a PRI flip-up front sight on a SR-15 Match rifle? Just curious, I might consider upgrading my KAC SR-15 to a pseudo SPR rifle...That's right I said Pseudo, not a replica or even a copy... Any thoughts on this type of project? Thanks as always-
Link Posted: 6/16/2003 9:24:18 AM EST
[Last Edit: 6/16/2003 9:31:25 AM EST by Yojimbo]
Originally Posted By WSAR15: Thanks Yojimbo What is the difference between "clamp screws" and "opposing set screws"? - the photos seem the same. Given a choice, which is the better set-up and why?
View Quote
Sorry for the late reply. The clamp screw modell has a full length screw that goes through the pin holes. The set screw model has four shorter screws that do not pass all the way through the pin holes. According th PRI the set screw model is mostly for match or precision rifles so that you can adjust windage on the front sight. It sounds like a toss up as far as witch one is better. Wes seems to prefer using the the set screw model and his reasoning for it is sound. As for me I would probably get new clamp screw version as PRI recommended.
Link Posted: 6/16/2003 3:08:17 PM EST
Sorry I just wanted a response and was getting upset you had not chimed in so I was speaking a bit out of turn I suppose. The front hole is open on the bottom in the front hole but the rear one is just barely closed on the barrel by a 1mm piece of ultra thin barrel. If I filed out the bottom just a tiny bit would this allow propper seating? I really should not have posted something that could have been construed as implying you were dishonest in any way but I was getting worried since you never replied. Sorry about that.
Link Posted: 6/16/2003 5:00:49 PM EST
Link Posted: 6/16/2003 5:34:03 PM EST
Thanks Wes. Are you saying I should only go to the tightness I can get with the short arm then do an extra half turn with the long arm of the hex key?
Link Posted: 6/16/2003 5:51:34 PM EST
my colts are 1 3/8 ,but i have a wilson upper that measured 1 1/2 center to center.does this mean a PRI cant be installed?
Link Posted: 6/16/2003 7:08:21 PM EST
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