Vertical POI shift after removing mag screw

[Sarge]

I tore my 20" 45 colt down to refinish the stock a few weeks ago. The mag tube retainer screw was way tight and appeared to have thread-locker on it, once removed. When I replaced it, I snugged it down good and noticed it was shooting about 4" higher at 100 yards, than it did before the refinish.

There is no guesswork involved in this finding. I am the most OCD SOB you will ever find about having my guns zeroed with my bulk load- in this case a Lee 255 RF over 8.5 grains of Universal for 1180 fps from the R92. Prior to refinishing, I had just mounted a 0.410" brass bead that facilitated an exact 100 yard zero with the elevator on the lowest notch and a good 200 yard zero on the second one. All accomplished by careful, rested shooting on calm days.

Has anybody else noticed a vertical POI shift after removing and re-tightening the magazine retainer screw? I may re-torque this one a tad looser and add some Loctite to insure it stays put.

[mr surveyor]

I think you may have the right idea. The "factory" just may have the official torque setting for that screw to stay close to the needs to maintain proper barrel harmonics .... and just use a dab of locktite (or Brazilian equivalent) to stick the screw.

May just be me, but it does sound like a case of off balance barrel harmonics.

I still need to tinker with my old Marlin 336 screws since it's never shot the sub MOA groups I was accustomed to before the complete makeover several years ago. It may just prove my re-loads (beginning shortly after the gun re-do) aren't as crappy as they sometimes appear to be.

jd

[Sarge]

This one was overlapping bullet splashes at 100 yards with the aforementioned loads and still shoots about that well, just a tad high. The stock is done and there's no reason not to relieve the torque a little and secure that adjustment. I can always apply a little heat to the screw should I ever need to remove it again.

[GasGuzzler]

Cut the center out of the top of the forearm.

[Ohio3Wheels]

The screw could be a tad long and putting pressure on the barrel. Neither of my '92s had thread locker on that screw and as Gas suggested the fore arm may be the problem.

Make smoke,

[mr surveyor]

The screw could be a tad long and putting pressure on the barrel......
Make smoke,

This


jd

[Sarge]

I figure the screw should bottom out in its corresponding recess, under the barrel, w/o causing undue upward pressure on the barrel. I don't want to shorten it much because the last thing I want is for the mag tube to take a walk.

[Ohio3Wheels]

Yes, it should bottom out but only just. It wouldn't take much more than a couple thousands extra to cause undue tension. I haven't convinced myself that the "pin and dimple" serve any useful purpose other than maybe keeping the magazine tube from rotating and coming loose. In the scheme of things that and friction are the only thing keeping the tube from moving forward under spring tension and recoil. This being the case the pin has to engage the hole but it shouldn't press up on the barrel. I seem to recall a thread where the same problem came up and the solution was a couple of swipes with a fine file and a polish with emery cloth and done.

Make smoke,

[mr surveyor]

I found that it may (definitely) require more than a couple of swipes on a file to get a new screw down to length. A couple of years ago I had to order a new screw for my .357 R92 and the unthreaded tip of the screw was way over needs. I suppose those screws are originally constructed for use on any of the different caliber models when trimmed to fit .... but that idea really don't make much sense. More likely, they just grabbed a mag plug screw out of a random bin and sent it.

jd

[HarryAlonzo]

I picked up a Winchester Model 71 in July, and just about the very first thing I did was grind a bit off the mag plug screw. That mag tube is threaded, so anti-rotation is the only purpose served by the tip & dimple.