Off center front sight

[Gopher]

O.K. , after living with this 7 or 8 years, I've decided I want to fix the problem. I'm coming to this forum because I believe the most knowledgeable people are here and hopefully will offer guidance.
I have a semi-auto Mk II built by Historic Arms. It's a wonderful build except somewhere, something got a little off. The result is that the front sight is .12 inch to the left in order to be on target at 100 yards. I spoke to Len about this shortly after I got the gun and never got a resolution.
Here's what I've thought about doing. Someone please tell me if I'm nuts.
First, messing with the receiver doesn't sound a good idea. I'm not willing to risk ruining it to correct a problem which some people wouldn't consider a problem.

I have 3 Mk II barrels, 2 which I have moved the front sight to the left after test firing. The other one I have left centered as a control so I don't believe the barrels are bent. When all three barrels are mounted, in turn, there is no play in the mount.

My proposed solution is to move the rear aperture to the left an equal amount which would allow the front sight post to be centered. I wonder if the aperture block could be heated enough to allow the metal be stretched the .12 needed.

So what do you guys think? Am I being too anal over nothing or am I totally wrong in my thinking. I want to keep the stock appearance but I would really like to quit looking at a cocked up front sight.

Information

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[tankhunter]

If I were you. I would NOT touch the rear sight!.....
If you grip the barrel in your LEFT hand, with the flash hider in the palm. & Your thumb under the front sight bracket. Is there ANY radial Movement whatsoever?.. If so, the barrel is loose, & this defect WILL affect trajectrory.
It is easily remedied, by fitting barrel nut (Locking Lever to you Guys!) the next size up.
If this is NOT the problem. It is POSSIBLE. That if your gun was put together from a kit, as a Re-weld. The receiver sections MAY not have been alined correctly before welding. OR, the welding process MAY have warped the receiver a little?
Until you check these areas. Do NOT try to 'Stretch' the top of the receiver with Heat!.....

If you don't wish to touch your receiver etc. an EASY way to correct your problem at your end is. to acquire a spare front sight, of the same size as the one you have on your gun at present.
Remove the .12 that you want gone, By removing metal from the Left side of the sight element. Refit & test shoot. Adjust lateraly, for the movement required on your target.

[Peter Laidler]

Are you saying that to zero the gun at 100yds the complete blade is .12" over to the left? It's worth bearing in mind that to zero a Bren, the MPI of the 7 shot single shot group should be 1" to the LEFT of the aiming mark at all distances. So I'd get the zero corrected first and then come back and tell us again.

If it is currently correctly zeroed at 1" to the left and the blades of all barrels is .12" off centre to achieve this then it sort of indicates that it is a gun fault a opposed to a barrel fault. BUT if this was a service gun with an otherwise perfectly serviceable barrel then we say that so long as the edge of the foresight blade is clear of the foresight protector then it is acceptable.

Like Tankie says, don't try faffing about with the body or backsight

[jmoore]

Had to offset the front sight on my Historic Arms Mk.Im. Hasn't been any great distraction. Don't remember the exact amount, but it's visibly offset between the "ears".

[CINDERS]

Thanks Peter never heard of "faffing" but can pretty much guess what word it refers to, looks like some Aussie rubbed off on you while you were here.

[Peter Laidler]

You're dead right Cinders. We have a friend and his wife from Qld staying here for a few weeks. Wifes friend from school (a pom emigrant) and he was 7RAR same time as I was with 8. All the Australian just returns from the memory banks so I've got some clean strides on to go and get some tucker later........ Going over next year, back to Enoggera where I can learn to hurry up and wait again!

[Gopher]

Thanks for the replies.
Tankhunter, the barrels show no movement when twisted as you said. The barrel locking nut was machined to fit the opening that was left when the receiver was welded up. This is a kit build. The barrel nut has some movement but when a barrel is installed, that movement goes away. The hole that the barrel shank fits into is very tight and takes all play out of the mount. I do have a spare barrel nut but I don't think it could be machined any closer than the original.

I have no doubt that the problem is in the receiver and I have no intention of heating the receiver. I was speaking of heating and stretching the aperture block of the rear sight. I have 2 spare rear sights, one of which I have disassembled, so I would be adding heat to the aperture block only.

Peter, the center of the front sight blade is .12 to the left. This puts me dead on at 100 yds. Based on what you say, I've probably over corrected the front sight blade. That's easy enough to correct.

jmoore, if you get a chance I would be interested in a measurement of your sight offset.

[TactAdv]

Ya'll are overthinking this waaaaayyyy too much...... ;-))

It's a cut & re-welded gun already so, ahem, some "creative" work is allowed.

It's also a MkII, so you're on easy street with the fix.

Disassemble your rear sight APERTURE piece from the assembly/slide. Take that aperture, and saw cut it just to the RIGHT (when viewed from the rear) of the circle, fabricate a PLUG the needed .120" in length, then TIG weld back the plug in-between the circle and the arm of the aperture piece. Hand file/trim/contour for cosmetics. Re-assemble your sight assembly. Done.

You have just moved the POI the needed offset distance to allow the FRONT BLADE to mechanically zeroed in front sight block/holder on the barrel.

No one will ever be able to tell the rear aperture is now "longer", i.e., offset.

-TomH

[Peter Laidler]

I know where you're coming from Tom but surely BEFORE Gopher goes down that path, it's better to zero the gun CORRECTLY for deflection before he does. Because if you don't, the accumulative error at lesser and greater ranges will simply multiply. Correct is that the MPI....... and so on. Only when this is achieved will the altering the cursor slide trick be accurate. That's because if it's not zeroed correctly before the alteration then it still won't be correctly zeroed after the cursor slide alteration. The foresight might now be in the centre of the foresight block there will STILL be accumulative as before at greater or lesser ranges.

As a matter of interest, is this a common 'fault' with re-welded guns? Or is it that new gun owners just zero it in as they would a rifle instead of the MPI being over to the right of the PoA

[TactAdv]

Common fault? Yes, it can be.

All depends on the original level of due diligence used by the "(re)manufacturer" in establishing both a proper set of welding fixtures, then in proper weld technique itself.

Typically though, I have seen LESS problems like this in guns that have a very thick-wall receiver.....BREns, DP's, etc. Worst of all are thin wall, sheet steel receivers......tube receiver SMG's, etc.

Common troubles are MG-42 receivers......low carbon steel, improper heat techniques (lack of heat sinks behind welds) that REALLY cause warpage as the weld joints cool.

(you're no doubt fully remembering how they "straightened" the tube of the Sterling during manufacture.....a programmed warpage in cooling after a pre-set off-set. Somebody wrote a book about that......)

We like to say "Too little brain, too much heat".

I had to fix a badly warped '42 receiver that was VISIBLY misaligned.....there was not enough adjustment in the iron sights to accommodate the offset.....fixed by cutting again, then welding it back with a LOT of filler on the "short" side gap.

I think we're probably the only market on the planet where re-welded guns are such a thing. OTOH, we've collectively got back and running a TON of cut guns......that HAS to hurt someone, somewhere......which I love.

---------- Post added at 03:23 PM ---------- Previous post was at 03:21 PM ----------

Oh yeah, Peter, two words never heard here.....

"Enfilade" & "Defilade". You can probably also throw out "beaten zone" , too.

Semi-autos are pretty much regarded as rifles here, on all levels.