a3 front sight post

[ssgross]

I ordered a 1.225 aluminum bushing, and the lead shims brownells sells for their vise for this purpose - they are .045 thick. This with some rosin should get me nice and snug. My barrel is 1.2 exact - another forum reports a3 barrels are 1.195 - I suppose the extra .005 could be the park finish. Brownells has a 1.2" steel bushing, but being my first time using this vise, I didn't want to chance it slipping with no room for a shim. Others have advised and succeed using an undersized (1.15 or 1.175) aluminum bushing for its malleability.

[browningautorifle]

This with some rosin should get me nice and snug

You HAVE rosin? I thought the stuff Brownell used to peddle was unavailable now? What do you have? I need some...

[ssgross]

https://www.amazon.com/TOURNA-ROZ-3-.../dp/B009ZALIAC
works for bowling balls. should work for this too. Couple of the other forums I saw mention it being acceptable. Although I doubt I'll need it with a lead shim over clean rough seemingly newly parkerized barrel.
EDIT: quick search found this https://www.midwayusa.com/product/1006358655

[browningautorifle]

Don't know about the bowling ball resin but the stuff from midway would be worth a look.

[ssgross]

let me know if they won't ship to Canada. I'll be your resin mule. (Isn't resin one of the hot commodities, along with dirt and paper in the movie "Water World"?)

[browningautorifle]

"Water World"

Was one of my favorite movies back then.

[ArtPahl]

I am wondering what is going to happen to the headspace when you twist that barrel. Your OP said the sight was at 11:00. That's 1/12th of a turn (30 degrees). At 10 t.p.i., that's backing off .0083 and, of course, headspace tolerance is .006. The out-of-plum condition is probably not that bad but even at only 10 degrees (which would be hard to notice), that's adding .0027 to the headspace, which is a pretty good chunk of the .006 tolerance.

Is the barrel going to be loose? Will the torque from firing in the RH twist tighten it up again?

I still say move the sight and leave the barrel alone to avoid more problems.

BTW: What about the rear sight? Is that centered with the front sight cock-a-skewed? Are you going to have to relocate that, too?














































btw;

[Doco overboard]

Theirs that much crush at the barrel shoulder and receiver face when the barrel is re-tightened.
I wouldn’t worry too much about it especially if the shoulder is peened or rolled meeting the marks dead on or just proud of them one way or the other.
He’s going to have to do that anyway or it will be way past them I bet.

[ssgross]

Your OP said the sight was at 11:00

That was rough estimate. The point was to stress that it is obviously off. After looking at the extractor groove, I don't think it is nearly that far off. It looks better or worse depending on what angle you look at it or take the picture from.

that's adding .0027 to the headspace

Thanks for the specs.

What about the rear sight? Is that centered with the front sight cock-a-skewed? Are you going to have to relocate that, too?

At zero with the skewed front sight, you can see the rear sight location skewed left of center to compensate. Rear sight is easy to adjust/drift on this rifle and I'm not worried about it.
Actually, with some simple trig we can figure out the exact degree of rotation required, using the rear sight offset (easy to measure) and the height of the "A" blade above the bore. Let me measure. That will at least give better than an eyeball ballpark.
Angle = arcsin(D/H), where D is the distance the rear sight is drifted to zero, and H is the sight height.

[ssgross]

Its ~6.25 degrees off. Which is indeed enough to notice when looking through the rear sight (drifted .127 left).
For anyone else that finds this, the height of the "A" blade at 1.167 above the bore center.
6.25 degrees is still a ballpark - this assumes the rifle was perfectly level when zeroing and not "canted". But we can figure out that case too.
If it was canted, the rear sight base would have been on an angle. This means the "level" drift of the rear sight would have a lowerbound of cos(6.25)*0.127 = 0.1262ish. Using the previous calculation, a minimum for the amount of cant is ~6.21 degrees.
If you skipped all that, my barrel is between 6.21 and 6.25 degrees over-timed.
My grad. school advisor gave sound advice for presenting mathematics..."never ever do computations in public".
Attachment 114211
so no more than 0.0017361ish increase in headspace.