Barrel Index, Need Help

[Doco overboard]

Installed a barrel onto a Garand receiver, the shot group is left of mechanical zero, moved front site all the way left and it wants to overhang the base of the gas cylinder, which way do I need to turn the barrel. I think it needs tightened, could anyone help?

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[browningautorifle]

Send it to Chuckindenver, he's a gunsmith that has done lots. I'd do it for you but I'm across the border and that's it's own problem. Go search Chuck out in the members and send him a PM and mail it off to him...

Try this to find him... https://www.milsurps.com/member.php?u=5812

[M94/14]

Yes, Barrel needs to be tightened more.

This is a common problem with M1's, M14's/M1A's due to a lack of index marks on barrel and receiver.
With the M1, try to mount it in a vise or something so that the receiver is level, then push the gas cylinder, (without front sight) onto the barrel splines and place a flat piece of metal about 4" long across the top of the flat on the gas cylinder where the front sight attaches. If the barrel is indexed properly, the 4" piece of metal should be level. If it tilts one way or the other, adjust as necessary. There are many other measuring methods than the one described that also work and accomplish the necessary result. Use the one that you are most comfortable with.

[Bruce_in_Oz]

They didn't use index marks because they used a VERY nifty machine to wind in and torque up the barrel to its correct location.

This machine used a "split collet" sort of arrangement. If you have ever wondered about the "odd" profile of the rear end of the barrel, wonder no more. The "step" on either side fits the clamp shells, which, in turn are attached to a drive mechanism actuated by a longish lever.

Part of the trick is to select a barrel that pulls up by hand to a position "X" degrees short of final, torqued-up alignment.

When I find the appropriate instruction here, I'll post it verbatim.

[Bruce_in_Oz]

So far:

The reference is:

Ordnance Field Service Base Shop Data.
U.S. RIFLE, CAL. 30, M1
Base Shop Data - Issue Of 4-20-43 (I guess that means 20th April, 1943)
Sheet 3 of 18

(This replaces Sheet 3, Unit No2, Issue of 1-8-43)

See also:

The Jerry Kuhnhausen book:

The U.S. .30 Calibre Gas Operated Service Rifles
A Shop Manual
Volumes 1 & 2

Page 105 illustrates the actual machine ( Barrel/Receiver Assembly Fixture; Stock no. 41-F-2987-250), AND describes the alignment and operation procedures.
That illustration is itself lifted from:
TM9-1275, dated June 1947.

Go to it, lads! (and lasses!), whilst I get the scanner dusted off and cranked up.

[browningautorifle]

This is not something for the basement fiddler to sort out. If you don't have the wrench and vise for it then you'll damage the rifle trying. The barrel has already proven to him that it's out of index so no further testing or proving is needed, now it needs to be fixed.

[Doco overboard]

When I seated the barrel, I used a close fitting steel drill rod through the sight ears and a 36" Aluminum yardstick on the front sight base. Then I checked against a machinist bubble level on the same and it was as close as it could be. With the FS tightened at the edge of the gas cylinder base, the rear sight is 4 clicks right. I even went back and checked again after a few range sessions removing the FS leveling the work and using the level on the flat behind the rear sight. The combo shoots inside of that at 200yd and the settings are repeatable when the rear sight is adjusted. I would at the very least like to be able to get the front site post over about 2 min while staying inside the first set of graduations at the rear sight. I thought the barrel could stand a tighten to tidy things up a bit if that was the right way to go with it. I have the tools to do the adjustment but perplexed when I go over the procedure in my mind before I start. Thanks for the direction and everyone's input, I want to learn how to get it right myself and keeping fixing it till its broke..... then Ill see Chuck after its really out of of wack! In the interim I'm going to check out the literature that has been suggested and wait for replies before I get any tools out. Thanks again, Brian.

[browningautorifle]

a machinist bubble level

No, you need an angle meter. This will allow correct adjustment, the bubble is too subject to interpretation. This is a cheap enough tool to allow you to read exactly how many degrees out you are. Use the front sight base with the front sight removed and the flat behind the rear sight on the receiver. Here's the one I have.

I did have an occasion to have a bent barrel. It was bent so far back you wouldn't have believed it. It was bent since the factory...it had to be...and couldn't be zeroed with all the indexing in the world.

[Doco overboard]

Using the angle finder like the one BAR posted I found the barrel to be over indexed 1.5 degrees. So if my thinking is right I need to bump or rotate the barrel back if that's able to be done. Something else I did was affix the rod and yardstick that was originally used and then cast a bright light from the rear after careful leveling, onto a clean wall in dim light and the mistake was clear as a bell. After going through all this I realized front sight left, back-site right, oversimplifying things I have to make the two meet which equates to, if I'm right and please correct me, barrel to tight by a smidge. Thanks, Brian

[browningautorifle]

The angle meter makes it clear and there's no more guess work. If the back is one degree leaning left, then the barrel needs to match... I tried all the other ways that were posted on here and they didn't work for me. I still have yet to figure out the sheet of glass thing that Peter and some of the others use... This one works and unless the barrel is bent or front sight base is damaged...then you're good... To recreate crush factor with a barrel shank, you may have to tap the shank at the edge all the way around to give yourself some metal to crush again.