TDC/Timing: sight-in problems?

[Rat A Tat]

If so how much can just a little off TDC affect you. I was over indext by just a smudge and was hitting 16" to 18" to the right. 5" to 6" with the rear Wind adjusted all the way to the left. Could this be to the TDC by it self or is my berral bent?

[Mike A]

RATT,
I recently experienced this myself.

Long story short, my TDC was short (under-torqued) by only a couple of degrees, but with my rear sight fully adjusted to the right, still the POI was 3"+ left of POA. That was at 100yds. At 200, this was over 12 inches.

Yes, it makes a HUGE difference!
Check your TDC before you sign off your barrel as being bent.

Cheers,
Mike

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“Molon Labe"
["Come and get them"]
- Leonidas to Xerxes at the Battle of Thermopylae when
told to lay down their arms and they would be spared.


moamike@ix.netcom.com

[EMDII]

"BTDC or ATDC makes a huge difference....." is right! I got to experimenting w/ my perfectly good Hesse FALO-C one day. Wound up 4"D, 8"L. This weapon was shooting to POA at 250m before I played monkey w/ a wrench!

Sent it to George Gouger, a fabulous gunsmith and interesting guy. Got his 'blackened blue' (looks like MilSpec M16A2 finish, but is bluing). He d/a'd the whole shooting iron, blued, and reassembled to proper torque and TDC. VOILA!
http://www.fnfal.com/forums/biggrin.gif

Here's a quick TDC check. Clear your weapon, then insert an empty magazine. Move the backsight to it's highest setting. Turn the weapon upside down onto a flat surface. My wife let's me use the kitchen table!
Balance the weapon on its front and rear sight assemblies. Look down the long axis: IF your magazine is not STRAIGHT up (very easy to discern) then you have a TDC problem, or the gas block was misaligned. Either causes the off-set you've described.

One of our good smiths can do you right. You may be able to do it yourself, but be careful.


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1*...........Train Like You Fight: Second Place is NOT an Option.

E.M. (Ted) Dannemiller II

[This message has been edited by EMDII (edited August 07, 2000).]

[Mike A]

EDMII,
I tried your example, but if you're only a couple of degrees off, you won't notice it that way.

What I did was take off the handguards, top cover, and remove the bolt/carrier. Insert magazine. Close upper and lower. Rest bottom of magazine on a flat surface (table top/counter top), using it as a pedistal supporting the entire weapon in an upright, barrel slightly down attitude.
Take a perfectly straight rod or drill bit and put it through the handguard screw hole so it protrudes evenly on both sides. Now take another one, the thinner the better, or a thin piece of flat stock (perfect machinist's rule works well) and put it on the top of the upper receiver rails, again even on both sides. Now, get in front of the muzzle and look at the two rods/pieces of stock. If they are perfectly parallel, you're TDC. If they have even the slightest "X" to them, you're off. From your view point (muzzle end), if the rod by the gas block is low on the left, then your barrel is BTDC, Low on the right is ATDC. Works like a charm and removes the human error by eye-ballin' the upright magazine.

I'm not knockin' your technique, but I was told about this one after I tried your technique and it did show what the other failed to do. I was BTDC a couple of degrees, so it was tightened slightly, and now shoots dead on.

Hope it helps!
Cheers,
Mike

------------------

“Molon Labe"
["Come and get them"]
- Leonidas to Xerxes at the Battle of Thermopylae when
told to lay down their arms and they would be spared.


moamike@ix.netcom.com

[Rat A Tat]

I took the hand guards off. Held the rifle upright out in front of me. then useing one eye I focused on the gas tube and then the berral behind it making sure they were uniform from receiver to gas block. This seemed to work the easiest and best for me.
I am sure it is dead on now. As soon as I can get back to the range we'll see wat happens.

[EMDII]

Nice technique Mike. I'll keep that one in the pocket.
http://www.fnfal.com/forums/cool.gif

JEN, oh MIGHTY JEN: Post this to a FAQ section, maybe?
http://www.fnfal.com/forums/biggrin.gif


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1*...........Train Like You Fight: Second Place is NOT an Option.

E.M. (Ted) Dannemiller II

[Mike A]

Ted,
Thanks for the kind words. I only wish I could take credit for it, but an individual on the forums told me about it a couple of weeks ago when I had the same problem. I tried to find his name to give credit, but I can't seem to find it.

I used it and it works GREAT! http://www.fnfal.com/forums/wink.gif

Cheers,
Mike


------------------

“Molon Labe"
["Come and get them"]
- Leonidas to Xerxes at the Battle of Thermopylae when
told to lay down their arms and they would be spared.


moamike@ix.netcom.com

[Dirtfarmer]

BTT

[boing]

I tried the rod in the handguard thing, or I tried to try it. The hole for the handguard screw isn't cleanly machined, so the rod won't set straight. I haven't shot the rifle yet, so it might be a moot issue, but I wanted to check it anyway (it's a Century).

[EMDII]

Take the handguards completely off. The through-way in the gas block is machined, so you'll have a true representation. Use rods (brass hobby rod works fine, too) that approximate the size f the hole.

http://www.fnfal.com/forums/wink.gif

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1*.....Train Like You Fight: Second Place is NOT an Option.

E.M. (Ted) Dannemiller II

[boing]

I did take the handguards completely off. http://www.fnfal.com/forums/smile.gif But then there's this hole, and while it's clearly machined, it's not cleanly machined...there's a burr or some such thing in there. I have a rod that would fit perfectly if it wasn't for the burr. I hesitate to try cleaning up the hole with a drill bit because I'm not sure I can keep the bit true, orientation-wise.

I'm waiting on shooting the rifle until my DSA mount arrives, then I'll sight in the irons, and see if I have a problem to fix.

Mostly I just wanted to play with my new gun. http://www.fnfal.com/forums/smile.gif