[teacherman]

I am totally new to this posting thing! have read the comments for two or three years but this is my first time and the water is a bit chilly. I have been impressed, maybe intimidated by the excellent information given by members of the forum!!!! as my title says I do not quite get hedsp. & tmng , esp. timing!!! I have read as much as is written,but still don't quite get how one actually does it. would appreciate any directions members will share!!! please make it slow, simple and complete. thanking you all in advance!! t'man----- make that teacherman ! t man still scares me!!!

 

[Armorer]

Someone asked this question a few weeks ago. The short answer on timing is for a semi autos forget about it. It serves no purpose on the semi-auto.

Headspace, short and simple is how far the cartridge case sticks out of the back of the barrel when the bolt is locked shut and ready to fire. It must stick out a given distance for the extractor to grab it and to compensate for expansion as the gun heats up, but if it sticks out too far the cartridge case will expand to the point of rupture or may shear of the entire base of the cartridge. Nobody needs an explosion like that. In a normal firearm you may never need to worry about it unless there is a lot of wear like on the locking surfaces of the bolt lugs. In the Browning guns (.30 and .50) the barrels are removeable and replaceable due to rapid heating and wear in the full auto mode. No two barrels are the same so an adjustment must be made for each barrel and for every time the barrel is removed for any reason. Many modern machine guns have quick change barrels but even then the spare barrels are usually matched to a given weapon and are not always completely interchangeable.

Headspace may also be affected by the type of ammunition used. In the old days for the .30 cal it was all GI issue ammo and made to the same specs. Now there is a lot of foreign stuff on the market and some is of dubious specs and some probably should not be used at all. Some cases may be made from brittle brass or steel. I am not sure but I believe there may be differences in how thick the brass in the base is on some cartridge. People with more experience with ammo will likely chime in on this.

 

[Roc Rat]

Taint nothin to be afeared of old boy,, I will assume that you have a semi,, If so timing does not apply. Timing is set by the screw at the rear of your trigger lock, or if that is not present, then by bending the trigger. It "times" the bolt lock up to the time that the trigger engages the sear and fires a FA 1919,, as stated, does not apply to semi's. The head space is another matter,,, If you screw your barrel all the way into the barrel extention, and then pull the bolt to the rear, it will close just so far, but will not lock into battery. An easy way to see and feel the lock up is to unscrew the booster off the end of the jacket. With the bolt pulled back, and the barrel screwed in, slowly un screw the barrel,,,, you will see the bolt start to travel forward,, as you continue, it will close further,, all od a sudden it will clack forward and lock up,, the bolt will go all the way forward and the breach block that is a part of the barrel extension will slide up the breach cam ramp and slide up into the bottom of the bolt,,, it iis now locked into battery,,, the final head space is normally two or three clicks further out (unscrewed). At this point the gun should cycle easily and smoothly. The trigger should engage the sear and release the firing pin.
You can do this with the booster on, but you will have to hold the bolt back as you insert a small screw driver into the barrel splines and click the barrel in and out one click at a time. The only reason to go the booster thing is to see it happen in real time. You learn a lot by seeing it lock up that way. HTH,,,,, Welcome and have fun.

 

[Lextech]

Sorry to post another FNG question, but in the instruction Roc Rat just posted, the finished gun is headspaced bolt to barrel, correct. So how do you correct for the ammo variations?

 

[stanamale1]

reheadspace

Each time you shoot diff. mfg. ammo you headspace. never mix different brands of ammo. sort and reheadspace for each. stan

 

[Armorer]

Roc Rat has described one way of setting headspace. The other way is to set the headspace outside the gun. It is done by removing the lock frame bolt ,barrel extension, and barrel from the gun. The lock frame and extractor may be removed. Withthe bolt in the barrel extension push the bolt forward and press the breech lock into the recess in the bolt until locked. Screw the barrel into the barrel extension until the barrel is stopped by contact with the bolt. Make certain that the barrel does not force the breech lock from its fully locked position. Unscrew the barrel until the breech lock falls free of its own weight. Then screw the barrel in one notch. That description was from TM 23-55 July 1965.They were referring to the 1919A6 and M37 but I see it was basically the same description as in the later in TM 23-55 July 1965 (all models) and TM 9-1005-212-10, April 1969 (all models except 1917A1).

They also state that the headspace should be rechecked after the parts are assembled into the gun. Of course the Army also had the benefit of usually having a headspace gage.

I have always found the method described by Rock Rat to be the easiest and probably best but I just included this for information purposes. If you use the method with the parts assembled in the gun and the booster removed you may find it difficult to turn the barrel especially if the muzzle end is chromed. I recommend a rubber strap wrench be used to get a grip. The headspace wrench works also if you happen to have one. The 1919A6 was eaisier as more of the barrel stuck out with the booster and or collar removed but that's another story.

 

[Roc Rat]

One additional thing you can do to make your life a lot easier on an Izzy 308 gun is to modify the spring that holds headspace into a 30 06 style spring,, I think there is a tutorial on doing this,, basically you are taking the square tab that sets into the splines on the head of the barrel and grinding it (CAREFULLY) into a "V" type that adjusts oh so easier that the square tab. If you do elect to take the internals out of the gun to check headspace,,,, if you remove the spring entirely,, you will be able to spin the barrel in and out easily,, its fun to experiment this way, and you will get a clear understanding of the entire functioning of the gun. I feel that building your own,, however daunting it may be,, gives you an intimate understanding of how a 1919 works.
Once you understand the headspace process, you will find that it is easy to hold the bolt back and turn the barrel in and out using a small flat screwdriver. Somebody here makes a special headspace adjusting spanner wrench that makes the job a snap.
Do yourself a big favor and do the headspace spring mod,, much easier.

Check here for a picture of the spring,,, its the second to the last picture at the bottom of the page. http://www.1919a4.com/tutorials/tutorial-headspacing.php

 

[teacherman]

thanking you all again!!

All of the info is useful and of course much appreciated!

 

[kkkriverrats]

Head space tip

Everyone shoots whatever they can find so head spacing is a serious safety issue. I only shoot my hand loads. I know what I am shooting.

So, I have prick punched the barrel notch and the barrel extension so I can visually check head space before firing There are actually two punches on the barrel the shortest head space is for handloads the longest is for CMP LC .30'06 M2 Ball ,they are one notch apart.

Since I shot all of my CMP stuff. I only look at the shortest setting.

This is only good with the barrel, barrel extension, bolt, and ammo that is currently being used in this particular firearm.

Change any anything and everything is subject to change.