M14 Forum

MemphisMachinists · February 14th, 2012, 08:05 AM

I posted a while back about a barrel that I have that was rough chambered (not short chambered) and I have been trying to figure out the best way to finish it with out ruining it. Yesterday I decided that I had thought about this long enough and have it almost finished.
Here is my question. When you chamber a barrel (off the reciever) how do you measure the depth. Do you put in a guage and depth mike from the outside edge of the barrel? This seems like the most likely answer to me, but I am swimming in new water here. If this is the answer what guage does one use and what is the distance?
I only want to get it close enough to finish it with the barrel installed and the bolt already lapped. Basically I want to short chamber it.

leadbug · February 14th, 2012, 08:23 AM

I thought that is what headspace gauges were for. I guess I'm confused.

Dale Rader · February 14th, 2012, 10:29 AM

Use a depth mike and measure from the receiver face to the bolt face with the bolt closed and rearward pressure on it. Write this dimension down.

Place a minimum sized headspace gauge in your chamber and measure from the rear of the gauge to the barrel shoulder and compare this measurement to your receiver measurement. Stop cutting the barrel when the headspace gauge is about .020 longer than the receiver measurement. Install the barrel and finish cutting it to final dimension.

Hope this helps!
Dale

MemphisMachinists · February 14th, 2012, 11:45 AM

That makes sense. Now the problem is getting the face of a depth mike on the guage when its in the barrel. Maybe I can figure something out. It makes more sense to measure from the shoulder of the barrel. Maybe I can measure from the back of the barrel to the shoulder and then mathmatically adjust my reading or use a small block of known size to space it out. Even if I am off a few thousandths it won't matter because the finish cut will be done with the barrel tight and the bolt pushing the reamer to the desired headspace. Thanks for helping me think this out.

Dale Rader · February 14th, 2012, 11:48 AM

You can use a parallel or a 1-2-3 block to lay on the back of the gauge and measure to the shoulder and then subtract the thickness of the block you are using. Give me a call if you wish to discuss it.

Dale

MemphisMachinists · February 14th, 2012, 11:51 AM

I think I got it, but once again you have been a great help.

Quote:

Originally Posted by Dale Rader

You can use a parallel or a 1-2-3 block to lay on the back of the gauge and measure to the shoulder and then subtract the thickness of the block you are using. Give me a call if you wish to discuss it.

Dale

kgcoker · February 14th, 2012, 12:09 PM

I have a book that gives exact instructions if you wan to borrow it.

KG

MemphisMachinists · February 14th, 2012, 02:29 PM

Tried measuring this on a new chrome lined barrel. Works perfect. The difference on the finished chamber is actually about 16 thousandths which is exactly what I would expect. I think I will leave a little extra just in case.Thanks Dale

I am going to read the chapter in McKees book before I finish it out Thanks KG.

I don't have headspace guages so I am using a new piece of brass that I sized for a guage. I know it is not right, but I think I can get away with it. My reamer has produced good chambers in the past. All I have to do is get the chamber opened up enough to get it in behind he bolt. It is a slow process, but it seems to be working.

Quote:

Originally Posted by Dale Rader

Use a depth mike and measure from the receiver face to the bolt face with the bolt closed and rearward pressure on it. Write this dimension down.

Place a minimum sized headspace gauge in your chamber and measure from the rear of the gauge to the barrel shoulder and compare this measurement to your receiver measurement. Stop cutting the barrel when the headspace gauge is about .020 longer than the receiver measurement. Install the barrel and finish cutting it to final dimension.

Hope this helps!
Dale

Dale Rader · February 14th, 2012, 03:52 PM

I can send you a set of headspace gauges if you promise not to slam them closed in a rifle. If you want to use them, let me know. I also have a Mo's gauge if you want to make brass "gauges" of different sizes and label them to size.

Dale

MemphisMachinists · February 15th, 2012, 05:54 AM

The distance from the face of the reciever to the face of the bolt is .658". Does this sound correct? I'm measuring about .642" on the chrome lined barrel from the gauge to the shoulder.
This may not be interesting to the rest of you guys, but I am learning a lot with this project and having fun. I hope it is not boring.

Dale Rader · February 15th, 2012, 10:20 AM

Those sound like the right lengths but one thing concerns me; the headspace gauge to the barrel shoulder distance needs to be LONGER than the distance from the receiver face to the bolt face. That way, you can finish chamber once the barrel is installed. Please double check the dimensions...I hope you didn't go too far!

Dale

I just re-read your post. Those measurements are on a FINISHED barrel. That makes sense now. I thought that was the barrel you were short chambering. Sounds like you have it whipped! Good luck with it all!

Dale

Devil · February 16th, 2012, 07:55 AM

There is another way to double check your math before proceeding. Screw the barrel you will use into the receiver you will use. Make it tight by hand and put your flash hider you will use for the build on the barrel. Lay it on a level surface and use an angle finder with dial indicator or digital readout. Place it on the flat behind the rear sight base and the front sight base. Note the difference in angles and record. Check headspace with guages at this time with the bolt you will use. For every 3.6 degrees of rotation on the barrel to get to correct index, it will move the barrel back .001 Subtract the difference in angles and divide by 3.6 and this will give you how much reaming you need for short chambering.

donker2 · February 16th, 2012, 10:15 PM

Polish it when your done. And post pictures.

MemphisMachinists · February 17th, 2012, 06:09 AM

I am having trouble getting it finished. What I did on this was to put the barrel in a very small lathe with the chamber end facing the tailstock and use a pull thru reamer. The lathe is small enough for the barrel to stick out past the spindle and I used a live center to apply gentle pressure to the rear of the reamer turning the reamer by hand. It worked great at first I could move the reamer 1/8" easily and then remove it and clean away the chips. As I got further into the bore and more surface was being cut it sloooowed down. At some point the pilot of the reamer was too tight in the rifling and I had to remove enough of this to get clearence. This pull thru reamer is designed to remove small amounts of metal and the flutes are very shallow. The surface finish in this chamber is excellent, much better than any I have seen on other barrels I bought.I am using a lot of Tap-matic. I am probably not able to advance the reamer more than ten thousands without stopping and cleaning the flutes. I got frustrated and quit when I started having ideas about how to speed this up. I hate to buy chamber reamers at this point, but it may be the best solution. What I normally do when I am not certain about how to proceed is to do nothing so that is where I am at.

Edit: I am definitely open to suggestions.

Quote:

Originally Posted by donker2

Polish it when your done. And post pictures.

Dale Rader · February 17th, 2012, 03:27 PM

Measure the smallest portion of the reamer (just behind the shoulder) and use a drill just smaller than that size. DO NOT GO TOO DEEP! The drill will follow the bore and give you a larger pilot hole for your reamer to follow. Also, when you run your reamer, attach a coolant line to the muzzle and keep a constant flow of coolant running through the barrel to keep the reamer flutes cleared. All of the drilling/reaming should be done with a floating tool holder also.

Dale