300 BO won't cycle

[roysha]

ALL FIXED. Please see #12 post.


I posted this in the CB Loads/ Military before I realized I should have posted here. Long story short, my 300 BO will not cycle with the carbine length gas system so I want to turn the barrel back to allow installation of a pistol length gas system. Before I start cutting I want to make sure I have my dimensions correct.


1. From the front of the shoulder on the barrel extension to the center of the port in the barrel is 3.90". Correct?

2. From the rear of the gas block to the center of the port in the gas bock is .265.

3 Using the above data the length from the front of the shoulder on the barrel extension to the shoulder on the barrel where the gas block abuts should be 3.635".

Please, before I start cutting, will someone either verify my numbers or give me the correct ones. This project has been a study in frustration and I really don't want to make it any worse.

[roysha]

Yes, I checked those things after reading your (or someone's) post and although I didn't respond to it, everything checked out virtually exactly the same as my M-4, the depth of the tube into the key, the diameter of the tube, both OD and ID, and the ID of the gas key. However, I don't know what is the correct depth for the tube into the key (I assume it should go in just a wee bit short of bottoming inside the key since that is what both do) so it may be that I have 2 guns that are both out of spec. exactly the same but because of the higher pressure at the port of the .223 cycles.

[skeet1]

roysha (http://castboolits.gunloads.com/member.php?7850-roysha)
May I ask what load you are using? Some powders work better that others. My 300 BO works well with 296/H110, IMR4227 and L'l Gun. I have shot the Lee 312-155 and the NOE 311299. without problem in cycling or bolt hold back all done in a 16" barrel. I'm not saying that other bullets or powders wont work, only that my rifle does not seem to be very fussy.

Ken

[roysha]

17.5 grains IMR 4227 and the LEE 312-155 and 16.25 grains H-110 with same bullet. Primers are looking very flat and it appears that there may be a tiny bit of leaking at the FP since the dent looks very dark. About 60-70% of the time it will just barely eject case but never even come close to stripping the next round from the magazine.

Also tried loads using Sierra and HOR jacketed bullets, 150 and 165 grains. Again, no joy.

I agree that it is a gas flow issue but I'm at a loss for what to check next therefore the plan to convert to pistol length.

[Artful]

have you tried factory ammo?
I'm using slower powders than you (5744 & 680) with my carbine.

[xacex]

I do not think you have your gas block aligned well if you have checked everything else. I noticed on my carbine gassed gun it was critical to get the alignment perfect or I was not getting enough gas. You also do not want your gas block right against the shoulder of the barrel. There need to be a gap there the thickness of a hand-guard cap for perfect alignment. Are you using a A2 stock, or M-4 stock? I did notice that A2 stocks were harder to run for some reason with that barrel as well. Since you are reloading yourself there could be a multitude of things wrong with not only the gun, but the load itself. Do diagnostics with factory ammunition.

[skeet1]

If everything is open and aligned the only thing I can think of is a blocked gas port.

Ken

[Artful]

Oh, and if you want to try to use pistol or carbine...
http://img.photobucket.com/albums/v355/rowdyfisk/FAL/bothports.jpg

[Moonie]

You really should determine why it isn't working with the loads you are using, they should function it properly. The symptom suggests no/not enough gas is getting to the BCG. Either the port, the gas block, gas tube, key or even issues with the rings on the bolt could be your issue.

[roysha]

Thank you all for your input with this situation.

Over the weekend a friend and I tore everything apart, again, and measured every conceivable dimension we could think of, even if it didn't seem relevant. We discovered that the shoulder on the barrel against which the forearm ring and gas block rest was .065" too far forward which caused the gas block to not line up for and aft, virtually blocking off the biggest part of barrel port. We compared this length to my M4 and his carbine since we didn't have a print to work from. After setting up the barrel in the lathe and turning back the .065" the ports line up as they should and the gun runs great with 16.0 grains of H110 and the LEE cast bullet.

I don't know if this is an aberration or if the manufacturer has a problem, but it's healed so all I can say is YAY!!

[xacex]

Thank you all for your input with this situation.

Over the weekend a friend and I tore everything apart, again, and measured every conceivable dimension we could think of, even if it didn't seem relevant. We discovered that the shoulder on the barrel against which the forearm ring and gas block rest was .065" too far forward which caused the gas block to not line up for and aft, virtually blocking off the biggest part of barrel port. We compared this length to my M4 and his carbine since we didn't have a print to work from. After setting up the barrel in the lathe and turning back the .065" the ports line up as they should and the gun runs great with 16.0 grains of H110 and the LEE cast bullet.

I don't know if this is an aberration or if the manufacturer has a problem, but it's healed so all I can say is YAY!!
Hmm, that's odd. That for aft alignment can be tricky as I mentioned, but having the shoulder set forward .065" is not good. Who was the manufacture?

[roysha]

Before I cause any adverse publicity for the manufacturer I want to contact them and see what they say. If I get smoke blown up my patute, I will most assuredly let folks know who made the barrel. However, if they come clean, I doubt that I'll say much since it seems 1 negative equals about 100 positives.

[Artful]

Congratulations on getting your firearm up and running - please keep us posted.

[M-Tecs]

Per the print the port should be .295" from the shoulder. When I first started turning AR barrels I measured some GI barrels and came up with .300" from the shoulder. All the ones a made are .300" from the shoulder. I have seen gas blocks with mislocated holes also.

[Moonie]

Great news.

[xacex]

Per the print the port should be .295" from the shoulder. When I first started turning AR barrels I measured some GI barrels and came up with .300" from the shoulder. All the ones a made are .300" from the shoulder. I have seen gas blocks with mislocated holes also.
I was thinking he may have got a bad gas block too, but since he already cut the barrel and it works no use in going back to the cheap part first. I usually work from the simplest and cheapest part determining a problem and move up from there. Another thing is he mentioned he tried another gas block and gas tube from another rifle, so it makes me believe he may be correct in his final determination. It all good and working now so that is what matters. Now if I can find a 40WT reamer to convert one of my barrels I would be a happy camper. I have this carbine 300 BLK barreled upper that just collects dust now. The SBR, and pistol gassed carbine get all the action.