I’m getting split necks on a new build I completed. Anyone know what the gas port size on a sionic 16" mid gas 1/8, medium lite weight barrel should be?
My brass is kicking out at 4 o’clock and landing 10 feet away. I see no stress marks on the case rims and no other damage besides split necks.
Ammo is steel Tula .223 ammo. Running a new BCM bcg with BCM H buffer and carbine spring. Recoil is heavier than it should be, but I see no stress on the cases other than a split necks about every 20 rds.
No it is not the ammo. I ran the same ammo through several other guns Saturday with zero issues, lite recoil and zero split necks coming out of the other guns.
Doubt its due to overgassing, as the brass is ejecting at 4 o’clock. That would likely cause ejection at around 1 o’clock.
If it was my rifle I would fire some brass cased ammo and mike the OD of the neck, before and after firing. Sounds like the neck is expanding a bit much, and steel being less maleable than brass, the necks split.
If the neck afte firing (brass case) is expanding more than 10 thousands, then would contact barrel manufacturer.
I went ahead and measured several of the tula cases I saved. Everything seems to be in spec. Most are expanding to .005 over loaded. Loaded cases are .245 at the neck and fired cases are .250, I found a few that were .255 which is just over the max spec. Spec called for a Max .253 to min .245.
What I did find interesting were a few of the cases compressing down 1.741. Most of the fired cases were 1.750
Loaded cases measure 1.755. The spec calls for a max case length of 1.760 to min 1.740. Source RCBS drawing #51199 10/15/86.
I wonder if some failed and went below the max length. I left the split cases at the range in the target stand shed, can’t get my hands on them until Saturday to measure length.
I will run some M193 when I go back and measure those. Interesting problem I have here. I cleaned the gun yesterday, chamber looks great, can’t see any problems. hmmm
Only steel cased ammo I have experience with is Hornady and have not noticed split cases.
Have you tried brass cased ammo?
If no splits, then its not the barrel. Odd about the cases compressing. They usually stretch, sounds like something about the steel cases does not play well with the chamber.
If all goes well with brass cases, doubt there is a problem.
Are you measuring the individual cases before and after firing, or taking batch samples? Ammo variation could throw off your data, I would measure and label each case before and after shooting to know what the real change is
Not yet. But will shoot some on Saturday. For all I know there may have been some trash built p in the chamber from the wk before. I cleaned it, will find out on Saturday.
Individual cases. I bagged up several from the bench that day but left the split cases sitting on a shelf with my stapler. Saturday I will sit down at the range and measure cases as they come out of the gun.
It doesn’t, just wondering if I should using a H2 buffer. The gun weights close 8lbs. It is recoiling too much and I am wondering why.
For sure. With an .080" port on a 16 mid, you might even like an H3. I have an .080 port on a 14.5 mid and it’s about right… 1.5 extra inches is all the difference in the world… you have plenty of room to buffer up.
All of our 16" midlength barrels have the .080 port size and have run very well, including the one that Trident82 tested. If you think there is a problem after you have checked your ammo, then contact SIONICS and it will be taken care of.
I don’t think he’s got problems. H1 is a pretty light buffer for anything other than a .076" 14.5 middy. If he’s feeling the thump, I’d bet an H3 will make his ammo/barrel combo much smoother.
Problems! The only problem I have is I can’t find my third tungsten weight to finish my H3 buffer, It does not stay hard like it use to and I have to go to Florida in three weeks.
You ever been to Florida gunz? It sucks, lots of strange people. Anyway, I don’t have problems. I have no doubt Sionic’s would go above and beyond to fix any issue. So far only thing I see is a good running gun producing one hole groups. A 5.56 chamber does not compress cases, trash in the chamber would, this issue is on me.
Mark is right, I need to slow it down by running a H2 or H3 and give it time to extract. My fault for not building it correctly.
