Bolt fails to completely close on 6x6.8, then can't pull the charging handle out

DiRTY DOG

Well-known member
New BHW 6x6.8 barrel on a proven upper/lower. Empty upper cycles fine. Loaded, it cycled fine the first dozen rounds. Then the bolt started failing to close all the way on the first round, it would stay open 1/8 inch. I was not riding the charging handle forward.

Ammo is pulled FC brass, Redding bushing die, 58 Vmax and 55 NBTLF. All loads about 10-15 thousandsths off the lands.

First time I didn't notice and got a "click" when I pulled the trigger. The charging handle was REALLY hard to pull back, the live round was really stuck in there!

It happened several more times, same thing. Some rounds would fully seat if I pushed hard on the forward assist, others would not. It got worse and worse the more rounds I fired.

After 25 rounds in the new barrel, the bolt would not close no matter what. I banged up my knuckles yanking the charging handle open repeatedly. It "felt" like the chamber was too narrow?

1. Bolt was lubed, is not new. Cycles great w/out bullets.
2. Gas tube apprears aligned fine
3. Ejection is at 4 o'clock, bolt holds open on last shot.
4. Head space seems fine, fired shoulders measure 0.004" more than loaded.
5. Adj gas block adjusted so the bolt just holds open on the last round.
6. Case length is within spec.
7. Bullets are 10-15 thou off the lands.

Any ideas? Tight chamber?
 
Originally Posted By: 204 ARIt sure sounds like headspace to me. Might be worth a double check. That was my first guess but a dozen fired case shoulders measure fine vs unfired.

Maybe the pulled FC cases have wonky shoulder/neck junctions from being pulled? I did not touch the shoulders when I sized them...
 
Originally Posted By: DiRTY DOGOriginally Posted By: 204 ARIt sure sounds like headspace to me. Might be worth a double check. That was my first guess but a dozen fired case shoulders measure fine vs unfired.

Maybe the pulled FC cases have wonky shoulder/neck junctions from being pulled? I did not touch the shoulders when I sized them...

I suspect that's a BINGO.

Greg
 
I think you need to full length resize your brass and you may have to trim again to spec.If I don't full length resize in my ar type rifles Ill have the same issues.If you don't have go no go guage after sizing before you load cycle them thru 1 at a time to see if they fit.You may have to adjust your FL resizing die some more,Good luck.
 
Thing is, the first dozen rounds fed perfectly. Then it started hanging up, got worse and worse, until eventually the bolt would not close at all.

That makes sense if the chamber is really tight and it started hanging up as it got dirty.
 
Originally Posted By: GLShooterOriginally Posted By: DiRTY DOGOriginally Posted By: 204 ARIt sure sounds like headspace to me. Might be worth a double check. That was my first guess but a dozen fired case shoulders measure fine vs unfired.

Maybe the pulled FC cases have wonky shoulder/neck junctions from being pulled? I did not touch the shoulders when I sized them...

I suspect that's a BINGO.

Greg
If that's the problem, what's the fix? Bump the shoulder back a little on the new pulled cases?
 
The FC Pulled brass i found is real short, was meant to go through machine gun and run without problems. About .008 to .010 short on head space to be exact.
 
Originally Posted By: DiRTY DOGOriginally Posted By: GLShooterOriginally Posted By: DiRTY DOGOriginally Posted By: 204 ARIt sure sounds like headspace to me. Might be worth a double check. That was my first guess but a dozen fired case shoulders measure fine vs unfired.

Maybe the pulled FC cases have wonky shoulder/neck junctions from being pulled? I did not touch the shoulders when I sized them...

I suspect that's a BINGO.

Greg
If that's the problem, what's the fix? Bump the shoulder back a little on the new pulled cases?

Give us a measurement of unfired to fired cases using a comparator.
 
I think I see the problem? The Redding bushing die didn't size the neck/shoulder junction. It won't fit in the chamber.

Left: Failed to chamber. I pushed on the F/A with no luck. It was also very difficult to remove by pulling the charging handle back very aggressively. In the right light, you can see an indented ring around the top of the shoulder where it ran into the chamber wall. On the Right is a fired case same chamber.


My .330" Hornady comparator measures the case lower closer to the body/shoulder junction.

So what is the solution?
 
Originally Posted By: DiRTY DOGI think I see the problem? The Redding bushing die didn't size the neck/shoulder junction. It won't fit in the chamber.

Left: Failed to chamber. I pushed on the F/A with no luck. It was also very difficult to remove by pulling the charging handle back very aggressively. In the right light, you can see an indented ring around the top of the shoulder where it ran into the chamber wall. On the Right is a fired case same chamber.


My .330" Hornady comparator measures the case lower closer to the body/shoulder junction.

So what is the solution?

You are running the bushing too low. They aren't supposed to size all the way down to the neck/shoulder junction.

It should have a slight float in the die. It doesn't ever touch the shoulder. It appears to me the sized neck is much taller than the fired ones but that might just be my poor comparator eye sight.

The shoulder can be bumped but you can't have the bushing pushing on the top. If you experience hard extraction it is 90% insufficient bump in my experience.

Greg
 
Originally Posted By: DiRTY DOGI think I see the problem? The Redding bushing die didn't size the neck/shoulder junction. It won't fit in the chamber.

Left: Failed to chamber. I pushed on the F/A with no luck. It was also very difficult to remove by pulling the charging handle back very aggressively. In the right light, you can see an indented ring around the top of the shoulder where it ran into the chamber wall. On the Right is a fired case same chamber.


My .330" Hornady comparator measures the case lower closer to the body/shoulder junction.

So what is the solution?

Use your 30(I think) bushing as well to measure closer to the neck/shoulder junction as well and use both measurements when setting your die/bushing. The 33 comparator will tell you where to set your die body and the 30 comparator will tell you how tight.... or loose to have your bushing in the die.


I just checked, it is the 30 cal comparator. Indexes smack dab in the center of your buldge. That area of the shoulder is not there in the 6.8 die so if you push the shoulder too far or have your bushing to far down the neck it creates the bulge in the unsupported section of the shoulder.

To salvage that case you can install you first stage bushing and push it down some, same as bumping the shoulder. Measure before hand, ease slowly into it ad push it back a thou or 2. You are probably not to far off from getting it to chamber.
 
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Originally Posted By: GLShooter

You are running the bushing too low. They aren't supposed to size all the way down to the neck/shoulder junction.

It should have a slight float in the die. It doesn't ever touch the shoulder. It appears to me the sized neck is much taller than the fired ones but that might just be my poor comparator eye sight.

The shoulder can be bumped but you can't have the bushing pushing on the top. If you experience hard extraction it is 90% insufficient bump in my experience.

Greg
The bushing has a slight float to it, it jiggles when shaken. It is set up EXACTLY per your instructions. I even made up a stencil to make sure I loosened the stem the exact amount. If my bushing is too low, then to raise it I'd have to loosen the stem 1/4 turn or maybe more, which is double+ the instructions I've seen.


The two cases are not aligned perfectly so judging which is taller or shorter based on the pic won't work. I just tossed them on the table for a pic.
 
Anyways I thought Redding type-s dies were not designed to size the neck all the way down? How is mine sizing TOO FAR down the neck?

(Silly me for following instructions).
 
I figured the optical variation came into play.

Use the 350 insert for your measurements in setting up the bump. Once I have that set I drop my bushing in with the float. This prevents any muffin top on the shoulder. I use two bushings for my initial size down. I float the second, smaller one, more than I float the first. Maybe an extra 1/16 turn.

I'll do a case and then run it in my chamber by hand checking for cat gut smooth chambering and extraction just using my fingers for seating. If the first one works I do four more to check. I do this with the upper off. 0.003 to 0.004 on the bump ss compared to my fired case. Since you have a couple of those you are half way there.

On my initial sizing I am able to see a definite area above the shoulder on the neck that is not sized.

Greg
 
Originally Posted By: DiRTY DOGAnyways I thought Redding type-s dies were not designed to size the neck all the way down? How is mine sizing TOO FAR down the neck?

(Silly me for following instructions).

Too much bump will shove the bushing down as you are basically making the necks a tad longer when it contacts the junction. This can cause a bulge preventing your full case insertion mimicking a tall shoulder issue that would normally cause the hard extraction requiring more bump.

It's difficult to convey the nuances of fitment on these dies in written instructions. My goal is to just get three cases I can shoot so I know what I'm dealing with. I just did this on a new 20LBC AR chamber today using some old brass. I got three loaded thid morning and found that this chamber is about 0.006 longer than my old one in head space. It'll be a bit greater in the stretch on firing but that's only on the first go around. When I do my Savage I'll shorten the chamber to nimimum on purpose.


Greg
 
Originally Posted By: GLShooter
Too much bump will shove the bushing down as you are basically making the necks a tad longer when it contacts the junction. This can cause a bulge preventing your full case insertion mimicking a tall shoulder issue that would normally cause the hard extraction requiring more

Greg
I'm not bumping these new cases at all. Not touching the shoulders at all per my comparator measurements before/after.

I only did 30 pieces that batch so I'll have to try some more and see if I can figure it out.
 
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