Puzzled (rounds not chambering)

[SGK]

Went to the range today with 50 rounds of 6mm Creedmoor only to find almost half of them wouldn't chamber (at least not without a real shove). So clearly pushing hard into the lands. Thought I must have really screwed up my last reloading session. Came home and measured them. Seemed to measure ok. Decided to chamber and measure again the dummy round I had used to determine "touch". It chambers easily and measures the same. Yet these rounds that measure within 1/2 thou (at worst) of this round and don't want to chamber. Berger 105 gn Match Hybrid. Defiance Deviant Elite CRF action/bolt. (Brass is Lapua 4x loaded.)

Only other thing I noticed is that some of my fired rounds are getting scuffed on the bolt face. These fired cases chamber easily (without being resized).

 

[praveen]

You may not be pushing hard into the lands. Check the base of your brass. Even a .001” expansion in a tight chamber could do this.
Run the brass through a small base sizing die and try to chamber it.

 

[jbj]

You may not be pushing hard into the lands. Check the base of your brass. Even a .001” expansion in a tight chamber could do this.
Run the brass through a small base sizing die and try to chamber it.

Looks like it's time to bump your shoulders a few thousands. If you aren't already.

 

[SGK]

I think must be differences in bullet curvature between above where my Forster Datum Dial kit measures. On the bottom two rounds below you can see where the lands have scuffed the bullet. My datum Dial Kit measure a few mm below this point. You can see where the Datum Dial has marked the bullet versus the scuff.

 

[SGK]

I bump the shoulders 1-2 thou every time. Fired brass chambers easily. Unfired brass from which I loaded these rounds (FL resized, trimmed, chamfered/de-burred, annealed) chambers easily.

 

[Whisky Tahoe Foxtrot]

Can you give us a list of things that are different between these rounds that won't chamber and the rounds you have fired? Factory ammo, bullet type, etc.

Tell us about the brass you used to load the 50 rounds that wouldn't chamber.
Virgin, 1x fired, from another gun?

You said that previously fired brass will chamber. You could resize one and see if that is still the case (pun)

Praveen is correct that expansion at the case web (above the groove) can prevent easy chambering which happens with over pressure loads or brass fired in match chambers over time. Shrinking the web requires a small base (slightly tighter web dimensions than saami spec). Very good for semi auto chambering.
308 small base dies work for this though there may be a specific SB die for you as well.

Somewhere the case dimensions of these 50 rounds exceeds your chamber.
Measure the neck of a fired case that chambers and compare to the neck of a loaded round that won't chamber. If that dimension is larger, your chamber may have a tight neck dimension and with a bullet seated the neck dimension could exceed or be very close to your chamber neck dimension

Shoulder bump is the next thing but does require a bump/shoulder gauge to check. When you size brass it is possible to lengthen the case if the die is set too long which happens on a lot of factory dies

Another thing is how are you measuring length? Base to Ogive or Overall cartridge length.
depending on bullet design similar over all lengths can have different base to ogive measurements between differing bullets.

I know these sound like basic questions but it helps to focus the experience you will be able to tap into

 

[Bill Norris]

I bump the shoulders 1-2 thou every time. Fired brass chambers easily. Unfired brass from which I loaded these rounds (FL resized, trimmed, chamfered/de-burred, annealed) chambers easily.

Did you check the measurement @ the 200 line to make sure the die is sizing that portion enough ? I have seen this happen to several people. Maybe need to screw the die down a touch.

 

[SGK]

As noted above, same 100 (actually 98) lot of Lapua brass now 3x Fired (always from this same rifle). All brass processed the same. Fired brass from this batch today, now 4x fired, chambers easily (even without resizing). Unfired brass from this batch chambers easily. All brass is bumped when sizing. I find it hard to believe it's the brass because both unfired and fired chamber easily, ie they're not too long (even after firing).

Forster Datum Dial Kit measures cartridge base to ogive for seated cartridges.

"@ the 200 line"?

 

[SGK]

A bit later today I will seat one of the rounds 1 thou or so deeper to rule out the case

 

[Lone Hunter]

Do you have access to a bore scope to check for a carbon ring?

 

[Lone Hunter]

As noted above, same 100 (actually 98) lot of Lapua brass now 3x Fired (always from this same rifle). All brass processed the same. Fired brass from this batch today, now 4x fired, chambers easily (even without resizing). Unfired brass from this batch chambers easily. All brass is bumped when sizing. I find it hard to believe it's the brass because both unfired and fired chamber easily, ie they're not too long (even after firing).

Forster Datum Dial Kit measures cartridge base to ogive for seated cartridges.

"@ the 200 line"?

He means what is called the .200 line right above the base. Attached is my crude drawing showing location. Not an artist. Some times the die doesn’t size that far down and you will have to use small base dies or competition shell holders to reduce the area.

 

[PopCharlie]

Do you have access to a bore scope to check for a carbon ring?

That was my first thought....a carbon ring. I've had similar experiences.

PopCharlie

 

[75vmax]

Had same problem and my dad sent this to me

 

[jelenko]

Personally, I'd want to first try to chamber a few pieces of brass without any bullet - trying to sort out if it's the sizing of the brass or the bullet into the lands.

 

[3Sigma]

The "scuff" on your picture looks like it would be close to the leade to the lands if it is a 1.5° and SAAMI spec. My first guess would be carbon ring, second is bullet variance (seating depth tests should use either multiple pieces). The bullet is hitting something.

Especially if fired brass chambers fine.

Just my thoughts.

 

[Carl S]

Personally, I'd want to first try to chamber a few pieces of brass without any bullet - trying to sort out if it's the sizing of the brass or the bullet into the lands.

Take the firing pin assembly out and the ejector plunger so you can get a proper feel on the empty cases.resize them so
the bolt just closes on them nicely.also
check the chamber for crud or any foreign
material.

 

[bozo699]

A bit later today I will seat one of the rounds 1 thou or so deeper to rule out the case

.001 won’t do it, find one that won’t chamber, find one that will and take a ton of measurements compare that should give you some direction but if not then seat the one that won’t chamber at least .005 more and see if it chambers
Wayne


Edit:
If it does your bullet seating for whatever reason isn’t consistent or your bullets aren’t consistent also depending on your round count in the rifle you may have hard carbon a quick look with a borescope will let ya know

 

[Jager]

Not enough shoulder bump. Your problem is showing up now because your lot of brass is has now fully fire-formed.

And you need to be checking that shoulder bump measurement after FL resizing. (I mention that because you've mentioned twice that your fired brass chambers okay).

Classic case of fixating on one problem (bullet into the lands), when it's something else altogether. Has happened to us all.

 

[SGK]

As to the brass (again):

So as mentioned I'm using a single box of Lapua brass. Started with 100 cases. 1 was used for the dummy round to find 'touch' using the Wheeler method. 1 was damaged or lost at some point. That leaves 98 3x fired cases. All prep'd in an identical manner (including bumping the shoulders). I loaded 50 before heading to the range today. As far as the cases are concerned, the only differences between these 50 and the 48 left in my cartridge case at home are: primed, mandrel through necks for 1 thou tension, powder added and bullet seated. All, every single one, of the 48 that were not loaded chamber without issues. All of the cases that I fired today chamber without issues (and without resizing or anything). If it were a 'shoulder bump issue' I'd expect to have an issue with at least one of the 48 that were prepared in the same way and didn't have a bullet seated in it.

"He means what is called the .200 line right above the base." As best as I can measure this is 0.470".

I measure shoulder bump after resizing to confirm the desired bump. I use my Whidden shoulder bump gauge for this.

(FYI my bolt is controlled round feed. There is no ejector.)

Carbon ring / "seat the one that won’t chamber at least .005 more"

I've looked with my Teslong and there's nothing obvious. Perhaps I need to look more carefully. Would one expect a carbon ring after 300 rounds? (The scuff that appears on the bullet if I give the bolt a firm push doesn't appear all around the bullet.) I took one of the rounds that I couldn't chamber and step by step seated the bullet deeper. Seating 12 thou deeper and it chambered but the bullet is still sticking on extraction.

 

[SGK]

At 20 thou deeper I'm getting an easier bolt close. Also, you can now see better the scuffing on the bullet, always in the same area butt spreading further back as I seat deeper. It puzzles me that as I have randomly placed the cartridge in the action why the scuffing isn't forming all around the bullet...