Bullet size effecting chamber fit in 300 BO

[Motor]

I've been working on a cast boolit load for my 300 BO. Typically I size all my cast boolits for 308 groove diameter barrels .311" and it's always worked great.
It seems with this cartridge the shoulder to neck relationship is causing my .311" boolits to effectively move the shoulder forward just enough to make them stick in the chamber.
If I seat a .308" jacketed bullet there is no issues.
Has anyone else experienced something like this with the 300 BO?

Motor
PS: A .309" size die is in route. 👍🏻

[popper]

Neck is 335, throat is 309 (+002 - none for both). End of throat has a taper. If you hit that taper, most likely jam city.

[HATCH]

you most likely need to sit the bullet deeper in the case.
Just be aware of case pressure if your seating it deeper then the data specified.

[Motor]

Neck is 335, throat is 309 (+002 - none for both). End of throat has a taper. If you hit that taper, most likely jam city.popper. You are absolutely correct. You dimensions plus your comment is right on. I tried to post a photo of the dummy round with the ring showing through the sharpie at the neck/shoulder junction but it says "invalid request" [emoji2369]

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[Motor]

you most likely need to sit the bullet deeper in the case.
Just be aware of case pressure if your seating it deeper then the data specified.The boolit is a 168 cast bullet. There's as much of it inside the case body as in the neck. [emoji6]

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[HATCH]

this is a pointed long nose boolit??

[Motor]

Ah. Figured it out. The photo posting that is. 283634

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[Motor]

Yes. Maximum OAL is 1.860" I load them
.010" to .015" off the lands. 283636

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[HATCH]

your not putting a crimp??
I would reduce the OAL and put a lite crimp on it.

[Motor]

It's crimped with a Lee FCD and the neck is the same diameter or a little smaller at the mouth.

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[HATCH]

ok, what I am seeing is the chamfer then.
reduce the OAL length

[Motor]

There's now reason to reduce the OAL. As the photo clearly shows the interference is at the neck / shoulder junction.
Plus as popper pointed out the chamber neck is .335" My necks are .333" plus because my boolits are .311"
I'm certain the .309" boolits will solve this issue. I was asking if anyone else has experienced this and by popper's response I'd say they have.
I'll do a fallow up post after the .309" die arrives. If I'm wrong I'll post that I was wrong. [emoji6]

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[HATCH]

Ok. Let’s do some basic trouble shooting.

Size your brass but do not do anything else.
See if the brass drops into the chamber and the bolt closes.

If the problem is the shoulder then you are either not sizing it correctly when you form the brass OR
When you are crimping the brass it is pushing the shoulder out because it’s pushing the neck down.


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[HATCH]

And BTW i load 240 grain lead using Dillon dies and never had a issue


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[HATCH]

I have another quick test.

Take the decaping assembly out of your sizing die.
Size the loaded round and check it.
You can do that without changing your OAL
If you still have a issue then it’s the oal


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[Motor]

I've already done everything you suggested except size a loaded round which you should never do because if you do the neck sizing portion of the die will swedge the bullet down within the case neck.

Motor

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[popper]

Sizing die is the problem, neck isn't back far enough. Screw the die down farther. If it bottoms on the holder, time to grind some off the bottom of the die, NOT holder! Holder is MUCH harder than the die. The angle of the shoulder in your chamber and your die are not the same - and never will be. Yup, instructions say bottom the die on the holder but tolerance stackup gets in the way. My BO die is Lee and press is Lee S.S. It doesn't 'cam' over. Cam over is to make sure the sizing is 'complete', i.e. you didn't short stoke. Which wears out the bushings fast. I got a bullet sizing insert from NOE (0.330 IIRC) for neck dia and use it on ALL loaded rnds to insure no jamming. I PC so made(?) a 'nose' checker' from a 30/30 Lee mandrel type sizer die. Take the mandrel and fingered part out, place a spacer to fit under the cap. Hole in the upper 'slug' is just right for my bore. If loaded case head sticks above the bottom of the die, seat deeper. Works for my 30/30 also, different 'spacer'.

[Motor]

Sizing die is the problem, neck isn't back far enough. Screw the die down farther. If it bottoms on the holder, time to grind some off the bottom of the die, NOT holder! Holder is MUCH harder than the die. The angle of the shoulder in your chamber and your die are not the same - and never will be. Yup, instructions say bottom the die on the holder but tolerance stackup gets in the way. My BO die is Lee and press is Lee S.S. It doesn't 'cam' over. Cam over is to make sure the sizing is 'complete', i.e. you didn't short stoke. Which wears out the bushings fast. I got a bullet sizing insert from NOE (0.330 IIRC) for neck dia and use it on ALL loaded rnds to insure no jamming. I PC so made(?) a 'nose' checker' from a 30/30 Lee mandrel type sizer die. Take the mandrel and fingered part out, place a spacer to fit under the cap. Hole in the upper 'slug' is just right for my bore. If loaded case head sticks above the bottom of the die, seat deeper. Works for my 30/30 also, different 'spacer'.I recieved my order today which included a case gauge and .309" bullet size die.
My casings fit the case gauge easily.
My dummy round with .311" boolit gets snug just before going all the way in. It will go but it's a light interference fit.
I then assembled a cartridge using a .309" boolit. It falls into and out of the case gauge perfectly.
As the scrape on the old dummy round clearly shows the larger boolit was actually making the same effect as having the shoulder not set back enough.
I also noticed a perfectly formed lead ring around the tip of a jammed round when shooting the .311s which was obviously shaved off of a boolit while entering the throat.
I'm pretty much convinced the issue was oversized boolits but will confirm after range testing. 283902

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[popper]

Wilson case gauge will not check neck dia, just a datum point for H.S. I saw the mark at the shoulder junction and thought that was the problem. Glad you got it solved. Note though that the lead ring can be formed by the expanding bullet scraping, not always from chambering scraping. My CVA does that on 310 sized even though they chamber fine.

[jimb16]

Sounds to me like you are crimping in the same operation as seating. Otherwise how are you getting the lead ring? Make sure you crimp in a separate operation. If this isn't what you are doing, then the .311 bullet is snagging on the edge of the throat and shaving lead that way.

[Motor]

Sounds to me like you are crimping in the same operation as seating. Otherwise how are you getting the lead ring? Make sure you crimp in a separate operation. If this isn't what you are doing, then the .311 bullet is snagging on the edge of the throat and shaving lead that way.Yes crimping with FCD in separate operation. Only found the ring after firing not after seating. I also noticed this load was VERY compressed. I wonder if that wasn't making the case swell just a tad also. I'm going to back it off for my next range trip.

Motor

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[Motor]

Wilson case gauge will not check neck dia, just a datum point for H.S. I saw the mark at the shoulder junction and thought that was the problem. Glad you got it solved. Note though that the lead ring can be formed by the expanding bullet scraping, not always from chambering scraping. My CVA does that on 310 sized even though they chamber fine.popper,
It's a RCBS min chamber gauge. Tonight while loading some test rounds I found another contributing factor.
The brass I made from PPU headstamp has at least .002" more neck wall thickness. The resulting larger loaded neck diameter makes for a light interference fit in the chamber gauge.
The other brands fall in and out of the gauge without any resistance.
This has been a learning experience. If this was a bolt action I probably wouldn't have ever noticed.
Motor

PS: It turns out the interference was at the case mouth. No doubt because of the thicker neck wall but I was able to adjust the FCD and correct it. They don't fall in and out like the thinner ones but they fit easily enough.

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[Motor]

Finally got back to testing. Sizing the boolits .309" has resolved all of the chambering issues.
Now it's on load development, again. It shot a 5 shot group at 100 yards today that has an extreme spread of 2.5" which isn't bad but I know it can do better.

Motor

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[Texas by God]

What twist does your barrel have? I'd be tickled if my 1-7" .300 BO AR carbine shot cast like that.

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[Motor]

What twist does your barrel have? I'd be tickled if my 1-7" .300 BO AR carbine shot cast like that.

Sent from my SM-A716U using TapatalkI honestly don't know what the twist rate is. I got the upper from my brother. I'll try to find out. After I get settled on a load I'll post photos and details.

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[jimb16]

Twist rate is often marked on the barrel. Take a look. It will probably be marked with something like 1-7 or 1-9.

[Motor]

Twist rate is often marked on the barrel. Take a look. It will probably be marked with something like 1-7 or 1-9.I just changed the free float handguard on this and didn't even find the caliber marked on it let alone the twist.
It's a Hardened Arms upper. From what I've seen on line I believe its 1:8

Motor

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