Bullet size effecting chamber fit in 300 BO

[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.

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I 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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