RCBS Small Base Sizing issues?

[Gkramirx]

I recently got into the world of AR10s. Have some issues with reloading. Have been reloading for my bolt gun for a couple of years and didn't really get into the weeds of it. Worked up a decent load and been shooting that. But with the AR10 I've had a few failure to feed and blown a couple of primers with factory Norma 168 smk. So I've tried to learn has much as I can reloading for gas guns. But I am currently stumped.

Size of the case appears to have been sorted with the SB resizing but I do have questions about the shoulders. Equipment I am using is the Hornady headspace comparator and a set of Mitutoyo calipers. I understand I'm currently measuring for a comparison. My new FGMM brass is measuring around 1.6225 with the comparator. Fired brass is coming in around 1.6275 to 1.6280 with 10 different cases. After resizing with small base resizing die I getting a reading of 1.6310. From what I can gather it's the brass getting worked around the web/base that is causing this growth in shoulder.

The question is do I screw down the die more than the factory suggested 1/4 turn and bump it back near the factory set point of 1.6225 or the fired 1.6275. Or should I trust the fine folks over at RCBS and leave it alone and trust that know more than I do. Again I understand that it could be my measurements being off. But the big head scratcher is the fact that I'm getting such a big gap between the factory new brass and what I'm getting after resizing.

Any help would be greatly appreciated.

 

[spife7980]

I recently got into the world of AR10s. Have some issues with reloading. Have been reloading for my bolt gun for a couple of years and didn't really get into the weeds of it. Worked up a decent load and been shooting that. But with the AR10 I've had a few failure to feed and blown a couple of primers with factory Norma 168 smk. So I've tried to learn has much as I can reloading for gas guns. But I am currently stumped.

Size of the case appears to have been sorted with the SB resizing but I do have questions about the shoulders. Equipment I am using is the Hornady headspace comparator and a set of Mitutoyo calipers. I understand I'm currently measuring for a comparison. My new FGMM brass is measuring around 1.6225 with the comparator. Fired brass is coming in around 1.6275 to 1.6280 with 10 different cases. After resizing with small base resizing die I getting a reading of 1.6310. From what I can gather it's the brass getting worked around the web/base that is causing this growth in shoulder.

The question is do I screw down the die more than the factory suggested 1/4 turn and bump it back near the factory set point of 1.6225 or the fired 1.6275. Or should I trust the fine folks over at RCBS and leave it alone and trust that know more than I do. Again I understand that it could be my measurements being off. But the big head scratcher is the fact that I'm getting such a big gap between the factory new brass and what I'm getting after resizing.

Any help would be greatly appreciated.

It’s squeeIng the base and that is pushing the shoulders forward since they aren’t supported. Screw the die in until the cases read 1.626 which is .002 less that the 1.628 fired case reading you reported. Since it’s a semi auto you might want to go back a thou or two more even.
Once the die is low enough those shoulders will hit and the brass will take its proper sizing.

 

[Gkramirx]

It’s squeeIng the base and that is pushing the shoulders forward since they aren’t supported. Screw the die in until the cases read 1.626 which is .002 less that the 1.628 fired case reading you reported. Since it’s a semi auto you might want to go back a thou or two more even.
Once the die is low enough those shoulders will hit and the brass will take its proper sizing.

Perfect thank you.

 

[FLIGHT762]

I shoot two 308 gas guns. I would go along with what spife said. I'd turn your die in to bump down to 1.624". You'll need to keep those cases segregated from any other 308 rifles you own.

 

[nutation]

Depending on how your gas system is tuned, the brass could be ejecting while there is still a fair amount of pressure in the chamber, which will cause the brass to stretch a bit more than the actual length of your chamber. This is a standard consideration for M14 rifles, which have a very fast action; it's less of an issue for AR10s, but it can still happen. If you have adjustable gas, you can turn it off to get your actual headspace measurement; you'll want to bump about 0.003 - 0.004 back from that.

 

[nutation]

Also, it's possible that you may run out of downward adjustment on your die, in which case you can sand down the shellholder a bit. I ran into this problem with an RCBS 6.5 Creedmoor small base die, so I chucked my shellholder into a drill press, and pressed it against a cheap whetstone for a minute or two.

 

[Gkramirx]

Unfortunately don't have a adjustable gas block. But this whole ar10 adventure seems like it's going to be learning experience. I used to be pretty lax about reloading with my bolt gun. As long it was printing pretty groups and decent velocity I was happy. But I guess that's the world of bolt guns and 308. There is so much information. Currently I have 80 cases that I have to learn on my brass that has gone this rifle. But I guess what is the difference between shaving down the shell holder vs screw in the die more?

 

[Gkramirx]

Nevermind. Re read the part about running out of space