Full length bump sizing brass that’s different dimensions

[Unrat3d]

Hey guys, after firming brass in my axmc I notice that there is a 3-5 thousandths difference in some of the brass after firing and testing different reloads. So how should I go about bumping the shoulder back To get them all the same, or is that not possible until I fire the cases with the same powder charge.
thanks for any advise

 

[whatsupdoc]

Are you checking them with the primers removed?

 

[Unrat3d]

Are you checking them with the primers removed?

Yes sir

 

[whatsupdoc]

If you are testing different powder charges depending on the number of times the brass has been fired and the
difference in chamber pressure you may see some variation in the brass.

 

[Tokay444]

Anneal and size.

 

[Unrat3d]

Anneal and size.

So I should take the smallest one and bump it back 2 thou, and then run the ones that are bigger through the die and size them? So pretty much I’ll be sizing the bigger ones more?

 

[Chargerguy]

I pull my ejector and cocking piece on my AXMC bolt and go by feel when I set up my die for a 0.002” bump. When I’m there there’s no resistance on the bolt and I’ll check it by putting a 0.003” piece of scotch tape on the case head (cut with a razor blade) and there will be resistance. Then just be consistent in your lubing and size them all.

 

[Supersubes]

So I should take the smallest one and bump it back 2 thou, and then run the ones that are bigger through the die and size them? So pretty much I’ll be sizing the bigger ones more?

No, bump the longest case till it fits with zero clearance(which may be where its at currently), then adjust .002 from there. With the die backed out slightly the case will grow longer on the first sizing. Work the die down to establish a zero clearance case. Record that measurement, subtract .002 and thats your target.

Dont remove the ejector. The ejector holds the case forward, and thrusts the bolt back to the lug abutments. The tape trick still works, and additionally you can thrust the bolt forward and feel the gap. This is a tool to be used.

 

[Tokay444]

So I should take the smallest one and bump it back 2 thou, and then run the ones that are bigger through the die and size them? So pretty much I’ll be sizing the bigger ones more?

Does the smallest one chamber without resistance? Do any and all chamber without resistance?

 

[CK1.0]

It can take a few firing/loading cycles for all of your cases to be blown out to their max length (matching the inside your chamber).

Measure ~5-10 of your fired cases and set ~2-3 of the longest ones aside, set your sizing die so it bumps those longest ones back ~2 thou, then you can run all the rest of the cases through the die.

After ~2-3 firings all your cases will end up the same length within a thou or so.

 

[4O6shootist]

Take your longest case from the hottest load, size it back 001. Strip you're firing control assembly and plunger ejector(if you have one) slip the sized case under the extractor, and see if the bolt closes. If there's a lil resistance, size it back in 001 steps until the bolt basically drops shut on its on handle weight. This is your chamber length, I'd size it another 001, and call that your Bump. Us this as your reference, some cases will exceed that length, some will barely get there on first firing, some won't.

 

[ScottVA]

If they have only been fired once, or twice even, they are probably not fully formed to your chamber. If that's the case, see if they chamber easily. If they do, just set your die up to size the neck only and shoot them until they are fully formed. Then set your die up to size to whatever dimension you like.

 

[918v]

Take your longest case and resize it for zero shoulder bump. That means you carefully run the case up into the die until you feel the shoulder of the case touch the shoulder inside the die.

Now take that case and try to chamber it. Does the bolt close? It probably won’t.

Now screw the die in using small increments until that case gets enough shoulder bump to enable you to close the bolt with some drag. That’s your zero headspace.

Take a measurement off that case and set your die to bump it .002”

Size all your cases using that die setting. You’ll find they will all be pretty close to one another. It won’t matter for accuracy. Eventually, after a couple reload cycles, they will all be the same.