Case Headspace Question

Joker18

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I have been reloading for forty plus years however I have not until now reloaded any ammo that headspaces on the case mouth.
I have just reloaded a box of .450 Bushmaster to factory specs, 37 gr. Hodgdon LiL-Gun powder, W-W small rifle primer, Hornady 250gr. FTX bullet.

All the reloading data I read available for the .450 Bushmaster stated that one couldn't use a roll crimp or factory crimp die and that a taper crimp die was necessary because the case headspaces on the case mouth (like 9mm). I have and used the Hornady taper crimp die that was included in the Hornady four die set.

My question is this; I customarily use a Lyman inside/outside chamfering tool on the case mouth after sizing/depriming. The case mouth measures a nominal .480 and it was recommended to taper crimp down to .475 to hold the bullet securely. All this I have done, however I am wondering since the case headspaces on the case mouth, will the outside chamfering of the case mouth affect the head-spacing?

The Hornady guy said one should be able to run one's finger over the bullet toward the case and feel the edge of the case. I can do this although on my reloads the edge does not feel quite as sharp (probably due to the chamfering). Should I not chamfer when using a taper crimp on cases that head-space on the case mouth? Should my reloads be OK with respect to head-spacing (I am using an AR rifle)?

I plan to start loading 45 acp which I also understand headspaces on the case mouth so the same rule of taper crimping should apply, am I correct?
 
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In my opinion, a small amount of chamfer is not going to hurt anything. All you really want to do is knock off the burrs. If you put an excessive amount of chamfer, or roll crimp the case, the mouth will start to slide into the chamber too far.

I'm interested to know how your loads work. I have a 450B that I have only shot factory ammo in it. I have all of the same components you mention, though.
 
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Spacing on the case mouth is normal for most semi auto rounds. Unless you went ape sh*t crazy with the chamfering process you should be okay. Perform the plunk test on several rounds to make sure they stop where they should.
 
No I didn't trim the brass. I checked each case after sizing with the caliper and they were well within case length specs. Hopefully I didn't go ape on the chamfering because I used one of those little Lyman inside/outside deburring and chamfering tools. The .450 case just fits inside the three cutters and is a pain to keep centered.
I do have a question about the ker-plunk test. I did think about that and I suppose I could drop a factory round in the chamber and see where it stops and then drop each reload in and see if they stop at the same place. I only loaded 23 rounds because that was all I shot at the range the last time I was there so if I have a problem I can pull those rounds and start over.

23 rounds at the bench wearing only a tee shirt against that hard A2 stock was enough!:eek:
 
Ok, did the ker-plunk test! By the naked eye, the reloads did not appear to seat any deeper into the chamber that the factory ammo. I tapped the factory ammo when seated with my finger and had to use a cleaning rod to back the cartridge out. Just the weight of the cleaning rod was sufficient to dislodge the factory cartridge. I did the same with my reloads and it took slightly more pressure however not what I would say significant, to dislodge the cartridge. I think I will be ok, but no more outside case chamfering. I am concluding that the cartridges are headspacing OK and the chamfer is making them slightly sticky in the chamber .
 
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