m1903a1 tryout results

[browningautorifle]

I suppose I should just rent a pull through reamer and lightly "chase" the chamber?

I'd stay away with reamers, try a paper polish first. Use a mandrel made of wood dowel with a slot cut for machine paper with oil on it. Try turning it with a low speed drill and in and out. That should remove any offending chatter marks. It doesn't take much.

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[ssgross]

So I've been measuring all morning.
The rounds I was shooting were Hornady 150 SP with mixed brass (I got 1k of them a few years ago with rebates, and use them to get on paper or any other just for funnies shooting). I shoot these with low-powered loads to account for the variance in case thicknesses amongst mixed brass.
I just loaded a bunch more, took out the firing pin, and selected one that does not chamber at all - there was variance in my lot even though all were trimmed to same length and full length sized.
I measured the max case base to ogive (CBTO) with my Hornady gauge and one of these bullets - 2.676. My handholds are seated to the middle of the cannelure on these bullets at 2.620. Plenty of room.
Then I sorted the 100+ rounds I loaded into 3 piles - smooth chambering, sticky, and no go's. The dozen or so no-go's were all military brass (LC), and a couple greek HXP's - including the one I tested.
Next, I FL sized both test cases - one was RP (chambers fine) the other HXP, and started measuring the neck. Indeed, the HXP case is 2 thousandths wider at the neck - pretty normal as military brass is thicker. I colored the case with a sharpie and chambered - the neck is not the issue. The contact is all on the shoulder. I measured all other parts of the case and they are the same. The only thing I can't measure effectively is the shoulder itself - which must be the issue by elimination.
I then took a brand new piece of never-fired Hornady brass, and FL sized it and it chambers fine. Something is screwey. I worked the HXP case in and out of the FL die about a half a dozen times out of pure frustration, and WALLA! case chambers just fine - a little sticky, but just fine.
I guess my lesson learned is that the chamber on my 1903 is very, very tight at the depth of the shoulder - I tested the above cases in all my other 30-06 rifles and they all chamber fine with no noticeable difference.
The "problem" could be the chatter where the shoulder was cut - seen in my picture above, or it could be that the chamber was not reamed deep enough - or maybe the barrel was installed and never reamed, and I got lucky - it is after all a SA replacement barrel.
Next step is to get proper gauges and make sure there is no tightness on the go gauge. Depending on those results, I'll either need to simply polish like BAR suggests, or if it's worse I'll need to finish ream it.
I'll order some gauges - inletting black is on the way anyway, and report back. I have a hunch that this one was assembled and sold, with fitting or other work completed. I feel privileged in that case since I get to do all the final fitting myself and have a very nice shooter at the end of it!