Shoot 10 or 20. If they group, obturate, and form OK, use the rest. If not, pull down, neck size, reload. Maybe discontinue crimping for SMLE - unnecessary variable if properly sized.

Looking at Hodgdon online data, their Max load is only 43600 CUP - well below SAAMI max 45000 CUP. Pretty conservative.

150 GR. HDY SP
H4895
Starting: 36.0grn 2,447fps 40,300 CUP
Maximum:40.0grn 2,627fps 43,600 CUP

Note that QL estimates are piezo "psi" (SAAMI max 49000 psi).

Just for grins, take a look at Hodgdon online .30/40 data with H4895 and 150 grain bullet. Should give an idea how conservative their .303 data might be.

(Usable volume of .30/40 case is about 1 grain more than .303, thanks to longer neck and normal OAL of .30/40. Load to same OAL and there's almost no difference.)

Carbon Outlaw, on the loose barrel it looks like the chamber is OK? That is for demo purposes, correct?

The barreled action does look like the case is sitting proud. If it were mine I would try an EMPTY case with black Sharpie marks all over and barely tap it in a little, then tap it out through the barrel. It does not need to be forced, just get it stuck a couple of times so you can tap it out with your palm. I would expect that you will see the marks on the brass were your interference is coming from.
If it is actually not finished reamed it could be finished by hand without unscrewing the barrel. See the last item or 2 in my thread:
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If you can borrow or rent a Krag standard reamer you can use my brass extension to drive it. My reamer is 35/40 and I just sold it to a fellow KCA member who is building a sporter with a 20 inch barrel. He is supposed to be taking pictures to share here later.
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There is a possibility you just have some dry crud stuck or glued in the chamber, if so you could hack saw and file a case in half and use it like a "cleaner" reamer, just need a way to rotate it. If you put 1/4 -28 threads through the primer hole my driver could be used to turn it.

Would sure hate to see you stop on your project.

it is a aftermarket barrel ... it looks like a barrel you put on then cut your dove tails or add sights and then finish by hand reaming the chamber ... looks like they never reamed it ... probably the reason why i got it so cheep ... I have seen reamers on ebay for sale and lots of YouTube videos .. got lots of time to figure it out ... thanks for your help ...

Reporting back.

Got a field gauge. Bolt didn't close with fingertip pressure. Maybe only half-way rotated down into battery. Unless I'm an idiot, I'd say that this rifle is not too long in the headspace.

I'll be happily fire forming brass for it.

Thanks all for the advice.

Took it out for a test shoot. I'm already in love with this rifle. Slick action, shoots nice. 5" high at 100 yards with factory 180gr SP Hornady.

Inspected the fired cases. Maybe some imperceptible-to-the-naked-eye bulging forward of the case head, but I honestly cannot tell-looks like the fired cases in any number of rifles. I did the paper clip feeler test as a sanity check and couldn't detect anything. Will cut one open in a couple days when I have access to a saw.

Krag cases sometimes appear to bulge in that area... but it's perfectly normal.  Most of my cases have that.  Neck size only and anneal occasionally, and you'll be fine.