Are my slugging results normal for 300blk? .304?

[gidaeon]

Slugged my 300blk barrel in anticipation of casting\reloading. My barrel slugged repeatedly at .304-.305 :? So.. I verified calipers using several feeler gauge sizes to thousandth and calipers are good. Yes, I'm rotating slug to get max reading for not just measuring the wrong spot.

1) Is this "normal"? I expected .307 or .308 (Hardened Arms upper btw)

2) What does this mean for my sizing? is going .004 over with a .309 sizing kit too dangerous for pressure? do I need a .308 resizer instead?

3) I am using the C312-155-2R Mold & Powder Coating which means I have quite a jump down in size. Not sure if going to .308 is practial if needed? I really don't want to blow anything up. I'm brand new to reloading.

[RED333]

Barrel make?
It dont sound right, .304 is a bit small.

[gidaeon]

Hardened Arms upper. I think they use cheap no-name barrels maybe (given the total upper price of 250)? All I know is its 4140 chrome-moly.

I am confident the slug measurement is good. I just ran my other .30 cal barrels and found the Garand in the usual higher range from .308 up to .311 for one Mosin.

[skeet1]

gidaeon (http://castboolits.gunloads.com/member.php?37821-gidaeon)
Are you sure you are not measuring the bore diameter instead of the groove diameter?

Ken

[redhawk44]

Maybe the barrel has an odd number of grooves and you are measuring groove to land?

[gidaeon]

I am measuring these slugs the same way as my mosin and garand slugs which read higher. I tried measuring both directions by moving slug perpendicular in calipers and rotating 360deg as well.

[RED333]

I would be getting a hold of the seller and ask a few questions, sound like you have a bad barrel.

[gidaeon]

Just figured this 300blk barrel has 5 lands and 5 grooves. So 5R style? I'm told that is "harder to measure" correctly somehow. I would think I'm still capturing max dimensions with my methods but had better ask.

I've read some guys wrap the slug somehow and then measure subtracting wrap?

Any tips for measuring compared to other even # barrels that I know measured fine.

[Quiettime]

Just figured this 300blk barrel has 5 lands and 5 grooves. So 5R style?


Figured that immediately. My FNS is like that.

Don't worry too much about the groove dia, size to fit the throat and shoot

[gidaeon]

The problem with just sizing to fit throat is I still don't know what re-sizer to go with as I don't have any .30 sizer kits yet.

I'm still not clear on why the 5R slug would give me a low reading. I mean I measured it rotating for max both directions. If anything I would have expected a "false high"

[RED333]

Just figured this 300blk barrel has 5 lands and 5 grooves. So 5R style? I'm told that is "harder to measure" correctly somehow. I would think I'm still capturing max dimensions with my methods but had better ask.

I've read some guys wrap the slug somehow and then measure subtracting wrap?

Any tips for measuring compared to other even # barrels that I know measured fine.

Wrap the slug in the thinnest feeler gauge you can find, measure, then subtract the feeler gauge times 2.

[Quiettime]

The problem with just sizing to fit throat is I still don't know what re-sizer to go with as I don't have any .30 sizer kits yet.

I'm still not clear on why the 5R slug would give me a low reading. I mean I measured it rotating for max both directions. If anything I would have expected a "false high"

think of a wheel hub with 6 lugs. It's easy to get the bolt circle because there are always two studs opposite each other. 5 lug is harder to measure because there are no studs straight across. Or think of taking a boolit and grinding a small flat on one side. When you measure the flat you'll get a small reading.

You could always do a pound cast to get your throat dimension. Goodsteel has a very well-written tutorial on doing a pound cast