Once fired neck dia. question

[BlackGrouper]

New 32" 6.5x55 barrel in a Barnard P, new blue box Lapua brass with 46gn H4831sc 140 Berger HB. No velocity measured, didnt have crono setup.
Loaded dia. .2950"
Fired case neck coming out .2955"
Reamer specs unknown.

Would you try skimming the necks a little and test again? Looks a little warm for that powder charge to me.

 

[LHSmith]

Looks OK. Bolt lift normal? How does a bullet fit into the fired necks?

 

[BlackGrouper]

Looks OK. Bolt lift normal? How does a bullet fit into the fired necks?

Bolt lift ok, bullet gets stuck hard soon as bearing surface meets case neck, pointy end first. Almost needed pliers to get out, was only in about .010"
Lapua wall thickness .0155" new brass.

 

[David Christian]

Did you measure the lands to determine seating depth? If you have a lot of jump combined with a lighter load you may not have formed/blown out the neck when firing the virgin brass. I’d verify this before deciding to turn necks.

Did you measure the shoulder lengths before and after firing? That could also help you verify the above.

 

[BlackGrouper]

Freebore measures about .206" from what I can tell. Jump tested from .020" to .050" off light jam.

Also fired:
140 SMKs w/ 45gn same powder, jumped .020" measure .2635" dia. Only fired 5 or so for group while sighting in but grouped well.

139 Scenar @ 46gn .020" jump grouped about same as Bergers, around 1 1/2" to 2" at 200yds, calm conditions.

Shoulders moved from .0005" to .0015" after firing, not formed well yet.

 

[RegionRat]

Reamer specs unknown.

Just a suggestion.
When in this situation and there is no path to research your way back to the original smith... this is the time to think about a chamber casting and close inspection before you screw the barrel on.

I would take a step back and completely inspect the chamber dimensions to understand what position I was in, in terms of turn or no-turn, seating depth to lands, shoulder datum/headspace, diameters, etc..
Good Luck either way and I hope it turns out to be a hammer.

 

[LHSmith]

I have added a layer or layers of scotch tape to the case neck OD in order to get an idea of the chambers neck diameter. Just remember to remove it.

 

[akin]

New 32" 6.5x55 barrel in a Barnard P, new blue box Lapua brass with 46gn H4831sc 140 Berger HB. No velocity measured, didnt have crono setup.
Loaded dia. .2950"
Fired case neck coming out .2955"
Reamer specs unknown.

Would you try skimming the necks a little and test again? Looks a little warm for that powder charge to me.
View attachment 1414225

Little hot

 

[nksmfamjp]

Does a bullet slide down the fired neck?

 

[Bill Norris]

If the bullet is tight going back into the case of the fired un-sized brass I would definitely give it more clearance by turning the necks a little.

 

[rsbhunter]

Going off the loaded neck O.D., and the fired O.D. I'm seeing a .0005 difference ? Except on tight necked target rifles, I was under the impression that a "normal" clearance was .003-.004. Some F Class guy's are saying they are getting accuracy with .005 clearance. I would definitely take maybe 3 cases and turn necks to .014 or even .0135....and check for pressure signs compared to case in pic. Also, mic the web approx .200 above extractor groove and check expansion difference between new and fired.....alot guy's here alot smarter than me will contribute also...rsbhunter

 

[BlackGrouper]

That's what I'm thinking, cut .001" off the neck diameter and retest.
No telling what springback is on fired but yes, it is a .0005" difference on loaded vs fired on all loads tested so far.
This is for a 1000yd yd prone rifle.
Hodgdon max charge lists 47gn with 140s but that is at old Swedish mauser pressures. I tested 45 to 46gn.

 

[gunsandgunsmithing]

More neck clearance, for sure. That's a good starting place. I'd go .003 under(loaded) the fired case neck. It needs done and it can only help. If a bullet won't slip inside of a fired case, it's too tight.

 

[Walt Schmidlin]

260 Rem, .295” fired neck OD. Worked well with R-P & W-W brass with a loaded round neck OD of .293-.2935.
”Upgraded” to Lapua brass, loaded neck OD .295, ejector marks on brass, stiff bolt lift. Neck turned to ..013-.0135, no ejector marks or sticky bolt.

Purchased a 260 Rem Manson reamer for a new barrel with a stated .298 neck. Measured fired Lapua brass neck of .2975 (probably my “high quality” caliper).
No ejector mark or sticky bolt.

No noticeable difference in accuracy (sling shooter not F Class) at 600yds.

I was told that a .002 clearance between loaded & fired neck OD is recommended, works for me but I’ve also heard that .001 to .004 clearance is also the preferred.

With my .295 neck barrel I had 2 choices, neck turn or have the neck reamed. I can neck turn so I did that.

A chamber casting is a great idea if it will also provide the free bore of the unknown chamber. There are numerous 6.5mm bullets available, some are very long requiring a longer free bore, nice to know what you have.