Live and learn--primer-flashhole size--large and small?

[Laurie]

I'm not changing the hole size either, as I'm sure Lapua or Peterson etc., just didn't pick that size out of a hat.

This has been heavily researched on the benchrest ranges in PPCs and BRs over the years. Concensus is that 0.070" is the key value, ie stay well below it. Open flash-holes to that size and both groups and ES/SD values increase. Small increases over the nominal 0.059" size have never been shown to have a negative effect on precision cartridge performance, but the uniforming effect (if needed) has positive results. That's why PPC/BR uniformers are normally dimensioned at 0.061", a 0.0002" increase over the nominal manufacturer's size.

 

[johara1]

This has been heavily researched on the benchrest ranges in PPCs and BRs over the years. Concensus is that 0.070" is the key value, ie stay well below it. Open flash-holes to that size and both groups and ES/SD values increase. Small increases over the nominal 0.059" size have never been shown to have a negative effect on precision cartridge performance, but the uniforming effect (if needed) has positive results. That's why PPC/BR uniformers are normally dimensioned at 0.061", a 0.0002" increase over the nominal manufacturer's size.

1 think you will find it is .0625, but you will also find that diameter will not clean up a 100% .... jim

 

[Laurie]

1 think you will find it is .0625, but you will also find that diameter will not clean up a 100% .... jim

Thanks for that upgrade. Yes, I agree it's not a 100% clean-up, but certainly takes any very small examples out. I've yet to find a Lapua case (BR, 6.5X47, and 308 Palma) whose flash-hole produced no resistance at all to turning the uniformer, but some produce close to nil. There are usually a few noticeably 'tighter' ones though in every box. In my 223 Rem F/TR days, I had a couple of Lapua 'gold box' lots that each produced two cases that were well under spec size - the reamer tip would barely enter the hole. Those were the larger 2mm size of course.

 

[cw308]

I like to have my 308 cases used only for benchrest shooting to be close to exact as possible , I also experienced flash holes that were smaller , I used a drill bit to match the larger size then deburred . I would think different sizes would have a different burn rate . I'm not as technical as most here but makes sense to me. I also uniform my primer pockets , both only have to be done once on the cases . Works for me.
Chris

 

[wkdickinson]

Is deburring the flash hole necessary/helpful for lapua small rifle cases?

My understanding is lapua 6.5x47 cases, and I think all lapua cases, have their flash holes drilled, not punched, meaning there is almost no (I think) likelihood that a burr would form in the drilled flash hole like it can for other cases whose flash holes are punched. Since I am having...

forum.accurateshooter.com

My mistake (and Bryan Litz's apparently), thanks for enlightening us!

 

[johara1]

My mistake (and Bryan Litz's apparently), thanks for enlightening us!

They are not drilled ..... Look in the holes with a bore scope. Use a reamer to uniform them, a drill leaves burrs ..... jim

 

[johara1]

Thanks for that upgrade. Yes, I agree it's not a 100% clean-up, but certainly takes any very small examples out. I've yet to find a Lapua case (BR, 6.5X47, and 308 Palma) whose flash-hole produced no resistance at all to turning the uniformer, but some produce close to nil. There are usually a few noticeably 'tighter' ones though in every box. In my 223 Rem F/TR days, I had a couple of Lapua 'gold box' lots that each produced two cases that were well under spec size - the reamer tip would barely enter the hole. Those were the larger 2mm size of course.

I found ES gets very consistent with the .0625 reamed flash holes...... jim

 

[max1120]

Good read and learning something all the time

 

[Dusty Stevens]

My mistake (and Bryan Litz's apparently), thanks for enlightening us!

Its a common misconception. Their flash holes are always perfect

 

[griffgil1]

I learned today, after trying my Lyman flashhole deburring tool on my Peterson 6XC cases, the the tool's pilot snout will not enter my 6XC cases' flashholes.. Discovered that my 6Creed cases' flashholes are about 0.077" diameter while my 6XC cases' flashholes are about 0.65".. I can't find a flashhole deburring tool that is spec'd for that.. What am I missing?

...been reloading for 60+ years and dint no this...

K&M .59 (small flash hole) de-burring tool. Just got mine for Lapua 6.5 CM with small flash hole and it's great. And yes, many of my Lapua cases do need it....they are not drilled flash holes, contrary to popular belief, and many (of mine anyway) do have "burrs" or slivers of brass protruding into the hole. I also just learned about the large vs small flash holes.....and almost the hard way with a bunch of new Lapua.