.265 neck =.011" neck turned ?

[michaeljp65]

Just getting a new barrel chambered with a .265" neck, Mike Bryant 6PPC reamer
print. Just checking if my math is right before i start neck turning. So a .265 equals a .011" neck thickness?

 

[BoydAllen]

Let's do a little math. .011 x2 = .022+.243= .265 which leaves you with an interference fit if your bullet measures slightly over .243 as many do. To get to .003 total clearance you will need to cut your necks to .0095 minus a couple of tenths if your bullet has a pressure ring.

 

[michaeljp65]

Thanks for the very quick reply Boyd. Lucky i did ask the question. You mentioned .003" clearance. Why .003 and not what ive heard .002" or is it a personal thing?

So the .011" i mentioned would have left me no neck clearance when loaded. So i needed to subtract some clearance ie, the .003"

 

[BoydAllen]

Some of the top shooters use around.003. If you want to know a lot more from a highly qualified source watch all six of Jack Neary's videos on you tube.

 

[michaeljp65]

Thanks Boyd. I'll watch and learn some more.

 

[PatMiles]

As Boyd said, Jack Neary's videos hold a wealth of good info. Watch and learn.

 

[gpoldblue]

One of the all-time great shooters,Ed Watson,in a March 1984 Precision Shooting magazine article about case preparation stated he turned his case
neck so that the measurement with bullet seated would be .001" less than chamber neck. He used a .261" chamber and loaded round of .260".
I use .0015" total clearance with perfect satisfaction in a .268" neck.
The main thing is to have adequate and consistant neck clearance. The shooter has more input about small groups than anything else. Small groups are the result of many things coming together at the same time. Neck clearance is but one very small aspect.
Good luck. Dan

 

[ridgeway]

I turn to .009" for a ∅.264" neck...

 

[Webster]

Thanks for the very quick reply Boyd. Lucky i did ask the question. You mentioned .003" clearance. Why .003 and not what ive heard .002" or is it a personal thing?

So the .011" i mentioned would have left me no neck clearance when loaded. So i needed to subtract some clearance ie, the .003"

I like .003" for a margin of safety. Maybe with barrels in the future you can tighten it up. Don't know if anyone can prove 0.0015" or 0.002" clearance is more accurate. If you cannot shot aggs under .220" or better you will be at the end of the list any how.

 

[BoydAllen]

I changed to more clearance for reasons of accuracy, not safety. If you watch the Neary episodes you will learn why. My friend Gary Ocock owns and has owned a number of records, many in unlimited class. He once told me that he tries for about 2 3/4 thousandths. My late friend Dennis Thornbury, who I believe is still in the record book, told me that he liked to be somewhere between two and three, and that increasing the clearance was about getting a cleaner, more consistent bullet release. Neary says that this becomes most obvious at 200 yards. In the past there has been a tendency to just accept the idea that smaller clearances are always better. More recently, testing by really qualified shooters has shown that this may not always be the case. I am not saying that you cannot shoot small with close clearances but benchrest is won by the smallest average group size.

 

[fyrewall]

For my applications of casual use rodent & steel shooting with my 6mm's I use a Forster F/L dies that have been opened up to .268, a clean up neck turn reduces neck walls to .015, loaded rounds measure .269. Fired cases measure .275. Guessing some brass neck diameter spring back would make the chamber neck somewhat more than .275, possibly .276. Clearance (diameter) should be .276 - .243 - .015 - .015 = .003

Of concern is adequate neck tension to hold the bullet(s) in place while being swept up from the magazine and slammed into the chamber. Looking at this aspect: .268 (Forster die neck diameter) - .015 (west neck wall) -.015 (east neck wall) = .238. Or .238 - .243 bullet diameter = - .005. This provides security. Bullets easily slip fit into fired cases and brass life is good.

My casual standards are .5 MOA at 300. I have acquired some aversion to picky stuff but have picked up on this thread with interest.

 

[michaeljp65]

I like .003" for a margin of safety. Maybe with barrels in the future you can tighten it up. Don't know if anyone can prove 0.0015" or 0.002" clearance is more accurate. If you cannot shot aggs under .220" or better you will be at the end of the list any how.

I'll be at the bottom of the list anyways Webster. Im not naive enough to think i'll be anywhere near the top half.

 

[michaeljp65]

Thanks for all the replies gentlemen. I'll go with Boys recommendation of about .0095"ish.

Cheers

 

[Boatschool02]

I turn & seat one and then measure with a 0.0001 Mitutoyo. (collet puller at the ready)
You'll will be able to rotate to see how consistent your turning is.
I have a quality tube mic as well, but I never quite get things perfect enough to go on that number alone.
The number above, your overall loaded round, is ground truth.
The 9.5 referenced above assumes a .2430 bullet. (None of mine measure that) Go slow and plan to do this a couple times as you work your way down to the final number (0.2620 overall) accounting for the pressure ring which on my limited selection of flat back bullets has been between 0.2433-0.2436.
-
FWIW, When starting out in this hobby, I made several choices for monetary economy that have caused frustrations, inefficiencies, and outright errors costing many times over whatever money I thought I was saving. You'll be making two, possibly three cuts to get down to your final thickness. I highly encourage you to consider buying no less than one, preferably two, dedicated cutter assemblies and leaving them alone once you lock in on your final pass. I now have several independent cutter assemblies from 21st Century and I wouldn't be without them. I like learning & shooting with my own work, but in all honestly, I may never wear out enough barrels and brass to have really done better (true total equipment cost PLUS time) than just paying DJ to make very high quality brass to order in the first place.

 

[michaeljp65]

I turn & seat one and then measure with a 0.0001 Mitutoyo. (collet puller at the ready)
You'll will be able to rotate to see how consistent your turning is.
I have a quality tube mic as well, but I never quite get things perfect enough to go on that number alone.
The number above, your overall loaded round, is ground truth.
The 9.5 referenced above assumes a .2430 bullet. (None of mine measure that) Go slow and plan to do this a couple times as you work your way down to the final number (0.2620 overall) accounting for the pressure ring which on my limited selection of flat back bullets has been between 0.2433-0.2436.
-
FWIW, When starting out in this hobby, I made several choices for monetary economy that have caused frustrations, inefficiencies, and outright errors costing many times over whatever money I thought I was saving. You'll be making two, possibly three cuts to get down to your final thickness. I highly encourage you to consider buying no less than one, preferably two, dedicated cutter assemblies and leaving them alone once you lock in on your final pass. I now have several independent cutter assemblies from 21st Century and I wouldn't be without them. I like learning & shooting with my own work, but in all honestly, I may never wear out enough barrels and brass to have really done better (true total equipment cost PLUS time) than just paying DJ to make very high quality brass to order in the first place.

Thanks for your advice Boatschool. All taken onboard, i have 2x 21st century cutters and their new power lathe. But this is not my 1st PPC, i have one with a .262 neck. This one that is being chambered is a new .265 reamer and just trying something different with this one. Using Barts 68gn FB Ultras. My .262 is using local made 67gn projectiles. I'll mic a few of the 68gn at the pressure ring and see what they come up to.

Cheers

 

[joshb]

I like .003-4 clearance. I tried an experiment today with my new 6br barrel. I had some loads for another rifle on hand and wanted some foulers. I measured the necks on 10 rounds and they were .0015 smaller than my .268 neck. I had read about guys running them tight and figured I’d try it. My test loads were turned for .264 loaded round. The first tight fouler shot seemed a little hard on bolt lift. Hmmmm! The second fouler felt hard on bolt lift and blew the primer. That ended my experiment. No more close fits for me.
My test rounds shot great with no pressure signs to 30.3 grains Varget. The foulers were 29.4 grains Varget. Same Berger’s 105 in all rounds.

 

[Dusty Stevens]

Thanks for your advice Boatschool. All taken onboard, i have 2x 21st century cutters and their new power lathe. But this is not my 1st PPC, i have one with a .262 neck. This one that is being chambered is a new .265 reamer and just trying something different with this one. Using Barts 68gn FB Ultras. My .262 is using local made 67gn projectiles. I'll mic a few of the 68gn at the pressure ring and see what they come up to.

Cheers

Just add .0015 to your .262 brass cutter and be done with it. Nobody uses tight fitted necks anymore. Your brass will be trashed in a ppc long before the effects of too much clearance pops up. Too much is better than too little as much as bullet dia changes on flat base bullets

 

[BenPerfected]

Just add .0015 to your .262 brass cutter and be done with it. Nobody uses tight fitted necks anymore. Your brass will be trashed in a ppc long before the effects of too much clearance pops up. Too much is better than too little as much as bullet dia changes on flat base bullets

Dusty, in your experience at what point does too much neck clearance effect accuracy?
Ben

 

[Dusty Stevens]

Dusty, in your experience at what point does too much neck clearance effect accuracy?
Ben

It doesnt. Ive used plenty of .262 brass in .268 and .268 brass in a .275 and .278nk.
Should say brass cut for .262 and cut for .268 so even smaller than that