I'm currently shooting a 6XC in f-class. Chamber has a neck about 0.275" and I'm shooting 105gr Lapua Scenars over 38.4gr of 2209, CCI BR primer and 1st Gen Norma brass, which I turn to about .013", giving me a loaded round diameter of approx 0.269"
I FL size with a die built for me by Neil Jones, using a .267" neck bushing. Both fired and sized cases (using this die) are very concentric, with TIR about .001" or often less at shoulder/body junction and neck, using sinclair concentricity gauge.
Where things get a bit weird is when I seat bullets - also using a Neil Jones threaded micrometer seater. When I measure TIR on tbe seated bullet - just shy of the ogive, it blows out to about .004"-.005". I note the odd difference in apparent seating force required but the runout variance is across the board.
Does anyone have any suggestions on what the problem might be or what I might try to remedy things? My thought was that maybe sizing down about .008" in one step might be creating some issues but again - the concentricity tool seems to indicate not.
Press is a forster co-ax and shellholder has no problem - clearly no issues here given no runout issue when sizing.
Any ideas?
Thanks, Justin
concentricity issues?
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chris.tyne
- .270 Winchester
- Posts: 1440
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I have made hundreds of dies over many years with many of them being seating dies. The best to date is the dies i now use that are a replication of the chamber so they can double as a seater and with the removal of a narrow spacer they just nudge the shouder back for ease of bolt closure. A taper die is used to control the web area. After the taper and bump dies are used the TIR is 0.0003 or less. Even with the chamber seater and precision made seating stem i still get an average of 1 to 2 thou TIR runout on the bullet nose.
Having said all this, the only way you will ever get perfect TIR in your ammo is to straighten it like most all the 1K etc shooters do. It is a rare set up that gives all loads with 1 thou or less runout. I have never seen it in hundreds of dies.
Tony Z.
Having said all this, the only way you will ever get perfect TIR in your ammo is to straighten it like most all the 1K etc shooters do. It is a rare set up that gives all loads with 1 thou or less runout. I have never seen it in hundreds of dies.
Tony Z.
Neil Jones make good threaded dies
You are talking close tolerances but as you shoot f class I guess you need every drop of milk out of the cow!!
The chamber is a fair way out at .275 on a finished 0.269 round on a 269 you should be using a 271 or 272 max chamber (talk to Shane Clancy he’s the gunsmith and man around here) or some of the BR guys they are pretty cluey and more of an idea than me e.g. Rinso, Ackley improved, ogre6br tony z and hiwall and the likes, but all that aside you mentioned that after case prep they are good so you can forget about all that chamber stuff being the seating problem.
Is the neck out of concentricity after seating as well you only mentioned the bullet ogive?
Like trev said check projectile,
Some other suggestions;
are you reaming the inside of you cases or did you neck sizing then expand with the correct tool eg an expanderon etc. before neck turning or did you fire form then size, expand etc. before neck turning???
How much variation is their in seating tension? because you are neck turning to 013 things should be good? My guess is that your necks weren’t prepped right before turning because when they go through the neck sizer that just takes care if the outside then it gets pulled over the expander ball, get your neck wall micrometer or if you got a K&M turner with the dial indicator on you can check it with that and check thicknesses on fire formed cases? If you didn’t prep case right and they were concave or convex or wavy when you turned them the case slips over the turner pilot and rests on the tightest points the you go and turn the out side of the neck turning then parallel with the tightest point then on your first shot at 50000psi flattens out the neck walls to chamber dimensions and the thinner/thicker sections are back because you never got rid of them in the first place you only took out the high points. You may need to try new brass my opinion is your case walls are already to thin for your chamber.
Are you deburring the case mouth enough?
Pull the die apart check the seating stem isn’t damaged eg. Has a nick or burr in it or has a build up of rubbish on it?
That’s about it for me, please don’t take anything as gospel it’s just the way my warped head has looked at the problem
All the best
John
You are talking close tolerances but as you shoot f class I guess you need every drop of milk out of the cow!!
The chamber is a fair way out at .275 on a finished 0.269 round on a 269 you should be using a 271 or 272 max chamber (talk to Shane Clancy he’s the gunsmith and man around here) or some of the BR guys they are pretty cluey and more of an idea than me e.g. Rinso, Ackley improved, ogre6br tony z and hiwall and the likes, but all that aside you mentioned that after case prep they are good so you can forget about all that chamber stuff being the seating problem.
Is the neck out of concentricity after seating as well you only mentioned the bullet ogive?
Like trev said check projectile,
Some other suggestions;
are you reaming the inside of you cases or did you neck sizing then expand with the correct tool eg an expanderon etc. before neck turning or did you fire form then size, expand etc. before neck turning???
How much variation is their in seating tension? because you are neck turning to 013 things should be good? My guess is that your necks weren’t prepped right before turning because when they go through the neck sizer that just takes care if the outside then it gets pulled over the expander ball, get your neck wall micrometer or if you got a K&M turner with the dial indicator on you can check it with that and check thicknesses on fire formed cases? If you didn’t prep case right and they were concave or convex or wavy when you turned them the case slips over the turner pilot and rests on the tightest points the you go and turn the out side of the neck turning then parallel with the tightest point then on your first shot at 50000psi flattens out the neck walls to chamber dimensions and the thinner/thicker sections are back because you never got rid of them in the first place you only took out the high points. You may need to try new brass my opinion is your case walls are already to thin for your chamber.
Are you deburring the case mouth enough?
Pull the die apart check the seating stem isn’t damaged eg. Has a nick or burr in it or has a build up of rubbish on it?
That’s about it for me, please don’t take anything as gospel it’s just the way my warped head has looked at the problem
All the best
John
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chris.tyne
- .270 Winchester
- Posts: 1440
- Joined: Thu Jun 07, 2007 9:56 pm
- Favourite Cartridge: 6BR
- Location: Usually underneath
Jump70,get an intermediate bush such as .271,if your chamber is .275 allow .001 spring back so were @.274,now I could be wrong but if the neck thickness is .013 your necks should be .269 with out a projectile seated,wouldn't try to go in steps bigger than .003 when sizing down.
Depending on the projectile used as some have a larger pressure ring a loaded round should measure .270,have you tried a .268 sizing bush if not may be worth a try,having said all that,it may have no bearing whatsoever on the runout.
It would be a benefit if you had accurate measuring tools,that way you arn't stacking the variables like 1/2thou here 1/2thou there and the end measurement would mean something.
Is the rifle a factory that has had a rechamber job or a rebarrel,how does it group on the target,if it shoots well don't worry so much as I would consider .003-.004 run out acceptable for short range BR but as I dont shoot F class you may need all you can get.
If you are using the expander ball in the die pull it out and throw it to the shithouse,another superfluous item not needed.
I tend to think that you neck turning may be giving you inconsistent neck thicknesses,if you mark the case when checking is the measurement consistant as in the location on the cases also are you talking about TIR or just runout there is a difference.
Chris.
Chris.
Depending on the projectile used as some have a larger pressure ring a loaded round should measure .270,have you tried a .268 sizing bush if not may be worth a try,having said all that,it may have no bearing whatsoever on the runout.
It would be a benefit if you had accurate measuring tools,that way you arn't stacking the variables like 1/2thou here 1/2thou there and the end measurement would mean something.
Is the rifle a factory that has had a rechamber job or a rebarrel,how does it group on the target,if it shoots well don't worry so much as I would consider .003-.004 run out acceptable for short range BR but as I dont shoot F class you may need all you can get.
If you are using the expander ball in the die pull it out and throw it to the shithouse,another superfluous item not needed.
I tend to think that you neck turning may be giving you inconsistent neck thicknesses,if you mark the case when checking is the measurement consistant as in the location on the cases also are you talking about TIR or just runout there is a difference.
Chris.
Chris.
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jump70
Thanks for all the helpful replies, gents.
In answer to some of the questions (in no particular order).
The rifle was built for me by Terry Cross of KMW in the U.S and he chambered the krieger barrels (I have a spare) with a semi-match reamer as the rifle is designed to feed from AI mags. It is a surgeon tactical action.
In hindsight, the use of a .275" necked chamber was excessive and I wholeheartedly agree with John that around a .272" neck would have been ideal. Unfortunately, this will mean setting back and rechambering the barrels. Shane Clancy isn't in a position to do this quickly, given his workload and I'm not sure if my other Oz gunsmith (who is a BR guy) has a reamer. &^%$#!!!!!
Neck wall thickness is 0.013" - so yes, loaded round diameter is 0.269" (0.013" x2 + 0.243"). I turned the necks with a kinneman neck turner and measured them on a .0001" capable electronic ball micrometer. My other mainstay measuring devices are mitutoyo 0.0001" electronic calipers (best $$ i ever spent) and a sinclair concentricity gauge with .001" dial indicator. I don't think the tools are lacking but I think my ability to work with them doesn't stress their capabilities too much...
I might try sizing down in steps as Chris suggested and see if this helps. My FL sizing die is from Neil Jones Custom and has no expander ball - I never use one on any of my dies.
I've measured a sample of my Lapua 105gr scenars and they are uniformly 0.2425" at the pressure ring and on the bearing surface, so my loaded rounds are 0.2685"/0.269". Unfortunately, my concentricity gauge won't allow me to check their circumferential runout.
I've just pulled out a box of loaded rounds and some fired cases. These are the types of measurements I'm seeing.
5 sized/loaded rounds ave:
- Runout on bullet bearing surface (I've moved backwards from having been measuring further towards the bullet ogive): 0.002"
- At case neck midpoint: 0.0013"
- At case body/shoulder junction: <0.001"
5 fired cases
- At case neck midpoint: < 0.001"
- At case body/shoulder junction: < 0.001"
Noted as a result:
- As I move further towards the nose of the bullet, the runout increases but I'm thinking this may be due to jacket tolerances...?
- Neck concentricity gets slightly worse also after the sizing/seating operation
I get the distinct feeling that if my measurements are right and taken at the correct point on the projectile, neck and case, that I'm just being a big girl's blouse and tilting at windmills. I think I've just hit the limit of tolerances of the dies, my reloading techniques and measuring gear capability.
Because I shoot LR, I'd like to get it all down to .001" or less but I think that I'll have to move to an inline seating die to achieve that.
The rifle is shooting well but I'm getting the odd inexplicable flier that hits either low or high right - and I'm not talking cold bore shots either. I can generally shoot well enough to know when it was me who stuffed up (quite often), so this is doing my head in slightly, as it were...
Thanks again everyone, for your help.
Justin
In answer to some of the questions (in no particular order).
The rifle was built for me by Terry Cross of KMW in the U.S and he chambered the krieger barrels (I have a spare) with a semi-match reamer as the rifle is designed to feed from AI mags. It is a surgeon tactical action.
In hindsight, the use of a .275" necked chamber was excessive and I wholeheartedly agree with John that around a .272" neck would have been ideal. Unfortunately, this will mean setting back and rechambering the barrels. Shane Clancy isn't in a position to do this quickly, given his workload and I'm not sure if my other Oz gunsmith (who is a BR guy) has a reamer. &^%$#!!!!!
Neck wall thickness is 0.013" - so yes, loaded round diameter is 0.269" (0.013" x2 + 0.243"). I turned the necks with a kinneman neck turner and measured them on a .0001" capable electronic ball micrometer. My other mainstay measuring devices are mitutoyo 0.0001" electronic calipers (best $$ i ever spent) and a sinclair concentricity gauge with .001" dial indicator. I don't think the tools are lacking but I think my ability to work with them doesn't stress their capabilities too much...
I might try sizing down in steps as Chris suggested and see if this helps. My FL sizing die is from Neil Jones Custom and has no expander ball - I never use one on any of my dies.
I've measured a sample of my Lapua 105gr scenars and they are uniformly 0.2425" at the pressure ring and on the bearing surface, so my loaded rounds are 0.2685"/0.269". Unfortunately, my concentricity gauge won't allow me to check their circumferential runout.
I've just pulled out a box of loaded rounds and some fired cases. These are the types of measurements I'm seeing.
5 sized/loaded rounds ave:
- Runout on bullet bearing surface (I've moved backwards from having been measuring further towards the bullet ogive): 0.002"
- At case neck midpoint: 0.0013"
- At case body/shoulder junction: <0.001"
5 fired cases
- At case neck midpoint: < 0.001"
- At case body/shoulder junction: < 0.001"
Noted as a result:
- As I move further towards the nose of the bullet, the runout increases but I'm thinking this may be due to jacket tolerances...?
- Neck concentricity gets slightly worse also after the sizing/seating operation
I get the distinct feeling that if my measurements are right and taken at the correct point on the projectile, neck and case, that I'm just being a big girl's blouse and tilting at windmills. I think I've just hit the limit of tolerances of the dies, my reloading techniques and measuring gear capability.
Because I shoot LR, I'd like to get it all down to .001" or less but I think that I'll have to move to an inline seating die to achieve that.
The rifle is shooting well but I'm getting the odd inexplicable flier that hits either low or high right - and I'm not talking cold bore shots either. I can generally shoot well enough to know when it was me who stuffed up (quite often), so this is doing my head in slightly, as it were...
Thanks again everyone, for your help.
Justin
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Ackley Improved
- 6mm Dasher
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chris.tyne
- .270 Winchester
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- Location: Usually underneath
,what scope have you got mounted there.
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Ackley Improved
- 6mm Dasher
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woob614271
- 17Rem
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