Is my .260 neck too tight

[Deleted member 10043]

Fired round neck OD .2965 - loaded neck OD with bullet .2935 = .003. Neck thickness .155 and if I'm doing the math right I should be right about .002 neck tension on a fired case.

Lapua 260 Rem Brass. I think I can actually reload the fired brass without resizing the necks. Anyway, trying to figure out why I'm getting cratered primers and/or slight ejector marks with normal velocity @2750 fps even as far off as .100 off the lands. It is nothing about carbon ring or anything like that. Rifle has shot this way since day one and the brass is lasting forever. This is the same .260 I posted earlier that takes about 20 rounds to settle down to an actual zero I can work with. This is the same rifle I started thread on here. I'm just looking at everything...

https://www.snipershide.com/shooting/threads/20-rounds-and-changing-zero.6910910/#post-7331823

 

[spife7980]

Loaded neck diameter equals .2935?
.2935-.264=.0295/2=.01475 of neck thickness per side.
If your fired diameter is .2975 and your loaded round is .2935 that is .004” of clearance for .002” of clearance per side which should be adequate.
Your numbers aren’t adding up.
A fired case shouldn’t have any neck tension.

Edit: Ignore this, his post was updated for corrections

 

[PinesAndProjectiles]

I had a similar experience.

I had a 6 Creed spun up and I was sizing down Petersen 6.5 Creed brass. I could seat a round in the fired case and get about .001" neck tension. I ended up neck turning all my brass.

But, I never saw high pressures during load development.

If I knew then what I know now, I would have sent the barrel to a Smith and have him open the neck a few thou.

Neck turning sucks.

 

[Deleted member 10043]

I can seat a bullet by hand into a fired case but can't pull it out by hand.

 

[Deleted member 10043]

Shit, typo in post #1, Spice. Fired case neck OD is .2965. I changed it up there. But my tension is not -.002. Fired neck ID is .265 and bullet is .2645. It is a tight fit.

 

[digrazir]

I had the same issue with my AI Bartlein 260 barrel. Fired cases still had enough neck tension to hold a bullet..I neck turned the Lapua brass down to .014, basically slightly more than a cleanup..problem solved, the bullets will freely drop into a fired case..I also noticed a big improvement on my targets. Ray

 

[Deleted member 10043]

Thanks, this chamber is .260 KMW/Surgeon. Aka, Ft. Bragg, aka T. Cross aka Match. NK = .297. FB = .060

http://pacifictoolandgauge.com/260-cal-274-cal-nopix-chamber-reamers/10751-260-remington-match.html

.260 Rem SAAMI NK = .298 or .299???

 

[digrazir]

Based on my not being able to drop a bullet into a fired case the neck was obviously too tight for the chamber. I would think an off the shelf Bartlein barrel would not require neck turning..didn’t make sense..For me it made more sense to just turn the necks than send the barrel out..Ray

 

[spife7980]

Thanks, this chamber is .260 KMW/Surgeon. Aka, Ft. Bragg, aka T. Cross aka Match. NK = .297. FB = .060

http://pacifictoolandgauge.com/260-cal-274-cal-nopix-chamber-reamers/10751-260-remington-match.html

.260 Rem SAAMI NK = .298 or .299???

saami is .299 and tapers down to .298

Your fired brass is .2965, thats half a thousandth under your .297 neck. So that seems in line.

If your loaded diameter is .2935 that does leave you with .0035 of clearance which is at the minimum but shouldn't be unsafe unless you let your chamber get nasty and built up with crud.
Turning a 3/4 of a thousandth off the neck thickness (thats .0015 off total diameter) should give you what I would consider my ideal clearance of .005 but there are many that like the neck tight for a pure accuracy and keeping stuff concentric. But then again those people would probably be turning necks to hit their goals, not the other way like this situation but it could turn up in the same place. Turning that .00075 should clear up most of the lapua brass thickness discrepancy. Turning still might not clear up your issues with this barrel though, not sure if its the source of your troubles but its possible.




What else I notice is that your freebore is small. Saami has (2.180-2.0615=) .1185 of freebore.

You arent inadvertently jamming your bullets real bad are you?
What bullet are you using?
How far do you have it seated off the lands?
Did you get your lands measurement with a hard jam or is it actually a touch measurement?

 

[Milo 2.5]

To me, necks growing .003" is perfect, that means the neck in chamber is at least .297" or greater, brass springs back after firing. I honestly would set a barrel back with a different reamer if a bullet dropped freely into a fired case. Being I use bushing dies, oversize necks create problems.
^^^ I had this typed before you posted chamber specs, you could try doing a skim pass on 10 or so cases, send them off if needed, then duplicate your practices.
Give us more detail on load, running a silencer, etc... 2750fps should not be hot unless you are running a fast powder.

 

[Deleted member 10043]

136 Scenar L. I seat them .02 off the lands but have seat them as far as .100 just to see if does the same thing and it does. 42 grains AA4350.

 

[lightman]

After going through this myself and turning case necks for a few different tight neck chambers, I don't consider knowing the diameter of the fired case neck to be important. The important numbers are the chambers neck diameter (.297) and the diameter of the neck on your loaded round ( .2935). My math shows .0035 difference. If you are turning the case necks this should be enough clearance. If you are not turning the necks you may have enough variation in thickness to reduce that .0035 to the point of creating pressure problems. Are you confident in the chambers neck diameter? Have you cast the chamber and measured it? I have 1 rifle that I run between .0015 and .002 clearance. But I turn the necks and I'm confident in my measurements. And yes, I probably could reload the cases without resizing them.

Turning case necks in not that troublesome if you have to go that route. It is another step though! I use a cordless drill with a Sinclair shell holder run at the slowest speed possible. I crowd the feed (rate of advance) very slowly and after making the cut I'll hold a piece of steel wool against the new cut to smooth it even more. I arrive at my numbers by the neck wall thickness X 2 plus bullet diameter.

 

[Deleted member 10043]

One thing for sure is I have a problem at both ends the barrel.

 

[ranger3]

I have a 260 I thought had a tight neck but ultimately determined that I was loading the bullets a little bit too long. It also has a tendency to raise the zero vertically after 10 - 15 rounds.

 

[Deleted member 10043]

Thanks for the math and other things. Looks like the neck has just enough room but I'm never going to get a match chamber again. I like vanilla. As for the pressure part in combination with the time to get this barrel running is a waste of ammo.

 

[Deleted member 10043]

Fuck me raw. This thing closes on a go and no-go gauge but not a field gauge. I'm going to Remage it up.

 

[spife7980]

Criterion, McGowan, mcrees, xcaliber, pva, bugholes?

 

[Deleted member 10043]

I've done criterion and X-Caliber and like them both. I've got a good shooting 6.5x284, along with .244 Rem, 25-06, .308. All have barrel nuts. The '06 is 7 twist shooting Blackjack 131 grain. I'm thinking of a 22-250 1:9 that is on the shelf for 69 gr SMK. I have one regular R700 built by Randy Selby in .300 H&H. That one is built right and will be my last gunsmith rifle.