Ream or not to ream? 260 Remington formed from .308

[rockydoc]

Brass for .260 Remington is either scarce, expensive or both. I bought some Nosler Custom .260 brass which is excellent, but costs over $1.00 per case. I have access to Winchester .308 Match brass that costs me nothing ( I have a friend on the SWAT team and they use and practice with Winchester Match factory ammo, no reloads).

How do I determine if neck reaming is necessary?

I sized the necks down with a full length sizer with the expander removed (I tried it once with the expander in place. That didn't work! I had to cut the case off of the expander, even though I lubed the inside of the neck with mica).

Here are the measurements of the outside case neck:
Loaded round in Nosler .260 brass= -----------------------------.2887"
Sized down Winchester brass in .260 sizer before loading= ---.2886"
Loaded round in Winchester .308 brass sized to .260 =--------.2928"
This round chambered in my rifle OK.

SAAMI outside neck diameter specifications are:
Maximum cartridge diameter= .2970"
Minimum chamber diameter= .2980"

It appears to me that since my loaded cartridge with .2928" is smaller than the cartridge maximum of .2970" and it loads easily in my rifles chamber that I do not need to ream these cases after resizing. Is this assumption correct? I don't like proceeding into unknown territory based on assumptions!

 

[highlander 5]

If you have RCBS or Redding dies you can get a carbide expander ball for them,that might help. What you need to do is get a dial/digital vernier and maesure the thickness os the brass at the neck. A tubing micrometer would be better. I've made 7 mm Mauser from 30'06,40/65 from 45/70 and have never had a problem. My current project is 300 Blackout from 223 and the thickness of the brass at the neck is.013-.015. The other way is to take the outside neck diameter and subtract you bullet diameter and divde by 2. In your case that is .016. Perhaps your expander is out of spec. Again a vernier or micrometer is a useful tool.

 

[243winxb]

(I tried it once with the expander in place. That didn't work! I had to cut the case off of the expander, even though I lubed the inside of the neck with mica)

A donut may have formed at the neck shoulder junction. The expander should move donut to the outside of the neck. Your neck diameter is OK, if the measurement is the same at the neck shoulder junction, under .297"

 

[Clark]

The 260 SAAMI drawing tolerances for the chamber neck are:
a) .299 - .301" at the rear of the neck
b) .298 - .300" at the front of the neck


As best I can measure with pin gauges, my 260 [long chambered at Douglas] is:
a) .299" at the rear of the neck
b) .298" at the front of the neck


I have used 308 brass, 243 brass, and 260 brass in my 260.
My experiences are consistent, but not a complete verification of the synopsis I offer here of internet folklore mythology I have read about the 260:
1) 7mm-08 brass is the best, good fit between chamber neck and ammo neck
2) 260 brass is second best
3) 243 brass is third best. It gets a donut formed at the base of the neck
4) 308 brass is 4th best. Commercial brass will work. 10% of the time there will be a nasty pressure spike from a pinched bullet. These misfits can be sorted out, turned, or reamed.

 

[rockydoc]

The measurement at the neck/shoulder junction is .2927, so it looks like I am ok.
Rockydoc

 

[rockydoc]

Clark:
My rifle is a Kimber 84M Classic. A cast of the chamber measures .300 at the neck/shoulder junction and .298 at the mouth.
The rifling starts off tapering right at the neck rather than having a .020" or so leade with a diameter of .265, which it should have, if I am reading the SAAMI specs correctly. This is a short throat, to me. I can't load any bullet to .280 length. A Nosler 140 grain Custom Competition touches the lands at a length of .258".

 

[ranger335v]

"Is this assumption correct? "

Yes. So long as your loaded neck diameter is 2-3 thou smaller than the chamber neck you are fine. But, if you do anything to thin them use a turner, not a reamer. Turning actually makes necks more consistant, reaming only makes them thinner.

 

[Clark]

Here is the SAAMI drawing:
http://www.saami.org/PubResources/CC_Drawings/Rifle/260 Remington.pdf

 

[rockydoc]

Clark: Thank you for the reference to the SAAMI drawing of the.260 Remington cartridge and chamber. The leade of ".20 or so" I mentioned yesterday at 9:12 turns out to be exactly .2044". The cast of my chamber does not have this 'larger than bullet diameter' section of freebore which would allow seating of long bullets out to the maximum length of 2.80" without contacting the lands. This short throat cheats me out of some powder capacity. I can tolerate that as long as it doesn't create any pressure problems from compressed loads.



As you can see from this photo of the cast of my chamber the rifling starts as a gentle slope progressing to full depth, but it starts almost immediately outside the neck, rather than .2044" down the bore.

This short throat discussion may be off the subject of "Do I need to ream or turn the necks" but it is of some concern to me and I respect the considered opinions of your collective experience and knowledge.
Rockydoc

 

[jerkface11]

If the throat is too short it's not that big of a deal to get a gunsmith to lengthen it.

 

[Offfhand]

Rockydoc, can you chamber factory ammo in your .260 Kimber? The short throat in your rifle indicates that it may not. If not, you have a valid complaint and the logical thing to do is return it to factory rather than pay a gunsmith to correct the problem. I once had a Kimber that would not chamber some factory ammo and they quickly made it right, paying shipping both ways. The industry rule seems to be that if the rifle won't chamber factory ammo it's their problem, if it won't chamber reloads it's your problem. So make the test with factory ammo even if you don't intend to use it, and try every brand and bullet combination combination available to make your case, if even only one won't fit, you have a valid reason to return.
I've been shooting various .260 rifles in competition for several years and have had best performance with Lapua .243 brass necked up to .260. But there is no longer any need for that as Lapua now offers designated .260 brass. The samples I've worked with have very uniform neck thickness and are good to go with no need for neck turning to even them up.

 

[rockydoc]

Offhand:
I sent the rifle back to Kimber and they did indeed pay the shipping both ways. They said that both Winchester and Remington factory loads chambered and extracted without having the bullets stick in the barrel. They sent the gun back unchanged. They said follow handloading manuals for correct COAL. I can't seat any of my bullets to the length of any of the manuals I have, so I will just use my Hornady OAL guage and seat the bullets off the lands the same amount that I would have if I could have loaded the bullets longer.

I have a load using Noslers "Most Accurate Load" for 100gr bullets with Hornady 100gr SPs. That should do for the largest deer I can find here in north Florida.

I am trying to develop a load using Dan Newberry's Optimal Charge Weight system with 140gr Nosler bullets. The heaviest loads are compressed because of the short throat and the long bullets. I have the test series loaded but haven't been able to get out to the range because of the weather. I don't know if these compressed loads will develop too much pressure or not. The manuals show compressed loads frequently, so I am hopeful all will be OK.

 

[jerkface11]

Nothing irritates me like a short throat in a rifle. Which reminds me my 264 winmag needs to go to the gunsmith.

 

[PapaG]

Turning is the best approach to getting the cartridge case neck concentric with the bore. Reaming will not improve concentricity but will thin out necks that are too thick.

If you have the right diameter neck before seating a bullet but it is too big after seating, the thickness is too great and you'll have to either turn or ream. Don't be alarmed if when turning you don't clean up all the way around. It often doesn't happen.

 

[Offfhand]

Rockydoc, as the wise old saying advises us: "When you get lemons make lemonade." So consider the positive side of your short throated rifle and take advantage. Quite often, rifles do not achieve their full accuracy potential because the throats are so long that it's impossible to get the bullet close enough to the lands for top accuracy, a problem which you do not have.
Visit some successful bench rest competitors and you'll quickly discover that a common technique for developing highly accurate loads is starting with the bullet against the lands and proceeding from there. Occasionally top accuracy may be found with be bullet slightly off the lands, but over 80% of the time close contact or even a hard "jam"is proven to be the most accurate.. I have a few rifles in .260 caliber and all but a couple are most accurate with the bullet into the lands. (The reason these two rifle are exceptions is because their throats are too long to get the bullet into the lands if the cartridges also fit the magazines. I plan to have one of them, a DPMS, rebarreled using my own shorter throat reamer.) So what I'm getting at, is don't be misled by a belief that you have to keep the bullet away from the lands by a certain distance, as you seem to indicate in your comments. Start your load development with a relatively mild load and bullet touching the lands, increasing the load gradually and watching for excess pressure. Once you find the best powder/charge combination you might further refine the load by backing off the lands, but most likely you'll discover that the load with bullet into the lands is your best. Enjoy the lemonade.

 

[Clark]

As Offfhand explained, some of us have a hard time reaching the lands.

My 260 loaded with 100 gr Nolser Ballistic Tips can barely reach the lands with the case mouth having almost no contact with the bullet.

This is unacceptable for hunting, but makes nice groups.

 

[Afy]

I use a hard jam into the lands with my .260 using the 139 Scenar. Have excellent accuracy, and can keep sub MoA at 100 quite easily, and half that when I actually concentrate on my shooting.