.260 Remington C.O.A.L

[HALODIN]

Quick question - What COAL would you set for rem .260 with 139 scenars and v-N560? My Speers bible doesn't have a specific for 139, just 140 which it says should be 2.745". The Lee bible says 2.795 min OAL for a 139 grain jacketed bullet.

Any ideas?

Cheers,

Craig.

[HALODIN]

Don't worry about replying I'm going with 2.795".

[The Gun Pimp]

Your COAL should bear some resemblance to YOUR rifle surely. My COAL may not work in your chamber. You need to measure your own COAL - various devices are available for this purpose.

[Alpha1]

COAL ? I use ammunition in mine. :lol:

[HALODIN]

This is my understanding and I fully accept I could be wrong... I thought the values published in reloading manuals were `generally` accepted for most rifles, whilst of course there may be the odd exception. I was advised to test a non primed round in the chamber before reloading the rest of the brass. If the bolt either doesn't or is difficult to close then there's a problem. The variance I believe is down to the headspace of the chamber. To add to this, you can improve on accuracy by adjusting the COAL so the difference between the ogive and the lands (the jump) is optimal for your rifle/bullet etc... There are of course tolerances that mustn't be ignored. Is that correct?

Your COAL should bear some resemblance to YOUR rifle surely. My COAL may not work in your chamber. You need to measure your own COAL - various devices are available for this purpose.

[HALODIN]

:lol:

COAL ? I use ammunition in mine. :lol:

[Laurie]

This is my understanding and I fully accept I could be wrong... I thought the values published in reloading manuals were `generally` accepted for most rifles, whilst of course there may be the odd exception. I was advised to test a non primed round in the chamber before reloading the rest of the brass. If the bolt either doesn't or is difficult to close then there's a problem. The variance I believe is down to the headspace of the chamber. To add to this, you can improve on accuracy by adjusting the COAL so the difference between the ogive and the lands (the jump) is optimal for your rifle/bullet etc... There are of course tolerances that mustn't be ignored. Is that correct?

Your COAL should bear some resemblance to YOUR rifle surely. My COAL may not work in your chamber. You need to measure your own COAL - various devices are available for this purpose.

COALs quoted in manuals are usually based on SAAMI / CIP nominal values and/or what will likely fit the magazine in the approriate action length. In some cases, where the bullet is shorter than most, a shorter COAL will be quoted that provides a calibre depth of bullet shank in the neck.

As The Gun Pimp says, these figures bear absolutely no relationship to the situation that applies in an individual rifle. If the COAL quoted in the manual is the ideal value for your rifle, that's simple happenstance. You need to measure your own rifle's chamber throat for that particular bullet.

[HALODIN]

Yes I think that is basically what I was trying to say above. When you say "ideal value for your rifle," you're only referring to accuracy and not safety aren't you? As I understood it, the book value for COAL provides safe values, but to improve accuracy you need to measure your COAL. Is that a fair summary?

[pe4king]

I load mine to 2.826" seems to work for me, but whatever suits your rifle start at 2.800" and take it from there.

[Laurie]

Yes I think that is basically what I was trying to say above. When you say "ideal value for your rifle," you're only referring to accuracy and not safety aren't you? As I understood it, the book value for COAL provides safe values, but to improve accuracy you need to measure your COAL. Is that a fair summary?

In very broad terms, yes that's correct. The quoted cartridge OAL for each individual bullet should fit a chamber with a throat / leade configuration that complies with the minimum SAAMI value for that area. That assumes we're talking mass produced factory rifles. Any custom, or rebarrellled rifle may or may not be 100% SAAMI compliant.

The small 6.5s (260R, 6.5X47L, 6.5mm Hornady Creedmoor) are often chambered to suit most 120-130gn weight bullets seated optimally. Seat a 139-142gn model at the SAAMI max COAL and the bullet may be jam seated to such a degree that the round won't chamber easily or even at all. That applies to both my 260R and '47L rifles.

Conversely, many factory rifles have massively excessive amounts of freebore built in by their manufacturers, especially if American or if they're to be sold in the US market. Manufacturers know that many buyers will handload despite warnings that warranties etc are void with such fodder. They also know that if some idiot owner blows his rifle up and injures himself with an unsafe handload, he'll still try and sue the socks off the rifle maker. So, they play safe by putting in LOTS of freebore, which usually not only degrades precision, but seriously reduces pressures and MVs.

One of the objectives / benefits of handloading for many shooters is to optimise the cartridge to the firearm, ie to produce a custom piece of ammunition. Use the quoted COALs and you should be safe - I wouldn't guarantee it though - but sometimes these same bullets will be seated way down in the case which is an undesirable situation especially if avoidable.

It often leads to restricted usable charges, and/or very heavily compressed charges. If the rifle has the freebore to allow the bullet to be seated further out and still be a reasonable amount off the rifling lands, the promised MVs in the manual are most unlikely to be achieved, real MVs may in fact be very well down on those expected. Freebore and bullet seating have a huge effect on pressure and velocity.

Taking the 260 Rem and Sierra's 2.765" COAL for its 140/142gn bullets and maximum charge of 39.9gn N150 for 2,700 fps in a 24" barrel Savage 12VSS.

Let's assume first that the freebore and hence COAL is roughly as per SAAMI and that Sierra's quoted figure is optimal for the rifle chamber.

QuickLOAD says PMax and MVs are:

140gn Sierra SBT ............. 2,675 fps / 57,883 psi
140gn Sierra MK .............. 2,689 fps / 59,317 psi
142gn Sierra MK .............. 2,699 fps / 62,422 psi (2,400 psi in excess of maximum SAAMI allowed)

However, if the chamber is longer throated than the SAAMI standard, such that it would allow 2.9" COAL, that 39.9gn N150 is now computed to produce:

140gn Sierra SBT ............. 2,632 fps / 53,627 psi
140gn Sierra MK .............. 2,645 fps / 54,836 psi
142gn Sierra MK .............. 2,655 fps / 57,489 psi


Sticking with our 'optimal' 2.9" COAL for the chamber, and increasing charge weights to suit we get:

140gn Sierra SBT ............. 41.5gn N150 / 2,718 fps
140gn Sierra MK .............. 41.1gn N150 / 2,710 fps
142gn Sierra MK .............. 40.5gn N150 / 2,687 fps

Charges being the maximum computed that produce pressures within the 260's SAAMI maximum 60,088 psi.