The .260.

[6.81star]

I am having a .260 built.
Heres the specs:
Trued Rem 700 SA
Bartlien heavy varmit 8.5twist with a length of 22 ins.
My smith asked me for a dummy round. I want to run a dbm so I think I am limited to the overall length of case, but not for sure. From what I understand the 140,139,142 bullets will perform best. Is that what I want to set my chamber up with according to the twist? So what should my overlength be, go easy I am new to reloading. New rifle, new reloading gear gonna be lots of learning.

 

[bohem]

Re: The .260.

If you haven't picked a bullet you want to shoot, then the dummy round is somewhat of an issue. Especially with keeping them at or in the lands with mag-length.

The idea with the dummy rounds is that you load the bullets to mag lenth (2.860" IIRC) and the gunsmith will cut the chamber so that the leade (throat)is setup so that you can get the bullets to touch or slightly jam into the lands as you feed from the magazine.

You need to pick a bullet then, since the distance from the meplat (tip) to the bearing surface/ogive juntion (where it stops being curved nose to being straight and the rifling contacts the bullet) is different for each one of the bullets you meantioned above.

If you're not sure which one you want to use. I'd suggest then that you pick the shortest ogive of the 3 and use that to have the chamber cut. This way you can load the longer ones slightly deeper into the case to accomodate for the short throat.

The 260 will burn the throat out to allow you to seat longer and longer as the barrel wears, and with most 6.5mm's it will do it much faster than the 30 caliber it's based upon.

In fact, just to keep the throat length managable for longer, I might suggest you load the COL of your rounds to 2.80" and hold onto the extra 60 thousandths for chasing the lands as the throat errodes over the life of the barrel.

 

[4Rail_Gunner]

Re: The .260.

An AICS Mag Is 2.900" Internal Deminsions

My .260 rounds with 142 SMK measure as follows
2.835-2.838 OAL
Ogive Length with my comparator tool is 3.238 and im .025 off the lands.
The way I'm Setup i can chase the throat .050 thousandths before I have to stick to a dedicated mag length.

 

[ChadTRG42]

Re: The .260.

Actually, the 10 round AI mags have a max of ~2.860". The 5 rounders are longer and are 2.90+".
Like stated, you need to pick the bullet you want to shoot so he can chamber the barrel. Since the smith is custom cutting your chamber, I would have it cut at around 2.820" to whichever bullet you want to run. This will give you a little room to grow and chase the lands some after 500-1000 rounds are through the barrel.
If you need a dummy round, let me know. I'd be happy to send you one. I have the 130 and 140 VLD, 142 SMK, 140 A-max and 139 Scenar.

 

[bohem]

Re: The .260.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChadTRG42</div><div class="ubbcode-body">Actually, the 10 round AI mags have a max of ~2.860". The 5 rounders are longer and are 2.90+".
Like stated, you need to pick the bullet you want to shoot so he can chamber the barrel. Since the smith is custom cutting your chamber, I would have it cut at around 2.820" to whichever bullet you want to run. This will give you a little room to grow and chase the lands some after 500-1000 rounds are through the barrel.
If you need a dummy round, let me know. I'd be happy to send you one. I have the 130 and 140 VLD, 142 SMK, 140 A-max and 139 Scenar.

</div></div>

Thanks for clarifying that. I don't have a 260 and was relying on memory for the exact dimensions. Good to see I wasn't too far off with the 2.860 COL.

 

[rmfield]

Re: The .260.

I had a reamer made by PTG for the purpose of shooting various 140 grain bullets with a AICS magazines in SA rifle. It has a freebore (lead) of .040 and a 1.5 degree throat. When seating bullets just touching the lands, it results in the following COALs:

139 Scenar - 2.795"
Berger 140 VLD - 2.855"
142 Match King - 2.812"

This works perfectly for me and still allows some room to chase the lands. If you are interested in the actual reamer drawing, let me know.

 

[ChadTRG42]

Re: The .260.

If yo plan to shoot the 140 VLD, then you will already be at max. If you run the 142, you're golden.

 

[michael_aos]

Re: The .260.

I shoot the Lapua 139gr Scenar pretty much exclusively.

GA Precision had Black Hills do a run of 260 Remington with the 139gr Scenar with a COAL of ~2.82". COR-BON also markets a 139gr Scenar load.

With that in mind, when I moved from the 123gr Scenar to the 139gr I just started with ~2.82" and it performed so well I haven't changed anything.

 

[Rovieairto]

Re: The .260.

I'd load up a 139 Lapua scenar to 2.80" and have him cut the lands out for a 0.010" jump.
1.5 deg ramp.

rmfield gave you some very valuable data that you can use to make a do-all chamber with.

 

[6.81star]

Re: The .260.

So if i run the 142s that leaves me 48 thou which will be plenty of room in the mags, correct? Also will out of coriousity will 120 amax perform at all.