Short throated chambers???

[jtoews80]

I have been waiting until I could turn some necks to load for a tight chambered 264 I had built. After turning a few and then turning them a bit more I realized that it seems short throated as much as tight. The rifling is touching with the bullets seated .18-.20" deeper than spec.

I should have been more careful choosing the reamer. I beleive it is tighter than spec too, but it seems short throated.

Correct me if I am wrong.
From what I understand: in a short throated chamber, some BR guys will turn the neck quite down to quite thin and shorten it a few tenths to allow the bullet to actually be seated a couple thou by the rifling and align the bullet almost perfectly, eleminating runout.
In a hunting rifle this is not workable because the bullet could fall out of the case or be jarred loose by recoil while in the magazine. Unless one were to use it single shot and be very careful in handling the loaded rounds????

It will chamber loaded rounds without turning the necks, but the OAL just off the rifling with a 140 SMK is 3.18" or a 130 grain NAB 3.16" spec is max 3.34".

I got to fire it a couple times, but that was just proof firing the new barrel twice into a gravel pile with a string on the trigger. Now to load some test loads and start breaking in the barrel..... :grin:
I will still turn the necks and try that, but very lightly. just a polish basically. The range results will dictate what I do with this. I must admit that I am VERY curious what the chrony will tell me about that long 31" barrel....... :?: :?:

 

[baltz526]

i think i would want a normal chamber cut for a hunting rifle, with a long throat for the long 264 bullets. it will be interesting to read your velocitys with the 31" barrel.

 

[jtoews80]

Range results were not bad for a break in session. Fired 20 rounds and cleaned, and cleaned and cleaned. Did I mention I cleaned???

The sierra 140 SMK's over 62 grains of IMR 7828, Fed 215GM primer, Nosler Custom 264 win brass necks turned down 1 thou, seated just into the lands grouped 0.7 and 0.73 outside edge to edge @ 111yds(100M). Minus .264 and that is a .44 group, not bad for breaking in. The 130 grn Accubonds I shot in pairs going up a grain each time. Started @ 67 grains of retumbo, velocity was 3280 & 3297, @ 68 3343 & 3359, @ 69 I nicked the shoulder while turning and consequently blew a hole in the neck, 3309 & 3337 @ 70 grains 3435 & 3385. The 67 & 68 grains pair at around .7 & .8, 69 & 70 were scattered and not useable.

I speced this rifle to shoot 140 & 142 grain match bullets and possibly up to 160 grain. The way it shoots the 130's is just bonus.

CC.

 

[wingnut]

jtoews80-

What twist is your barrel? Just want to compare it with my 28 inch 1:8 for speed. I'm shooting a 142g SMK at 3250 fps with H50BMG, OAL 3.452 touching the lands.

 

[jtoews80]

Rate of twist is 1:8.5 polygonal rifling. I can go higher on the charge. It didn't like the 130 grain bullet with the higher charges.
I want to try the 142's for the .595 BC.
CC.

 

[wingnut]

Just FYI-

With a 1:8 3 groove, I've had Berger 140g VLD's self destruct at 3100 fps and 142g SMK's self destruct at 3300 fps. I know there are custom bullets for the caliber but my beer budget keeps getting in the way. :wink:

It's another reason for the need of a 6.5 mm 140g AB.

 

[Antelope_Sniper]

Jtoews, I like what you have done.
yes, your heavy varmit benchrest guys will turn their necks really thin. Thin enough they are able to seat the bullets with their fingers. They will leave the bullets all the way out, and will actually be seated against the lans as they chamber the round. they use mild loads, and only neck size.

With a tighter throat you might be able to some of the long VLD style bullets closer to the lans, and still load to magazine lengh and not have a single shot.

Personally, If it was my gun, I would trim my brass a little short ( I usually do anyway), turn my necks down to where they would chamber easy, I felt I had very even neck tension, but still sufficent to hold the bullet of my choice in hunting condition.

I felt my one mistake on my last rebarrel for forgeting to tell the smith I wanted a shorter throat for the reasons we discussed.

I probably don't need to say it, but just for everyone else reading, a shorter throat will cause higher pressures so work up carefully.