PDA

View Full Version : KMW 260Rem Range Report


Vu 308
03-16-2008, 12:14 AM
I was able to sneak out to the range this past Friday for about an hour or two to finalize a load for my KMW 260Rem. Barrel has less than 70 rounds through it.

Temp: 63 Degrees
Wind: 3 to 5MPH from 6oclock
Range: 200yards

Load Data:
Remington Case
139gn Scenar
F210M Primer
47.0gn of H4831SC (work up to this load, it is compressed)
2.235 to OGIVE
My loaded neck OD is .291
I used a .289 bushing to give me .002 tension and that seem to do the trick. Same load with less tension did not shoot as tight for me. YMMV.

All groups were measured center to center.

I fired 4 groups of 3 and 1 group of 3 as a speed drill/function test of the action and magazine.

1st group: .611", 2nd group: .896", 3rd group: .816", 4th group: .446" That gives me an average group of: .692" @ 200yards.

I think I can live with that. :43:

http://img.photobucket.com/albums/v287/vuhpham/CIMG0003-1.jpg

rksimple
03-16-2008, 12:21 AM
I could live with that as well. Looks good.

ar15barrels
03-16-2008, 12:43 AM
I used a .289 bushing to give me .002 tension and that seem to do the trick. Same load with less tension did not shoot as tight for me. YMMV.

If you ever get really into internal ballistics, you will read about the theories where the bullet stops 2-3 times in the bore.
The first time it's stopped is when it's sitting in the case as the primer goes off, which is actually before it gets moving...
Now some pressure is building and the bullet moves forward until the bullet seats into the lands at the throat until preasure builds some more.
There is much debate about whether the bullet stops a second time while obturating in the throat or not as pressure is not peaking yet at this point.
Then it accelerates down the barrel.

I only mention this to talk about neck tension.
Neck tension is the force holding the bullet still when the powder first starts burning.
The reason you may get better accuracy with that tighter neck is that the powder is starting to burn more consistently.
When the neck tension is lower, it allows the bullet to move forward to seat in the throat in a less consistent manner.
As the bullet moves forward, the case capacity (and therefore the burn rate) changes.
You also see crimping of handgun cartridges with a lot of slow powder to have an accuracy benefit because it helps the powder burn more consistently.

Experiment with neck tension until you find just what it likes.

MarcS
03-16-2008, 8:18 AM
Nice groups for sure Vu. Less than half minute. Don't forget that's with YOU shooting it too :p

Interesting. I've heard people mention the concept of bullets stopping before but without the details of the process.

I generally go for at least two but usually three thou tension with the same Redding S bushings just so they run through magazines reliably. Never checked to see what accuracy differences I could find with different amounts of tension.

I was under the impression that BR guys used as little tension as possible. I only heard that from somebody who heard it from somebody so you know how that goes :rolleyes:

Marc

PUFF
03-16-2008, 1:30 PM
Marc,
Most BR rounds are either in the lands or soft seated. If your in the lands .002 is the average neck tension to get consistent seating into the lands. .001 tension is for soft seating the bullet into the lands. The reason for this is consistent pressure build up. Soft seating[using the lands to final seat the bullet] is very consistent through a long match as the seating pressure is the same as the throat moves forward. It might only move .0001, but every little bit counts in that game.
With Vu's 260, .002 is about minimum with H4831.Jumping the bullet and the slower burn rate needs that extra resistence to build pressure consistently from shot to shot.. Y'all don't turn necks so a thicker neck will build more pressure before the bullet releases. The tighter neck tension evens out the pressure build up between the different neck thickness.

Steve

PistolPete75
03-16-2008, 2:41 PM
nice groups. good shooting.

MarcS
03-16-2008, 9:47 PM
I saw Vu's rifle today and it's freakin' sweet. There is that little problem of the bolt being on the wrong side but other than that it's perfect.

You should get some pics of the rifle and the action it's built off of on here Vu.

Thanks for that Steve. Are you "Bolo" Steve?

Marc

Timberwolf
03-16-2008, 10:13 PM
Thanks for that Steve. Are you "Bolo" Steve?

Marc

With the screen name Puff I'm guessing none other - of course I may be wrong

MarcS
03-16-2008, 10:23 PM
Yep that's him! Saw some of his posts on the other thread about the WEGC match in June.

I shot my .260 across the course high power match rifle today all slung up with a coat. Man I miss that game. I'll shoot my first high power match since 1990 on the 26th of this month. I can hardly wait.

Hey Bill remember that "white box" smallbore ammo you were talking about? I found some in my storage unit today. I still have one left from high school. Probably about 1983-ish. As soon as I saw it I remembered your mention of it.

I truly feel sorry for people that don't shoot LOL.

Marc

Timberwolf
03-16-2008, 10:32 PM
I found Steve's post in another thread where he said someone else was using BOLO so he's using PUFF. Its beginning to feel like homecoming around here, kinda like the old 'Hide days.

Anyway Bob out at the range scrounged up a brick of the old white box ammo for me after he gave me a box of 50 a couple of months ago and watched me coo over it - it was steel greasy like I remembered it. I haven't had the heart to open the brick yet and shoot it. Kinda like an old bottle of Scotch, you relish its taste but hate to open it.

Timberwolf
03-16-2008, 10:39 PM
By the way been seeing alot of M1 GArands at the range lately and today a freind of mine came out with a neighbor who had one. I put 3 or 4 clips through it and and on the last really hunkered down instead of plinking. I'd forgotten just what a pleasure they were and am now thinking hmmmm the Garand matches - service rifle hmmmmm. Yeah I feel sorry for people who don't shoot except when they have to explain to the wife why they want, need, desire a NM Garand. LOL

ar15barrels
03-17-2008, 12:48 AM
I was under the impression that BR guys used as little tension as possible.

They also "breech seat" which is to purposely seat the bullets long so that the bullets stop in the rifling as the case is chambered.
This eliminates the variable where the bullet jumps that 1/16" before it stops to obturate.