Who has a 6.5mm - 300 Win Mag? Need Pet load data.


Well-Known Member
Jul 13, 2009
Border City (on the poor side}:-()
In the process of getting a 6.5mm - 300 Win Mag built. It will have a 1-8 twist barrel & be finished in the 24 1/4 - 24 3/8 range. Neck is throated to have a COL with a 140gr Accubond of 3.550.

Looking for powder suggestions & load charges.

Retumbo, RL25, H870, AA8700 & US869 are the slowest powders I have in the cabinet.

For those of you who shoot this cartridge I'm looking for a good baseline.

This will be a deer hunting rifle.

An accurate 3150 - 3200 FPS with a 140gr is my goal.

I have one/had one, don't know if I still have it. I shoot the 264 STW mostly now instead which is about the same thing and I can give you loads for that if you are interested. They would be close enough for starters. These two require lots of slow burning powder to reach there potential and require a longer barrel than yours. Your rifle will not be able to outperform the 264 win mag by much because of this. I have clocked these two at over 60 fps gain per inch of barrel. You are going to achieve a lot of muzzle flash.

My 6.5-300 wby shot best with H-870 and H-570. The latter hasn't been made for about 30 years though. When I worked with it all the new stuff wasn't made yet. But the STW likes all the ones you mentioned and is about the same thing. I think with that short barrel you will need to go with a faster powder though for best performance.

Sorry, I thought you said 6.5-300 wby. I went back and saw that you said 6.5-300 win mag. You would do better with the 264 win mag than this wildcat in a short barrel. Same performance, better barrel life.
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I have a 264 Win mag with a 27 3/4" barrel and it loves Retumbo. 66.5 grs and the 130 Accubond averages 3350 fps and is a one hole shooter at 100 yards. I killed 4 deer with it this season and I really like the Accubond bullet. I recovered one from a buck that I shot at 111 yards in the front edge of the left shoulder as it slightly quarted toward me. The bullet destroyed the shoulder made soup of the vitals and was found in the right ham. The bullet was a text book mushroom with the lead core still in the jacket and the recovered weight was 71 grs. The other three deer were shot through the shoulders or in a shoulder and exit behind the offside shoulder. All were exit with golf ball size holes. All were bang flop shots from 98 to 275 yards. You have chosen a good bullet to try. With your barrel length I agree that you may want to go with a bit faster bruning powder than Retumbo. H-4831 would be a good one.
My fear with a faster powder is I won't produce the speed. This rifle started life as a 264 WM. My max charge of RL22 with a 140gr was 59gr which put me just under 3000 FPS.

After finally coming to the conclusion that this rifle was only going to run the 140gr bullets in the 2950 - 3000 FPS range at safe pressures (even with H870 which I don't understand why?). I decided to have it opened up to the 6.5 - 300 WM.

Thinking it was a build problem, my gunsmith pulled the barrel to confirm there was nothing wrong with the build which turned out to be the case. He also had the 6.5 - 300 WM reamer & this wildcat is a simple neck size which doesn't require any major fire forming, I figured I'd open it up to get some more speed out of it. Plus he cut me a great deal on the re - chamber job.

I owned a 264 WM before this one that would easily run 3200 FPS with 140's & a 74.5gr charge of H870. That was my goal with this new one, such was not the case. Sold the old 264 rifle because it had a Magna Port & I hated the noise. To chop the barrel down on that one would have left me around 23"'s to boot which I wasn't excited about. That Magna Ported barrel copper fouled something fierce but it did shoot good.

I am sure a 6.5 - 300 WM will be capable of more than 3200 FPS, but I will be very happy with an accurate 3150 - 3200 140gr & no pressure issues.

A guy who has one was what turned me on to the cartridge. He says he can go 3300 FPS with a 140gr in a 24" barrel & a charge of US869, but his best accuracy is with Retumbo in the 3150 -3200 Range. Bingo, that's what I am looking for. Didn't like the 6.5mm STW because of the length & the fact I'd have to seat the bullet deeper than I like. With a 300 WM parent case I can seat the bullet out to 3.550 COL & still fit nice in my 3.600 Mag box.

Still frustrated the 264 WM let me down when 3150-3200 should of been a snap for it. :(

I have a 264 Win Mag Rem 700 CDL SF with a 26 inch barrell and could only get about 3000 fps with 140 grain bullets and Re22 powder. I switched to 68gr of Retumbo and Berger 140's and am getting 3150 fps, not too much pressure and shoots 1/2-3/4 inch groups.
Unfortunately you have a slow barrel. Do not spend any more money on it. You are comparing it to a 6.5-300 win mag with a fast barrel. You are not going to get his velocities with your slow barrel. The velocities will likely be very similar with your barrel.
The chamber has been re-cut already, so ditching it is out of the question.

Up here in Canada Ted's barrels have a reputation of being a very good barrel


I wouldn't write it off to being a slow barrel just yet. With the data that has been supplied to me, I'll see how close I get to his speeds as I work up. I don't think my goose is cooked just yet. Stay tuned. :D
Here is how they stack up beside each other.


It's done! It finished at 24 1/2" barrel length. .298 neck. Simple neck size & trim to form brass from 300 Win Mag. My wife picks it up for me tomorrow. Now to find the magic load. A pressure free 3200 FPS with a 140gr should be easy now :D

I hope she is good now. On his test fires he ran it up to 65gr IMR 4350 which is 9gr over max 264 WM data. Bolt lifted fine & primer was just starting to crater, so things look promising.
Well it was -31 this morning when I put it to paper. Today was our last day of Whitetail season, so I wanted to load it with something accurate & fast enough so I could just put it to paper & continue on my day hunting.

Last night I pondered where to load this thing at. I decided on 79gr H870. Why? I figured this would be enough powder to get me some speed & not get me in trouble. I also sized & loaded the two test rounds after the build to see if I was going to have a once fired issue again. Bot rounds fired & extracted no problem. Here is what it did. Keep in mind it was -31 & the shooter may have rushed a bit. Mind you I do like what I see :)


Top shell was the 2nd shot after a horizontal & vertical adjustment. The first shot hit the target beside this one (not shown). The next 2 were fired after another correction & the last three were after another adjustment. I am not sure why the rifle wandered a bit back to the left? There was no wind it was just bloody cold. After the 3 shot group I made one more correction to the right & fired at the other target (not shown) & it was dead center of the top dot. Good enough to go hunting. Man what a muzzle flash though :)

The chrony did not work in the AM, but I did set it up when the sun poked out for 1 cold bore shot. 15 feet from the muzzle gave me 3274 FPS ;) Judging by the group I think I may be pretty close. Some tweaking when it is warmer out & we should be in the ballpark.
I did neck size one round when I got home and put a primer in the case. Primer pocket still very nice & tight. Not like some reloads I have done over the years ;) The re-sized shell goes back in the chamber like nothing :)

Here is the load details

Hornady 300 WM brass necked to 264 & trimmed to 2.610
Federal 215M Primer
79gr H870
140gr Accubond
COL 3.530. 20 thousandths off the lands.
.295 neck before firing & .298 neck after firing.
.514 at the expansion ring.

Nothing to shoot at today, not even a coyote :( Had one doe tag left, but in -31 weather it was going to have to be big to get my hands dirty. :D

So far all looks good. :D
6.5-300 Win Mag as it sits now.

Here are some updated photos of my 6.5mm-300 Win Mag. It now sports a 4.5x14x40mm 1" DPLX with CDS. The stock will be painted in a spiderweb paint finish in the new year. I may have the barreled action powder coated also.






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