How much is too fast?

[TackDriver284]

I did my first ladder test today ( one round each charge ) for the 300 Win Mag and 180 AccuBond pushed by RL 22 / CCI250 primers with charge weights from 73.4 to 76.2 grains and jammed into the lands .005" When I shot the 73.4 grain charge, I was taken by surprise that the velocity was 3,134 fps which is a tad fast for a low charge with the 26 inch barrel. I assumed there may be a pressure spike / velocity because of the .005" jam into the lands. The 76.2 charge was at 3,283 fps and the last two charges of 75.8 and 76.2 grains shows a faint ejector mark on the brass, I barely missed it until I observed carefully under some sunlight. I did not encounter any case swipes or heavy bolt lift. I believe the pressure is over 65k at this point because of velocity and the ejector sign on the case head so I stopped right there and won't be using the last two charges ( 75.8 and 76.2 )in the future. I have determined what my max pressure is. The #1 ( 73.4 ) and #2 ( 73.8 )charge ( 3,134 and 3,155 fps ) grouped together nicely about 3/4 inches apart at 300 yards, so I'll be working on a new load starting with 73.6 grains and see how it does with .005 jam". I did not like 300 yards to do a ladder testing because its grouping too close together. It's tough to find calm conditions this time of the year to be able to shoot 400 -500 yards where your groupings will be further apart from each other and easier to pinpoint groupings.

Was doing the .005" jam a bad idea? I read a few articles from some benchrest shooters using this method for ladder testings. Backing off the lands .020" will lower my pressure and velocity. Should I redo the ladder testing again with .020" off the lands if .005" jam was the incorrect way to begin with?

Here is a pic of the case head, see the ejector mark between the a and the g with 76.2 grains RL22 and .005" jam.

 

[gbflyer]

That looks pretty warm to me.

I'd avoid the jam for hunting rounds. Sometimes get a nasty surprise of the case coming back with no bullet when you clear the chamber. Makes a mess. I'd venture a guess you'll lose a little pressure and probably not lose much accuracy with a .010 to .020 "jump".

 

[kraky1]

Fwiw.... I had a 300 Weatherby that would do 3300 FPS with 180s and not show pressure signs.... my current 300 Weatherby with 26 inch barrel shows pressure signs anything above 3250..... the chronograph and that ejector Mark are definitely screaming stop and go back.

 

[Dwh7271]

It's your rifle but I'd either back it down or jump them a little(or both :grin: )The ABs I shoot seem to like a little jump. Being out of the lands may flatten the top of that pressure curve a little also.
I'd check the primer seating on that brass and see if it loosened up a hair on you too.

 

[TackDriver284]

I have backed off the lands .005 this time and 3 round charges from 73 to 74.8 grains, hopefully find a sweet spot. Will keep you posted soon on 200 yard testing. will do the seating depths lastly.

 

[thatguySHM]

New brass or once fired? If once fired, how much are you bumping the shoulder back? My 300 WM will leave an ejector mark with new brass if there is a greater than 0.010" headspace jump. I was getting the mark with 74.5 grains of H1000 and a 215 Berger on some new brass, but not all. So I loaded some without the ejector mark at 75 after bumping back .003" after fire forming and brass looks great. Plus I found that it preferred about .045" off the lands.

Just my experience with the big Winny.

SHM

Sent from my XT1650 using Tapatalk

 

[TackDriver284]

New brass or once fired? If once fired, how much are you bumping the shoulder back? My 300 WM will leave an ejector mark with new brass if there is a greater than 0.010" headspace jump. I was getting the mark with 74.5 grains of H1000 and a 215 Berger on some new brass, but not all. So I loaded some without the ejector mark at 75 after bumping back .003" after fire forming and brass looks great. Plus I found that it preferred about .045" off the lands.

Just my experience with the big Winny.

SHM

Sent from my XT1650 using Tapatalk

Actually fired 3X's, all shoulders bumped back .002" on each full size with .333 neck bushing.

 

[Bbear]

I'd second the call to jump the bullets some. In every cartridge I use the AB's in, they seem to prefer .05-.1" of jump for best accuracy. I'd suggest re-doing the ladder starting at .05" off the lands.

 

[MAinAR]

I'd second the call to jump the bullets some. In every cartridge I use the AB's in, they seem to prefer .05-.1" of jump for best accuracy. I'd suggest re-doing the ladder starting at .05" off the lands.

+1 I initially start all AB's at .075 off myself.

 

[SJB358]

That is really quick for a 300 Win for sure. All depends on how it was chambered and the reamer that was used.

I agree with the others, for the Accubonds, I don't mess around any closer than .050" from the rifling.

 

[efw]

One thing I've done when working with a load I'm unsure whether I'm comfortable with is to pick 3 random cases that give the appearance of potential "heat" and pull them out. Every time I go to the range, no matter what rifle I plan to "play" with, I make sure to pop off those three rounds.

First thing it tells me is whether the load really is a winner or if it just happened to be a great group once.

After 5-8x (I like to get a solid 8x w/o primer pocket loosening) I know whether the "heat" signs or real or not.

Good luck!