.264 once fired brass question

[AG74]

I found a great load with Nosler (new) brass, 140gr NPT and CCI primers. 68 grains Retumbo gave just over 3100 fps with great accuracy.

I neck sized the brass, prepped, cleaned and reloaded with the same ingredients. The point of impact shifted right by about 6" at 330 yds and while I haven't checked speed with a chronometer, based on the trajectory it seems to be 100-200 fps slower.

Does the increased case capacity from new brass to once fired, neck sized brass lower the pressure and hence velocity? I'm not sure how much the case capacity increased, but I'd imagine at least a few grains.

Another factor: when I speed checked the first batch, it was summer and warm out. The second batch was fired under colder temps. I can't imagine 80 degrees to 35 degrees ambient temp would slow a bullet that much, but I noticed when firing in the summer, the second and third rounds would each come out a little faster as the chamber and barrel temp increased.

The rifle is a Rem 700 action with a 26" Lilja #4 contour barrel, HS Precision stock.

Thanks
Al

 

[Engineering101]

Even though Retumbo is and "Extreme" powder no powder is immune to temp change so that is what I would bet has happened. You can mess up a good load with a lot less temp change than 45 degrees. That is why I do most of my load development for hunting in the winter when the temp is similar to what I expect to see when hunting with that load.

 

[Mikecr]

This is why you should do load development under the conditions of use. This, including fire-formed and sized as you will brass.
In your case two changes, and at the same time..

 

[red dawg]

Hey A G, just my opinion but with 86grns of powder you may have swelled the shoulders a bit and may need to F L resize and bump the shoulder back and then trim, I have had this before on a 7mag when it was border line hot load! And my accuracy came back

 

[Bart B]

My .264 Win Mag shot most accurate with new cases of full length sized ones. Both case types shot Norma 140's with 72 grains of H870 and WLR primers into 4 to 5 inch 10-shot test groups at 600 yards. Bullets were seated a few thousandths short of rifling contact.

Better accuracy with 30-338 cases with IMR4350 and 190 and 200 grain Sierra pills. No neck sized cases; new and full length sized ones only.

Sierra Bullets convinced me to stop full length sizing belted cases. And with belted cases, new or full length sized ones produced best accuracy if a second body die sized the fired case body all the way back to the belt.

Shot them all in temperatures from 30's to 90's F. No significant accuracy problems. That said, if your bullets are shot barely fast enough to stabilize and shoot accurate in warm weather with the rifling twist used,
a few tenths grain more powder often helps in cold weather. Some benchresters add 2/10 grain or so their charge for every ten degrees less than the temperature at load development; subtract that much for higher temperatures.

 

[LoneTraveler]

You say you cleaned the brass. What kind of cleaning system did you use? If you used the walnut nut or corn cob media there may be carbon left in the neck and it is acting as a lubricant between the case neck and the bullet. The bullet may be moving before pressure has built proper. It will take a few minutes, but anytime you are load developing for a rifle, Set up your chronograph every time you go to the range. It tells you if velocity has changed and you have real information you can work with. If the rifle keeps shooting right something may have moved, Action and barrel moved in the stock, Check and make sure stock is not touching. Check the scope and scope bases something may have moved. Good Luck in finding the cause and cure.

 

[AG74]

one of the RCBS, 4 in 1 plug in tools. A brush scrubs the neck. After its scrubbed and chamfered, it goes into the corn cob media for 24 hrs. I'll check the necks on the next batch I clean and check for carbon. Good tip, thanks

 

[Bart B]

You say you cleaned the brass. What kind of cleaning system did you use? If you used the walnut nut or corn cob media there may be carbon left in the neck and it is acting as a lubricant between the case neck and the bullet. The bullet may be moving before pressure has built proper.

A decent grip on hunting bullets needs about 30 pounds of force to push the bullet out of the case neck. For 26 caliber bullets, 30 pounds against the bullet happens with pressure at only 548 psi.

 

[Mikecr]

There is nothing wrong with carbon in the necks.
Truly, if need led to invention of the perfect neck treatment -it would have ended up being the carbon layer we're lucky enough to get for free.

And bullets are not pushed out of case necks on firing. They're fully released with the slightest of expansion.
Of course tension sets the pressure needed for this expansion, but it's important to understand that tension is grip on a bullet, and not pull friction.

 

[TOM H]

one of the RCBS, 4 in 1 plug in tools. A brush scrubs the neck. After its scrubbed and chamfered, it goes into the corn cob media for 24 hrs. I'll check the necks on the next batch I clean and check for carbon. Good tip, thanks

It is a shame that you didn't do any load development with fired cases if that's what you were going to hunt with. I'm not shooting factory chamber rifles and I use bushing dies and I don't notice big difference between neck/FL sizing on fired cases.

You might want to FL size some and maybe start little under max see if that helps. As someone mention might want to check scope/mounts/bedding.

Almost forgot Welcome