Reduced load word of caution!!!

[Wis65x55]

I am trying to work up some light loads for a 260 Remington. Have run across an interesting observation. Low velocities have led to poor case to chamber sealing in my Remington model 7. The small amount of gas leakage combined with low pressures can allow powder fouling to build up in the case neck area of the rifle chamber. The expansion of the case neck compounds the problem as it becomes a ram, compacting powder fouling against the neck area of the rifle chamber. When powder residue builds up in this manner, pressures become high and accuracy becomes extremely poor. As a result I have had to keep an extremely close eye on the chamber and use suitable cleaning methods, preferably, an oversized caliber bristle brush and solvent rotated about the chamber.
Keith

 

[sask boy]

Thank you for the heads up!! I can never get enough new knowledge :wink:. Now if I could only get this old mind to keep it.

Blessings,
Dan

 

[RiverRider]

That's another reason I think it's best to run powders near or at least approaching the correct pressure limits. You need relatively high pressures to make the case seal the chamber, and powders will operate best (most consistently) when pressures are in the neighborhood appropriate to the powder in question anyway. In other words, don't load rifle powders down to 18,000 psi to to keep velocities down if that's what you're after...go to a faster burning powder and load it up so that it's operating in the correct pressure range. I think it's also a good idea to make sure you're not operating a powder at pressures beyond its intended use. We gotta remember what "progressive" burn rates are all about!

 

[Wis65x55]

I was experiencing the above listed problem when I was using a 23.5 gr charge on IMR SR4759 with a 120gr bullet. I got the above charge information from IMR so I didn't think the operating pressures were too low. Guess that I am at a loss as to why this happened.
Keith

 

[RiverRider]

What's the listed pressure?

 

[Wis65x55]

IMR data for 23.5 gr of IMR SR4759 has a listed pressure of about 57,000PSI.
Keith

 

[HeathSexton]

The chamber of your 260 might be like the one in my Ruger 30/06, gigantinormous. I would treat sr4759 like any other powder go up until you find good pressure. I shoot 30grs in my 358 Win with the 200gr Hornady, it's .5 grs over what IMR says but I have zero problems.


Loads that my 30/06 Ruger says, "thank you, may I have another" makes my Remington 30/06 say, "please open me with a Hammer."


Bigger chamber has to have more powder to get equal pressures, or so I read.

 

[RiverRider]

I would guess 57kpsi should be sufficient. Puzzling.

QuickLOAD shows 7mm-08, with a 120-grain Ballistic Tip and 23.5 grains of AA5744 to yield about 2400 fps @36kpsi. Unfortunatelt, QL does not include SR4759, but it shows the 4227s and 5744, which reside on either side of 4759 on the burn rate chart I consulted. I wonder if there's a typo involved in the IMR data on SR4756...