sanity check on 260rem/120amax

[darth_ritis]

I shot my first batch of loads in my new 260, and I got some interesting MV numbers.

Loading lightly, using the 9th Hornady manual. Lapua brass, CCI primers, and 120gr Amax bullets, C.O.L. as specified in the manual. I worked up to 43.5gr of IMR4831 (max is 45.7) and identical loads of PowerPro 2000MR.

I got 2997 fps from 43.5gr of the 4831. The same load of 2000MR gave 3152 fps. No signs of over pressure. CRAZY! Weather was 67F, 22% H, 5164ft, 29.5 in. Hg. This is with a brand new Savage 12 LRP, 1:8" twist.

I wonder why these speeds are so far off. Hornady manual error? Miracle barrel? High altitude effect? Powder scale broken? Chronograph broken?

 

[darth_ritis]

Anyone?

To make the question more general, at what point should I become worried when I'm getting much faster speeds than the manual says & with lighter loads?

 

[EOD350]

I would not worry about the velocity, only pressure issues. By the burn rate chart I thought your charge weight was kind of HIGH. the Alliant site only recommends 40 grains of 2000MR with a 120 class bullet. If you have a book with your data in it it may be ok, but I have a feeling you are too high. I would do some more research before I shot that load again.
And, with that much increase in velocity the throat of that rifle will be toast in short order. I would keep a very close eye on that, even after I verified the data.

 

[BGE541]

My 6.5 Creed with 120's est 3,030fps but actual is 3,130fps... no pressure no worries.

 

[Sniper260]

Reloading manuals are very "safety" oriented. Their testing they do with their rifle means nothing really. Your rifle is totally different.. Probably each aspect is the testing with their test and with your reloading test is different.. Sooo I would not watch published velocities a whole lot, better to just play in the safe range and watch pressure signs on bolt lift and primers etc.. get some other data too from other published places... berger data, hodgdon data, etc etc... combine your findings and it gives you a better idea. 120's should shoot well out of a 260. I have had good luck with AMAX bullets before too.

What I do... I work up a load, figure out what the rifle likes... then test the velocity on my final pet load just for shits and giggles.. Velocity does not = accuracy!

 

[darth_ritis]

Thanks guys!

I would not worry about the velocity, only pressure issues. By the burn rate chart I thought your charge weight was kind of HIGH. the Alliant site only recommends 40 grains of 2000MR with a 120 class bullet. If you have a book with your data in it it may be ok, but I have a feeling you are too high. I would do some more research before I shot that load again.
And, with that much increase in velocity the throat of that rifle will be toast in short order. I would keep a very close eye on that, even after I verified the data.

Is the Alliant site giving a maximum load, or just the load they tested? 2810 fps for a 120gr bullet seems a bit low, given that they list a 90gr bullet pushed by 48.2gr powder going 3440. That seems like a big jump in powder charge. I don't know, maybe I'm reading that wrong.

Now that I'm sufficiently worried, exactly what should I look for in examining the throat? I definitely want this rifle to be a tack driver yet last as long as possible.

... get some other data too from other published places... berger data, hodgdon data, etc etc... combine your findings and it gives you a better idea. 120's should shoot well out of a 260. I have had good luck with AMAX bullets before too.

What I do... I work up a load, figure out what the rifle likes... then test the velocity on my final pet load just for shits and giggles.. Velocity does not = accuracy!

I am trying to research as best I can - I have 3 manuals, and the Internet which is never wrong ;-) and I'm starting with that seems very safe and working up. I'll grab a Berger manual the next time I'm in the shop. I've also picked up some Nosler 140gr Custom Comp, some Lapua Scenar 139gr, and the 140gr Berger Hybrid Match Target. I'm looking forward to seeing how the heavy bullets fly.