Load discrepancy

[119er]

Here's the facts: Rem 700 SPS Varmint - 26"
7mm-08 - 150gr SMK, 39.5gr RE-15, Hornady Case, Fed. 210M.

The load from the Sierra book states that this is max load and velocity ~2700fps. I have exceeded the 2.780 max OAL by .032" Length to Ogive is 2.282" being .015 before lands. OAL is 2.812.

The 20 shot average velocity is 2512fps with very low ES/SD numbers and great accuracy but there is about a 150fps difference in velocities. I am assuming no fault with the chronograph as it has performed very well in the past.

Is this seating depth enough to cause pressure to drop enough to effect velocity this much?

Lot to lot powder differences?

I am not a velocity freak but I want the most I can get safely without sacrificing accuracy. There are no pressure signs on cases or primers and I am thinking about very cautiously going over the published data watching for pressure. My thought is that Sierra safely achieved the stated velocities with that powder and that exact bullet so why should it be unsafe for me to do so? I am no physics major or ballistician, but velocity is a function of pressure assuming consistent friction and other factors that have shown themselves in the chrono data(SD/ES).

I'm not asking anyone to condone this and I will not post any data should I choose to exceed the listed maximums, but has anyone done what I am thinking about?

 

[noylj]

Manuals are only a guideline and show what they got with their specific firearm and lots of components.
Barrels differ.
Chambers differ.
COLs differ.
The all combine.
If you weren't concerned about velocity, they you wouldn't be using a chrono and worrying.
Before you go above book max, do an exterior ballistics calculation and see if there is anything to gain with more velocity at any distance you will be shooting. You will probably see that accuracy is more important than 150fps of velocity.
You are firing a cartridge that will give you lots of pressure signs, so, if you really need that extra 150fps, study all the signs and watch for them. In particular, watch for any change in case head dimension or any problems with bolt lift or extraction. Those are all signs that you are well past any safe pressure.

 

[119er]

It's not really about a need as much as a want. If I can get the same accuracy at a higher velocity that's what I want. I'm simply trying to achieve the same results in terms of velocity as the bullet manufacturer did, not try to push any faster than that. 150fps seems like a lot to me.

 

[gamestalker]

First of all, the published loads are what the manufacturer's are getting using their test barrels.

Maybe try switching to a bit slower burning powder? It's usually a closer match to published data with slower burners. They commonly take me to published velocity, and maximum for the cartridge.

GS

 

[blarby]

FWIW- Gamestalker said it all.

I know its crazy, but give RL-19 a try in that'n.

My wife swears its the best thing since Mauser actions in her 7.

 

[119er]

That sounds good to me. I'll try a little slower powder and see what I get. The gun used in their data was a Savage 12VSS w/26" barrel and is my point of confusion. Seems like it would be apples to apples, but apparently it isn't. Maybe I have been lucky so far but this is the first real discrepancy that I have seen when getting on the high end of data. This is what make this hobby interesting! Thank you for your suggestions.