Nosler Load Data - 250-300fps faster than manual. Normal?

[Mustbenice1214]

Thank you in advance. First time running into this problem. I used nosler load data, 7mm RUM, H1000, 26" barrel, nosler brass, 160gn accubond, only difference between load data is I used FED215 instead of WLRM. Autotrickler. COAL same as book. Labradar chrono. Was shooting my 6.5prc at the same time, getting consistent number for that load on the labradar.

Manual data lists starting load at 86.0 gn and 3086. I started my ladder at 85gn. I shot 85 and 85.5 and was getting 3255 and 3302fps. Stopped the ladder and didn't go further. No pressure signs. But these are very high numbers, both are higher than the max load of H1000 (91 gn).

Is there something that would be making this rifle shoot so much faster?

 

[Hawk in WY]

The big one would be the bullet jammed into the lands. This can be dangerous.

The other two I can think of immediately are case capacity and COAL. Measure both and compare them to the Nosler data. Less case capacity and bullet taking up case capacity can lead to higher pressure and velocity.

Finally, individual lots of powder have different burn rates by as much as 10% and some barrels are just faster than others.

What was the temperature where you were shooting? Do you trust your chronograph?

Let us know what you find.

 

[918v]

Your chamber could be tighter than the one used in the Nosler test barrel.

 

[RegionRat]

Good idea to hold till you figure it out.
Check to be absolutely certain you didn’t accidentally use the wrong Bullet, Powder, Data, etc., etc.
The list of things is long, but to play it safe go over everything.
Get a qualified friend to double check you if you don’t find anything.

The pressure difference for an extra 250 - 300 fps is not trivial, so something will explain it.
Good Luck and be safe!

 

[Mustbenice1214]

The rifle is a custom rifle and I was told it is tighter than normal by the gunsmith. I will give him a call and figure out what exactly this means.

The COAL is correct and the bullet is not jammed into the lands. I actually load close to the lands with other rifles but because the case is so big on this caliber I was surprised of how much jump you need to load the cartridge just so it will fit into the mag. It, because of its own structure, has to be loaded set pretty far back from the lands. So again not jammed into the lands!

As for lots of powder @Hawk in WY, I use this powder in my 300PRC and it is great. Very consistent and mirrors most load data available. I was shooting at 85F. I shoot in this weather also with my 300prc without a very big jump with this powder. I trust the chrono. I used it today with my 6.5 prc as well. I have never had an issue with velocities being this far off manual data with any other calibers.

 

[918v]

The rifle is a custom rifle and I was told it is tighter than normal by the gunsmith. I will give him a call and figure out what exactly this means.

You can measure the case expansion and see for yourself.

 

[Mustbenice1214]

@918v is this how I would measure expansion? Sorry for the ignorance. I honestly don't know what else I would be measuring.

 

[supercorndogs]

You measure the base of the case before you fire it with micrometer, then see how much it expands after. An online search would bring more detailed info.

 

[918v]

The case expands in every direction to seal your chamber. Measure how much it expands in your chamber vs saami. Assuming .001” springback, your measurements will tell you where your chamber is tighter.

I suspect your problem lies in the area of the neck.

In any case you need to figure it out before you lose primer pockets or blow primers and fuck up your bolt face.

 

[WeiserBucks]

The SAAMI spec chamber for a 7 RUM has a ton of freebore, like .400" to reduce pressure. If your gunsmith used a custom reamer there's a chance that the freebore is much shorter and that could potentially explain the situation.

 

[TheChief]

Are you sure you werent looking at loads for a 7Mag instead of a 7RUM? 3000fps seems slow for a 7RUM with that class of bullet. Hell, I sent 180 Bergers at 2900FPS with a 280AI.

 

[Mustbenice1214]

I was getting 3250 well below the starting load in the manual. Higher velocity than the max load. Yes it is the correct load data.