pressure /velocity....which?

[Steve Ladino]

I'm getting very high velocities ( according to my old Chrony which has been recording reasonably over the years) anyway my question for those of you who know is....now that I'm 200 to 300 fps above what is stated as the most accurate speed for a given bullet and powder amount to achieve 3000 fps. should I download the charge to get to 3000 fps. ( stated most accurate speed for my bullet) thereby reducing the pressure, or work within the speeds I have from my 27 " barelled 40x Rem. 7mm mag. 162 A-Max, Winch. LGMR primer ? I'm wondering if the drop in pressure to get to 3000 fps matters much. Thanks!

 

[JohnKielly]

I'd try shooting over another chronograph.

 

[SheepDog]

The groups on your targets should be your guide. Every barrel is different and what may look good on calculations may not look good on your targets.

 

[Ned Ludd]

I would qualify the velocity/pressure question such that as long as you aren't going well over MAX pressure, groups on the target will tell you at which velocity you are getting the optimal precision. There is no "most accurate speed" for your bullet that can be generalized to apply to every single rifle setup; all are different and you must determine empirically what is optimal for your setup. Certainly, optimal velocity "ranges" or "windows" are common to rifles having comparable chambers and the same barrel lengths when using a specific bullet/powder/primer combination. However, even then there can be subtle differences that require optimization. My biggest concern in the situation you described above would be whether you are actually loading well in excess of MAX pressure, given the 200-300 fps greater velocity. If not, it sounds to me as though you simply need to carry out some fairly standard charge weight testing over a wide enough range to determine exactly where the load is optimized. Once you have done that, you can tune the load further via seating depth.

 

[Steve Ladino]

"... now that I'm 200 to 300 fps above what is stated as the most accurate speed for a given bullet and powder amount to achieve 3000 fps. should I download the charge to get to 3000 fps."

Why do you think that 3,000 fps is the most accurate speed?

According to information I have read (caption at Reloaders nest for the 7 and the 162) plus most other references seem to state that the speed of 3000 fps is (old Lyman manual) the best and most accurate but I realize that that is subject to specific conditions they used and figured that to be a good place to shoot for. At 3300 fps the 162's with R-22 are looking the best for me now. Was just trying to put together all the variables sensibly ie: pressure/brl. time... bullet obturation, weather or not the higher pressure was a real advantage over a lower one, RPM at 3300 etc., maybe to fast for shorter distances where a bullets ability to settle in flight may not be achieved yet. Briefly I'm trying to identify the most reasonably smooth progression of a cartridges activity once it is put into action.

 

[rimfiremac]

From my data, powders produce about 60fps/grain at top pressures- for a ballpark. A three grain reduction should put you back where you would like to be.

 

[Steve Ladino]

From my data, powders produce about 60fps/grain at top pressures- for a ballpark. A three grain reduction should put you back where you would like to be.

I think you are correct and I tried that reduction but the 7 still likes it's faster node according to my results at 200 yds., maybe my 27" brl. has something to do with that, accuracy I mean. Appreciate your input ~ Steve

 

[CharlieNC]

So this is a new barrel, rifle, etc and to get an accurate load you are trying to match a published velocity? Or is this a change from where you were previously with this rifle and load?

 

[rifleman700]

pressure=velocity

 

[AckleymanII]

Shoot over another chronograph, yours is probably wacked.

I have shot the 162's in several 7RM, about 3150 fps is giving 2-3 reloads on a case, then pockets are loose but accuracy is great. I am shooting 71.5g of Retumbo, fed 215, 162 with a slight jam, REm brass, 26" barrel.

At 3300, especially with R#22, the primers should be laying on top of the follower when you eject the case.