Pressure and velocity

[Ed kof]

Just wondwring if anybody can explain this to me. I just purchased a 6.5 rem mag. Using 3 different bullets and 3 different powders the results are the same. I have to drop back right a 3 grains of powder or I get flat primers and hard bolt lift. The thing that has me confused is that with that low a charge I am still getting 3015 fps with the 140 bullets.
Any ideas how a 3 grain under max can get me that velocity. Edk

 

[L.Sherm]

I know its a belted cartridge but how far you bumping your shoulders?
3100 or over is not uncommon in a 6.5 Rem mag with 140's.
How long a barrel you using and what powders and primers?

 

[jwv2001]

At first glance, your rifle isn't the same as the test rifle that supplied the data that you followed. Did you chronograph the loads yourself? Are you happy with the velocity that you're getting? Lastly, how well do your loads shoot? Flat primers aren't necessarily a problem, the hard bolt lift is another matter.
I'm assuming the rifle is not doing that with the load that's 3 grs. less powder.
If it shoots well, go with it.

 

[Jager]

You likely have a tight chamber and/or a tight barrel. Either will cause greater pressure/velocity than a rifle with looser specs.

Neither is a problem as long as you're getting the accuracy you want and velocity expected.

Book values are based on the rifle or universal receiver used at the lab producing the data. They vary too.

The benefit of a chronograph is you know what you've got. I wouldn't worry about it. Just know that your starting load when beginning with a new power or bullet is likely to be at or below the starting loads shown in most manuals.

 

[Coyotefurharvester]

So you started at a data suggested max load and had to reduce the powder charge because of a potential high pressure result? Are you also seating bullets to make contact with the lands? Factory barrel, what is the brass history?

 

[Ed kof]

It is a custom barrel so maybe it is tighter thus causing more pressure. I’m not worried about the lower load being safe. It just seems that 3 grains less than the books show for the bullets is quite a difference. Bullets aren’t jammed. It shoots ok at 1 inch more or less.
I’m just curious as I’ve never run into this in40 years reloading.edk

 

[jackieschmidt]

Three grains is quite a bit.

Is this in a Remington 660/600 ? Does it have a SAAMI chamber.? If so, it should handle any 140 grn load in the 2959 to 3000 fps range.

You might have an exceptionally tight barrel.

I wouldn’t worry too much about the flat primers, but the hard bolt lift would be a concern.

The only other thing is do you trust your chronograph.

 

[Ed kof]

No I didn’t start at max. Being unfamiliar with the gun I wasn’t sure if it was hard bolt lift or not for the gun. I tried up and down with different powders and bullets.

 

[Ed kof]

Browning action. Not sure of any specs except it was built on along action so the bullets can be seated farther out. Edk

 

[TC260]

I had something like that happen years ago when I'd formed 280AI cases from some nickle 280 cases. Hit max velocity way early but I don't think it was 3 grains, probably more like 2. I doubt I have any notes on it cause I pitched them and went back to brass.

The only other thing I seen personally was a buddy having something off with his scale (can't remember what it was now). He didn't have any check weights so I brought mine over and it was way off.

 

[Ed kof]

I’m using my Rcbs 1010 scale. Checks out perfect. I know my load is safe and over 3000 fps but I was curious because I have never encountered this before.

 

[TSFineGuns]

I had something like that happen years ago when I'd formed 280AI cases from some nickle 280 cases. Hit max velocity way early but I don't think it was 3 grains, probably more like 2. I doubt I have any notes on it cause I pitched them and went back to brass.

The only other thing I seen personally was a buddy having something off with his scale (can't remember what it was now). He didn't have any check weights so I brought mine over and it was way off.

Similar with my 280ai.

I started with Nosler brass and was able to load to max load and get a bit more velocity than the books listed.

Then I scored 100rds of Peterson Brass from
Grafs. I started by backing off two (2) grains and surprisingly had pressure signs (Stiff bolt lift). Now I’m 3grs lighter with the Peterson and getting same velocity.

With Nosler Brass I loaded up to 61.5gr of IMR 7828SSC and saw around 2,980fps.

Now with Peterson Brass I load 58.4gr of IMR 7828SSC and I’m seeing 2,960fps.

 

[WAMBO]

I was working up a load for a friend's Christensen Arms 338 Lapua and had a much greater discrepancy.
I was 7 grains down from max, 85grs from 92grs and getting higher velocity than listed for max but the rifle did have a 2" longer barrel, 26" vs 24", than what what was listed in the Hodgdon data so it was close, 2580fps vs my 2630fps.
I was using the same bullet, primer and powder as listed in the data, 300 SMK, Fed 215M and H1000.