Some advice on pressure testing?

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longarm21

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Hi all, I'm fairly new to reloading and I have been pressure testing a load for Hornady 168 BTHP match .308. I use Lapua Brass (new full length sized - I will neck size on the next round) and BR2 CCI primers.

I started at 32.6 and did a full 5 rnd work up all the way up to 41.7grs of Varget. At 41.7 I was noticing a very very faint circle from the ejector on the bolt. It wasn't as prominent as other marks I've seen on other loads, but it was there nevertheless.

The same thing happened with my hunting load using Hornady SST 165 gr. I was showing pressure signs well before the max load of H4895

The published max by Hornady calls for 44.0 grs of Varget. Why am I seeing pressure so soon?

My rifle is a Rem 700 PSS from the mid 90's.

I have a few theories.
- increased pressure from excess lube ( I wiped it off) from full length sizing the brass
- COAL being set at 2.830 (maybe I'd get less pressure if it was closer to the rifling?)

Any advice would be appreciated.
 
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Actually the pressure usually increases as the bullet is seated closer to the lands. As to reasons for pressure signs at below book max loads, there are reasons that the max loads vary from manual to manual, that being differences in chambers and barrels, as well as in lots of components.
 
I wish I had a chrono to see what kind of muzzle velocity I'm getting. I guess I'm afraid with my best load being at 40.4 grs of varget my velocity is going to be quite low. I do have a 26" barrel but I dont' know if that makes much of a difference.
 
Working up in 2 grain increments in a medium-small case like the 308 is too much.

If you are getting brass flow in the case head you are probably more than 5000 psi over maximum.

Reloading manuals are not gospel and you may reach the maximum load in your particular rifle before you hit the book max.

Also, there is no need to " full-length" size new cases. You are only working them more than required and will reduce the number of times they can be reloaded.
 
I worked up in .5 gr increments till I got near the max, and then moved to .3 gr increments. As far as full length sizing, I read that it should be done, but I will not do it with my next lot.
 
My mistake - I misread and thought you moved up in 5 increments between low and high.

So if I get this right you loaded around 50 rounds to test? If so how long did it take to shoot them off? If you did it in one session how long did you let the rifle cool between groups?
 
stubblejumper said:
Actually the pressure usually increases as the bullet is seated closer to the lands. As to reasons for pressure signs at below book max loads, there are reasons that the max loads vary from manual to manual, that being differences in chambers and barrels, as well as in lots of components.
Click to expand...

Pressure will decrease seating closer to the lands UNTIL you start jamming the bullets, then pressures will again increase as bullet is jammed further into the lands.

If bullet is seated .010 off the lands you have given yourself maximum case capacity making for less pressure for given load.
 
As mentioned before, max loads are all relative to the components and the firearm itself.

The books listed maximums are SUGGESTED maximums only. Some rifles reach a critical point well before the listed max load is reached.

Take up the offer to join UM in his very generous offer. Even if you have to travel a bit to do so, it will likely turn out to be an enlightening and worthwhile trip. Likely you will pick up some pointers from and experienced hand loader. Most of the time, when a hand loader goes to the trouble/expense of using a Chronograph, they have a bit of real savvy.

These days, brass is hit and miss. I find Winchester brand to be excessively hard for my tastes and some of the Remington brass to be excessively soft. It all depends on the materials available to the manufacturer at the time of production.

I like your choice of powder/bullets/primers. All proven components is a great way to start.
 
I'm just in awe that my max load is 41.7 gr of Varget when most target shooters with the same brass, and primers are shooting 168 SMK's up to 44 and even 45 grs of Varget.
 
CyaN1de said:
Pressure will decrease seating closer to the lands UNTIL you start jamming the bullets, then pressures will again increase as bullet is jammed further into the lands.

If bullet is seated .010 off the lands you have given yourself maximum case capacity making for less pressure for given load.
Click to expand...

It depends on the bullet, and the individual application. Monometal bullets for instance often show significant increases in pressure at even .030". from the lands. Cup and core bullets can start to show increase in pressure shortly before jamming into the lands., although the pressure increase becomes most significant once the bullet is seated to the lands. A jump to the lands can reduce pressure more than a slight increase in case capacity.
 
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if it were on the lands according to my measurement, it would be around 2.986 COAL. Right now I'm seating 2.830 COAL.

The Rem 700 PSS has an unusually long throat.
 
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Velocity is a good hint of pressure. With correct powders, the two are linked.

The book refers to THEIR rifle, not yours. When you see the ejector mark on the case head, you are getting into proof round territory. Back off, don't argue with the gun.
 
longarm21 said:
I'm just in awe that my max load is 41.7 gr of Varget when most target shooters with the same brass, and primers are shooting 168 SMK's up to 44 and even 45 grs of Varget.
Click to expand...

The thing is, you don't KNOW you are at maximum. You are just guessing, apparently going by one sign of what may be excess pressure.
A quick look at Hodgdon's on line shows 45 grains of Varget with 168 grain bullet for a velocity of 2737. Therefore, you will have to have chronograph records of your shooting and if Varget will raise the velocity to around 2700 fps you know you are at normal, full power loads.
Now don't bother saying that all rifles are different, I know that.
They are different in the amount of powder it takes to get to a certain velocity. Using a proper powder for a cartridge, pressure=velocity and velocity=pressure, pretty closely.
In any rifle that I have ever had I could bring the velocity of the bullets up to what was standard for that cartridge, without excess pressure. However, it may easily take different amounts of powder to equal the same velocity.
Thus, you will require velocity readings before you can proceed very far in determining a maximum load for your rifle, particularly when, as you state, you have limited experience in hand loading.

Edited to say, Ganderite, I didn't see your post until after mine was posted.
 
They are different in the amount of powder it takes to get to a certain velocity. Using a proper powder for a cartridge, pressure=velocity and velocity=pressure, pretty closely.
Click to expand...

So why is it that the different manufacturers data often varies by over 100fps and sometimes more, using the exact same components, and the exact same barrel length? After all, the manufacturers have access to pressure measuring systems that the average handloader can only dream about, and they supposedly load to the same SAAMI specifications, yet their data varies. Why don't the manuals simply state use X bullet with Y powder, with Z primer in a given case, and increase the powder charge until you reach a certain velocity? Obviously the pressure vs velocity relationship isn't as simple as some people would have us believe.
 
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