Load pressure

[Matt15598]

This may be a dumb question but here it is. I understand that increased temperature of the round will increase the pressures in the chamber. That being said I tend to do my load development at a moderate temp usually around 60°. That way I don't go over if I shoot on a 90° day. But the question is would the increased air density and the possible contraction of the chamber in 30° weather do the same thing? Saw some unusual pressure the other day that what brought it up.

 

[canezach]

First, you have things a little backwards. If you do load development in 60º, you could be over-pressure in 90º. Depending on the temp stability of your powder, you could see a distinct increase in pressure and velocities in higher temps.

To the issue of seeing pressure in the cold, I don't think a 30º drop is going to constrict your chamber enough to cause pressure issues. I'd look into your reloading practices for a cause. You didn't mention what pressure signs you saw, so I'm taking a best guess here.

 

[Matt15598]

First, you have things a little backwards. If you do load development in 60º, you could be over-pressure in 90º. Depending on the temp stability of your powder, you could see a distinct increase in pressure and velocities in higher temps.

To the issue of seeing pressure in the cold, I don't think a 30º drop is going to constrict your chamber enough to effectively shrink your chamber enough to cause pressure issues. I'd look into your reloading practices for a cause. You didn't mention what pressure signs you saw, so I'm taking a best guess here.

Ok so I can see how I wasn't quite clear. I did my load development at 60 rather than doing it in the middle of winter to lessen the temperature swing to my max summer temp. I am using Varget and am 1.3 or so below listed max charge. I am using LC brass so I took that in to account when doing the initial work up. I am seeing the occasional sticky bolt and a bit of primer flattening.

 

[918v]

The listed max, was it based on Winchester cases? If so, then 1.3 grs below is over max in LC brass.

 

[canezach]

Varget is pretty temp stable and a drop in temp shouldn't cause an increase in pressure. I don't usually concern myself with a bit of primer flattening. Do you full length size or neck size?

 

[Lead_Whisperer]

There are many factors that can change the pressure. How close to the lands are you loading? The ogive can vary some from bullet to bullet, if it's touching the lands or into the lands you will see higher pressure. Primers can also make large differences in pressure. Case capacities can also vary quite a bit even within the same manufature. Increased temps = increase pressure. If any of your components have changed, you should back down and work your load back up again.

 

[Doom]

You're using a temp stable powder so temperature is probably not an issue. As noted LC brass is much heavier than Winchester and if that was the Max Load brass then you may be pushing the limit. Also if you aren't weighting each charge you may be overthrowing on some or you have some heavy cases. Either way your load is pushing the pressure limits.

 

[Matt15598]

Took the time to look today. I'm at 43.7 with a 168 hornady match. Hodgdon listed max is 46 grains with 168SMK. I am using a charge master lite.

 

[918v]

How far off the rifling are you?