Long Range Hunting Online Magazine


Go Back   Long Range Hunting Online Magazine > Rifles, Reloading, Optics, Equipment > Reloading

Reloading Techniques For Reloading


Reply

IV vs Barrel Pressure

 
LinkBack Thread Tools Display Modes
  #1  
Old 10-05-2011, 09:20 AM
Junior Member
 
Join Date: Oct 2011
Posts: 7
IV vs Barrel Pressure

We all know that reloading manuals are to be used as a guide only. Each gun is different, and the variables are endless. Most reloaders are primarily concerned with muzzle velocity and are only concerned about pressure when indications start to show up on the primers or the case itself.

Because we canít measure barrel pressure, my question is this:

As long as the powder type, bullet, and muzzle velocity is the same as whatís published, is it reasonable to think that the barrel pressure will correspond to the published value, regardless of what our powder charge weight is?

For example, say Iím loading for my 30-06. The IMR manual says that with 165 grain Sierra SPBT and charge of 51.2 grains of IMR 4320, they get 2869 feet/sec, which will result in 58,600 psi. Now lets say, if for me to get 2869 ft/sec in my gun, I must use 53 grains with IMR 4320 and the same bullet, will the barrel pressure still be about 58,600 psi ?

Also, if so, now because we are talking about muzzle velocity, would a different bullet of the same weight, say a Hornady 165 grain SST at the same velocity (2869 ft/sec) and using the same type powder (IMR 4320), produce about the same pressure (58,600 psi) ?
Reply With Quote
  #2  
Old 10-05-2011, 11:36 AM
Platinum Member
 
Join Date: Feb 2009
Location: Sedalia, MO
Posts: 1,253
Re: IV vs Barrel Pressure

Blackfly,

You've already touched on the answer here, but in short, no, you're talking about an entirely different set of circumstances and variables. Even if you're using the "same" components, they're from a different lot than those used in the manual. This can mean some substantial differences when speaking of powders, and can vary substantially when we're talking about different lots of the same primer. Cases vary from one run to another, even within the same make of brass. Add to that the individual history of the brass, i.e. how it's prepped, its hardness, the neck tension exerted on the bullet, etc.. Add to that the fact that bullets may vary as much as .0005" or so from one run to another with many manufacturers, and there may even be differences in jacket thicknesses or core hardness (alloy). I've seen all these factors in play during various production runs over the years, and can assure you that they do exist. And finally, we have the rifles themselves. Even if you were to use the very same ammo, actually loaded by the lab that did the manual, it's going to show different results when used in another firearm. Different throating, variable in chamber dimensions, bore/groove diameter variations, and even bore finish are all going to play a role in the final results.

You already touched on the right answer here; the guns vary considertably, as do the components, even when we attempt to perfectly match what's in the manuals. They are a guide, nothing more, and need to be regarded as such. Personally, I've always thought it best to view any reloading manual as a simple report, essentially saying, "we tired this particular combination in our rifle, and this is the result we observed." Follow that up with the ever-present caution that "your mileage WILL vary" and you're a long way down the road in understanding how to read a manual.

Hope that helps,
__________________
Kevin Thomas
Lapua USA
Reply With Quote
  #3  
Old 10-06-2011, 12:17 PM
Junior Member
 
Join Date: Oct 2011
Posts: 7
Re: IV vs Barrel Pressure

Thanks Kevin. As you can see I'm new to the site here and I figured if anyone would or could give me a reasonable answer it would be here.I don't ever see much info about pressure other than what to look for and this was something I've woundered about
Reply With Quote
  #4  
Old 10-06-2011, 12:44 PM
Platinum Member
 
Join Date: Dec 2005
Posts: 2,114
Re: IV vs Barrel Pressure

One other reason muzzle velocities are all over the place for a given load and rifle is the shooter. I've seen as much as 60 fps difference between my shooting and a friend's shooting the same rifle and ammo with the rifle resting on bags atop a bench. Others have reported about 100 fps difference. It depends on how hard one holds the rifle against their shoulder. Shooting prone usually puts bullets out faster than shooting offhand/standing.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes


Similar Threads for: IV vs Barrel Pressure
Thread Thread Starter Forum Replies Last Post
Big magnums developing pressure signs as barrel warms? Marine sniper Reloading 15 10-05-2011 01:41 PM
Barrel twist rate's affect on pressure airstream Rifles, Bullets, Barrels and Ballistics 9 03-04-2011 09:20 PM
Too much pressure? land308 Reloading 9 06-27-2009 07:36 AM
Stock Pressure on Barrel FullCurlHunter Rifles, Bullets, Barrels and Ballistics 5 09-15-2008 01:26 AM
45-70, to much pressure??? remingtonman_25_06 Reloading 5 08-16-2008 05:53 PM

Current Poll
Where in the US do you live?
West of the Mississippi River - 60.81%
897 Votes
East of the Mississippi River - 36.88%
544 Votes
On the Mississippi River on a houseboat - 2.31%
34 Votes
Total Votes: 1,475
You may not vote on this poll.

All times are GMT -5. The time now is 04:45 AM.


Powered by vBulletin ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Management Powered by vBadvanced CMPS
All content ©2010-2014 Long Range Hunting, LLC