Pressure vs Jammed

DsrtRat

DsrtRat

Regular
Rating - 100%
27   0   0
Location
Guelph
I have been doing a fair amount of reading about bullet jumps and jammed into the lands etc...

My question is this. How much more pressure will I get compared to say 0.020 jump? I currently have tested some loads in a new gun that are within the limits of my reloading books. Only one load has started to show minor signs of getting warm but nothing serious. If I were to try and work up that same string of loads, will pressure signs start to show up sooner from a 0.010 jammed bullet vs the 0.020 jump?
 
Sorry to be like this but..... maybe, maybe not.

If I had to bet, I would bet on the jammed one showing pressure first. But I have found no 100% certainty for anything in reloading.
 
Is it not a given that it would show signs first? Im just curious as to how much quicker.

I was always under the impression that the closer to the lands it sits, the quicker pressure builds up.
 
You're right that pressure must be higher when bullet are jammed in the lands since they don't have a running start before encountering resistance when getting deformed.

Unless you've tested your rifle and are positive that jamming the bullet give optimal accuracy, you should stay at least 0.020 - 0.040" off the lands and keep your cartridges under maximum AOL if possible.

Here is a great article on optimal seating of VLD bullets (the most difficult bullets to optimally seat).
http://bulletin.accurateshooter.com/2009/03/berger-tips-for-loading-vld-bullets/

Alex
 
Then why ask?
Click to expand...

Because I don't know the answer. As I said, I always assumed it would be higher. I was just looking for information from people who have experience with this.

AlexF,

Thanks for the article.
 
Just read the article. WOW! I knew that deeper seating meant more pressure but in this case, it outdoes jammed by a big margin. Interesting for sure. Think I will try their method of finding the optimal jump.
 
Either way, I think I will back off the load and try some depth changes. With some bullets the recommended minimum OAL is longer than the suggested jumps for my .223.

It doesn't say anything about powder charge. Does that matter? Can I assume that you pick a charge that will be no where near max pressure, shoot it, and the info about seating depth will be there for you? Once found, start working up powder loads?

Interesting stuff as my Remington 700 shoots best with long jump (around .05 for most bullets.
 
You can check it but many benchrest shooters now use the "optimal" 0.050" jump and get better accuracy then when using the traditional -0.020" jam.
Some competitive F-Class shooters get outstanding accuracy with 0.150" jump (that's a long 4mm!).

It's true that you should be careful about pressure because some cartridges are very sensitive to seating depth. (I'm thinking 6mm PPC) but 223 Rem (5.56 NATO) and 308 Win (7.62 NATO) are both millitary cartridges and tend to be very easy to reload and have predictable behavior.

Finally , get yourself an Hornady OAL gage. It's a magical tool!
http://www.6mmbr.com/catalog/item/1433308/977259.htm

Alex
 
Many shooters start there testing jammed, and wait for pressure signs. Then move the bullet further off the lands. By doing this way you should be able to increase the powder charge.ie less pressure. The other way around may not be so good.
 
You must log in or register to reply here.
Back
Top Bottom