Jam or Jump and throat erosion

[MDM]

Is there any concensus on what causes more throat erosion, jamming in, or jumping bullets to the lands?

 

[RonAKA]

I would think no significant difference. It is the fire behind the bullet that is the problem, not the space in front of it. That said, if you are loading to the max, you may get a little more powder in with a jump, and more powder means more burning of the throat.

 

[Yellow11]

Ron, I think youi got that back to front.

Surely you ment to say jammed, as that will leave more space in the brass

 

[RonAKA]

Ron, I think youi got that back to front.

Surely you ment to say jammed, as that will leave more space in the brass

Could be wrong, but I think the effect of reducing case capacity is likely to be less significant than the jam/jump effect. In my experience the jam gives higher pressures and velocities for the same powder weight. So if you jump you can feed it more powder for the same pressure.

 

[22BRGUY]

In my mind the jumped bullet would hit the lands with more velocity that would/could
cause more erosion but what do I know.

 

[Dave M.]

In my mind the jumped bullet would hit the lands with more velocity that would/could
cause more erosion but what do I know.

I don’t think the tiny distance the bullet is jumping (likely maximum of 60-80 thousandths) is enough distance to create the kind of velocity to cause damage. The fire burning behind the bullet is what does the damage. That being said, personally I’ve found jamming bullets has a larger effect on throat erosion than jumping them (comparing throat erosion per 100 rounds fired).
Dave

 

[22BRGUY]

I don’t think the tiny distance the bullet is jumping (likely maximum of 60-80 thousandths) is enough distance to create the kind of velocity to cause damage. The fire burning behind the bullet is what does the damage. That being said, personally I’ve found jamming bullets has a larger effect on throat erosion than jumping them (comparing throat erosion per 100 rounds fired).
Dave

If you have done the actual comparison, then I respect that. Thanks for the info.

 

[D-4297]

I've learned two things about throat erosion . It occurs at a faster rate when certain faster burning powders are used , and also when heavier bullets are used , even with some moderate powders .
Example : Shooting a .308 , If you are shooting nothing but 200.20x / Varget at 2660 /2670 range , and jumping .015 , because that's where your rifle shoots best . You may expect to see a round count of anywhere from 1,800 to 2,300 before Accuracy begins to deteriorate , Or even sooner , with some barrels . MMV .

Where-as , if you are shooting a 185gr Jugg with , say H-4895 , or one of the 4064 powders , your Round count may go as high as 3,000 or 3,500 . But accuracy will go away much faster as you approach the higher round count . And you can then add ; "Chasing the Landes , or increasing velocity to compensate for throat erosion . The "FUN" never ends .

Also included in this fun exercise , is the common information that a "Throat" will extend at a certain "rate" with-in the first 100+ rounds , or what we refer to as the "Break-in" period . After that , it will progress at a generally steady rate of , X = thousandths per 100 rounds , as a general rule . The problem with establishing general "RULES" , is that we all shoot different loads , different powders , using different barrels and different weight bullets , set at different seating depths . So there are no "REAL" constants to this Voodoo science . But I have no knowledge regarding Jamming bullets . Not something I do .

 

[Dave M.]

If you have done the actual comparison, then I respect that. Thanks for the info.

I have done this test. I had two 308 barrels for the same gun that shot the same load, and one I exclusively jumped bullets for and the other I exclusively jammed bullets with. I measure throat erosion every 2-300 rounds and the jammed bullets barrel wore the lands at a rate of over 25% more than the jumped bullets barrel. To be honest, I was somewhat shocked by these results.

 

[22BRGUY]

I have done this test. I had two 308 barrels for the same gun that shot the same load, and one I exclusively jumped bullets for and the other I exclusively jammed bullets with. I measure throat erosion every 2-300 rounds and the jammed bullets barrel wore the lands at a rate of over 25% more than the jumped bullets barrel. To be honest, I was somewhat shocked by these results.

THANKS
I assume there was a comparable loss off accuracy as erosion evolved?