To Jam or to Jump?

[gilream]

Why do some bullets shoot better jammed (Berger) while others need to be jumped to reach their full accuracy potential (Sierra match)? Is it related to the ojive shape? Flat Base vs. boat tail? Inquiring minds want to know.

 

[artbosco]

Why do some bullets shoot better jammed (Berger) while others need to be jumped to reach their full accuracy potential (Sierra match)? Is it related to the Ogive shape? Flat Base vs. boat tail? Inquiring minds want to know.

It's not the bullets, it's the barrel that shoots better. The barrel will tell you what it likes. It's your job to feed it different foods [bullets (jammed, touching, jumping), powders, primers, etc.,] to find out where its accuracy is at its optimum. To find out when its in tuned.

 

[spclark]

Good question. One that's been bandied back and forth for years.

Trouble is there are so many factors that influence how a given bullet shoots in a particular rifle, it'd be nearly impossible to answer that question once and for all time.

For years I took as gospel that VLD's need to be jammed, until the day came I grabbed the wrong (different rifle) box of ammo on my way to do some testing.

Loads considerably shorter than what I'd set up for the rifle I was testing shot better than anything I'd ever tried before, even though they were loads that had Berger's 105VLD jumping about 0.060". Go figure.

You just need to take the time to find out for yourself - though I admit I firmly believe forums like this one can help you cut down on how much time / effort / bullets / powder / barrel life you spend doing it, if you think to ask before you start.

 

[markm87]

We've had good luck jumping secant bullets in our 308s... With our stock REM 700 barrels, I think we'd run out of case neck before we could even try to jam.

 

[amlevin]

We've had good luck jumping secant bullets in our 308s... With our stock REM 700 barrels, I think we'd run out of case neck before we could even try to jam.

That's definitely the case with my 700 5-R Milspec. My 175 gr Nosler Custom Comp's get a nice run before they hit the lands. If I were to try and jamb them I'd be better off just cutting the case neck down, loading the powder with a foam plug to keep it in place, and then just stuff a bullet in using a dummy case. 8)

 

[markm87]

Yep... one of our 308s is the 5R. I think it has a jump of 0.193 or so with a Match King seated to mag length. They're great shooting factory guns, but man do they have a lot of leade.