how much jump is to much for an AR?

[dave_the_ss]

Just finished my 6mm arc build. I chose to run 70 grain nosler varmageddon bullets. With cfe223 (it’s what I have and easy to find)

Max OAL is 2.090 I loaded to 2.094 cause I had so much jump.

My jam is 2.230

Is that way to much jump for an ar?
If I increase the OAL is that going to cause pressure To go up or down?

I fired a few rounds today to check pressure and have no pressure signs. And cycled just fine. All the way to max load data of 33.0gr.

Now I’ll put my thermal on and go sight in and shoot for accuracy

[r.tenorio671]

Just finished my 6mm arc build. I chose to run 70 grain nosler varmageddon bullets. With cfe223 (it’s what I have and easy to find)

Max OAL is 2.090 I loaded to 2.094 cause I had so much jump.

My jam is 2.230

Is that way to much jump for an ar?
If I increase the OAL is that going to cause pressure To go up or down?

I fired a few rounds today to check pressure and have no pressure signs. And cycled just fine. All the way to max load data of 33.0gr.

Now I’ll put my thermal on and go sight in and shoot for accuracy

....bullet profile & magazine internal length have the most influence on attainable COAL in regards to MAX COAL.

...an increase in OAL may decrease pressure, but not always.

...when increasing OAL, just ensure the seating depth has sufficient bullet in the neck.

FWIW, excellent "performance" can be obtained at multiple jump distances, it comes down to testing....each barrel is unique. I have the same bullet loaded up for testing and my data is CBTO 1.6415 / COAL 2.1215. With these measurements these rounds fit easily in my Duramag & E-Lander mags and chamber & extract from MY barrel's chamber with no issues, and have sufficient bullet in the neck for retention. Pre-installation measurements of MY barrel had these bullets registering a max COAL (touch-point) 2.2246 and the CBTO being 1.7061 at that max COAL.

[dave_the_ss]

Just finished my 6mm arc build. I chose to run 70 grain nosler varmageddon bullets. With cfe223 (it’s what I have and easy to find)

Max OAL is 2.090 I loaded to 2.094 cause I had so much jump.

My jam is 2.230

Is that way to much jump for an ar?
If I increase the OAL is that going to cause pressure To go up or down?

I fired a few rounds today to check pressure and have no pressure signs. And cycled just fine. All the way to max load data of 33.0gr.

Now I’ll put my thermal on and go sight in and shoot for accuracy

....bullet profile & magazine internal length have the most influence on attainable COAL in regards to MAX COAL.

...an increase in OAL may decrease pressure, but not always.

...when increasing OAL, just ensure the seating depth has sufficient bullet in the neck.

FWIW, excellent "performance" can be obtained at multiple jump distances, it comes down to testing....each barrel is unique.  I have the same bullet loaded up for testing and my data is CBTO 1.6415 / COAL 2.1215.  With these measurements these rounds fit easily in my Duramag & E-Lander mags and chamber & extract from MY barrel's chamber with no issues, and have sufficient bullet in the neck for retention.  Pre-installation measurements of MY barrel had these bullets registering  a max COAL (touch-point) 2.2246 and the CBTO being 1.7061 at that max COAL.

 so what would you say is a sufficient amount of neck to be in th neck ? ive never ran into this issue with any of my bolt guns. its a new problem that when i started reloading i didn't think i'd be having.

thank you for the information and knowledge i really appreciate it.

[StoneHendge]

I've shot thousands of the 70 gr Nosler Ballistic Tip Varmints in my 6x45 AR. They are almost exactly the same as the Varmageddons except for the small boat tail and a little better accuracy and are interchangable from a load standpoint. I load them at 2.30 which is the longest a mag will allow them (ASC gives the longest COAL in 223 mags). I have no idea what the jump is, but the ogive is right at the case mouth. Meaning it's a BIG jump and they don't mind it at all.

In 6mm ARC I would be more focussed on being deep enough in the neck as r.t said. The general rule of thumb is depth should be equal to diameter, but I've certainly gone less. There's an old thread about these somewhere. I played with them a little but stopped to conserve since they're my 6x45s favorite bullet. I'd start with around 0.2" of grip in the neck and see where that takes you.

[r.tenorio671]

Just finished my 6mm arc build. I chose to run 70 grain nosler varmageddon bullets. With cfe223 (it’s what I have and easy to find)

Max OAL is 2.090 I loaded to 2.094 cause I had so much jump.

My jam is 2.230

Is that way to much jump for an ar?
If I increase the OAL is that going to cause pressure To go up or down?

I fired a few rounds today to check pressure and have no pressure signs. And cycled just fine. All the way to max load data of 33.0gr.

Now I’ll put my thermal on and go sight in and shoot for accuracy

....bullet profile & magazine internal length have the most influence on attainable COAL in regards to MAX COAL.

...an increase in OAL may decrease pressure, but not always.

...when increasing OAL, just ensure the seating depth has sufficient bullet in the neck.

FWIW, excellent "performance" can be obtained at multiple jump distances, it comes down to testing....each barrel is unique.  I have the same bullet loaded up for testing and my data is CBTO 1.6415 / COAL 2.1215.  With these measurements these rounds fit easily in my Duramag & E-Lander mags and chamber & extract from MY barrel's chamber with no issues, and have sufficient bullet in the neck for retention.  Pre-installation measurements of MY barrel had these bullets registering  a max COAL (touch-point) 2.2246 and the CBTO being 1.7061 at that max COAL.

 so what would you say is a sufficient amount of neck to be in th neck ? ive never ran into this issue with any of my bolt guns. its a new problem that when i started reloading i didn't think i'd be having.

thank you for the information and knowledge i really appreciate it.

....Advancements in bullet design, use of neck bushings for neck tension, etc. give the reloader more flexibility to find what works for them, but for use in mag-fed semis, enough that the bullet isn't able to be knocked askew/tilted during the feeding phase.  You will probably get a gazillion answers to "how much", but one of the oldest "rule of thumb" answers would be for the bullet base to be at least at the junction of the neck and shoulder but no more than 25% above that junction.

[r.tenorio671]

...here's a couple of links that could be useful. I recommend reading them in the order listed below as some "concepts" become better clarified and the relationships emerge..

https://bergerbullets.com/wp-content/upl...3/COAL.pdf

https://bergerbullets.com/vld-making-shoot/

[GRH]

I don't know that it would be a problem unless it's short enough that it would come out of the case, except for accuracy reasons. Bullet jump will "effectively" increase case capacity and generally lower pressure. The bullet jumps against the lands and stays there until the powder develops enough pressure to start engraving and push the bullet down the barrel. So it's artificially creating a longer case with greater capacity.

Using GRT the projections sometimes don't coincide with real world chrono results, adding the measured bullet jump to the model often times brings FPS within exceptable percentage of the chrono results.

So yes bullet jump does have an effect, you just need to find the closest node that still fits in the mag and feeds reliably.