Bullet seating Jam or Jump?

[jgh4445]

I am wondering, suppose you have developed a load for your rifle. By starting with your bullet jammed into the lands and gradually moved back so it will jump from different seating depth, you have found it likes a .005 jump. Can you assume it will be the same seating distance off the lands with all similar bullets? Or, will each bullet type. ie, Nosler Accubond and Nosler Partition, ( Same weight) require testing at different seating depths? Has anyone found a rule of thumb that each rifle likes only one seating depth?

 

[WestKentucky]

Bullet geometry will change things. Rifle bullets are typically similar enough that it's not a huge difference, but it WILL be different, especially if you start changing bullet types or weights.

 

[Axis II]

Could have just been my rifle but 55gr v max and 55gr Varmegeddon HP measured differently with my Hornady OAL tool. 50 and 55gr V max also. I assume you have the tool so why not just get measurements for each bullet and write it down just to be safe?

 

[Blue68f100]

Every type and mfg will be different even between lots. Also as the throats erode you will be constantly changing the length every few rounds to compensate.

 

[Varminterror]

Different bullets like different jumps. Secant vs. tangent ogives, partitions, mono metals, etc... they all have different preferences. Monos and partitions like a lot more jump, tangent and hybrids are tolerant of a broader range, secants tend to want to be jammed or kissing...

 

[RussellC]

Measure for each different bullet type, even if the same brand. As an example, Sierra load info recommends 2.260 for their SMK 69 grain for 223 Remington, which works fine in my Savage 12FV...in fact it can go quite farther before touching the lands. However, the 52 and 53 grain SMK in .223 Remington will not allow the recommended 2.250 in the same gun. Because of the different shape of the bullet ogive, it will jam up before this, necessitating having to bring it down to 2.235 or so. Just an example. Distance to the lands can vary with different shaped bullets.

Russellc

 

[Slamfire]

I prefer to use jump insensitive bullets. When Bergers first came out in 223, miraculous claims were made by the shooters making outstanding scores with the things. Then, a match or two down the road, the shooters who were previously Bergers were using something else. Bergers were jump sensitive, with a little throat erosion, the groups got big.


I can say that my 168 SMK’s and 175 SMK’s are jump insensitive and I can use them set to the same setting depth in every rifle and they will shoot well. I have had great luck with 68 SMK’s in the 223. I do not like seating bullets on the lands, or too near the lands. If you ever shot at Camp Perry, at some time during the 600 yard match, some boater gets in the impact area. Then everyone on the firing line has to empty their rifle, stick in their OBI, and wait till the authorities chase the fisherman away. I have found, as have others, that a bullet jammed in the throat has a tendency to stay there if the cartridge is not fired. Sometimes the case will come out, spilling lots of powder in the mechanism, and you have to find someone with a cleaning rod to knock the bullet out of the throat.

 

[RussellC]

Yup, that is why I measure each one. Whether or not the bullet is jump sensitive is a separate matter from where a particular bullets ogive meets the lands. Bullet sticking not only can cause an extraction mess, it can also affect pressure.

Russellc​

 

[MDof2]

Each bullet is going to be different due to their respective geometry.
Best to invest in a OAL Gauge to figure out what your guns likes with specific bullets.
https://www.hornady.com/reloading/p...tools-and-gauges/oal-gauges-modified-cases#!/

You can use their comparator once you know your land and rifling length for your specific rifle, and measure each bullet in question.
https://www.hornady.com/reloading/p...ools-and-gauges/lock-n-load-bullet-comparator

 

[Bartojc]

I am wondering, suppose you have developed a load for your rifle. By starting with your bullet jammed into the lands and gradually moved back so it will jump from different seating depth, you have found it likes a .005 jump. Can you assume it will be the same seating distance off the lands with all similar bullets? Or, will each bullet type. ie, Nosler Accubond and Nosler Partition, ( Same weight) require testing at different seating depths? Has anyone found a rule of thumb that each rifle likes only one seating depth?

I would not assume that at all. I would assume they would be at least slightly different. What type of accuracy are you looking for ?

For me most of my rifle ammo is for hunting or playing around with targets (no competitions). I never try to chase the lands. I have the tools and know where they are for a given projectile. I set my OAL accordingly, but I never push it. I have been able to find at least acceptable results for what I am trying to do without chasing the lands.

-Jeff

 

[jgh4445]

Thanks guys. I do have the OAL gauge and inserts. Looks like I'll be doing a bunch of measuring and writing until I settle on a bullet and load. Probably gonna be between the Accubond and the Partition. Leaning toward 115 Partition. Using the comparator, I don't find a lot of freebore in my Number One. Not gonna be able to seat real long anyway.

 

[Driftertank]

I'm kinda old school. I just set an example of the exact bullet i want to use in a fired case and seat it gently in the chamber, then draw it out gently and take an OAL measurement. Repeat 3-5 times with different individual bullets from the box, make sure they all match up within .001-.002 or average. Then i set my seating depth somewhere around .020-030" shorter than that measurement to make a test ladder. Once i find a good node, i sometimes play with small OAL changes to see if they improve consistency.
I don't use bullets that need to be so close to the lands that minor ogive variatons or adverse chamber condition can cause major pressure changes. I always assume my guns will be used in "field conditions," and so like to have a bit of error margin my loads.

I repeat the length-to-lands test any time i switch bullets. Of course, that assumes that magazine dimensions allow for seating at my preferred jump length. If mag length dictates OAL, i load there and see if they'll shoot. If not, i try a different bullet. No point going afield with a repeating firearm if i have to single load it, IMO.

 

[quest4perfection]

I would not assume that at all. I would assume they would be at least slightly different. What type of accuracy are you looking for ?

For me most of my rifle ammo is for hunting or playing around with targets (no competitions). I never try to chase the lands. I have the tools and know where they are for a given projectile. I set my OAL accordingly, but I never push it. I have been able to find at least acceptable results for what I am trying to do without chasing the lands.

-Jeff

Buying in lots of 500 will avoid lot number variances