Bullet jump

[5Tom]

So I'm about to try a lighter pill in my Tikka .243 and the pills I'll be using is the Sierra 70gr Blitzkings. I attached my dummy case to the Hornady OAL gauge, slipped in the projectile and pushed the case right into the chamber. After determining the projectile was just touching the lands, I pulled it out to find that my projectile can't be used because the boat-tail end loosely sits in the neck!

To use this pill, I would be seating it a considerable length (I read at least the diameter of the projectile should be in the neck) away from the lands thus a rather big jump.

I can't imagine getting any decent accuracy with this so it got me thinking that perhaps I should try a heavier pill? I don't plan on seating on the lands, I was hoping to set it between .010 and .020 thou off.

The rate of twist is 1:10 so I would imagine 90gr to 100gr should stabilize better and minimalize bullet jump?

[Blackened]

What is the COAL you're setting to have these off the lands?

Even at max recommended COAL of 2.71" inches, the diametre of the bullet would be in contact with about 70% of the neck or so, which should be plenty to keep the bullet firmly seated.

Any chance it's a neck sizing problem? Have you tried seating one in an actual cartridge with a properly sized neck and found it's still loose? Or just your dummy case?

[Harts]

A little jump isn't the end of the world. A few rifles prefer it in fact.

Since you're measuring up to the lands, I assume you're a little over max COAL?

If you still want to do some load testing with the bullet, I'd push on and just seat the bullets at the textbook COAL of 2.709"

Do the regular spread of .5gr powder charges to get a feel for things.

If they don't shoot well, then it's only got you a few bullets and an hour of your life.

If one load groups well, try 0.1gr loads on either side and make your decision from there. You could be pleasantly surprised.

[Rippah]

The rate of twist is 1:10 so I would imagine 90gr to 100gr should stabilize better and minimalize bullet jump?

Yeah should be fine, no longer though.

Long 100gr match hollow points and the like might be border line, but for your average hunting boat tail you should be ok.

Try a 90gr or 95gr first though I'd say.

Flatter shooting and still plenty of wallop.

[Jessie]

I can't imagine getting any decent accuracy with this so it got me thinking that perhaps I should try a heavier pill? I don't plan on seating on the lands, I was hoping to set it between .010 and .020 thou off.

I've always just set mine at max coal in the book TBH. Couldn't be bothered fiddling it down to a few thou off the lands and all that.

I still get inch groups at 100m.

My 2c anyway. I'd still try them at max coal and give them a shot anyway. You never know.

[Lorgar]

The rate of twist is 1:10 so I would imagine 90gr to 100gr should stabilize better and minimalize bullet jump?

I've since switched to 87gr pills as my regular .243 load, but I was shooting 95gr and 100gr in my Ruger for a while which has 1:9 twist. Shot them fine.

90gr in your 1:10 twist should be no problem at all.

IMO there is no need to have the entire bullet diameter contacting the inside of the brass neck, as long as it's stable.

Like above, if you haven't already I'd try seating it in a proper cartridge too and see what you get. Don't just rely on a dummy one that could have a loosened neck.

[1290]

I wouldnt be too concerned with trying to seat the short projjies on the lands; a bit of freebore never hurts (over 19mm for weatherby mags) just seat them with enough neck to hold them in nice n tight.

[5Tom]

G'day
According to Nick Harvey, Max case length is 51.94mm and Trim-To length is 51.69. My cases have been trimmed to 51.80 +/- .01mm. The case I'm using in the Hornady OAL gauge is a fire-formed case from my rifle, which hasn't been resized to allow me to move the projectile around with the OAL gauge.

To Harts and Blackend, where did you get the max OAL from? That OAL length will work with my 70gr BT (in a resized case) but if that's the recommended maximum length, it means my bullet jump for this projectile is 0.12"

I guess the lighter (or shorter) the projectile is, the bigger the jump if you have a set case OAL?

[Baldrick314]

I seat my projectiles to just off the lands in my .308 for shooting at the range. When I developed a hunting load for my rifle I made the OAL so that the rounds can be fed from the magazine. The difference between the two OAL's was about 200 thou and the difference in accuracy was negligible although the point of impact was about half an inch lower for the shorter rounds.

[Harts]

According to Nick Harvey, Max case length is 51.94mm and Trim-To length is 51.69. My cases have been trimmed to 51.80 +/- .01mm. The case I'm using in the Hornady OAL gauge is a fire-formed case from my rifle, which hasn't been resized to allow me to move the projectile around with the OAL gauge.

What your cartridge length though? Adding with your comment below, the COAL you measured to have the bullet just off your lands is about 2.829 inches is it?


When at this length, how much of the brass neck is contacting the bullet diameter roughly? A .243 neck is about 7mm high, is the bullet diameter contacting 6mm? 5mm? 4mm? How much?

To Harts and Blackend, where did you get the max OAL from? That OAL length will work with my 70gr BT (in a resized case) but if that's the recommended maximum length, it means my bullet jump for this projectile is 0.12"

A few manuals on online resources. That's maximum recommended COAL but as you've obviously seen with your measurements that might not be ideal for your rifle. If you can seat the bullet safely and it will fit in your magazine and feed properly a longer COAL might be needed for you.

I guess the lighter (or shorter) the projectile is, the bigger the jump if you have a set case OAL?

Only if you have to seat the bullet lower for it to stay in the neck.

e.g. if you had a 90gr bullet and an 80gr bullet that were both seated to the same cartridge length, the base of the 80gr bullet would be higher, the tip wouldn't be lower.


Let us know regarding the cartridge length and neck contact questions and we'll see what we can do.

[5Tom]

What your cartridge length though? Adding with your comment below, the COAL you measured to have the bullet just off your lands is about 2.829 inches is it?

with my dummy case at 51.64mm (2.034in), 70gr projectile length at 22.68mm (.893in), Cartridge OAL to lands is 71.9mm (2.829in).

When at this length, how much of the brass neck is contacting the bullet diameter roughly? A .243 neck is about 7mm high, is the bullet diameter contacting 6mm? 5mm? 4mm? How much?

2.5mm The bullet's boat-tail sits just outside of the case.

I guess the lighter (or shorter) the projectile is, the bigger the jump if you have a set case OAL?

Only if you have to seat the bullet lower for it to stay in the neck.

This is most likely my scenario. The 2.710in length will work and will fit my magazine. I have normally shot 87gr pills but never measured the distance from the lands until now that I have the dummy case for the OAL gauge.

[Harts]

When at this length, how much of the brass neck is contacting the bullet diameter roughly? A .243 neck is about 7mm high, is the bullet diameter contacting 6mm? 5mm? 4mm? How much?

2.5mm The bullet's boat-tail sits just outside of the case.

Aaaah.

Yeah, well in that case obviously seating them off the lands won't be an option. Having the bullet fall out of the brass is usually a bad thing

In terms of accuracy, I've found (just in my experience anyway) that the most important factors are the right bullet, and the right powder charge.

Once you've got a combo with decent accuracy then you can fine tune the small things like seating depth.

In that case, I'd do you're spread of test loads all seated at 2.710" to get the ball rolling. They might not be great, but you might find an accurate load anyway despite the COAL not being ideal. Dunno until you try.

If you find a load at 2.710" COAL that's decent, then you can see how far out you can extend that while still gripping the bullet. That will be the final test.

That's my advice anyway.

[5Tom]

Awesome, now I can start some reloads tomorrow

[Vati]

Awesome, now I can start some reloads tomorrow

That's the way mate.

I'm sure some of the other guys will back me up on this... Trying some loads is the only way to figure it out. You can read all the theory and advice in the world and it can all mean nothing once you get down to it.

This has been said a million times before, but what works for someone else doesn't meant it will work for you. Nothing to do but get loading and get shooting