Bullet Comparator Question

[Velocity]

Oso

I guess all the posts I was reading here was about bolt rifles, my mistake.

Thanks

[Klem]

Velocity,

Correct - With a Grendel, if the gunsmith reams the chamber to SAAMI specs then the magazine will be shorter than the chamber. For bolt guns and other calibres its often the reverse, and this would be our preference.

The upside is, that relative to all other factors that make bullets go where it do, jump-to-lands is overrated.

[LRRPF52]

With a true SAAMI chamber with the compound throat, you’re not far from the lands with any bullet profile basically.

With a conventional freebore and 1.5 degree target leade, it just depends on how new or worn the reamer is.

[Velocity]

Klem, LRR

So with a max COAL of 2.260" and my chamber measurements, your saying that a .75" to .155" jump, depending on the bullet is normal for AR's?

Thanks Guys

[Kosh65]

Klem, LRR

So with a max COAL of 2.260" and my chamber measurements, your saying that a .75" to 155" jump, depending on the bullet is normal for AR's?

Thanks Guys

I don’t know about AR’s………..but that’s not all too uncommon in bolt guns. In 1 of my .22-250’s, I’m jumping .210” with absolutely no accuracy loss.

[Klem]

Vel,

Here's the deal in a Lilja group-buy barrel
[ATTACH=CONFIG]18702[/ATTACH]

Measurements in mm.

If you load to the max magazine limit (58mm) then these are the jump-to-lands. Note how as the bullets gets smaller, lighter, your jump gets shorter. 0.5mm is 2-thou in Imperial so only the lightest bullets get close.

But, loading close to the lands, or even mag length comes at a cost - which is neck tension. Note the amount of neck in contact with the bullet shank at 58mm OAL (right-hand column). The lighter bullets that can get closer to the lands also have less neck tension than the heavier bullets.

The convention is to have at least the calibre's diameter in contact at the neck. With Grendel it is 6.5mm of neck in contact with the bullet's shank. Length here is of course a proxy for what you really want which is neck tension. You can get away with less neck length in contact as long as the case is ductile [elastic] and gripping that bullet firmly. After repeated reloads the neck loses ductility and so grips less. Some shooters try to restore some of it by annealing.

Another way to hold the bullet still is to crimp, and in doing this the amount of shank in contact is less important than if you don't crimp.

So, any attempt to load to the classic 2-thou off the lands will be thwarted by the magazine in an AR. Which is just as well because loading long costs you in neck tension. You need neck tension in an auto loader more than any benefit a shorter jump might give you.

Bottom line is you don't need a 2-thou jump to achieve good results in an accurate semi-auto. Sub MOA repeatable with long jumps is perfectly achievable if you look after everything else.

[Velocity]

Klem

Learning more every day.

Thanks

[Dt219]

Agreed. Klem is pretty slick on many many things that get asked on here. Sure some people take him the wrong way here and there but he’s a huge help to many. If ever in doubt just ask !! Him or somebody will answer. This place has learned me a lot and I thought I knew most things already, I was wrong

[Velocity]

Klem was telling me about the importance of neck tension in AR's so here is a question.
I purchased two bags of PPU 120 gr. bullets and the bags display "Prvi .264 / 6.5mm 120 Grain Hollow Point Boat Tail (100 ct).

The diameter measures .262" are these bullets ok to use? I ask because there will be less neck tension, right.

[Dt219]

I would say they will go bang can’t promise nothing else. but if that’s true a .262 will have less neck tension than a .264 if the case is sized the same way

[Dt219]

Some dies will produce .002 neck tension consistently. Others will have more. If the die or bushing only produces .002 for a .264 bullet it will not grip the bullet any

[Velocity]

Just sized five cases and the neck ID measures .257" .

[Velocity]

I had sent a email to Powder Valley yesterday about the bullet diameter differences and received an email from them today, asking if I would send a photo of the measurement so I did.
No more than 15 minutes later I received a phone call from Powder Valley, he said he contacted PPU (Prvi)?? and PPU told Powder Valley to send the email and photos I had sent and they (PPU) would take it from there and contact me. RUH-RO

[Dt219]

Goood deal, a lot of people measure their neck tension by measuring a sized case o.d. Then measure it again once a bullet is seated. That’s the supposed neck tension

[Klem]

Gents,

Here are the diameters of a range of 6.5mm bullets. They have been measured with a micrometer (not calipers) and a few of each for precision.

Lapua is a relatively thick case at 0.0130" at the neck, sometimes 0.0135". If the outside diameter of the neck is sized down to 0.286" then when the bullet is seated they expand about 0.004" which is a serious grip. To do this the expander ball has been removed from the Forster depriming stem (you don't need it), otherwise it would grip a bit less.

[ATTACH=CONFIG]18706[/ATTACH]

All 14 different bullets are close to 0.264" so your 0.262" is an issue.

Yes, you can shoot a smaller diameter bullet but it might not obdurate and spin properly. I have heard 6MOA groups for a 3MOA rifle is typical when using 30cal bullets - never seen or done it however. Lee Enfield .303 shooters sometimes use 308 bullets at a pinch. A 303 is .311 calibre and in this case would be shooting 30cal bullets. Same with the Mosin Nagant. Those old rifles, especially ones made during wartime can have bores that were out of spec but shooters try what they have on hand, as long as it's not the reverse.

[SCJim]

if you really want to get serious about neck tension throw away your expander ball and start using expander mandrels instead. You will get less runout and more consistent neck tension. I personally go with .003 neck tension on everything from .22 cal to .30 cal. From benchrest to plinkers. Also start annealing or
make sure all your cases have the same number of firings. When you mix cases with different numbers of firings you will get necks with different plastic/elastic deformation properties and therefore different neck tension. Not sure how much this matters with 1 MOA gas rifles but with >.3 bolt guns you will see fewer flyers

a video on their use

https://www.youtube.com/watch?v=TRc4juuh-c8

[Harpoon1]

if you really want to get serious about neck tension throw away your expander ball and start using expander mandrels instead. You wil get less runout and more consistent neck tension. I personally go with .003 neck tension on everything from .22 cal to .30 cal. From benchrest to plinkers.

https://www.youtube.com/watch?v=TRc4juuh-c8

I bought into that too, turns out, it’s NOT the expander ball causing the issue! It’s the bushing you’re using. I switched over to the Short Action Custom bushings (and still used the factory expander ball also) and get mandrel like runout. That is .001 or less total is the norm! The mandrel works but, with the new SAC bushing, I find it a completely redundant unnecessary step. “As simple as possible but no simpler”! A.Einstein

I heard LE Wilson has had tapered bushing for a while, I have ordered a few to compare against the SAC, will post my results. The SAC bushing fits in the Whidden dies and with the Whidden adjustable expander ball kit, you’ve now got full control over neck sizing and tension in one step with minimal runout!



https://youtu.be/D2Gei8Wo6UA

https://youtu.be/P16Mhe3TMFQ

[SCJim]

oh I went through my bushing die phase

[ATTACH=CONFIG]18707[/ATTACH]

I really need to sell all these. now I use non bushing full length dies and mandrels. Best results I have ever had

[Harpoon1]

oh I went through my bushing die phase

[ATTACH=CONFIG]18707[/ATTACH]

I really need to sell all these. now I use non bushing full length dies and mandrels. Best results I have ever had

I went through that phase too, until I tried the SAC bushing. Now I find using a mandrel a complete waste of time!

[Harpoon1]

oh I went through my bushing die phase

[ATTACH=CONFIG]18707[/ATTACH]

I really need to sell all these. now I use non bushing full length dies and mandrels. Best results I have ever had

Oh I went through that phase too. All full length sizing dies, then all bushing dies. Then pulled all of the expander balls and used a mandrel. Luckily I tried the SAC bushing before blowing it off as just another bushing. Now I find using a mandrel a complete waste of time! YMMV.