Question for Hand loaders (.308)

[NENick]

Hey Guys,

I'm cooking up an accuracy/long distance load for my Tikka T3 Lite (.308) and figured I better consult our NFOA knowledge base before I blow my gun/self into pieces.

Bullet: Hornady 168gr BTHP
Powder: Varget
Primer: Winchester Large Rifle
Brass: Hornady Match

Tikka Factory Barrel: 21" 1/11
XLR Element Chassis using AICS Mags (2.880 Max COL)

The powder charge was started at 42.2 and increased in .2 increments up to 44.8. Hodgdon's site recommended: Start 42gr - Max 46c gr.

The rifle produced great results at 42.8, 43.8, and 44.8 without any pressure signs. The groups were all less than .5 MOA with the smallest around .4MOA.

Rod loaned me his Chrono, so I'll have FPS data next time I go out. I'm working up loads through 45-46gr. Hopefully 45.8 follows the pattern and will give good velocity and tight grouping.

My question - Hornady's loading manual calls for 2.800" COL. The Hornady OAL tool indicates that the bullet is engaging the lands at 2.889". I weighed the bullets, took the heaviest/longest (168.2gr). My theory is that if the cartridge is safe with the longest/heaviest bullets, the then I should be pretty safe.

The first rounds I tested were 2.800" as the manual indicated. I'd like to use the real estate available in the magazine and load to 2.880" (closer to the lands). What are the dangers in loading longer cartridges? Can I fit a bit more powder in the casing safely? I'm a bit surprised at how long I can make the COL without engaging the lands. What are you guys seeing in your rifles?

At this point, I've been weighing cases, bullets, primers, trimming the cases to a consistent length, and uniforming the primer pockets.

Thanks!


Nick

[DR4NRA]

Magazine length is the limiting factor. If you have at least 1 bullet diameter in the neck for sufficent bullet grab then go ahead and seat out to mag length. More powder in the case is possible by working up slow and watching for pressure signs. Be very careful.
 That being said, some rifles shoot better with a kiss, and some like the jump. Sounds like your rifle has already indicated what it likes but it won't hurt to try.

[unfy]

If you've got the Hornady book (sounds like you do) - at the front of the book they have some lengthy discussions about distance to the lands and how it affects pressure.  Lots of pics and stuff, too.

It will depend entirely upon your rifle, but the generic guide is to not be quite on the lands (but really really close to them).  In this way, the bullet travel from case mouth to the lands is minimal - and pressure spikes should be reduced since the initial pressure build up doesn't have to overcome both the case mouth bullet retention and the friction of the landing grooves.

Lastly, as DR4NRA mentions - proper / safe operation of the magazine is your other limiting factor.


As an aside, do the "old timers" COAL test by loading one of your final rounds into the chamber carefully / slowly.  And slowly / carefully eject the live round.  Check the ogive/shoulder/nose of the bullet for any markings left by the lands of the rifling.

Similarly, you can take an empty and sized cartridge (not primed), loosely put a bullet into the case mouth just a bit and load the round into your rifle carefully.  Bringing the round into battery will seat the bullet into the cartridge case as the nose contacts the lands.  Carefully eject the cartridge and measure it's COAL and you should get a number real close to your hornady gauge.