Balancing case capacity & .308 bullet weight for long distance target shooting

[abosely]

What are some brands and weights of .308 target bullets weights to checkout using a case with about 32gr case capacity?

Sorry for long post, but probably be helpful to explain a little about the rifle & cartridge.

Ok first off, I know this isn’t a target rifle.
So… I’m building a custom Ruger Mini 30 rifle. It’s not intended to be a target rifle, but want to see what it is capable of at longer range, because curious and find it interesting.

It is being built to as good of level as a 5804 SS Mini 30 can be built and is being chambered in a wildcat cartridge I made.
Ray Gross at Mansion Reamers designed the chamber dimensions to have neck, throat, leade & freebore optimized for accuracy and sent him several dummy rounds also.

Everything part/piece has been smoothed and polished to remove casting surface finish and mild lines on all the surfaces.

ASI is building rifle, custom chamber reamer will be here first week of April, the barrel is Kreiger SS 5R .308 1:12, chamber is .910" thick, then tapering for 1" down to .750" to muzzle, 18" barrel, so fairly nice and stiff barrel, adjustable gas block and 3.4" M1A style short Harmonic Barrel Stabilizer II with adjustable gas block.Trigger group has been smoothed and polished and ASI Advanced Trigger job with 4lb trigger weight.
Going in a custom English Walnut stock patterned along the lines of factory wood stock, pillar bedded and reviver area glass bedded.

Cartridge is 30-220 Russian, based on 220 Russian case, using Lapua 220 Russian brass necked up to .308, neck walls turned to .012", COL is 2.225".
Reason for designing this cartridge because 6.5 Grendel, 22mm & 6mm ARC, and PPC cartridges have to straight of case walls top feed from Ruger Mini 30 magazines. Wanted to be able to use Lapua SR brass and design chamber for optimal accuracy.
Case capacity is about 2gr less than the other cartridges.
Neil Jones will make set of reloading dies to match chamber from cases fired in rifle.


Again sorry for the long explanation of rifle & cartridge, just thought might make little more sense with it.

For hunting bullets will start out with Speer 125gr TNT, Maker Bullets 110gr expanding and for subsonic Maker 169gr expanding and for supersonic and subsonic plinking, Berry's 150gr Round Shoulder bullets.

That brings me to the actual question, what would be good weight/s bullets for long range target shooting, considering the case capacity. Heavier bullets (for caliber) have higher BC, but as go heavier velocity is lower so what would be good weight ranges and brands.
This is for fun long range target shooting out to around 600ms, not any kind of competition shooting.

Will be fun and interesting to see what a build Mini 30 can do.

Cheers, Allen

 

[fkimble@charter.net]

Your 12 twist will limit your bullet selection. I'm quessing around 168/175, maybe 185, non VLD. Also depending on neck length and throating, your usable case capacity could be reduced, reducing velocity. And lets not forget mag length. I'm assuming this gun started life as a "mini-30" ??

Frank

 

[SVT_Tactical]

The smk 168 is true and true and somewhat short in length which might be good in your situation. Pulled this photo of the main site on the 308 page.

You are being redirected...

 

[abosely]

Yes it started out as Mini 30 and max COL is 2.225.

I think bullets will need to be about 1.2 length to fit in mag and not intrude into case too much.

I’ll post case dimensions so can get idea of case capacity & bullet seating depth.

 

[Fast14riot]

30-220 Russian sounds like 7.62x39. Might look at some of those ballistics tables to get a good idea of what you want.

 

[abosely]

Yes it is a wildcat I designed, similar to 7.62x39 but chamber is designed to optimize accuracy.
The 7.62x39 is loaded to 45,000psi and the 30-220 Russian is 52,000psi.

 

[abosely]

I ordered a box of Maker 300blk .308 125gr tipped expanding bullets.
They are 1.155 long so when seated to 2.225 COL the base of bullet will be just barely below neck, but not below shoulder. I believe will get MV between 2600fps to 2650fps, they have .370 BC and from what others are saying they are very accurate.
Will know what they will do when work up loads and fire them.
The Speer 125gr TNT with .341 BC and are usually very accurate. So will work with them also to see what can do out at longer distances on targets, not game.

 

[JimSC]

Sounds like a .30 Grendel/.30 Major/.30 BW. I take a 6.5 Grendel necked up to 30 caliber. I use a 115 gn flat base Berger and N133 out to 300 yards with mine. Due to the low BC it runs of of steam before 600 but @ 300 and less it is deadly accurate.

 

[Walt Krafft]

I wish you luck. I tried this 25 years ago. I saw how good National Match prepped M1As would shoot and figured my Mini-30 should do a lot better than it did. First I sent it back to Ruger. They put a new barrel on it and returned it with a test target that was not impressive, at least to me. I tested and averaged 5 inches at 50 yards. Worked on the bedding and ammo and got it down to 2 inches at 50 yards 5 shot groups. I quit there and sent it down the road.

 

[Zero333]

Berger 150 gr Flat-base. 0.39 BC and extremely accurate.

 

[abosely]

Sounds like a .30 Grendel/.30 Major/.30 BW. I take a 6.5 Grendel necked up to 30 caliber. I use a 115 gn flat base Berger and N133 out to 300 yards with mine. Due to the low BC it runs of of steam before 600 but @ 300 and less it is deadly accurate.

Yes very similar reason for making it is to have something close top .30 Grendel/.30 Major/.30 BW that will feed through Ruger Mini 30 mags. The cases are straighter than 7.62x39 cases that Mini 30 mags are made for and don't feed with Ruger mags.

I made 6-220 R & 6.5-220 R versions also, to be able to have 6mm & 6.5mm cartridges that will feed in Mini 30 with Ruger mags. Not trying to 'improve' performance over existing cartridges, just to have similar cartridges that will feed in Mini 30.

The 30-220 R has about 2gr less capacity then the other cartridges, but feed form Mini 30 Mags.

Rifle is heading to Accuracy Systems tomorrow for work.

I'll post pics of rifle and what it does when it's finished. I'm not making any claims about how it will shoot, because really don't know. I figure it will shoot pretty good, but how good will have to be determined when working up loads and testing.
Will definitely have others shoot it, I'm not exactly a world class shooter.

 

[abosely]

Few pics of some parts smoothed & polished.




Assembled before being boxed up to be mailed to Accuracy Systems tomorrow.