7BR with cast boolits

[PhilC]

Rifle data:

Savage PTA timed/trued by Fred
Target AccuTrigger @ 10oz
26" SS Shilen Select Match, heavy varmint contour, custom throated
Vintage B&L 24x
Bobby Hart LRT
Weighs 12.5lbs

Load data:

RCBS 168-SP, Lyman #2, gas checked and sized to .285"
WLL X-lox 2500+ in first lube groove only
Peterson fireformed brass
CCI400
N135

Removed the 6.5CM barreled action from the LRT and put it back in the factory stock, then fit the 7BR barreled action to the LRT. Loaded test rounds about 2 weeks ago and was just waiting for a good weather window which finally happened Friday.

Pulled my bench out and set up. Re-zeroed the 6.5CM then set up chronograph prior to shooting 7BR. Shilen recommends shoot 1 & clean for 5 rounds, which I did while getting scope dialed in. Fired up the chrono then proceeded to shoot 4ea 3-shot groups. Rounds 6, 7 & 8 produced the group circled in green, I forgot to adjust elevation before the first shot of the next group circled in red...

https://i.ibb.co/wBXF5Rt/7br.jpg (https://ibb.co/wBXF5Rt)

I use corrugated plastic for backers and they were quite wet from morning fog, so waited to measure after they dried, the three holes on left measured .712"...

https://i.ibb.co/MM6JDKN/dry.jpg (https://ibb.co/MM6JDKN)

The final group at 26.5gr openend up a bit, but still respectable with only 17 total rounds shot...

https://i.ibb.co/rsB1zHv/final.jpg (https://ibb.co/rsB1zHv)

Disregard markings on targets, I save unused sighter targets for home practice. When I ran my borescope down the barrel afterward I found no lead fouling at all. Hats off to Shilen for a superb finish!

This is very promising and anxious to start a ladder test from 24.5 - 26gr. The 25gr load had avg vel 2048fps, ES 4.0, SD 2.0. :-)

[charlie b]

Nice start. What twist is that barrel?

I got my mold for the 6BR today (and sizing bushings). Will cast some up this weekend. It is also a Shilen barrel.

[PhilC]

It's 1:9, finished prepping remainder of my brass this afternoon. Back to waiting for another weather window as snow returns Thursday/Friday, then an arctic front moves in Sat night, highs drop to mid to upper teens and overnight lows near zero through at least middle of next week.

Good to hear your mold arrived, look forward to updates!

[charlie b]

You'll have the same problem with velocity that I will (1:8 twist). 2000fps will probably be fine. Will experiment a bit to see how fast it will hold up.

My 1:10 twist .308 holds up to just under 2100fps depending on powder being used (slower is better in it with heavy bullets).

[PhilC]

I spent a lot of time researching CBA match reports for 6BR & 30BR, powders, primers, molds, twist rates, charge weights, alloys, velocities, and resultant groups. I focused on the competitive averages and used that info in my decision process and in running variables in QuickLoad.

From that, I was "pretty sure" ~2000fps was going to be a sweet spot, sure seems to be so far. :-)

[charlie b]

I spent a lot of time researching CBA match reports for 6BR & 30BR, powders, primers, molds, twist rates, charge weights, alloys, velocities, and resultant groups. I focused on the competitive averages and used that info in my decision process and in running variables in QuickLoad.

From that, I was "pretty sure" ~2000fps was going to be a sweet spot, sure seems to be so far. :-)

I think the CBA website might be one of the most used resources I have. The other (for jacketed) is the International Benchrest site.

Yep, I find that my most accurate loads in the .308 are 1800-2000fps. My go to load right now with the 210gn bullet is 1950. The bonus is that long bullet is good for 500yd ranges. It is a little too slow for 600yd.

I'll be starting at 1900fps with the 6BR and work up until the groups enlarge, then back off 100 or 200 fps.

[PhilC]

Settled on a powder yet, Varget maybe? Was either the most popular, or 2nd most, in my research for 6 & 30BR. I couldn't find any at the time but am not displeased with my results using N135 which was another frequently used powder.

[charlie b]

I will start with Varget. Depends on if I can reach the right powder density with it. My .308 cast does good with several different powders, including Varget.

[Fuj']

Phil.....What is the length of your bullet, and what bullet profile ??

[PhilC]

It's a spitzer profile, with gas check it is 1.175".

[charlie b]

Phil,

Tried some of the 108gn today just to get a feel for things. Sized to .244 with .238 nose. But, I'm a bit high on vel right now I think, 2100fps. The IMR4198 loads seemed a little better than the Varget but I only shot 10 of each. 5 shot groups, 2 1/2" and 3" at 200yd. Decent start for the first bullets out of the mold.

[PhilC]

Sounds like you're getting there, 2 1/2" - 3" @ 200yds with the first boolits out of the mold is nice!

Shot a ladder Saturday some ok results with 24.4 - 25.0gr that playing with seating depth might improve, but 26gr, which is where I stopped, produced this...

https://i.ibb.co/9sfQznr/26gr.jpg (https://ibb.co/9sfQznr)

Hard to believe 25.8gr opened up that much and how tight 26gr performed. Am going to load another ladder from 26 - 27gr in .2gr increments to confirm. 83rds down the tube at this point with zero leading and have completed barrel break-in.

[charlie b]

Small cases can provide some surprises. I got the 2100fps with only 17gn of 4198. Will be interesting to see what a ladder looks like.

[Fuj']

Following.....

Where are yinz at in particular to jump or jamb for seating depth tests ??
I would assume a good jamb with light neck tension would be forgiving.

I have a good 50 years of casting. I always thought about finding a good
supply of half jackets for the 7's, but I'd go to a smaller case then the BR
cases. My theory since the speeds are low, the BR case is not efficient.
Always had my eyes on taking a 7.62x39 case and doing a 7mm half jacket.

[PhilC]

I'm seating to an imprint of lands on the boolit, on a scale of light --> medium --> hard, imprints are mid-way between light & medium. Neck tension is higher than I want and will correct that after fireforming the remaining 30 or so cases.

[charlie b]

Depends on the bullet. I usually shoot bore riders. I size the nose such that it is an interference fit in the bore. If I pull a cartridge from the chamber I want to see even rifling marks around the nose of the bullet. When seating the first drive band is engaged in the throat/rifling. If shooting a non-bore rider I also seat it jammed into the rifling. One thing I am aware of when shooting is how hard the bolt is to close. If one round is too hard or not hard enough compared to the others I will shoot it at my sighter target. Sometimes it is just enough off to mess up a group.

I am shooting cast in my BR as a lark. Maybe I will get a decent load and maybe not. It is just too much of a twist rate for good higher velocity work. Not a big deal since I set it up for long range with heavy jacketed bullets.

FWIW, I am considering a new barrel to replace my .308 (1:10). If I want to go long range (600+ a little) it will be a 29 or 30" .30-06 with a 1:12 or 1:14 twist. If I want to stay with shorter range (l500yd and less) it will be a 26 or 28" .30BR with a 12 twist.

[PhilC]

Have done some more testing and now have 101rds down the barrel. Turns out low 26gr range is looking pretty good. Will know more after my test session today, report to follow.

I've run gas checked, heat treated Lyman #2, lubed with WLL X-Lox 2500+ up to 2246fps without issue.

[charlie b]

Sounds like a decent 'spot'.

I am having too much fun with the Vtac bullets in the 6br right now. Will cast some more for it pretty soon. Meanwhile I have about 500 .308 bullets to load and shoot :)

[charlie b]

Fuj, it is certainly doable. There was a guy on the cast bullet forum who made up some cast for his .221 benchrest rifle. Not sure if he shot it at 200yd. He had some impressive groups with it.

[PhilC]

Due to cascading error effect my session was a bust. Despite that, I have settled on 26.4gr as it produced the best group in my last session and best load statistics. Weather conditions suck thru Tuesday afternoon, if I can't shoot prior to, I'll load what's shot best so far and hope for the best.