107 SMK early pressure sign?

[DB_23]

Rifle is a 6BR with 094 freebore 26" barrel, no turn chamber. Loaded and shot Alpha 6BR brass with a few different charges starting at 28.1 grains of Varget. Bullets were seated for .010 off the rifle lands. Got this result at 28.7 grains. Velocity was measured at 2734 using a Magneto speed. I had another step to go to 28.9 but stopped with this. I can't rule out inaccurate shoulder bump. This one could have slipped through at .004 bump. Sorry for the low-tech cell phone photography.

 

[SKWERLZ]

That jives with my internal ballistic calculator fairly well and it’s saying 67K of pressure.
I’m fairly sure alpha brass volume is about .2-.3 grains less capacity than my Peterson brass and used that for volume.

I personally feel a lot of people are running 6BR really spicy but the excellent lapua brass hid that well with stout bases and a bit more volume.

 

[DB_23]

That jives with my internal ballistic calculator fairly well and it’s saying 67K of pressure.
I’m fairly sure alpha brass volume is about .2-.3 grains less capacity than my Peterson brass and used that for volume.

Thanks for the response. That's an interesting pressure result. I used Gordon's Reloading Tool and measured my cases at 38 gr water. My results showed 52000 and change at the charge used in that picture. Regardless, I will be backing down quite a ways and then doing some seating test. Had very good (for me) 3 shot groups so far at 100 yards. Looking to use these for entertainment shooting at 3-800 yards.

 

[SKWERLZ]

M

Thanks for the response. That's an interesting pressure result. I used Gordon's Reloading Tool and measured my cases at 38 gr water. My results showed 52000 and change at the charge used in that picture. Regardless, I will be backing down quite a ways and then doing some seating test. Had very good (for me) 3 shot groups so far at 100 yards. Looking to use these for entertainment shooting at 3-800 yards.

My program uses useable case capacity and I estimated 32.3 which is a smidge less than I got with Peterson brass with a 107 at touch in a .104 FB chamber.
That’s why I went with a slower powder to get the speed without the pressure.


I’ve seen QL data that jives with your pressure predicted so that’s certainly a possibility as well but you are showing a ejector mark with means Alpha brass is super soft (like Norma) or your spice level is beyond 54 that QL predicted

 

[LCazador]

What was your new brass head dimension and how much expansion do you have now?

 

[Straightshooter1]

Thanks for the response. That's an interesting pressure result. I used Gordon's Reloading Tool and measured my cases at 38 gr water. My results showed 52000 and change at the charge used in that picture. Regardless, I will be backing down quite a ways and then doing some seating test. Had very good (for me) 3 shot groups so far at 100 yards. Looking to use these for entertainment shooting at 3-800 yards.

Maybe this can help you with what you're looking at . . .???

 

[Lance21]

M

My program uses useable case capacity and I estimated 32.3 which is a smidge less than I got with Peterson brass with a 107 at touch in a .104 FB chamber.
That’s why I went with a slower powder to get the speed without the pressure.

View attachment 1446855
I’ve seen QL data that jives with your pressure predicted so that’s certainly a possibility as well but you are showing a ejector mark with means Alpha brass is super soft (like Norma) or your spice level is beyond 54 that QL predicte

M

My program uses useable case capacity and I estimated 32.3 which is a smidge less than I got with Peterson brass with a 107 at touch in a .104 FB chamber.
That’s why I went with a slower powder to get the speed without the pressure.

View attachment 1446855
I’ve seen QL data that jives with your pressure predicted so that’s certainly a possibility as well but you are showing a ejector mark with means Alpha brass is super soft (like Norma) or your spice level is beyond 54 that QL predicted

Alpha brass is definitely not soft.

 

[DB_23]

What was your new brass head dimension and how much expansion do you have now?

New brass .375 up from the base was .465 and the one in the picture is .467-.4675. A different fired case measured .466. Don't know how much expansion is normal there. COAL on these were 2.354. 10 thousands away from the lands. Thanks for the info.

 

[shoot4fun]

@DB_23 Alpha 6BR brass is OCD, just the same as 6BRA brass and many other offerings.
You are going to see the same things most all the 6BRA guys have reported. This brass is VERY HARD and cannot expand far enough to grab the chamber walls and keep the hard bolt lift in check.
It may be that you won't notice hard bolt lift as much with 6BR over 6BRA but you will see what many have all the signs of over (or high) pressure.

 

[LCazador]

New brass .375 up from the base was .465 and the one in the picture is .467-.4675. A different fired case measured .466. Don't know how much expansion is normal there. COAL on these were 2.354. 10 thousands away from the lands. Thanks for the info.

Your head expansion should not be more than .001". Go to the Hodgdon website and see instructions on measuring head diameter, expansion, and pressure. At .467" you're at .002" of expansion according to your numbers.

 

[Clancy]

Is this a TL3?

 

[DB_23]

Is this a TL3?

Zermatt/Bighorn Origin

 

[SKWERLZ]

I’m not saying your load isn’t hot because that’s for you to decide, but sometimes you get that mark prematurely with a mechanical ejector.

I’m not a believer in that.
It takes pressure to get cartridge brass to flow and I’ve never had a normal load show marks including my biggest magnum than I know is spicy(67-68K psi?) in my mechanical ejection action.

 

[Clancy]

I’m not a believer in that.
It takes pressure to get cartridge brass to flow and I’ve never had a normal load show marks including my biggest magnum than I know is spicy(67-68K psi?) in my mechanical ejection action.

I could very well be wrong, always best to go with the most cautious approach

 

[DB_23]

Your head expansion should not be more than .001". Go to the Hodgdon website and see instructions on measuring head diameter, expansion, and pressure. At .467" you're at .002" of expansion according to your numbers.

 

[DB_23]

I was measuring at a arbitrary place on the case web. Measuring at the junction of the extractor groove and the body I get .468 and .468. According to articles, my digital caliper doesn't have enough resolution for the job.

 

[SKWERLZ]

I could very well be wrong, always best to go with the most cautious approach

You’re not going to see the effects of pressure fully on film without super slow motion and sensors.