determing twist rate and optimum velocity 7mm bore

[JackT]

Crusty I have a 7 mm Br with a 9 twist barrel Kreiger # 4 contour. The Speer TNT, Barnes 120TTSX, and Berger 140 VLD Hunting consistently deliver sub 0.5" 10 shot groups. I use H322 for the Speer TNT and H4895 for the Barnes and Berger loads. If you have Power Point on your computer I can send you a file with the printouts on the specifics of the loads. While my loads tend to be on the lighter side, it could prove to be a good starting point for you.

I could (I think) also convert them to Pdf file if that would help.

 

[Dusty Stevens]

Crusty I have a 7 mm Br with a 9 twist barrel Kreiger # 4 contour. The Speer TNT, Barnes 120TTSX, and Berger 140 VLD Hunting consistently deliver sub 0.5" 10 shot groups. I use H322 for the Speer TNT and H4895 for the Barnes and Berger loads. If you have Power Point on your computer I can send you a file with the printouts on the specifics of the loads. While my loads tend to be on the lighter side, it could prove to be a good starting point for you.

I could (I think) also convert them to Pdf file if that would help.

1/2” 10shot groups from a #4 barrel is astounding

 

[mikecr]

OP, you're lost as a nine-eyed dog..
Fire form your brass, pick a bullet, develop a load for it.
Stop worrying about twist

 

[crustyrusty]

OP, you're lost as a nine-eyed dog..
Fire form your brass, pick a bullet, develop a load for it.
Stop worrying about twist

well hell,,, so I would have to agree.....so I am gonna start with the 100gr exclusivley and finish fireforming my brass and move on from there.....

 

[dmoran]

@crustyrusty
My advice is to listen to @mikecr
Personally have never been burned by spinning bullets faster in fast twist barrels, but have been with to slow of twist barrels.

 

[crustyrusty]

Crusty I have a 7 mm Br with a 9 twist barrel Kreiger # 4 contour. The Speer TNT, Barnes 120TTSX, and Berger 140 VLD Hunting consistently deliver sub 0.5" 10 shot groups. I use H322 for the Speer TNT and H4895 for the Barnes and Berger loads. If you have Power Point on your computer I can send you a file with the printouts on the specifics of the loads. While my loads tend to be on the lighter side, it could prove to be a good starting point for you.

I could (I think) also convert them to Pdf file if that would help.

I have no idea what on my computer all I know is its windows 10 and with whatever comes with it but I would love to see your data.....

 

[Zero333]

I had 6mm 80 gr Berger Varmint blow up in my 8" twist 243win.

I'm responsible for giving the op the idea that maybe the lightweight 7mm bullets might be disliking the 9" twist.

 

[crustyrusty]

thats ok zero I have

I had 6mm 80 gr Berger Varmint blow up in my 8" twist 243win.

I'm responsible for giving the op the idea that maybe the lightweight 7mm bullets might be disliking the 9" twist

Thats ok Zero I am past all that panic and its all good.. after reading several different articles about twist I know I am good to go with what I have.... however If I do do a do over I will switch to a 1-12 twist to stay in the 100gr thru 145gr family and upgrade to a high quality barrel and not a economy barrel that I chose to go with. My major malfunction is eventho I have reloaded for what seems like forever I have never got into this kind of reloading where you start from scratch and build loads to gain to form and function and accuracy....so yes I am a little lost and need all the help I can get.....

 

[geo.ulrich]

@crustyrusty
My advice is to listen to @mikecr
Personally have never been burned by spinning bullets faster in fast twist barrels, but have been with to slow of twist barrels.

Donovan, This thread is a spin off where poster was complaining about accuracy using light weight 7 mm's .....

 

[crustyrusty]

Thanks guys for letting me vent, huff n puff hyperventilate and in general get all worked up basically over nothing So now I am being schooled in actual load development.....as this "type of reloading" is new to me and principals like OCW all I got to say is thank god for You Tube. I am learning that when you make new cases out of old cases things sometimes dont align up right and it may take 2-3 fire-formings to get things right the biggest challenge is figuring out where to start the load process(((now I know that I cant hurt the bullet out of my 1-9 barrel))and know where to stop(that I do know!!) so if I can have your knowledge on tap I am sure to have a success story for sure

 

[JackT]

Crusty the Speer TNT load used 31.1 gns of H322 and delivered a MV of 2672 out of a 22" barrel. I set the load up as a minimum pressure load to form brass while breaking in the barrel. It proved to be truly a powder puff load. Needless to say, lots of room for increasing MV.

The Barnes TTSX load used 30.8 and of H322 and delivered a MV of 2684. According to Quickload maximum chamber pressure was 52000psi. Another load with room to increase MV.

The Berger 140 VLD Hunting load used 31.5 gns of H4895 and delivered a MV of 2550. According to QL maximum chamber pressure was 55000 psi; still room to increase MV. I had planned to use this load on an antelope hunt because it should be good for 400 yards. Ended up not taking the gun due to circumstances out of my control, settled for shooting a soft load in a 308 WIN.

I tried some other bullets that were not as consistent which just proves the point on not giving up if your first loads do not work out. Also learned that trying different primers can shrink the groups.

 

[chromatica]

Both Greenhill and Miller's formula's are way outdated. Like 50 + years in Greenhills case. Go to JBM or use Mcgyro they are from this era....

Went to the JBM website and looked up stability. Took me right to a calculator that implements the Miller stability formula...

 

[Ballisticboy]

Went to the JBM website and looked up stability. Took me right to a calculator that implements the Miller stability formula...

If you go to the downloads page there are a number of alternatives.

 

[geo.ulrich]

Went to the JBM website and looked up stability. Took me right to a calculator that implements the Miller stability formula...

You might want to look again, as said there are way more up to date programs. I use a different one when I design bullets which is a cleaned up version of McCoys

 

[crustyrusty]

hey Geo. ulrich how far of base is that twist calculator that I initially posted earlier? I mean if its only about a 1/2 twist off how bad can that be? just go to the next whole lower twist....all good right?

 

[crustyrusty]

Crusty the Speer TNT load used 31.1 gns of H322 and delivered a MV of 2672 out of a 22" barrel. I set the load up as a minimum pressure load to form brass while breaking in the barrel. It proved to be truly a powder puff load. Needless to say, lots of room for increasing MV.

The Barnes TTSX load used 30.8 and of H322 and delivered a MV of 2684. According to Quickload maximum chamber pressure was 52000psi. Another load with room to increase MV.

The Berger 140 VLD Hunting load used 31.5 gns of H4895 and delivered a MV of 2550. According to QL maximum chamber pressure was 55000 psi; still room to increase MV. I had planned to use this load on an antelope hunt because it should be good for 400 yards. Ended up not taking the gun due to circumstances out of my control, settled for shooting a soft load in a 308 WIN.

I tried some other bullets that were not as consistent which just proves the point on not giving up if your first loads do not work out. Also learned that trying different primers can shrink the groups.

I have new load data to work out using H4895 and 145gr pills zero333 got me the QL data to go by so that is my new work up I will let you know how it turns out

 

[geo.ulrich]

hey Geo. ulrich how far of base is that twist calculator that I initially posted earlier? I mean if its only about a 1/2 twist off how bad can that be? just go to the next whole lower twist....all good right?

I ran both looks like 1.5 " all and all being equal. The one you used doesn't take into account nose length or meplat diameter which will affect b.c. and g.s. Program I used came in more conservative and is calculated to 1.5 s.g. I will add that somewhere along the line maybe late 80's the s.g number changed it was originally figured for 1.0 s.g was best but as programs improved 1.5 sg was used...

 

[crustyrusty]

The more modern formulas take in form factor closer to what we use now, in other words bullet length is not the only thing involved nose length or the length of nose radius , either more or less increases or decreases drag which changes sg...

George in this case what is SG? and how does it relate to bullet spin?

 

[geo.ulrich]

Gyroscopic stability longer bullet needs more spin

 

[crustyrusty]

ok that makes sense and it explains why those 175gr ELD's I had wouldn't stabilize in my rifle at a starting low velocity, which means low rpms if I understand correctly and even with the outdated millers equation it called for a twist of 1-8.5 for that same ELD bullet that I had so much trouble with