7mm Rem Mag, Accuracy, and COAL Questions

Shadowstalker · June 23, 2010, 04:29 PM

I was hoping someone could help with some other questions as I'm still very much a newbie. Heres what I'm using and done so far:
Savage 114 w/ Accutrigger and 1 in 9.5 twist, 24" barrel
Barnes 120g, 140g, and 150 g Tipped T ripple Shocks
Different (all under max) charges of IMR 4831, H4831, and H1000
Once Fired FL sized and trimmed to 2.493 +/- .002
COAL was 3.225 +/- .002
Loaded up 4 of each, shot and marked, let barrel cool, repeat (my wife thought I moved out), and found at least 1 load in each that the rifle liked more than others

After reading a couple of recent threads and doing a couple of searches; I inserted several 140g bullets into a fired brass and GENTLY closed the bolt to find the max OAL (or whatever the correct term is) and found and average was about 3.376.
If I use the loads that gave me the most accuracy, how much will my grouping open or close (hopefully close) up by varying the COAL. I've seen several recommendations of .030 less than the max OAL. That would give me 3.346 which is .006 longer than what Barnes call for; and a full .121 longer than what I shot my other rounds.
Is the 3.340 written in stone (assuming my magazine will hold them)?
Should I have gone about it differently?
Other than gaining experience, I'm hoping everything I've done to this point hasn't been a waste of bullets, powder, and time. Any other tips would be greatly appreciated.
Thanks in Advance

mehavey · June 23, 2010, 04:56 PM

Unless you use the Hornady (Stoney Point) gauge,...

http://www.midwayusa.com/viewproduct...tnumber=570611

...precisely determining the max OAL of an cartridge wherein the bullet is reliably up against the rifling is quite difficult. In the "old days" we used to use the "smoked bullet" method, but that was proven to be grossly unpredictable.

We also used to use the method you mention: use a very slightly resized neck to barely friction fit/push a bullet into the case when chambered and measure OAL when withdrawn. But that proved imprecise as well because the rifling could/would/might engage the bullet just enough to slightly pull on it when the bolt was pulled back -- resulting in a measured max OAL that was too long. (bad juju.)

If you don't have the Hornady gauge, the next best thing is a variation on the cleaning rod method mentioned in the 30-06 Cartridge Length subject string earlier today. http://thefiringline.com/forums/showthread.php?t=414132

But... to use this to any degree of safety if you are going to actually try to approach the rifling requires a digital caliper.

Do you have one?

Adjusting the best distance off the lands from that point is an art -- and purely experimental: Progressive trial & error with increasing distance off the lands/take the best after shooting multiple groups.

RWJOHN · June 24, 2010, 04:10 PM

I've been waiting for the guru's to chime in here. I'm thinking it's a typo but your C.O.L. of 3.340 is incorrect. The Barnes site list's a C.O.L. of 3.240, which you mentioned in another thread, for the style bullet you are using.
Your initial loadings mimicking the factory Federal Premium measurements was a good place to start. How did they perform?

I believe when you checked C.O.L. using fired brass the bullet was pulled out slightly as Mehavey mentioned. I use a fully resized case when I do this.

My initial reloading efforts with the 7MM mag was a nerve wracking experience for me. I used 160g Nosler Partitions and 175g Speer Mag-Tips. The C.O.L. difference between these two bullets had me scratching my head and puckering up when I pulled the trigger.

If the Barnes bullets don't meet your expectations I would recommend the Partition. My Ruger Model77 likes IMR 4831 and the 160g Nosler. I recently loaded some 162g Hornady BTSP with RL-22, neither of which I've ever tried. I'm anxious to compare these against the Partitions in terms of accuracy.

Peace

Shadowstalker · June 24, 2010, 06:51 PM

I was hoping the gurus would as well. Yes, it was a typo the COAL is 3.240.
I ended up with my best grouping using the H4831. With the 120g I found 2 loads (1 above min, and 1 just below max), that I got between 1/2" and 5/8" MOA groups with. With the 150g I found 1 load about 2 below max, that I got 1/2" MOA.
I varied those loads by .5 g of powder as I wasn't sure if I should go less or more than those variations.
Last night I made duplicate loads of 150g TTSX using H1000; with one group at 3.225 and the other at 3.245. I'm going to try and get to the range this weekend and see how the groups vary.

flashhole · June 25, 2010, 07:28 PM

Don't know that I'm in the guru category but I've had good success seating a flat base bullet in the case backwards and doing just what you described above. It tells you where the lands are because it can't go into them.

June 23, 2010, 04:29 PM	#1
Shadowstalker Member Join Date: April 2, 2010 Location: Tualatin, OR Posts: 26	7mm Rem Mag, Accuracy, and COAL Questions I was hoping someone could help with some other questions as I'm still very much a newbie. Heres what I'm using and done so far: Savage 114 w/ Accutrigger and 1 in 9.5 twist, 24" barrel Barnes 120g, 140g, and 150 g Tipped T ripple Shocks Different (all under max) charges of IMR 4831, H4831, and H1000 Once Fired FL sized and trimmed to 2.493 +/- .002 COAL was 3.225 +/- .002 Loaded up 4 of each, shot and marked, let barrel cool, repeat (my wife thought I moved out), and found at least 1 load in each that the rifle liked more than others After reading a couple of recent threads and doing a couple of searches; I inserted several 140g bullets into a fired brass and GENTLY closed the bolt to find the max OAL (or whatever the correct term is) and found and average was about 3.376. If I use the loads that gave me the most accuracy, how much will my grouping open or close (hopefully close) up by varying the COAL. I've seen several recommendations of .030 less than the max OAL. That would give me 3.346 which is .006 longer than what Barnes call for; and a full .121 longer than what I shot my other rounds. Is the 3.340 written in stone (assuming my magazine will hold them)? Should I have gone about it differently? Other than gaining experience, I'm hoping everything I've done to this point hasn't been a waste of bullets, powder, and time. Any other tips would be greatly appreciated. Thanks in Advance

June 23, 2010, 04:56 PM	#2
mehavey Senior Member Join Date: June 17, 2010 Posts: 1,997	Unless you use the Hornady (Stoney Point) gauge,... http://www.midwayusa.com/viewproduct...tnumber=570611 ...precisely determining the max OAL of an cartridge wherein the bullet is reliably up against the rifling is quite difficult. In the "old days" we used to use the "smoked bullet" method, but that was proven to be grossly unpredictable. We also used to use the method you mention: use a very slightly resized neck to barely friction fit/push a bullet into the case when chambered and measure OAL when withdrawn. But that proved imprecise as well because the rifling could/would/might engage the bullet just enough to slightly pull on it when the bolt was pulled back -- resulting in a measured max OAL that was too long. (bad juju.) If you don't have the Hornady gauge, the next best thing is a variation on the cleaning rod method mentioned in the 30-06 Cartridge Length subject string earlier today. http://thefiringline.com/forums/showthread.php?t=414132 But... to use this to any degree of safety if you are going to actually try to approach the rifling requires a digital caliper. Do you have one? Adjusting the best distance off the lands from that point is an art -- and purely experimental: Progressive trial & error with increasing distance off the lands/take the best after shooting multiple groups. Last edited by mehavey; June 23, 2010 at 06:50 PM.

June 25, 2010, 07:28 PM	#5
flashhole Senior Member Join Date: February 9, 2005 Location: Owego, NY Posts: 1,110	Don't know that I'm in the guru category but I've had good success seating a flat base bullet in the case backwards and doing just what you described above. It tells you where the lands are because it can't go into them. __________________ Gun control is hitting what you aim at..

June 24, 2010, 04:10 PM	#3
RWJOHN Member Join Date: May 4, 2010 Location: NC & SC Posts: 41	I've been waiting for the guru's to chime in here. I'm thinking it's a typo but your C.O.L. of 3.340 is incorrect. The Barnes site list's a C.O.L. of 3.240, which you mentioned in another thread, for the style bullet you are using. Your initial loadings mimicking the factory Federal Premium measurements was a good place to start. How did they perform? I believe when you checked C.O.L. using fired brass the bullet was pulled out slightly as Mehavey mentioned. I use a fully resized case when I do this. My initial reloading efforts with the 7MM mag was a nerve wracking experience for me. I used 160g Nosler Partitions and 175g Speer Mag-Tips. The C.O.L. difference between these two bullets had me scratching my head and puckering up when I pulled the trigger. If the Barnes bullets don't meet your expectations I would recommend the Partition. My Ruger Model77 likes IMR 4831 and the 160g Nosler. I recently loaded some 162g Hornady BTSP with RL-22, neither of which I've ever tried. I'm anxious to compare these against the Partitions in terms of accuracy. Peace

June 24, 2010, 06:51 PM	#4
Shadowstalker Member Join Date: April 2, 2010 Location: Tualatin, OR Posts: 26	I was hoping the gurus would as well. Yes, it was a typo the COAL is 3.240. I ended up with my best grouping using the H4831. With the 120g I found 2 loads (1 above min, and 1 just below max), that I got between 1/2" and 5/8" MOA groups with. With the 150g I found 1 load about 2 below max, that I got 1/2" MOA. I varied those loads by .5 g of powder as I wasn't sure if I should go less or more than those variations. Last night I made duplicate loads of 150g TTSX using H1000; with one group at 3.225 and the other at 3.245. I'm going to try and get to the range this weekend and see how the groups vary.