7mm Berger 180 Hybrid twist rate help

[jsimonh]

Thanks for the great responces guys.

I'll be shooting 50 of these Hybrids on Sunday. I've got several different powder/primer loads to try.

Running the Miller calculator gives me a stability of 1.31 when I run it for what the conditions are supposed to be. Can either of you guys point me in a direction on what is the bare minimal stability number that'll work?

I've read everything I could find and the number that seems to be the most prevelant is 1.4 at standard conditions. Most of my shooting will be done in the 1.150-1.3ish conditions. I know that the best way is just to shoot them and see what happens (which I will), but I'm just curious if anyone has experience with stability just above 1.

Thanks again.

 

[jsimonh]

Well, I finally had some good luck. Pretty much every load I tried shot under 1 moa at 100 and 300 yards with no signs of instability.

Best load at 100 was .43 with
Fed 215's
66gr Retumbo
Norma Brass
180 Hybrid

Best load at 300 was 1.87 with
Fed 215's
67gr Retumbo
Norma Brass
180 Hybrid

I also shot WLR primers and the results were right on par with what I was getting with the 215's. I wish I could find some GM215M to try.

I've got some CCI BR2's, but I'm not sure about lighting 67gr of Retumbo with such a mild primer.

Any thoughts on any of this?

 

[groper]

Well so long as your stability factor is above 1.1 then the bullets will fly... sometimes however, with very low stability factors close to 1.0, many people have observed poor accuracy just prior to the bullets tumbling. I dont entirely understand why this happens, as according to much research (including bryan litz`s publications) the larger epicyclic yaw angles cannot induce anywhere near this much dispersion, not from just the large yaw angle alone.

By far the biggest influence on dispersion, seems to be projectile muzzle jump - which contains many elements within it, including bore axis alignment and in bore balloting, projectile concentricity, projectile center of gravity axial alignment is a large factor, barrel vibration/movement and more...

Accuracy and projectile stability are 2 very different things, and although sometimes they seem to go hand in hand, it may not be for reasons relating to each other...

As far a stability goes, the industry standard seems to beleive the ideal stability factor to be 1.49... i think anything above 1.2 can work fine depending on your individual rifle system, just dont expect it to work when the weather turns and gets very cold etc. For example, the .375 cheytac system using the 350gr Lost river copper alloy solids from their 1:11.5 barrel has a stability factor of ~1.2 in a std atmosphere at sea level...

 

[Good]

Well, I finally had some good luck. Pretty much every load I tried shot under 1 moa at 100 and 300 yards with no signs of instability.

Best load at 100 was .43 with
Fed 215's
66gr Retumbo
Norma Brass
180 Hybrid

Best load at 300 was 1.87 with
Fed 215's
67gr Retumbo
Norma Brass
180 Hybrid

I also shot WLR primers and the results were right on par with what I was getting with the 215's. I wish I could find some GM215M to try.

I've got some CCI BR2's, but I'm not sure about lighting 67gr of Retumbo with such a mild primer.

Any thoughts on any of this?

Do you know your velocity with this load? I just picked up my first Savage (WOOHOO!!!) to use the action for a build and it's a 110, 7mm Rem Mag ($199 at the local pawn shop). I cleaned it up real good and lightened the trigger so we'll see what she can do soon. Nearest I can tell, it has a 1-9 1/4 twist and I'm not sure if I'm going Retumbo or H-1000 yet, but I'd like to shoot these 180s until the build. I wonder which of these powders fills the case closer to 100% at around 2900fps... gun)

 

[jsimonh]

Your Savage will probably have a 9.5 twist as nearly all factory Savages do.

I'm using 67gr of Retumbo which doesn't feel the case to full capacity but it gets me about 2875 and excellent accuracy. I've never tried H1000 although I here it's and excellent choice for the 7 mag.

This last Sunday I took 40 rounds loaded with
67gr Retumbo
Fed 215's
Norma Fire formed brass
Berger 180 Hybrids seated .015 off the lands

I only shot one group at 600yds and it measured 4". I spent the rest of the day shooting at 850 with good results. I still need more practice, but I think the load is about as good as its gonna get.

 

[schwabdog]

Before it slips my mind, here is a load from a recent client's Sendero:

Win Case
Federal 215 large magnum rifle primer
180gr Berger VLD seated to COAL of 86.8mm (bullet jump 1mm/40 thou)

ADI 2217 (H1000) powder.



Final load:

70.5 grains 2217/ H1000.

Velocity 2925fps.

Shot to shot max deviation 10fps.
Groups sub .25"


Like I say, twist rate is 1:9.25. You'll need to check the reloading manuals before trying to duplicate the above as it will most likely be above maximum and your rifle may well have different bore tolerances. These loads were safe in this rifle, client has probably neck sized and reloaded the cases around 5 times by now.



Good luck with your tests.

I know this is of topic but: I just got a 7mm rem mag and im looking for a good powder is ADI 2217 the same as H1000) powder?? only because the ADI 2217 is easy to get in Australia

 

[rifletuner]

I know this is of topic but: I just got a 7mm rem mag and im looking for a good powder is ADI 2217 the same as H1000) powder?? only because the ADI 2217 is easy to get in Australia

Yes, H1000 and AR2217 are one and the same powder, made by ADI.

 

[sport20]

i am having very bad grouping with my sendero 7mm mag. i've tried alot of bullets but not the 180 vlds. could this solve my problem