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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
7 mm SHERMAN SHORTMAG vs 7 SAUM
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<blockquote data-quote="Rardoin" data-source="post: 1945967" data-attributes="member: 114954"><p>First post. New 7SS Mag shooter. I decided to built an F-class rig around the long/heavy for caliber .284 offerings from Hornady (190 A-tip) and Berger (190 LRH). The latest LR F-class trend is going in the direction of .30 cal 215gr bullets using the .300 WSM cartridge; I don't want the recoil/percussion of that beast over 8 days of shooting and 350+ rounds. In discussions at our national last year a friend and I were discussing the 7 SAUM wildcat he was shooting that involved a set-back shoulder/body junction, longer neck, 40deg shoulder. He said it was easy to tune and the longer neck gave a little longer barrel accuracy life depending on powder. I had been struggling with keeping Berger 184's consistently in tune for 600/1000yd comps and found the case inadequate for the Berger 190's to perform to their best potential. John suggested not trying to reinvent the wheel and, if I wanted to pursue his cartridge, I should go with the 7 SS since it was nearly identical to his reamer design. The big advantage would be readily available reamers/brass/dies. I took his advice and chambered up a 7 SS mag using a rental reamer and throating it out with a throating reamer to accept a 190 A-tip with at least .030" of the base of the bearing surface above the neck/shoulder junction and still be at least 0.050 off the lands to give room for long jumps if that is what the load likes. The freebore ended up being a little over .300". I decided upon fireforming with the Berger 190 LRH's at 0.040" off lands/ 57.0gr H1000 based upon a fellow competitors use of 57.5gr H1000/ 184 Berger Hybrid in the same case. I shot 58/60 in under a .5" group at 100yds with the other two shots opening it up to .7"...not bad at all I figured, particularly since I had done essentially no charge development. I shot 5 charges with a 190 A-tip to get a velocity bracket then loaded up for a seat depth test from 0.010"-0.070" off the lands using a charge that was running right at 2700fps and shot it at 100yds. I repeated a fine seat depth test from 0.035-0.045" in 0.005" intervals and found 0.037" the sweet spot at 965yds. I then loaded a coarse charge weight test from 2600 fps to sweep through 2800 fps in .5gr increments using a 0.040" seat depth based on the prior test and shot it at 965yds. The charge of 60.0gr looks like the middle of a node at 2690 fps. I loaded up a fine charge test in .2gr intervals from 59.7-60.3gr. I had a brain fart and confused the first 3 shots of each group by grabbing from the wrong row so I ended up with 3 shot groups for the 4 test charges instead of 6 shots as planned<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite11" alt=":rolleyes:" title="Roll Eyes :rolleyes:" loading="lazy" data-shortname=":rolleyes:" />. Being I had a 1000yd match the next day and no time to test further I chose 60.2gr and loaded up 90rds. Over the complete match I had all of my 89 shots (60 record/29 sighters) at or under 10" of vertical which is pas bon but the windage on the A-tips was nothing short of phenomenal. I won the match with a 591-20X which is the second highest score at this very difficult range (Long Range Alley near Shreveport, LA). The second and third place guns were .300 WSM's running 215 Bergers around 2850 fps. The waterline of the WSM's were at/just over 5", which is excellent and where one strives to be for F-class and I think I can close the gap since I have only scratched the surface on load development. If this combination of bullet and very forgiving cartridge to tune pans out like I think it will I will have a rig that will have a ballistic advantage over the most common .300 WSM loads in wind hold as well as reduce recoil/percussion fatigue.</p><p></p><p>Robin</p><p></p><p>BTW... This set-up is with an 8.25 Bartlein 5-R 30" barrel. The BC of the 190 A-tip is accurate if not a bit conservative. My truing based on 1000yd and 865yd dial-ups under prevailing atmospheric conditions/velocity suggested a G7 closer to .43 vs published .422.</p><p></p><p>edited seating depth for the Atip to -0.037"....the 190 hybrid like -0.043"</p></blockquote><p></p>
[QUOTE="Rardoin, post: 1945967, member: 114954"] First post. New 7SS Mag shooter. I decided to built an F-class rig around the long/heavy for caliber .284 offerings from Hornady (190 A-tip) and Berger (190 LRH). The latest LR F-class trend is going in the direction of .30 cal 215gr bullets using the .300 WSM cartridge; I don't want the recoil/percussion of that beast over 8 days of shooting and 350+ rounds. In discussions at our national last year a friend and I were discussing the 7 SAUM wildcat he was shooting that involved a set-back shoulder/body junction, longer neck, 40deg shoulder. He said it was easy to tune and the longer neck gave a little longer barrel accuracy life depending on powder. I had been struggling with keeping Berger 184's consistently in tune for 600/1000yd comps and found the case inadequate for the Berger 190's to perform to their best potential. John suggested not trying to reinvent the wheel and, if I wanted to pursue his cartridge, I should go with the 7 SS since it was nearly identical to his reamer design. The big advantage would be readily available reamers/brass/dies. I took his advice and chambered up a 7 SS mag using a rental reamer and throating it out with a throating reamer to accept a 190 A-tip with at least .030" of the base of the bearing surface above the neck/shoulder junction and still be at least 0.050 off the lands to give room for long jumps if that is what the load likes. The freebore ended up being a little over .300". I decided upon fireforming with the Berger 190 LRH's at 0.040" off lands/ 57.0gr H1000 based upon a fellow competitors use of 57.5gr H1000/ 184 Berger Hybrid in the same case. I shot 58/60 in under a .5" group at 100yds with the other two shots opening it up to .7"...not bad at all I figured, particularly since I had done essentially no charge development. I shot 5 charges with a 190 A-tip to get a velocity bracket then loaded up for a seat depth test from 0.010"-0.070" off the lands using a charge that was running right at 2700fps and shot it at 100yds. I repeated a fine seat depth test from 0.035-0.045" in 0.005" intervals and found 0.037" the sweet spot at 965yds. I then loaded a coarse charge weight test from 2600 fps to sweep through 2800 fps in .5gr increments using a 0.040" seat depth based on the prior test and shot it at 965yds. The charge of 60.0gr looks like the middle of a node at 2690 fps. I loaded up a fine charge test in .2gr intervals from 59.7-60.3gr. I had a brain fart and confused the first 3 shots of each group by grabbing from the wrong row so I ended up with 3 shot groups for the 4 test charges instead of 6 shots as planned:rolleyes:. Being I had a 1000yd match the next day and no time to test further I chose 60.2gr and loaded up 90rds. Over the complete match I had all of my 89 shots (60 record/29 sighters) at or under 10" of vertical which is pas bon but the windage on the A-tips was nothing short of phenomenal. I won the match with a 591-20X which is the second highest score at this very difficult range (Long Range Alley near Shreveport, LA). The second and third place guns were .300 WSM's running 215 Bergers around 2850 fps. The waterline of the WSM's were at/just over 5", which is excellent and where one strives to be for F-class and I think I can close the gap since I have only scratched the surface on load development. If this combination of bullet and very forgiving cartridge to tune pans out like I think it will I will have a rig that will have a ballistic advantage over the most common .300 WSM loads in wind hold as well as reduce recoil/percussion fatigue. Robin BTW... This set-up is with an 8.25 Bartlein 5-R 30" barrel. The BC of the 190 A-tip is accurate if not a bit conservative. My truing based on 1000yd and 865yd dial-ups under prevailing atmospheric conditions/velocity suggested a G7 closer to .43 vs published .422. edited seating depth for the Atip to -0.037"....the 190 hybrid like -0.043" [/QUOTE]
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7 mm SHERMAN SHORTMAG vs 7 SAUM
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