activeviii Posted March 11, 2017 Report Share Posted March 11, 2017 Just a quickie, trying to find the G7 on the Sierra tmk 130gn, 6.5mm by?Let's. It can't find required information. Anyone able to shed some light Please. Thanks Phil Link to comment Share on other sites More sharing options...
BlueBoy69 Posted March 11, 2017 Report Share Posted March 11, 2017 Hi Phil, Sierra don't normally publish G7 drag coefficients, only G1. These can be looked up here (webpage) and here (PDF). Yeah, not much use as the are all G1, but there is a conversion programme on the JBM ballistics page which can be found here (link). Not sure how accurate the conversion is? Neil Link to comment Share on other sites More sharing options...
activeviii Posted March 11, 2017 Author Report Share Posted March 11, 2017 i'll give it a go and see. thanks for that. Phil Link to comment Share on other sites More sharing options...
gbal Posted March 11, 2017 Report Share Posted March 11, 2017 Phil,Blueboy is right,of course-Sierra give the three G1values for three velocity bands(more than most give!!) Applied Ballistics (Litz) G7 BCs for Sierra 6.5 130 TMK bullet seem elusive-maybe not tested yet? When AB did test the 308 bullets,they found some differnces in G1s....and not consistent,alas: 125g Sierra G1 average .338 AB G1 .343 G7 .176 1% diff 155 Sierra G1 average .476 AB G1 .464 G7 .237 -3% 175 Sierra G1 average .523 AB G1 .522 G7 .267 0% So,until there is actually an AB G7test,only a fair ball park figure can be extrapolated for 6.5 bullet,the link Blueboy gives will do so,and a ball park figure for G7 seems likely to be about 1/2 the Sierra G1 Averages...at least to the second decimal place/maybe .005..... ...which might help meanwhile....got to be better than JUST using the best G1 which most manufactures give.... ...and,if only interested in performance to some range,use only (average) the Sierra G1s in those velocity bands...(eg velocity at 400 will still be well over 2000fps,by 800y more like 1500fps,and 1000y maybe 1250 fps-better input,means better output...even in second/third place decimals :-) gbal Link to comment Share on other sites More sharing options...
activeviii Posted March 12, 2017 Author Report Share Posted March 12, 2017 Thanks for that. I have give up with it for the day as my data chart is not working as should. back at it today with fresh eyes Using both. g7 and G1 makes little difference. will try and calm down get a better idea on whats going wrong. its the 800-100 where is all goes wrong. im giving up with electronic apps and that and going back to old school with pen paper, oh, and calculator on the phone.hehe Phil Link to comment Share on other sites More sharing options...
Big Al Posted March 12, 2017 Report Share Posted March 12, 2017 Just a quickie, trying to find the G7 on the Sierra tmk 130gn, 6.5mm by?Let's. It can't find required information. Anyone able to shed some light Please. Thanks Phil I would be more concerned with getting the 130 TMK's to shoot well first. I know a lot of good shooters who have struggled to get good repeatable results with these bullets, even an email to Sierra didn't help. If you are getting small groups that are repeatable then please share your info, I know a lot of guys who would be interested Phil. Link to comment Share on other sites More sharing options...
activeviii Posted March 12, 2017 Author Report Share Posted March 12, 2017 I would be more concerned with getting the 130 TMK's to shoot well first. I know a lot of good shooters who have struggled to get good repeatable results with these bullets, even an email to Sierra didn't help. If you are getting small groups that are repeatable then please share your info, I know a lot of guys who would be interested Phil. I will put up the details later, in fact i think i did a while ago. RS62 42.1gn cci Primer Lapua large primed case(308 formed) 130tmk seated 5 thou off 28" bartlain/T3 built by Neil Mckillop. shooting good!. i Think Gunner on here has seen how well this rifle and bullet combo works. its taken a long long time and a lot of rounds but it shoots under 1" at 300 I have found what is going on today. Gunner and i spent the day scratching our heads as to what was going on. in the end we ran a 20moa box test on the scope. Hello. i Bought a knackered scope. with me not being able to do much, plus a new calibre rifle with all sorts of problems with brass and lack of data i never thought of checking the scope. didnt think it would be much an issue. So, i have no receipt, it came from Aimsports but no proof so not sure what to do now. wish i could afford high end but thats not going to happen. i can use a vortex viper for now but it doesn't have the 70moa travel like this S111 Link to comment Share on other sites More sharing options...
gbal Posted March 12, 2017 Report Share Posted March 12, 2017 Bummer with the scope Only consolation is that in the larger picture,equipment failure is less catastrophic than maths -and all based thereon-going random walkabouts! gbal Link to comment Share on other sites More sharing options...
gunner Posted March 12, 2017 Report Share Posted March 12, 2017 No doubt your rifle has great potential , just let down by scope , easily sorted now tho and we can get proper repeatable dope chart next time ! Atb Link to comment Share on other sites More sharing options...
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