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Effects Of Cartridge Over All Length (COAL) And Cartridge Base To Ogive (CBTO) – Part 1
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<blockquote data-quote="Carbine Kid" data-source="post: 1046206" data-attributes="member: 59686"><p>G'day Crashman1.</p><p> </p><p>You have a good rig there & as you have the reamer I would use it.</p><p> </p><p>When I set up my 6-284 I gave my gunsmith a dummy round with a Lapua Scenar 108 gn loaded with the base of the boatail level with the neck sholder junction specifically to gain max case capacity. At this length there was sufficient bullet shank in the neck to turn the necks (.270 neck in chamber) for a 2 tho grip.</p><p>I used an old 25-06 so mag length would not be an issue and checked feed before laying down the $$. As the Sierra 107 HP.BT. MK. was almost identical to the Lapua I could use either.</p><p> </p><p>A nominal jump of .030 was used to work up max loads for AR 2213sc, AR 2217, AR 2225, RL 22 & RL 25. Necked down & turned Lapua 6.5-284 cases & Fed GMM primers for ignition.</p><p>Temperatures in Oz vary from 0*c in Sambur country to 45*c (113*f) outback. As this rifle was for outback work I had the same consideration as you re. Temp stability. Ultimately the loads that gave the best average groups were chosen and then OAL's were increased.</p><p>I have been told VLD projectiles like to be in the lands and .010 in is where the Lapua's grouped best.</p><p> </p><p>- 47gn AR2213sc gave .35" groups @ 2995fps av & 65fps ES @ 86*f</p><p>-50.5gn RL 25 gave 1.1" groups @ 2986fps av & 9fps ES @ 86*f</p><p>-50 gn RL 22 gave .66" groups @ 3172fps av & 43fps ES @ 86*f</p><p>all shot ay 100m. and RL22 chosen.</p><p> </p><p>Lapua & Berger supplies in Oz are unreliable so Sierra 105 HP.BT.MK. were tried with the same procedure as above with RL22 being chosen. However when increasing OAL everything went smoothly as expected until the last increase to a .010 jam. The bolt was very hard to lift & when the case head was miked I had a 3 tho case head expansion and primers falling out. Hmmm, didn't expect that so suddenly.</p><p>The load ultimately chosen to use up the remaining powder was.</p><p>- 46.5gn. RL22 gave .95" @ 3081fps av & ES 36fps @ 95*f with a jump of 15tho. ie. 25tho different to the Lapua's</p><p> </p><p>OAL increases for AR2213sc was done due to the "sudden" pressure spike with RL22. Again 15tho was the best jump.</p><p>The final load chosen was 47.5gn AR 2213sc @ 2998fps av & ES 22fps @ 106*f. which has given sub 1" @ 300m on a zero wind day.</p><p> </p><p>I have been told by a friend who has some Berger hybrids that OAL is not critical & they shoot well up to .065 off the lands.</p><p>IME all Australian Defence Industries powders are very consistent across a large temp range. Just work up loads in the hottest temp you expect to shoot in then there will be no surprises.</p><p> </p><p>The xtra velocity from increased case capacity will be worth wile if you don't mind looking for the new sweet spot. In reality the reason we reload is to get the ultimate from our custom equipment.</p><p> </p><p>Action & stock is x Rem Sendero 25-06 accurised & bedded.</p><p>Lapua 6.5-284 necked to 6-284 & turned for a .270 neck</p><p>TruFilght 1:8 twist 28" with Sendero profile.</p><p>Fed gold medal match primer.</p><p>Sierra 107 HP.BT.MK.</p><p>ADI. AR 2213sc</p><p> </p><p>Keep well.</p><p>Steve.</p></blockquote><p></p>
[QUOTE="Carbine Kid, post: 1046206, member: 59686"] G'day Crashman1. You have a good rig there & as you have the reamer I would use it. When I set up my 6-284 I gave my gunsmith a dummy round with a Lapua Scenar 108 gn loaded with the base of the boatail level with the neck sholder junction specifically to gain max case capacity. At this length there was sufficient bullet shank in the neck to turn the necks (.270 neck in chamber) for a 2 tho grip. I used an old 25-06 so mag length would not be an issue and checked feed before laying down the $$. As the Sierra 107 HP.BT. MK. was almost identical to the Lapua I could use either. A nominal jump of .030 was used to work up max loads for AR 2213sc, AR 2217, AR 2225, RL 22 & RL 25. Necked down & turned Lapua 6.5-284 cases & Fed GMM primers for ignition. Temperatures in Oz vary from 0*c in Sambur country to 45*c (113*f) outback. As this rifle was for outback work I had the same consideration as you re. Temp stability. Ultimately the loads that gave the best average groups were chosen and then OAL's were increased. I have been told VLD projectiles like to be in the lands and .010 in is where the Lapua's grouped best. - 47gn AR2213sc gave .35" groups @ 2995fps av & 65fps ES @ 86*f -50.5gn RL 25 gave 1.1" groups @ 2986fps av & 9fps ES @ 86*f -50 gn RL 22 gave .66" groups @ 3172fps av & 43fps ES @ 86*f all shot ay 100m. and RL22 chosen. Lapua & Berger supplies in Oz are unreliable so Sierra 105 HP.BT.MK. were tried with the same procedure as above with RL22 being chosen. However when increasing OAL everything went smoothly as expected until the last increase to a .010 jam. The bolt was very hard to lift & when the case head was miked I had a 3 tho case head expansion and primers falling out. Hmmm, didn't expect that so suddenly. The load ultimately chosen to use up the remaining powder was. - 46.5gn. RL22 gave .95" @ 3081fps av & ES 36fps @ 95*f with a jump of 15tho. ie. 25tho different to the Lapua's OAL increases for AR2213sc was done due to the "sudden" pressure spike with RL22. Again 15tho was the best jump. The final load chosen was 47.5gn AR 2213sc @ 2998fps av & ES 22fps @ 106*f. which has given sub 1" @ 300m on a zero wind day. I have been told by a friend who has some Berger hybrids that OAL is not critical & they shoot well up to .065 off the lands. IME all Australian Defence Industries powders are very consistent across a large temp range. Just work up loads in the hottest temp you expect to shoot in then there will be no surprises. The xtra velocity from increased case capacity will be worth wile if you don't mind looking for the new sweet spot. In reality the reason we reload is to get the ultimate from our custom equipment. Action & stock is x Rem Sendero 25-06 accurised & bedded. Lapua 6.5-284 necked to 6-284 & turned for a .270 neck TruFilght 1:8 twist 28" with Sendero profile. Fed gold medal match primer. Sierra 107 HP.BT.MK. ADI. AR 2213sc Keep well. Steve. [/QUOTE]
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