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Post by onthedivide on Apr 30, 2017 16:14:12 GMT -8
I'm trying to understand which chambers are more efficient. More velocity with less pressure in the ar 15 format or even a bolt rifle. Also as it relates to bore size. Which is faster with less pressure, the 243 LBC or the 264 LBC? Which is faster with lower pressure the 260 Rem or 6.5 Creedmore? What are the considerations in chamber shape? The angle of the shoulder? Also how does this relate to barrel life assuming that one is loading for max performance?
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Post by GLSHOOTER on May 1, 2017 7:19:22 GMT -8
I'm trying to understand which chambers are more efficient. More velocity with less pressure in the ar 15 format or even a bolt rifle. Also as it relates to bore size. Which is faster with less pressure, the 243 LBC or the 264 LBC? Which is faster with lower pressure the 260 Rem or 6.5 Creedmore? What are the considerations in chamber shape? The angle of the shoulder? Also how does this relate to barrel life assuming that one is loading for max performance? Faster with less pressure, same size bore, will always go to the bigger case. This is because it will use more powder hence generating more gas for push. Loaded to SAME pressure the bigger case will always be faster. Simple physics. Day in day out the little guys are more efficient but not as fast. That being said you can often run the little ones at higher pressure because of bolt thrust and jump up to bigger case speeds. The A-30 will out run a 30-30, same bullet, because while it uses less powder the pressure is much higher in it vs. the old dog. The 243 LBC vs. the 264 LBC don't cross over much in bullet weight. This skews numbers. The 6.5 has less bearing surface than the 243 for a same weight bullet and should, theoretically, go faster than the 243 version at less pressure. The case capacity variation is negligible between the two. The 260 will match the Creed at lower pressure. Once again cubic inches rule. Chamber shape? Variation in neck diameter vs. case thickness will cause some change, longer throats will automatically lower pressures when loaded same length one vs. the other, leaded angel of 1.5 vs. 3 degrees will change pressure curves sharper is worse for pressure. Shoulder angle means nothing if capacity remains the same for speeds. It does help on case stretch in some versions. Shoulders make no difference in barrel life. Barrel life is more determined by quantity of powder used, pressure of the load and the powder choice as some burn much cooler than others. We see this in the big boomers a great deal. A 20 Practical will go 2,000 plus rounds, documented and still going, whereas a 20-250 MIGHT go 800 or so. Same bullet but 75%, estimated, great powder burned and torching down that hole. Not good for colony shooting. Barrels are consumable. MAX Performance? That is pretty nebulous. Warm or paper targets, Close or out yonder at 1000? Speeds eats barrels plain and simple. Different bullets will even wear a barrel faster. Monolithic bullets will probably decrease barrel life and we know steel sure will. That ought to give you some cogitating material. Greg |
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Post by onthedivide on May 1, 2017 12:42:13 GMT -8
Thank you, Greg, for spending so much time on your reply. I'm new to this, as you probably guessed. I do shoot a GAP bolt rifle in rem 260 and am just starting to reload for it. I'm able to get about 3/8 moa at 300 yards sometimes. That's with Nosler factory ammo. I'm working on load development. I'm also building an AR15 and am trying to decide on which cartridge to use. So I haven't ordered the barrel yet. I want an accurate flat shooting gun to hunt deer up to about 400 yards. So I need good terminal ballistics. I'm thinking 264 LBC or 243 LBC. I don't want to be pushing pressures to the limit in the AR, don't want to worry about things breaking. This gun will also be used for shooting targets so I want it to be better than I am. I would like to hear any ideas on the matter. Thanks.
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Post by GLSHOOTER on May 1, 2017 15:08:55 GMT -8
Based on your screen name I'm assuming the West with mulies? If so then I would go 264 LBC. If I were doing swamp land 90 pound Georgia deer I'd shoot a 243 LBC.
Always glad to share my opinions, Ritch, the other ADMIN, on here is also a wealth of information and will chime in at times. He likes me to do most of the answers since I am retired and he's still busy putting food on the table. I don't eat...lol
Greg
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Post by onthedivide on May 1, 2017 19:58:14 GMT -8
Yes, I'm in Colorado. We have two hunt camps at 9,000 and 10,000 feet. Great mule deer country, elk as well. Some long shots, 400 to 500 yards, and a lot of much shorter opportunities less than 100 yards. I have loved the 270 for decades and now the 260. I'm going to order the 264LBC for my AR for the aspen groves and the fur forest. I can hardly wait.
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Post by GLSHOOTER on May 1, 2017 20:41:33 GMT -8
An excellent choice for that setting.
Greg
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Post by onthedivide on May 2, 2017 5:57:35 GMT -8
Greg,
tell me about clambering the 264 LBC. Given the magazine length restriction, what is it 2.3"?, what does that mean for throat length and then bullet choice. I'd like to use 123 to 130 grain bullets in the high bc shapes. Is that a standard chamber that Rich uses or are there options? What about finding the best seating depth for those bullets and still be within the mag. restrictions.
thanks.
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Post by GLSHOOTER on May 2, 2017 6:11:31 GMT -8
The ASC will go 2.314 or so. More options for seating depth. The chambers will handle anything you propose. One chamber does it all very well. Look around and you will find great results even with the factory ammunition.
Greg
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Post by cosh on May 2, 2017 13:47:01 GMT -8
I cut the plastic tip off the Hornady and Nosler bullets (is that strange?) and get maybe .010 to .020 inches. I thought, at the range I would use it for medium game no worry with a little BC loss. I think I would 6.5x55 Swede for long shots.
I have not thought of the AR in my elk hunting group. LOL.
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Post by GLSHOOTER on May 2, 2017 14:58:51 GMT -8
Not strange but probably not necessary.
Greg
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Post by cosh on May 4, 2017 12:37:15 GMT -8
Ran Load From A Disk calculations. Only 12 fps estimated difference in velocity using H335 powder. I guess nothing gained unless accuracy with ogive more in the throat.
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Post by GLSHOOTER on May 4, 2017 12:41:53 GMT -8
Ran Load From A Disk calculations. Only 12 fps estimated difference in velocity using H335 powder. I guess nothing gained unless accuracy with ogive more in the throat. I use QL too. It does pretty well but once in a while it is so far off as to be laughable. Greg |
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