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I am trying to find a muzzle velocity (or a range of speed) that make me sure a perfect stabilization from the projectile to 150 yards and that it also obtains good accuracy. I know that the accuracy is the result of many factors, but to begin I would need to know to which range of speeds I have to aim my rehearsals. The projectile that I use is sierra hpbt 168 grains, and thebarrel twist rate it's of 1:11 ,. Mi very bad English one prevents me to know how to stuff the data ===> http://www.eskimo.com/~jbm/ballistics/drag/drag.html can you help me please? =================== Sic Vis Pacem, Para Bellum. | ||
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The JBM site will give you the long answer, but I'll give you the short answer: Don't worry about it. In the real world, to 150 M, all you need to know is that you either have enough twist, or you don't. An 11 twist with 168 gr. bullets in a 308 caliber is fine. The only time twist makes a measurable difference is with poor quality bullets or at extreme long range. "Too much twist" is simply nothing you should worry about, at all. Too little twist will show up immediately as key-hole shaped bullet marks on the target. HTH, Dutch. Life's too short to hunt with an ugly dog. | |||
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ok. It is ok. But till where can I take down the velocity (2700, 2516, 2418....0) without lose any stability in this case? thanks a lott =================== Sic Vis Pacem, Para Bellum. | |||
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Oh, probably 1,500 fps (500 Mps) or less. Here's what happens. The faster the bullet leaves the barrel, the faster it spins around it's own axis. That increases the stability. Now, the faster a bullet moves through the air, the larger the "overturning moment", that is, the tendency to turn over. This DECREASES the stability of the bullet. The first effect is a very little bit larger than the second effect. The increase in stability is slightly larger than the decrease in stability. The net effect of increasing bullet speed is a very small increase in the stability factor. In the real world, however, with normal bullet weights and twists, it is something you can pretty safely ignore. Hope that helps, Dutch. Life's too short to hunt with an ugly dog. | |||
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Madrid, I'm really not sure what you want to know to get started. 1- have a look at one or more of the reloading books. There you'll find that a standard 168 grain bullet with a standard load flies at about 2700 - 2800 fps. 2- check the eskimo ballistics calculator and find out the drop for your range. If the mean impact of your group shows less or more drop than the ballistic calculator shows, try to correct the BC input accordingly. If possible, repeat this for different shooting distances and make notes of the drop. Now you may change the drag function (see below) in the calculator and redo the calculations until you find the best fit. sidenot: I see that jbm does not suggest this method for not being eccurate enough, but it gives a first hint. 3- it is not the lack of language that may be your problem but the lack of knowing ballistics: it is easy to find out that a meplat diameter is the tip diameter, but it's much harder to say if a bullet has a secant or a tangent nose, and what's the ogive radius (these bullets are too small for us to measure them correctly): contact the bullet manufacturer or use bullets with known data. And last, but not least: the drag function. G1 is the most used, and most ballistics programs make use of this function exclusively. The eskimo program is one of a few offering different drag function. The G1 function is derived from experiments more than a century ago (G stands for Gavre) with the Krupp bullet with an extremely low ogive radius (I don't want to look it up, but if memory serves, it was a 1 inch diameter bullet with a 2 caliber (2 inches) radius). This shape is far from modern rifle bullets whose trajectory is described by function G5 to G8. You may want to try that out- this calculator is a great tool. (as you live in a metric world, don't forget to set the calculator for cm and m - I did forget it and found a drop difference of more than 30% on a 300m/yrd range). a last word: your twist should be even enough for up to 200grn bullets. The standard .308 twist is 13 to 14. ----------------------------- Too bad the only people who know how to run the country are busy driving cabs and cutting hair. ~George Burns | |||
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My intention is to use well the powder and to reduce the load (Tubal 3000), I don't need the bullet to fly more than 150 stabilizer yards because in my country unfortunatly we don't have any ground shot for more than it. I've tryed with many loads with different speed (when i have less load, of corse I have less speed, keeping the rest of the parameters as headspace, OAL, freebore...) What I'm trying to know is till where can I low the velocity without any stability problem, also I would like to make me sure that I don´t cause any problem of underpresion because of the reduced load/compresed load (I'm sorry , I hope it's well writting and taht you are understanding what I mean). =================== Sic Vis Pacem, Para Bellum. | |||
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I would recommend that you find what load shoots best.I shot a service rifle in the US.It shoots best when my 308 168 load has a Muzzle Velocity between 2550-2600.That is the sweet spot for this rifle.If I down loaded the cartridge my groups would open up.In the US factory Match 308 with the 168 are loaded to a velocity of 2600-2700 fps.Most of that ammo will shoot a MOA or better. Good luck with your match. Regards ,Mike | |||
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There aren´t many reloading books here, and what it is worse, neither we have many components,but 2700-2800fps it a speed for get a complete trajectory I only need a very small trajectory of 150 yards and that it's why I think that with less velocty is enough. Am I rigth? O Im wrong? You are rigth, it's also true, I know that I don´t know, that's why im asking to the people who know about it. Could I do that? Or this is not the way? Yes, but the problem is that I don´t have the piece of information of the sierra hpbt 168 grains and the manufacturer neither provide them to me Thank you, I've taken it into account, but the problem is to get the information of the bullet sierra htpb 168 gr. =================== Sic Vis Pacem, Para Bellum. | |||
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I do not think you will have a problem if you load to a velocity of 2500 fps.Under that and your groups may open up.This is what I have found on several of my rifles.I have shot 1/2 MOA groups with a MV of 2500.When I was doing some testing I found that My loads that were 2500 fps and my loads that were 2600fps were basically grouping in the same hole.So I do not think the 100 fps either way is gone to make a large difference.What is real important is how good your hold is. Good Luck in your match. Regards . Mike | |||
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There aren´t many reloading books here, and what it is worse, neither we have many components,but 2700-2800fps it a speed for get a complete trajectory I only need a very small trajectory of 150 yards and that it's why I think that with less velocty is enough. Am I rigth? O Im wrong? You are rigth, it's also true, I know that I don´t know, that's why im asking to the people who know about it. Could I do that? Or this is not the way? Yes, but the problem is that I don´t have the piece of information of the sierra hpbt 168 grains and the manufacturer neither provide them to me Thank you, I've taken it into account, but the problem is to get the information of the bullet sierra htpb 168 gr.[/QUOTE] ----------------------- Madrid, if you cannot get this kind of information in your place, order it from where it is available. You know, I'm from Germany, and I ordered any kind of shooting and ballistics information from the US because it was not available at my home place. It's easy enough - order from Sierra, from Sinclair, from eBay etc. they are well prepared for international deals. Do it today - you need this information for a safe reloading and shooting. With your kind of view, you need more information, imho: to shoot on a limited range does not mean that you can save on fuel as your bullet has only a short distance to travel. Load your ammunition properly (which is 40 grains of N140 behind your 168 SMK or something in this range)and you will have proper results, and forget about load reduction - your knowledge about reloading seems (to me) not appropriate for developing specal or reduced loads: BUY MANUALS ! (If you want to order the Sierra manual from US, it is a good idea to consider to buy the Infinity CD which has the reloading information of both handbooks plus the ballistics software, and you will save on shipping costs). No, I will not look up data for you - because I want you to have your own data pool and knowledge base: BUY MANUALS ! ----------------------------- Too bad the only people who know how to run the country are busy driving cabs and cutting hair. ~George Burns | |||
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With that long of a bullet and that rate of twist, I believe you need to keep the MV above 2500 FPS if possible. "Bitte, trinks du nicht das Wasser. Dahin haben die Kuhen gesheissen." | |||
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MADRID Check your private messages. | |||
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My old target load in 308 Win IMR 4895 @ 43.6 168 Sierra MK Fed 210 Match Primer WW Brass 2.80" COL 2600 FPS Almost one hole groups @ 100 yards. Jeff North Pole, Alaska Red Team 98 | |||
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Madrid: You are asking for information that is outside the normal operating conditions of most shooters. I would say that few shooters in my State are only interested in having the bullet travel 150 meters. However, to have a very slow bullet in the 308, you will have to find powders and powder charges that are compatible. Most of the gun powders on the market are sold to people who want high velocities. These powders do not work well in reduced charges. In fact it is “common†knowledge that using reduced charges of slow burning rifle powders is in fact dangerous. I am not reloading “reduced†velocity rifle ammunition. I have recently read an article in Handloading where the author was using AA5744 and cast bullets in a 30-06. The bullet weight was around 190-200 grains and the velocities were below 2000 fps. Accuracy was acceptable. Lead bullets at reduced velocities may be more acceptable for you to use in a confined area than jacketed bullets with standard charges. And in fact, I don’t see any reason why you could not shoot low velocity ammunition with jacketed bullets. You should do your research on that, and not worry about the stabilization of the bullet due to rifling twist. | |||
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Hmmmmm???? Very short range, low velocity, lesser "gas blast" or sound, not sure where this is really going?? As others have mentioned, buy some manuals and check them out and doubt if you will find what you are looking for other than some squip loads w/ lead round ball for projectile. Hey Madrid, any chance your rilfe muzzle has threads on it to facilitate the attachment of various devices?? Understand that silencers, or "moderators" as often referred to in Europe and England, are easier to obtain than in the U. S. for civilians and just curious?? | |||
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Madrid: Load between 2450 to 2600fps, stick with what gives you the best accuracy. I reccomend you try the 175 Sierra Match Kings in you TRG-22. They shot better than the 168's in mine.......................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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===>  .... very kind  ===>that it is not my interest SlamFire ==> that is the question ( you will have to find powders and powder charges that are compatible). djpaintles ===> thanks a lott =================== Sic Vis Pacem, Para Bellum. | |||
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Barrel harmonics, targets, and group sizes will tell you what you need to find. Just as one can use a starting load and work/ladder up, one may also work/ladder down. Use one grain, or better yet, 1/2 grain increments or smaller. A note of caution, Loading below starting load data with slower powders may not be a good idea due to possibilities of SecondaryExplosiveEvent(SEE). I'd bet that you will find a good accuracy node in 2100-2300fps range. Best-o-Luck | |||
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Madrid: So far I haven't seen what cartridge/caliber you're working with. Please clarify this. You can find many loading table's. Go to the powder mfg. sites. www.name of company.com and look it up. You'll be much safer doing it that way. www.sierra.com www.speer.com paul@sierrabullets.com is a real good place to start. www.lyman.com www.hornady.com You get the idea yet?? I'd highly recommend you send an e/mail to Paul Box at Sierra Bullets. Make sure you name the cartridge, brand of powder, bullet, primer etc you have access to. That will help get the right info for you. What are you intending to shoot with these loads? Wish you well. George "Gun Control is NOT about Guns' "It's about Control!!" Join the NRA today!" LM: NRA, DAV, George L. Dwight | |||
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Hmm, didn't see the full title of your thread. Sorry, I can see now it's .308. Very good cal. George "Gun Control is NOT about Guns' "It's about Control!!" Join the NRA today!" LM: NRA, DAV, George L. Dwight | |||
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