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Posted: 10/6/2003 12:14:02 PM EDT
Looking at a PCR-1 Ultramatch, and I'm still trying to understand everything so that I make sure everythgin I get works well with the other things.

So...

1) At what range is accuracy optimal for the 1/10" or 1/8" twist using M193 in a 20" barrel? I'm trying to decide which twist ratio to get.

2) How many inches of bullet drop are generally acceptable for trying to hit a target? I've seen the charts, which show that bullets drop a lot more than I would have guessed. Is it still reasonable to shoot at a target 600m away that has like 150 inches of drop?

3) what is best range to zero if I plan on shooting 75 to 500 m using the set up/bullets I have described? I read that 250 is average, but looks like 200 would have greater overall accuracy.
Link Posted: 10/6/2003 12:47:12 PM EDT
[Last Edit: 10/6/2003 12:48:08 PM EDT by El_Roto]
1) At what range is accuracy optimal for the 1/10" or 1/8" twist using M193 in a 20" barrel? I'm trying to decide which twist ratio to get.
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Twist relates to bullet length, not distance. If you're planning on shooting any of the new long bullets - say 75 grains or more - then you'll want the 1:8; 1:10 is fine for 40 to 69 grain bullets.
2) How many inches of bullet drop are generally acceptable for trying to hit a target?
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It's the horizontal velocity not the drop that affects accuracy. Conventional wisdom is that accuracy falls off once a bullet slows below the speed-of-sound. If you do your part and read the wind properly, hits past 600 meters are doable. Good shooters can push a 55gr. bullet out to 1000 yards and get hits.
3) what is best range to zero if I plan on shooting 75 to 500 m using the set up/bullets I have described? I read that 250 is average, but looks like 200 would have greater overall accuracy.
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I'm not sure where you're coming from here. Are you going to be using a scope or iron sights? For the former use whatever zero affords you the most flexibility with the elevation adjustments available, and a 50 yard/220 meter zero for iron sights.
Link Posted: 10/6/2003 1:50:15 PM EDT
[Last Edit: 10/6/2003 1:53:13 PM EDT by stuh505]
Twist relates to bullet length, not distance. If you're planning on shooting any of the new long bullets - say 75 grains or more - then you'll want the 1:8; 1:10 is fine for 40 to 69 grain bullets.
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On the contrary, I read in the AR15.com ammo FAQ that slower spin rates will not adequately stabilize longer range shots, and groupings will be erratic. Faster spin rates increases accuracy at longer ranges, but causes the bullet to take more time to stabilize, thus making it LESS accurate at close ranges. So my question stands..oh yeah and I would be using Winchester M193/Q3131 ammo, with the occasional Hornady V-Max/Sierra BlitzKing
It's the horizontal velocity not the drop that affects accuracy. Conventional wisdom is that accuracy falls off once a bullet slows below the speed-of-sound. If you do your part and read the wind properly, hits past 600 meters are doable. Good shooters can push a 55gr. bullet out to 1000 yards and get hits.
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Ok, I've heard that speed of sound rule of thumb before. But I'm not convinced that bullet drop is not a factor. Is it seriuosly true that a bullet dropping 200 inches from level is still gonna be right on target if it's going mach speed?
3) what is best range to zero if I plan on shooting 75 to 500 m using the set up/bullets I have described? I read that 250 is average, but looks like 200 would have greater overall accuracy.
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I would be zeroing it with a ATN 5x33L scope (which seems to be designed for 0-500 meters)
Link Posted: 10/6/2003 2:08:44 PM EDT
[Last Edit: 10/6/2003 2:25:19 PM EDT by DevL]
You mis read the ammo faq then. The bullet is stabilized right out of the barrel. There is no "distance of stabilization" it can wobble in flight but the accuracy s already ruined by that point and it does not get "more accurate" This will likely be a TOTAL NON ISSUE with a 1/8 barrel vs a 1/10. Yes you can have a bullet drop any number of inches and it still will be accurate. You just need to click off the scope the appropriate number of clicks and your through. I say sight in at 100 or 200m and memorize your clicks for hold over at each range you want to shoot at. Its the most reliable way to do it. If thats not appropriate I suggest a scope with a mildot reticle and memorize your data card for mils at various ranges.
Link Posted: 10/6/2003 2:22:01 PM EDT
The angle at which a bullet is traveling relative to the ground also helps determine how difficult a shot is. Just take a look at the trajectory table of any round. When a bullet is traveling parallel (mostly) with the ground, it's a relatively easy shot that can be made by almost anyone. For instance, you might have 300 yards of horizontal travel and only 8" of elevational travel. However, when you have a bullet that is basically dropping straight to the ground and traveling forward only ever so slightly, the shot becomes exceedingly difficult. Imagine a bullet traveling DOWN 100 yards and moving forward only 1 yard. Your shot has to be perfect. Somewhere between there you have what is generally accepted as maximum range you can expect to hit with a certain caliber, where that is, I'm not sure. It's heavily dependant on the skill of the shooter.
Link Posted: 10/6/2003 3:17:15 PM EDT
wyv3rn, what you are saying is exactly what I was stipulating. But it seems El-roto and DevL are saying you are wrong. It seems to me the logic is on your side so I dunno. As to the twist...I am a really particular guy, and even though it may not make a big difference, I know that there IS a difference between 1/8 twist and 1/10 twist...and I still would like to know which is BETTER for what I want to do.
Link Posted: 10/6/2003 3:32:48 PM EDT
Go w/ 1/8. Use Fed. 55 gr Balistic tip on small varmint & you can still shoot the 75/77 @ big varmint or long distance paper. Everything in between(68/69) will fly straight also. -Justin
Link Posted: 10/6/2003 4:06:04 PM EDT
[Last Edit: 10/6/2003 4:08:24 PM EDT by DevL]
I dont know how else to say this to make it any easier to digest. You obviously have no experience in long distance shooting. Angle means dick squat as to your accuracy. Distance means NOTHING to twist. OK The best rounds for long distance shooting have a good ballistic coefficient of friction. This means they lose velocity more slowly. This has to do with sectional density. You see if you take a heavy bullet and it starts off slower but loses speed slower. Shoot a light bullet and it starts off faster then speed dies off quickly. At some point the slow bullet passes the fast bullet becasue of better ballistic coefficient. Got it? Bullets all drop at the same speed. The difference is the amount of drop over time. This has to do with speed. Faster bullets drop less in a given distance because they covered that distance in less time and had less effect of gravity on them. Wind is a factor of speed too but also of mass. The heavier bullets are not pushed by wind as easily. SO... for long range shooting you want heavy match grade ammo for maximum accuracy. The best twist for longer bullets to make sure they are stabilized is the 1:8 twist. Now this is a SMALL factor when everything is considered. Barrel quality and ammo quality is MUCH MUCH more important to your accuracy. If you REALLY want accurate get a Krieger barrel. It is 1/7.7 twist and will whoop that Oly all day long. If you want to shoot long range use heavy match bullets. If you want to use heavy match bullets use a tighter twist to stabilize those rounds. Its that simple. Dont try to read all kinds of wack ideas into it. As for the angle you shoot at... jeez I dont know where you guys get these ideas. You just have to account for the change in point of impact. The more off 90 degrees the bullet is at a given range the more it will change your POI. This is a math equation pure and simple. The effect of 100 yards down and 1 forward IS NOT HARDER TO DO than 100 yards on level ground. Ley me give you a clue here... GO BUY A MILDOT MASTER AND LEARN HOW TO USE IT FOR SHOOTING UP OR DOWN ANGLES. DOPE YOUR RANGE, ANGLE AND WIND AND YOUR RIFLE WILL HIT ITS TARGET. NO SHOT IS ANY MORE DIFFICULT THAN ANY OTHER.
Link Posted: 10/6/2003 5:11:25 PM EDT
[Last Edit: 10/6/2003 5:47:28 PM EDT by stuh505]
ok...you are right I do not have a lot of experience actually shooting, but I know all the physics equations, I understand drag and BC, and I know how to use a mildot scope. I'm just confused about 2 simple things -- the affect of twist, and bullet drop. As for bullet drop, I don't know of any equations that would back up what I was thinking...so I suppose you are probably right. As to the twist...
Distance means NOTHING to twist.
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this is from the ar15.com ammo faq and it has a reference from somewhere else: [b]A bullet's flight is disrupted slightly as it leaves the barrel and after traveling some distance, will "settle down" into an even spiral, similar to a thrown football. The faster a bullet is spinning, the longer it takes to settle down. The most accurate twist rate for any length of bullet will be just a bit faster than what is required to stabilize it for its entire flight path (1.3 SG). [/b] I also know for a fact that a reputable gun company like Olyarms knows a lot about how to make an accurate barrel. And they make the 1/10 barrel stock. Anyway I read the FAQ a little more carefully and I understand why it uses a 1/10 twist...because that works better on a lightweight 55gr m193 round because it would be spinning too fast to be accurate.
Link Posted: 10/6/2003 5:40:06 PM EDT
[Last Edit: 10/6/2003 5:47:56 PM EDT by DevL]
No you are misunderstanding. Bullet quality, Barrel quality, propper cheek weld, quality optics, quality mounts for optics... these are ALL more important to accuracy that rate of twist over stabilizing your bullet in this case. Now, your seeming to have a problem understanding what its saying. What that sentence means it if you over stabilize a crappy lop sided bullet (which your not gonna do since you are so concerned with accuracy right?) then if you over stabilized the bullet it can wobble in a micro itty, bitty, tiny, little way. While it is doing this it can end up flying off at a TINY, TINY, TINY, TINY, off vector. Then it will stabilize and fly with no wobble. Well it can be pointed in any off vector from the wobble when it stabilises. It does not just wobble all around then get MORE accurate at a further distance. If your shooting 1 MOA at 100 yards you WILL NEVER shoot .9 MOA at 200 yards. It can get worse but never better. There is no "most accurate range" The most accurate range is 1 inch from the end of the bore. It gets progressively worse from there. If you are concerned with accuracy both up close and far away you will be using heavy match bullets. If you are concerned with maximum terminal ballistics for self defense you will be using heavy match bullets (for the .223/5.56 platfor anyway) so since you will be using heavy match bullets you will not have any kind of even this itty, bitty, tiny issue right? People shoot 55 grain ammo with 1/7 twist and get sub MOA results. The difference in 1/8 vs. 1/10 with say 69 grain ammo would be on the order of .01" at 100 yards or there about. It would be so small you would never be able to quanify it. I know people who shoot 1/9 barrels sub MOA with 52 grain ammo. Optimal weight for 1/9 is 62 grains. Its over stabilized yet they still can shoot under a 3" group at 300 yards from a NON MATCH CHROME LINED BARREL. Even the powders, primers, bullet seating depth or almost anything else will have more of an effect on accuracy than that a micro overstabilization of the bullet will cause. Get the faster twist to be sure you can stabilize the heavy stuff. Under stabilization is a HUGE problem. Over stabilization is MUCH less of a problem. Also if your that concerned with overstabilization there are 2 more things you can do. Dont use the reccomended 24" barrel. The faster the bullet moves down the bore given a fixed rate of twist the higher the RPMs thus the more stable it is. Next you can use .223 pressure ammo instead of 5.56 NATO pressure. Again the slower the bullet is moving the less the RPMs and the less stable it is once it leaves the barrel. A 20" 1/8 twist match barrel using .223 ammo should be super, duper accurate with 77, 75, 69 and 68 grain ammo. Id be willing to bet you will even be sub MOA out to hundreds of yards with 52 grain match too. Oh yes the 1/10 barrel is specialised for shooting very light varmint bullets that would be horrible for shooting at very long range or shooting people. Get a 1/10 if you plan on shooting 40 grain to 55 grain varmint ammo exclusively at ranges of a few hundred yards for killing little gophers and groundhogs. If you want to shoot to 600+ accurately or do lots of terminal damage to humans or deer sized animals you want the heavier stuff.
Link Posted: 10/6/2003 5:53:19 PM EDT
Will M193 be accurate in a 1:7 or 1:9 twist barrel? It may be marginally less accurate due to the fast twist rate
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Ok you seem to be misinterpreting what I was asking, so let me clarify. The FAQ clearly states that having a twist rate that is too high for the bullet weight will cause some small amount of innaccuracy due to spinning too fast. Now, a 1/10 twist barrel will spin a 55gr bullet slower, so it will be less wild and more accurate for some range. But a 1/8 twist will be slightly more accurate AFTER it settles down...so the question is, using a 55gr bullet, at what point does the 1/8 twist settle down vs the 1/10 twist?
Link Posted: 10/6/2003 6:04:39 PM EDT
NO NO NO NO NO!!!!!!! Damnit LISTEN! The wobble causes a deviation in flight path in a random direction! Then it quits going in a random direction! This will be in any number of outward radiating directions! 2 bullets from the 1/8 barrel of 40 grains will wobble one randomly stabilises at X yards and is going at a slightly right angle from its original path. Second bullet stabilises and is now goin slightly left angle from it original path. These bullets have deviated in a non paralell direction. They will NEVER get more accurate. They can only get further and further apart. Do you understand now? An easier way to look at it is under stabilisation. The bullets will wobble on exit. They go pretty much in a similar direction. Then they veer off in a random direction at a distance and accuracy goe s to 100% shit. It the over stabilized bullet the going off in random direction happens right out the barrel. Then they fly in straight lines in those random directions. The under stabilised rounds get worse and worse until they are flying yards apart. The amount of accuacy degradation in the over stabilised bullets is near nothing. Once they leave the barrel they are already flying apart from one anothers flight paths. Once they stabilise they dont get closer together they just go apart further and furhter at a slower rate. An over stabilised bullet can make you nick a golf ball instead of hitting it solid. An under stabilsised bullet can miss the whole paper target or fly several feet off in a random direction. Barrel to barrel variance will have more effect on accuracy than twist with 55 grain ammo. With 75 grain ammo the understabilised bullet will be flying WAY off.
Link Posted: 10/6/2003 6:10:58 PM EDT
Simple version: 1/10 barrel .1 MOA better accuarcy with 55 grain ballistic tips at ALL ranges then 1/8 twist. 1/10 cant shoot 75 or 77 grain ammo at all past 200 yards. It flies off in a random direction. Bullets dont get more accurate at any range with a specific twist, they only get less and less accurate.
Link Posted: 10/6/2003 6:16:37 PM EDT
[Last Edit: 10/6/2003 6:24:10 PM EDT by stuh505]
no longer prevalent
Link Posted: 10/6/2003 6:20:01 PM EDT
[Last Edit: 10/6/2003 6:27:24 PM EDT by stuh505]
Ok I just read your most recent post - missed it before making my last post. So what you are saying is...slower twist will give more accuracy at all ranges, as long as you have the minimal amount of twist to keep the bullet stabilized. Right? Well that makes a lot of sense. Now I understand why olyarms make such accurate barrels...they make the twist 1/10 instead of 1/9 so they are cutting it closer to the minimum necessary, causing less instability, but just barely giving enough twist to keep the bullet from veering off.
Link Posted: 10/6/2003 6:54:33 PM EDT
[Last Edit: 10/6/2003 6:56:24 PM EDT by DevL]
Yes the minimum twist necessary is what gives optimal accuarcy but overstabilization is a non issue unless its WAY overstabilised. You have seen the light!
Link Posted: 10/6/2003 7:48:30 PM EDT
Thanks Dev
Link Posted: 10/6/2003 11:11:40 PM EDT
Link Posted: 10/6/2003 11:35:17 PM EDT
Use the heavier bullets with the faster twist. This will give you the best results at the longer ranges. If your so torn in between a 1/8 and a 1/10 go with a 1/9. I assume that is not an option but I was thinking it all the way. LOL
Link Posted: 10/7/2003 7:05:28 AM EDT
it is 1/10 stock but it says swap to 1/8 for no charge. I wanted to understand twist before I made the decision. I do not know what grains I will be using until I examine a chart comparing the velocities of each grain as a function of distance so that I can select the proper grains for what I want. I am not even 100% positive that I will be using a 20" barrel...I could get that replaced with a 24" barrel for only $43 more...but I need to learn how barrel length affects things as well first before I make that decision. With 1/8 twist, a 20" barrel would have 2.5 revs...a 24" would have 3 revs...is that gonna make it more accurate for longer ranges? or does it have any drawbacks?
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