338 Lock base VS scenar (in TRG42)

Aloittaja Mike, huhtikuu 24, 2006, 15:29

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Mike

huhtikuu 24, 2006, 15:29 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä Mike
Hi all,

sorry, but my posts will be in english  :oops:



I would like to have your advise obout the accuracy of these two bullets beyong 1000M.

I have heard that the lock base retain his accuracy at longer range than scenar...what do you think about this ?

Furthermore some people say that the lastest TRG42 will have an 1/10" barrel twist...is it right ?



Thank you

HJu

#1
huhtikuu 24, 2006, 18:09 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä HJu
I have shot and seen people shoot 250 Scenars out to 1200m. At least that far Scenars beat LockBases in accuracy. If you ask Lapua they say Scenars typically have better accuracy than Lock Bases but of course rifles are individuals.



So far Sako has not offered any 338LM with anything else than 12" twist but of course they could offer any twist if they choose to do so. Today at http://www.sako.fi">http://www.sako.fi there was no mentioning aobut 10" twist for 338LM.



For military use TRG-42 does not really need to shoot 300 Match Kings because they can not be used by European armies because of their hollow point configuration. For 250 greiners 12" is plenty. TRG-42 in 338LM is in official military use at least in Finland, Switzerland and Italy.
Terveisin,


HJu

Mike

#2
huhtikuu 25, 2006, 16:15 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä Mike
Thank for your advise.

Which powder give better result with the scenar : N560 or N170 powder ?

Which bullet speed give the better acuuracy with the TRG? (i am looking for a +900m/s accurate reloading if possible).

JL

#3
huhtikuu 25, 2006, 17:59 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä JL
Well, i´m  one of those few mules who prefer lock-base instead of scenar.

Hot loads+scenar just doesent work as well in my 42-stick.

Difference is small, though.

Tested L-B up to 1600yds.



I used to use N165, but nowdays only N560.

Seems to save brass, pressure peak is milder than N165 when shooting +900m/s loads.



0.2



P.S.

AI:s best 338 testgroup ever is shooted with LockBase  :wink:

MJ

#4
huhtikuu 25, 2006, 19:38 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä MJ
Hi Mike,



like HJu already said 250 gr Scenars are a bit more accurate than 250 gr Lock Bases. This is basically due to Scenar's better BC compared to LB's (Scenar has better sectional density and form factor). These two elements decide the ballistic coefficient (BC); the sectional density (SD) and the form factor (FF).



Furthermore, as HJu also already stated, even Lapua tells you that Scenars are more accurate than LBs. Nevertheless, LBs are accurate enough for military sniper cartridges.



Therefore, if you are looking for absolute accuracy, then Scenar is the ammo for accuracy.



About powders; Vihtavuori N170 powder gives you + 900 mps velocities easily with the minimum pressure. It's slow burning powder without any nitroglyserine. Thus, N170 powder won't burn your barrel so easily as e.g. N560. You can ask either Vihtavuori or Lapua and they will tell you the very same thing.



Additionally N170 fulfills the whole case of the cartridge more than N560, which at least in theory leads to better burning of the powder and hence more consistant velocities.



I would seriously recommend you to use N170 powder instead of N560.



Either 860 - 880 or 895 - 910 mps velocities will give you accuracy.



For + 900 mps velocities (900 -915 mps) use something btw 6,18 - 6,32 grams (95,36 - 97,52 grains) of N170 powder. If you use moly Scenar bullets pressure will decrease a bit, but generally speaking moly bullets require more powder than "normal" copperjacketed bullets in order to achieve similar velocities.



Hence, e.g. normal Scenar may need 6,20 grams of N170 to reach 905 mps velocity and moly Scenar instead  may need 6,22/6,24 grams for the very same velocity. This was just an example.



Anyway, you need to test youself the amount of powder you'll have to have for the desired velocity and accuracy. 0,5 MOA accuracy should be achievable.



Carpe Diem,



MJ

Mike

#5
huhtikuu 25, 2006, 20:16 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä Mike
Does the scenar like a little "jump" or prefer to be seated in the land of the barrel ?

0.5MOA will be fine  :D  Is it possible to get more accuracy from this rifle ?

MSa

#6
huhtikuu 25, 2006, 20:25 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä MSa
Hi,



My standard TRG42 hot load for long distances with Scenar and N170 has light rifle touch. In good conditions I've been able to produce 4 x 5shot consecutive groups with an group average of 0.41MOA. Vo average is 890m/s @ 10C.



A milder load with same powder (N170) but Vo average 860m/s has proven to be a bit more accurate. The COL is the same, i.e. (light rifling touch).



MSa
[url=https]

MJ

#7
huhtikuu 25, 2006, 20:49 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä MJ
Hi Mike,



The COAL (cartridge overall length) for accurate Scenars is valid from 91,4 mm to 93,5 mm. In order words, if you have well under CIP/SAAMI tolerance barrel, the COAL should be closer to 91,4 mm than 93,5 mm and if you have std barrel (factory barrel), the COAL should be closer to 93,5 mm than 91,4 mm.



In the end of the day Scenars don't care whether there's a little jump or not (i.e. they are seated in the land of the barrel). Just follow the above main rule (not in the strict sense), but you'll be always fine when the COAL is btw 91,4 - 93,5 mm.



Yes, I know there's a lot of hype with this bullet has to be seated issue, but I don't believe in it and neither do any gunsmiths I happen to know (you can trust me - I know a lot of them). In addition, I haven't ever had any accuracy related problems with any of my long sticks, even I haven't "seated" bullets. And yes, I have shot several times 0,5 MOA groups within 1000 - 1500 meters range with .338 LM - not a big deal, since I know several shooters, who'll do the same.



Now, the bottom line is to know one's ballistics well enough and then the shooting itself is pretty easy. The hard part is to built valid and reliable ballistics.



Unknow distances present their own problems, mainly target verification, the accurate distance itself and of course the wind.



0,5 MOA accuracy out of std .338 LM TRG-42 should be a norm, not an execption. Hence, it's fairly possible to get more accuracy out of TRG-42 - just needs the right combo of handloaded Scenars.



Carpe Diem,



MJ

JL

#8
huhtikuu 25, 2006, 22:38 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä JL
Lainaus käyttäjältä: MJ
like HJu already said 250 gr Scenars are a bit more accurate than 250 gr Lock Bases.

This is basically due to Scenar's better BC compared to LB's (Scenar has better sectional density and form factor). These two elements decide the ballistic coefficient (BC); the sectional density (SD) and the form factor (FF).


Whats BC or trajectory flatness has to do with bullet accuracy itself?

After all, its only aerodynamical factor.



Worse BC bullet can shoot tighter groups than better BC.

MSa

#9
huhtikuu 25, 2006, 23:32 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä MSa
Lainaus käyttäjältä: JL
Lainaus käyttäjältä: MJ
like HJu already said 250 gr Scenars are a bit more accurate than 250 gr Lock Bases.

This is basically due to Scenar's better BC compared to LB's (Scenar has better sectional density and form factor). These two elements decide the ballistic coefficient (BC); the sectional density (SD) and the form factor (FF).


Whats BC or trajectory flatness has to do with bullet accuracy itself?

After all, its only aerodynamical factor.



Worse BC bullet can shoot tighter groups than better BC.


I think the _theoretical_ logic is that for extreme ranges (1000m+) the faster the bullet reaches the target the less wind will deflect the bullet and the less Vo std deviation of a cartridge affects.



MSA
[url=https]

Mike

#10
huhtikuu 25, 2006, 23:43 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä Mike
Lainaus käyttäjältä: MJ






 And yes, I have shot several times 0,5 MOA groups within 1000 - 1500 meters range with .338 LM - not a big deal, since I know several shooters, who'll do the same.







0,5 MOA accuracy out of std .338 LM TRG-42 should be a norm, not an execption. Hence, it's fairly possible to get more accuracy out of TRG-42 - just needs the right combo of handloaded Scenars.



Carpe Diem,



MJ


Whoww...if i can shoot some 1/2 MOA group at 1500m With the factory TRG42, i will be very happy  :D

MJ

#11
huhtikuu 26, 2006, 09:22 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä MJ
Hi,


LainaaWhats BC or trajectory flatness has to do with bullet accuracy itself?

After all, its only aerodynamical factor.



Worse BC bullet can shoot tighter groups than better BC.




Here comes the repetition of the few core issues of external ballistics once more:



Two key factors determine the external ballistics of a projectile:



1. The muzzle velocity (the advantages of a high muzzle velocity in reducing the time of flight are self-evident) and 2. The ballistic coefficient (to make the most of the muzzle velocity, we need to achieve a high ballistic coefficient).



The ballistic coefficient is significant because it determines the rate at which the projectile slows down, and in conjunction with the muzzle velocity this decides the maximum range (at any given elevation) and the time of flight to any particular distance. The time of flight in turn decides the amount by which the projectile drops downwards as this happens at a constant rate due to gravity. The curved path of the projectile which results from the muzzle velocity, the ballistic coefficient and gravity drop is called the trajectory. In most types of long-range shooting a short time of flight is considered desirable because it maximizes the hit probability by reducing the time of flight and flattening the trajectory.



There are two elements which decide the ballistic coefficient (BC):



1. The sectional density (SD) and 2. The form factor (FF).



The SD is a simple calculation as it is the ratio between calibre and projectile weight. The formula is:



For metric measurements: multiply the projectile weight in grams by 1.422, then divide the result by the square of the calibre in millimetres. So for a 12.7mm bullet weighing 40 grams: (40x1.422)/(12.7x12.7) = an SD of 0.353.



The higher the SD figure, the better the velocity retention (assuming equal form factors). What the SD measures is the weight (or momentum, when moving) behind every square millimetre of the projectile calibre (i.e. the cross-sectional area of the projectile). If projectiles were solid cylinders then for a given SD figure they would all be the same length regardless of their calibre. In practice, of course, the length varies with the calibre; a 40mm projectile will be about twice the length of a 20mm, and will therefore have about double the SD figure.



The FF measures the aerodynamic efficiency of the projectile's shape, and is much more complicated to calculate; without access to manufacturers' data, only approximate estimates can be made. It is obvious that a projectile with a pointed nose will have much less air resistance than a simple cylinder, and it will therefore have a better FF, but problems arise when you try to become more specific.



The first problem is that the FF is different at subsonic and supersonic velocities, because shapes which work best at subsonic speeds are not the best at supersonic velocities. At subsonic speeds, the drag caused by the low-pressure area created at the back or base of the projectile is significant, and major reductions in drag can be made by tapering this to some extent (boat-tailing). At supersonic speeds, it is the nose shape that is critical; finely pointed noses are needed, but the back end doesn't matter so much. Some taper towards the base is useful, but the optimum taper angle is different from that at subsonic velocities. The benefit of boat-tailing at very long range can be demonstrated by two .30-06 bullets, both weighing 180 grains (11.7g) and fired at 2,700 fps (823 m/s). At sea level, the flat-based bullet will travel a maximum of 3,800m, the boat-tail 5,200m.



It is possible to obtain some idea of typical FFs by comparing manufacturers' BC data with the calculated SDs for the same projectiles. In the case of small arms bullets, this provides the following approximate FFs (this figure should be multiplied by the SD to give the BC):



Flat-nose lead: 0.8

Round-nose lead: 0.9

Round-nose jacketed: 1.0

Semi-pointed soft point: 0.9-1.1

Pointed soft point: 1.2-1.6 (depending on sharpness of point)

Pointed full jacket: 1.5-1.8

Pointed full-jacket boat-tailed: 1.9-2.0



Comparing the BCs with ballistic tables for the ammunition gives the following results. These figures show the approximate percentage velocity loss over 100m for supersonic projectiles (900 m/s) with the following BCs:



BC 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

V loss % 25 18 14 11.5 9.5 8 7 6.5



Another type of Form Factor is traditionally used for artillery - and especially naval - shells. This is the "caliber radius head" (CRH) which measures how pointed the nose is. To give an example, if the curve of a shell nose is the same as that of a circle with a radius of 500mm in diameter, and the calibre is 100mm, then the shell has a CRH of 5. The higher the CRH, the better the FF.



In calculating SD and BC, it should be noted that the notional cartridge calibre is not necessarily the same as the actual projectile diameter, particularly with small arms. The bore diameter (ie the inside diameter of the barrel ignoring any rifling grooves) may be used instead, or some notional figure.



An important aspect of external ballistics is the stability of the projectile.



Rifling permits a high degree of accuracy over the maximum range of a weapon. There is a relationship between the rifling twist (the angle of the rifling to the barrel) and the length of the projectile. For a given calibre, the longer (ie heavier) the projectile, the steeper the twist has to be in order to stabilise it. Clearly, with a particular rifling twist some light projectiles will be very stable, some medium-weight ones marginally stable and some heavy ones not stabilised at all. This can have consequences for the terminal as well as the external ballistics.



The bullet's resistance to wind deflection also required a tweaking of the standard wind formula. A critical part of that formula is true flight time to the target.


Lainaa I think the _theoretical_ logic is that for extreme ranges (1000m+) the faster the bullet reaches the target the less wind will deflect the bullet and the less Vo std deviation of a cartridge affects.


Right on track MSA !



End of external ballistics repetition.







Gee, I wonder too what BC has to do with accuracy - just kidding; if it's not obvious read the text above, if it's still unclear, read it again. If it still remains unclear, study and learn more about ballistics, since I won't bother to teach ballistics on the pages of this forum; for the studies of ballistics, we run sniper courses. At these courses we teach ballistics.



Carpe Diem,



MJ

JL

#12
huhtikuu 26, 2006, 10:14 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä JL
Lainaus käyttäjältä: MJHi,


LainaaWhats BC or trajectory flatness has to do with bullet accuracy itself?

After all, its only aerodynamical factor.



Worse BC bullet can shoot tighter groups than better BC.




Here comes the repetition of the few core issues of external ballistics once more:



Two key factors determine the external ballistics of a projectile:

1. The muzzle velocity (the advantages of a high muzzle velocity in reducing the time of flight are self-evident) and 2. The ballistic coefficient (to make the most of the muzzle velocity, we need to achieve a high ballistic coefficient).



The ballistic coefficient is significant because it determines the rate at which the projectile slows down, and in conjunction with the muzzle velocity this decides the maximum range (at any given elevation) and the time of flight to any particular distance. The time of flight in turn decides the amount by which the projectile drops downwards as this happens at a constant rate due to gravity. The curved path of the projectile which results from the muzzle velocity, the ballistic coefficient and gravity drop is called the trajectory. In most types of long-range shooting a short time of flight is considered desirable because it maximizes the hit probability by reducing the time of flight and flattening the trajectory.



Gee, I wonder too what BC has to do with accuracy - just kidding; if it's not obvious read the text above, if it's still unclear, read it again. If it still remains unclear, study and learn more about ballistics, since I won't bother to teach ballistics on the pages of this forum; for the studies of ballistics, we run sniper courses. At these courses we teach ballistics.


Feeling relieved now?...  :lol:


Lainaus käyttäjältä: MikeHi all,

....accuracy of these two bullets beyong 1000M.

I have heard that the lock base retain his accuracy at longer range than scenar....


Bullet absolute accuracy in long +1000m ranges was Mikes original question, not trajectory or flight time.



Getting better hit probability due to better BC and bullet accuracy as an absolute value truly are two differend things.



Secondly, BC difference between LB and Scenar is minuscule, and therefore differences in flight path or trajectory  too.

Biggest single broblem in LB:s accuracy is shape of a tail. Or to be precise, shape of that bump where bare lead is visible.

In Scenar, tail shape is always exactlly same and that makes Scenar more accurate in practise. Not SD:s, FF:s or other fancy terms.



Situation remains even if you write 20 pages (or so) about sectional densitys and form factors. So, save your keyboard.

I´d guess that Mike would be more interested f.e. about your Lock-Base and Scenar tests in long ranges.

If you have some personally tested comparsion data to share.

MJ

#13
huhtikuu 26, 2006, 12:07 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä MJ
Hi,



If we discuss accuracy, the issue of ballistics is essential.



The hit probability is truly part of accuracy and one of the most determing factors of it.



And those fancy terms SD and FF just happen to determine bullets' BC. Unless you have invented a new universal law of ballistics - if so, that's very good; then head for the nobel prize.



Understanding ballistics is essential and like I already said I won't bother go any deeper in ballistics here - these issues are handled and taught during courses. This is already repetition.



And yes, I have both personally tested both bullets and have comparision data, other shooters' tested data and also the FDF's tested data. Some of the data I have already shared, but certainly not all.



LB's and Scenar's BCs do differ, starting already at Vo 3 m > LB 0,665 and Scenar 0,675. At supersonic speeds, it is the nose shape that is critical and later at subsonic speeds, the drag caused by the low-pressure area created at the back or base of the projectile is significant. Scenars maintain supersonic speed at longer distances than LB (starting velocity is the same).



No, I don't feel relieved, since I'm surprised and shocked how little some people know about ballitics, even they claim so. This is a classical example not knowing even the terminology, neither any other ballistics variables properly. In practise this means that basic and advanced ballistics need to be taught more during sniper courses.



It's totally upto Mike, which issues he's interested in. I think he appreciates all possible info related to the accuracy of .338 LM. Nevertheless, Mike can surely comment if he has liked/learned about info he has been given.



Carpe Diem,



MJ

Mike

#14
huhtikuu 26, 2006, 12:56 Viimeisin muokkaus: tammikuu 01, 1970, 02:00 käyttäjältä Mike
Yes, i am looking for experience about the accuracy of this particular rifle (trg42) at longer rdistance, more than theorical data.

But yours informations about BC are very interesting!

Scenar seem to be more accurate due to his design.

0.5 MOA at 100m is very easy, but the same at 1500m is incredible (with excellent weather condition of course); it mean a group of 22cm at this distance!

Have you some photo of great "grouping" ?
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