30 cal. RNSP - Why so hard to find?


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Bill_Rights
January 28, 2012, 02:52 AM
When thinking about .30 cal rifle ammo for defensive purposes, I wanted something cheap enough to practice with sometimes and with good stopping power/less over-penetration. I noticed that there are hundreds of pistol rounds with round nose soft point bullets, and pistols are all about defense (OK, there are a few pistol hunters). So I went looking for rifle ammunition with RNSP bullets. Dang few choices! But being a simple bullet type, the ammo is fairly cheap. I bought some and played at the range a bit. One thing I can say: The RNSP rounds make a way bigger "splash" of dirt when hitting the backstop mound than a spire point bullet does. I guess the RNSP has way faster bullet expansion or mushrooming - on the right track for stopping power. For reference, here's a photo comparing some typical factory-loaded .30 cal ammo with RNSP vs FMJ or similar spire-points:

http://i702.photobucket.com/albums/ww25/Bill_Rights/30cal_762x39mm_FMJ_RNSP_and_308Win_RNSP_matchHP.jpg

As I said, it was pretty hard to find the blunt-nose soft points (RNSP). There are a lot more loadings with pointed soft points (PSP). The 7.62x39mm Russian RNSP is by Prvi Partizan (http://www.midwayusa.com/product/641174/prvi-partizan-ammunition-762x39mm-russian-123-grain-round-nose-soft-point-box-of-20) (Serbia). The .308 RNSP is Remington Express 308 Winchester 180 Grain Core-Lokt Soft Point (http://www.midwayusa.com/product/249807/remington-express-ammunition-308-winchester-180-grain-core-lokt-soft-point-box-of-20), though it's weird that Remington calls it "SP" and not "RNSP".

So, a few questions to think about or impart your answer:
- What other brands/models of RNSP rifle ammo are available that you know of? That you recommend?
- Why aren't these RNSP loadings more available?
- I guess it's because we don't buy much of this ammo - why don't we like RNSP?
- How much different is the terminal ballistics performance of the PSP bullets versus the RNSP?
- The soft, fat nose of the RNSP bullets get dented, apparently just from manufacturing (these were nicely isolated in their shipping/sales boxes). Not too sexy, eh? Does that make you not want to buy them? Does this affect accuracy and groupings much? [I don't much care, for short-range defensive loads.]

I saw some info and opinions slightly bearing on these questions in a recent thread (http://www.thehighroad.org/showthread.php?t=635430) here on THR.

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Rustinthewheel
January 28, 2012, 03:29 AM
I imagine a lot of the popularity of pointed tips is based on reliability of feeding in semi automatics.

303tom
January 28, 2012, 08:52 AM
These are some of what I use & Midway has them on the shelf.

303tom
January 28, 2012, 08:54 AM
And these.........

NeuseRvrRat
January 28, 2012, 09:09 AM
you could always get into handloading and have exactly what you want for very cheap

CooterShooter
January 28, 2012, 09:25 AM
I've honestly never given it much thought...but if I had to guess I'd say it is an issue of accuracy. Most people don't consider rifle rounds for personal defense, but rather for hunting, in which case accuracy is more important than stopping power. Anyone have any stats they could post, grouping measurements? I'd like to see.

Woodyard
January 28, 2012, 10:17 AM
Pointed bullets have higher ballistic coefficients and therefore retain velocity better at long range and have flatter trajectories. When the German military switched to the spitzer (pointed) bullet prior to World War I, virtually every nation in the world followed suit. Round nose bullets are still common in cartridges like the .30-30 for use in lever-action rifles with tubular magazines.

Bill_Rights
January 28, 2012, 11:27 AM
Woodyard said:Pointed bullets have higher ballistic coefficients Yeh, I was thinking that too, but isn't ballistic coefficient basically the bullet diameter divided by the length? So, looking at the .308 rounds in the photo, the RNSP would have the same B.C. as the BTHP spire-tip? (But, I do see that the pointy-er bullet would have less drag and retain speed better.

wraith56
January 28, 2012, 12:03 PM
sectional density is the weight divided by the frontal area(diameter squared). Ballistic coefficient is a much more complicated formula.

B.C. is meant to enable an expert to calculate how fast the bullet slows down with air resistance. I have also read that there is more than one scale/model for B.C.

for reference:
http://www.sierrabullets.com/bullets/BallisticCoefficient-rifle.pdf

this a big table of the B.C. and sectional density for Sierra's bullets. Aerodynamics is complicated. Using the typical model of B.C. many bullets on the chart have different B.C.'s at different speeds.

To the original question, I share the delusion that long pointy bullets will improve my accuracy. I suspect that sensible hunters who know how small the difference is don't purchase as much ammo as optimistic rifleshooters.

helotaxi
January 28, 2012, 12:10 PM
isn't ballistic coefficient basically the bullet diameter divided by the length?Not even close. Your description more closely matches "sectional density" which is the weight of the bullet divided by the diameter. Sectional density plays a part in ballistic coefficient, but the shape of the bullet is the larger proportion. The G7 BC of a bullet is the bullet's G7 form factor multiplied by it's sectional density. Form factors can vary greatly, while sectional densities are mostly within a fairly small range.

Every 180gn .308 bullet for example will have the same sectional density (.271), but because of form drag, their BC's will differ quite a bit. Within the Hornady range, for example, the 180gn SST has a BC (G1) of .480 while the 180gn RNSP has a BC (again G1) of .241.

The BC has nothing to do with precision of the bullet itself. What is does determine is the effect of drag. Drag determines drop (which is predictable and consistent) and wind drift (which isn't consistent and much harder to predict as a result). Since drop and drift are factors of velocity (or the change in velocity) they are indicative of decreasing velocity and likewise energy. Bullets with a low BC have a very limited range. While they can be very accurate, at extended ranges, they have less energy to put on the target and the increased effect of wind means that any variability there makes it increasingly difficult to hit the target as the range increases.

HOOfan_1
January 28, 2012, 12:20 PM
for reference:
http://www.sierrabullets.com/bullets/BallisticCoefficient-rifle.pdf


Use that and a ballistics calculator

http://www.handloads.com/calc/

Take a 150 gr. .308 Pro Hunter spire point with BC of .336
Take a 150 gr. .308 Pro Hunter round nose with BC of .200

Assume a 2800 fps muzzle velocity and 100 yard zero
By 300 yards, the round nose is already dropping 5 inches lower, already has over 500 ft-lb of energy less (also less than 1000 ft-lb of energy) and traveling over 400 fps slower.

The spire point has more velocity and enegry at 500 yards than the round nose does at 300 yards

Stantdm
January 28, 2012, 09:38 PM
Federal still offers the RNSP in a 150 gr. .270 bullet. I have one box left of 100 gr. Hornady 6mm Rnsps I use in a .243 out to about 150 yards for Whitetail. I use spitzers for longer ranges but for short range I like the Rns.

Bill_Rights
January 28, 2012, 11:53 PM
wraith56, helotaxi and HOOfan_1,

I stand corrected. Thank you. That's a great thing about THR; you folks aren't shy about pointing out error or calling BS ("BS" does not equal "Ballistic Section"), when warranted.

Anyway, I think you answered my question- I guess it's because we don't buy much of this ammo - why don't we like RNSP?That is, we don't like RNSP because of a lot worse bullet drop and somewhat more and more unpredictable windage drift, than spire/spitzer/pointed bullets have. RNSPs also have less energy upon impact. So this is in-flight ballistics. (However, for short-range hunting and defense, we really don't want a pointy bullet to tunnel right through at high speed, causing minimum damage. I recall one of those Military Channel sniper documentaries wherein a sniper actually said that the .308 win (7.62x51 mm 175 gr.?) sniper round is more deadly out at 500 yards or so, once it slows down!)

What about my question about terminal ballistics:- How much different is the terminal ballistics performance of the PSP bullets versus the RNSP?

Finally, Rustinthewheel, I have heard your complaint about RNSPs before: I imagine a lot of the popularity of pointed tips is based on reliability of feeding in semi automatics. I am not saying it can't be true, but I shoot the 7.62x39mm RNSPs shown above in Ruger Mini-30s, which are semi-auto and are prone to magazine and feeding problems until they're worn in. I had two new Mini-30s and the corresponding magazine and feeding problems until I smoothed the front out-feed lip of the mag box (see here (http://www.perfectunion.com/vb/ruger-mini-14-mini-30/86786-magazine-lip-cartridge-hangs-front-lip-factory-mini-30-mags.html)). Since then I have had no FTFs or any other problems with the Prvi Partizan 7.62x39mm RNSPs shown.

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