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View Full Version : Estimated BC for a powder-coated bullet please!


Pond, James Pond
December 16, 2016, 07:50 AM
.311 cal (7.62x39), LRN, powder-coated, 195gr.

I'm trying to get a rudimentary BC going for this bullet so I can start to play around in Strelok.

If these heavy-bullet commercial reloads are not abusive to my slide-stop/receiver I may still use them so I want some idea of trajectory. Probably vertical by 300m, but only one way to find out!!

30Cal
December 17, 2016, 05:24 PM
0.25 is going to be pretty close for any RN bullet. Powdercoating doesn't factor into it.

Pond, James Pond
December 17, 2016, 05:30 PM
Thanks!
That is enough to get some idea of trajectory.

tobnpr
December 19, 2016, 12:48 PM
195 grain? :eek:
You bet it'll be vertical at that range...not even load data in my book for anything heavier than 150's. Even those are barely squeaking out at around 2K fps.

Why so heavy?

Pond, James Pond
December 19, 2016, 01:20 PM
They are powder coated bullets that make the x39 a major power factor round in IPSC.

I expect anything beyond 100m will be more lobbing that shooting...

T. O'Heir
December 19, 2016, 02:22 PM
A 195 grain bullet in a 7.62 x 39 will be far too long. Those are probably for .303 British. However, the BC formula is on-line. Might be in your load manual too.
BC = mass / d squared x i . d = measured cross section. I = Coefficient of form(mostly the length of the bullet). And all of that will vary. The actual shape of the round bit of the bullet will change the BC.
It's literally the 'Drag of the standard projectile' divided by the 'Drag of a test projectile'.
Read this my head is starting to hurt.
http://www.hornady.com/ballistics-resource/external
"....25 is..." That's the sectional density. Actually a tiny bit under it, but a Speer 180 grain .311 RN's BC is .328.
Powder coating does not make the x39 anything. Powder coating is just baked on paint.
"...expect anything beyond 100m will be..." Depends on the rifle, but a 195 grain bullet is far too heavy for 7.62 x 39. Isn't any load data either.

Pond, James Pond
December 19, 2016, 03:49 PM
Depends on the rifle, but a 195 grain bullet is far too heavy for 7.62 x 39. Isn't any load data either.

No load data needed. These are already loaded and ready to fire by a commercial reloading company.

tobnpr
December 19, 2016, 09:51 PM
So...I educated myself a bit on IPSC major power factor...
Wouldn't pushing bullets in the 150-160 class (like a 155 @ 2100) qualify and not drop so much like a rock, and with less recoil? No?

Pond, James Pond
December 20, 2016, 12:06 AM
So...I educated myself a bit on IPSC major power factor...
Wouldn't pushing bullets in the 150-160 class (like a 155 @ 2100) qualify and not drop so much like a rock, and with less recoil? No?

Probably, but for whatever reason the company opted for 195gr. Perhaps indeed because they can get these bullets already, but originally cast for .303...

I decided to try these bullets for 2 reasons. First was that thought that powder coated would cause less barrel wear than the ubiquitous bimetal jacket rounds for x39 and the other was that they were relatively affordable at "only" 20% more than the cheap Russian stuff.

Perhaps the recoil, given the lower velocity, will not be bad...

shootniron
December 20, 2016, 12:35 AM
Perhaps the recoil, given the lower velocity, will not be bad...

Lower recoil from lower velocity will be more than overcome by heavier bullet.

Pond, James Pond
December 20, 2016, 01:02 AM
Lower recoil from lower velocity will be more than overcome by heavier bullet.

Possibly. I'll have to see.

I've a plan to compare bimetal and powder-coated pretty soon, but I have previously found standard rounds to be pretty soft shooting in the VZ58 (far more so than an AK and that time it was folding stock VZ vs standard stock AK), so maybe the gun will tame this too.

Either way, if a bit more recoil is the price for a pampered barrel and wallet, then so be it!!

Chainsaw.
December 20, 2016, 03:20 PM
Cast and powder coat your own.

Model12Win
December 20, 2016, 04:18 PM
The standard 123 grain AK load is essentially an indirect area weapon with a rainbow trajectory that is only effective to about 200 meters in perfect conditions as it is.

A 195 grain load? Fuggeddaboudit!!! :D

Really though, it might be worth a shot! You'll need some holdover though, that's for sure!!

tobnpr
December 20, 2016, 07:55 PM
^^
Google "IPSC major power factor" and maybe your eyes will roll back in your head like mine did. Points aren't about how many x-ring hits you got. Crazy, complicated method of scoring that's difficult to follow (it was for the ten minutes I was willing to try ).

Which is why Pond is talking about recoil- it's a variable that affects your score. They chrono your loads, take velocity x bullet weight and divide by a constant...Never heard of this before, not as popular a competition here in the U.S.