vertical groups at distance

[aaronraad]

Aaron,
Cant use traillboss, the case isn't big enough with a 200gr+ projie so the easiest option is 2205 followed by 2400 and 296, cant remember what the VV powder was but I cant get any so it doesnt matter. I'm picking up a pack of Lapua 308 200gr factory ammo this week so I will pull one and see what the projie looks like.

Tin Star - VV?

Some good info on subs at Sniper Hide thread. http://forum.snipershide.com/snipers-hide-suppressors/178642-subsonic-308-projectile-recommendations.html

A few comments on Trailboss, H110 etc and the 300 AAC/308W.

The trajectory of the 30 cal subs starts to make a fast twist rifles 12GA look much more appealing. Sounds silly but you're almost better off fitting a scope with a laser range finder to hit targets past 50y accurately. Errors in range estimation at 100y by +/-5y suddenly shift the POI by inches not millimetres.

[AlanF]

...Page 181 of Applied Ballistics (The Nature of Bullet Dispersion) talks about 2 types of dispersion...

I haven't read Bryan's book Denis, but I think this is just a difference in the way he approaches the subject. He has chosen to divide types of dispersion in a different way. I have chosen to divide them into (1) those which CAN be detected with short range testing with a chronograph and (2) those which CANNOT. You can take most subjects and divide them in different ways, depending on what point you're trying to get across.

Alan

[DenisA]

...Page 181 of Applied Ballistics (The Nature of Bullet Dispersion) talks about 2 types of dispersion...

I haven't read Bryan's book Denis, but I think this is just a difference in the way he approaches the subject. He has chosen to divide types of dispersion in a different way. I have chosen to divide them into (1) those which CAN be detected with short range testing with a chronograph and (2) those which CANNOT. You can take most subjects and divide them in different ways, depending on what point you're trying to get across.

Alan

It all needs to be understood and applied.

My point is that for this cartridge, I believe 300 yards is long range and subject to long range principles, physics and requires LR attention to detail.
If it is bullet inconsistancy causing the characteristics of tight grouping up close and open groups out further as you and Dave have suggested, then it is still launch dynamics dispersion. The same subject/effect includes gun setup imperfections/harmonics, etc..................to my understanding..

I'm not saying that the gun needs to be modified, just that it may be a common characteristic with this cartridge at that distance where the platform is not perfectly setup to LR shooting.

Seddo, what is the stock, type of bedding and barrel prifle?

[DenisA]

I've been looking up some info on this cartridge and it seems that its a great tactical and hunting cartridge but has some idiosyncracies to be aware of.

Found a good description of it at:
http://www.300whisper.com/

A couple of points I thought were relevant, only describing minute of angle accuracy and the effect of slight load inconsistancies. It refers to powder, but I suggest that would be the same with seating depth, neck tension etc.

1. "The 240 grain Sierra Matchking launched at a muzzle velocity of 1040 FPS/576 foot pounds energy arrives at 200 yards with a velocity of 976 FPS/508 FPE while maintaining minute of angle accuracy from bolt action rifles and many autos".

2. "Normal shot to shot variations can change velocities substantially. Leaving a loaded round in a hot chamber can easily transform a sub-sonic round to sonic. In many loads, each one tenth of a grain of powder can change the velocity 30-40 FPS which is normally not a big deal".

Sounds like a sensitive and finicky cartridge.

[AlanF]

Denis,

I see your point. The Whisper starts out subsonic and gets even "subber", and normal F-Class ballistics characteristics don't apply. My approach is to always stay supersonic. The F-Open rules make that easily possible even at 1500 yards.

Alan

[mike H]

Have used 208 A Max's in Match Rifle to 2680 fps and more than happy with them,but that is not at subsonic velocities.The way I see it is that modern high BC projectiles are meant to get to the target in a hurry and not drop into subsonic levels.
The whisper and the newer 300 Blackout were never designed for long range,I would like one,but at the moment am happy to shoot around 200 grain lead bullets out of a .308.
Certainly an interesting project Seddo.
Mike.

[bruce moulds]

the 30 cal bullets cannot have the bc of 45 cal ones, because a large part of bc in this case comes from weight.
here are some actual comeups for a 40 cal 420 gn bullet.
100m 0
200m 12 moa 200- 300 13 moa
300 - 400m 13 moa
400 - 500m 15 moa
500 - 600m 14 moa
600 - 700m 16 moa
700 -800m 19 moa
800 - 900 m 20 moa.
as you can see, not many scopes have this kind of travel.
to run a long range target rifle , usually 0.010 on the rear sight is about 1 moa.
you need the rear staff to have 2" useable to be safe at 1000 yd when shooting with irons.
using a scope requires adjustable scope mounts, usually with windage on the front mount, and elevation in the rear, and vernier not click adjustable.
at these speeds high air pressure, cold air, and a headwind can offer a 20moa elevation requirement to the opposite at 1000 yd.
the old printed score books with plot sheets all had space to record temperarure normally and wet bulb, and a barometer reading, to better understand sight settings.
one advantage black powder has over smokeless is that it is not hard to get e.s down to 4 for about 20 shots. s.d variations are so small as to be meaningless.
casting bullets with no voids is critical, and in the old days guys used hammer swages to close up voids, thus producing better balanced bullets.
keep safe,
bruce.

[Seddo]

Wow, i didn't expect this to get into the second page. The reason i posted this question here was i thought the things that made my subsonic round go vertical at 300 would/should be the same as a 308 at 1000y.

Here is the rifle:



Winchester Model 70
16.5" 8 Twist Lothar barrel
Timney Trigger
Farrel 20moa base
TPS Rings
Clearidge 2.5-12.5x44 Mildot (90moa of travel)
Manners T5 Stock
CDI DBM with AICS Mag
Pillar bedded.

The rifle was built 3-4 years ago by a victorian gunsmith, bedded by a different victorian gunsmith and cerakoted by ADJA. I haven't fired it since its been cerakoted but i was planning on waiting for the new brass.

Here are 2 different rounds with a 223 and 308 case for comparison. THe 208 amax are what i fire out of the winchester, the 155gr (Nosler CC) load is what i fire out of my Rem 7615 pump so it has to be loadewd to mag length. Both of the chambers were cut with my reamer.



The subsonic load is 9.8gr AR2205, jammed 208 amax, Fed GM Primers and Remington 221 cases that have been FL sized and trimmed.

I have some Lehigh projies that have been designed to open in the 750-1250fps range but i wont get a chance to try them on game for a few months, it will be in the 50-100m range only.

Here are a couple of other weird ones...

[DenisA]

Beautiful looking rifle Seddo. Must be a dream to hunt with......... comfy and low recoil. Whats the weight?

[bruce moulds]

seddo,
if I were an investigative journalist, I might have sniffed a story.
rifle built by one gunsmith, and bedded by another?
could be more here to be discovered.
keep safe,
bruce.

[Seddo]

Bruce,

There is a lot to read between the lines but to save you the effort here you go, no names of course. Lets say this rifle was 1 of 2 rifles the first gunsmith gave me that didn't have to go back to be re-chambered. All 4 rifles shoot really well, it just annoyed me having to get 2 redone. Then gunsmith 2's attempt at bedding saw me not give him a second job. His pillar bedding job works well but looks terrible. There was almost no colour added to the bedding compound so its a whitish clear colour, I know its more about how it works than looks but it annoyed me. That gunsmith has built a rifle for a mate and its a tack driver so his work is good.

Denis,

I cant remember what it weighs, its not a featherweight but not overly heavy compared to most of my rifles. I haven't had it out of game yet, that trip is planned for March or April next year and I will be giving it a red hot go. I just hope I can get some 110 vmax by them as they were suspended. I picked up a Sightron SIII 3.5-10x44 for my DTA but can see one going onto the whisper in the future, having 120moa of adjustment will extend the range if I get the vertical sorted.

I find the mildot works well with the 208 amax. With a 80y zero you aim under the target at 50y by 1 mildot and then at 100y its just on top of 1 dot down and 150y is just on top of the 3rd dot down.