M14 Rifle

[Shannow]

Dark Jedi,
I wasn't referring to old equipment, but equipment that cannot shoot accurately.

A rifle that shoots a "10 shot pattern" cannot score well simply as a result of the shooter's skill. You simply cannot predict which direction, and by how much each shot is going to throw from the point of aim.

 

[savvy]

Shannow

That's an excellent and thorough definition of headspace ! You get an A+

Just a thought, I have always believed that a projectile is not a projectile until it is projected out of the barrel. While it is still in the chamber, or going down the barrel, but has not left the muzzle...... I believe technically it is just called a bullet.

[ February 16, 2006, 03:06 AM: Message edited by: savvy ]

 

[ALS]

If your shooting a .308 move up to 175 gn Seirra Match Kings at any distance over 400 yards.
I have no problems out to 1000 yards with the 175's. I'm loading 42.2 gn's of IMR 4064 with a over all length of 2.78 inches. That load gives me an average muzzle velocity of 2649 fps. At that velocity the bullet stays supersonic out past 1000 yards. BTW That is out of Rem 700 with a heavy 26" SS barrel with a tight match chamber.

 

[jmacmaster]

I'd get a bolt action rifle with a thick barrel. Some people call it a varmint barrel. The longer the barrel, the better. As said above, don't skimp on $ for the scope and get a scope that adjusts up to at least 12X. I suggest the .25-06 cartridge. You have all the power of the 30-06, but with the necked down bullet you're shooting a lot lighter bullet and it'll go a lot farther and do so with a flatter trajectory. I live in Montana, where shots of 400-600 yards on deer and antelope are common in the eastern 2/3 of the state. I don't know anyone who hunts with a .308 at that range, but the .25-06 is praised at that range.

 

[savvy]

quote:

---

Can you explain to everyone who may not know: At what temperature does your velocity averages 2649 fps, and what happens to your velocity as you deviate from that temperature up or down, and why.

Also would you explain to others : Why is keeping a projectile above supersonic desirable, and what happens to the round as it goes subsonic.

---

Anyone willing to take a shot at the questions ?!

Let's add a few other variables to the pot. How does altitude effect bullet impact assuming you use sea level and a standard 60F as your reference. How would you adjust your point of aim at say 8,000 ft @ 32F if your zero'd at sea level@ 60F ?! Of course the actual numbers depends on the S.D. the B.C. and the velocity of the bullet, but exclude those factors for now.

Should you aim

A) Higher
B) Lower
C) No adjustment needs to be made.

To make matters more interesting, now you have one shot available @8,000 ft @ 32F at a 30 degree downward angle. How do you further adjust your point of aim to account for the angle shot ?!

Should you aim

A) Higher
B) Lower
C) No adjustment needs to be made.


jmacmaster

I've heard many guys use a .25-06 for antelope. It was originally a Wildcat that some gun makers made available to the public. I did a lot of research on the .25-06. If I can remember correctly the throat tends to erode more quickly because it is somewhat overbore. Also from an accuracy perspective you cannot fill the case with a suitable powder ' as far as I remember ' so that you have a tightly packed case.

Even if you can pack the case @ 100%, your into an overbore situation. If you can shake your rounds and hear powder inside, your rounds will never be as accurate as they could be. A .25/06 is a great round, don't get me wrong. I think in a .25 caliber, the .25/284 is ballistically superior because of the shorter case. The 25/284 holds as much volume as the .25-06 which means a shorter powder column for more consistent ignition. Of course the .25/284 is a true Wildcat.

 

[ALS]

Savvy
Those velocity averages were Chronographed at temperatures of between 65 and 70 degrees.

The rule of thumb with 175 gn 308's on Temperature is at "1000" yards for each change of one degree there is a corresponding change of 1 inch in rise or drop. So if the gun was zeroed at say 60 degree's and the temperature is now 70 degree's at the same altitude you can expect the bullet to hit 10 inches high. Same is true if that second shot is made at 50 degree's you would see a drop of 10 inches off your center. So when shooting keep your ammunition covered so that any direct sunlight doesn't heat up the shells. Warmer the ammunition higher the pressure created by the ignition of the gun powder.

Same is true of altitude. For every 100 ft change you can expect a corresponding change of 1 inch at 1000 yards. So if zeroed at sea level and your shooting in Denver (5K ft) at the same temperature you can expect the bullet to hit 50 inches high. That is due to the air density change. Humidity has little effect on bullet performance. It's there it just is insignificant to most shooters.

The spinning of the bullet or Magnus effect (right hand twist) also will cause the bullet to drift up to 24 inches to the right at 1000 yards.

The rotation of the earth also has and effect on the bullets path. This is called the Coriolis effect. It has no effect if shooting East to West or West to East. But if you shoot North to South or South to North it will effect the path or windage L to R.

Keeping the bullet supersonic makes sure that the accuracy is retained by keeping the air from effecting the trajectory. If you notice on a match rifle bullet there is a tiny hole or hollow point in the tip of the bullet. There is a reason for that design. When fired the bullet creates a tiny air bubble in that indentation.
That air bubble is a buffer between the sound barrier or wave in front and the bullet itself.
Once that sound barrier is lost the bullet begins to be effected by the air it is passing through. The bullet begins to yaw or wobble as both the rotating and forward speed decrease.

The type of bullet you use matters at long or short distance. For example my 300 win mag is lucky to keep a 2 inch group at 100 yards with 190 gn match ammunition.
Yet I have shot 5 shot 2 1/4 inch - 2 1/2 groups at 700 yards with the same gun and ammunition. The reason is when the bullet leaves the muzzle it yaws or wobbles for a period of time before it settles down due to the effect of spinning.
If I shoot 155 gn factory hunting rounds it will group easy under 1/2 moa at 100-200 yards.

Let me add I have a separate Data book for each of my long range rifles.
Data Book

[ February 16, 2006, 04:27 PM: Message edited by: ALS ]

 

[savvy]

ALS

Everything you have said is totally accurate. I must be behind the times, the only indentation in the Meplate I am aware of was to gain a ballistic advantage by pushing the CG rearward. Some large caliber rounds use an aluminum Meplate to further extend the CG beyond what is capable in the typical Tangent or Secant ogive design.

Yes, when the bullet becomes subsonic, it destabilizes. There is not enough energy to sustain the rotation to maintain stability.

Yes, the Magnus effect, right drift in a RH twist. You can essentially cancel out the Coriolis effect in the northern hemisphere by using a LH twist.

Any deviation in shooting angle up or down from the horizontal position will require an adjustment. The greater the degree and distance, the greater the adjustment must be. If you are shooting at a 30 degree angle up or down, the impact will always be high in both cases.

You have a great deal of knowledge......... use it wisely.

 

[savvy]

ALS

Just as a side note.

I'm sure the dimple in the Meplat is valid science. Having said that, I have never shot a match grade round that had a indentation in it. I've never shot the 30 cal family of bullets, so maybe that explains it.

The last competing I did was with the FCSA ~ Fifty Caliber Shooters Association. I've shot bullets with a B.C. as high as 1.07@ 800 gr.

The issue of going subsonic is just a result of the bullets inability to maintain energy, and velocity. Thats where a high BC bullet comes into play.......it will resist drag better, and maintain velocity and rotation. All bullets must cross the subsonic threshold eventually. There is a marked increase in yaw, and destabilization at the subsonic threshold. I believe a round with a dimple in the tip behaves just like any other when crossing the subsonic threshold. Both exhibit yaw and destabilization as a result of less energy to maintain rotation. Rotation is the only thing that keeps a bullet stable. Without rotation, the bullet would just yaw and tumble. So in my opinion, a bullet will yaw and destabilize when the minimum rotation speed to keep the bullet stable no longer exists....... which usually coincides with the transition to subsonic.

As you mentioned, with some rounds, it can take several hundred yards for a bullet to stabilize. With 50's it can take five or six hundred yards before the round settles down and goes to sleep.

 

[1sttruck]

Most people shooting a 'service rifle' in highpower rifle used an M1A, a few still used M1 Garands but almost all were .308 models. The best shooting that I ever witnessed was at the 300 yard rapid, where you start standing with a loaded weapon and have 70 seconds to drop into position, shoot, reload, and finish your string. Our group was in the butts pulling targets for the guys shooting, where we'd switch when they were done. When the string was done the guy a couple of targets over couldn't count ten holes as the group was too tight. They made the guy reshoot, and again they couldn't ten holes. On the third string his groups finally opened up enough to count all ten rounds. Remember that this was rapid fire, and that in highpower you use iron sights.

Match grade M1As that were highly tuned didn't seem to stay that way for long, and they were expensive to set up.

 

[savvy]

ALS

Can you explain to everyone who may not know: At what temperature does your velocity averages 2649 fps, and what happens to your velocity as you deviate from that temperature up or down, and why.

Also would you explain to others : Why is keeping a projectile above supersonic desirable, and what happens to the round as it goes subsonic.