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Author Topic: Using 75gr while sighted in for 55gr
OLM-Medic
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I keep my AR-15 sighted in with 55gr M193. This is my ammo choice, besides heavier bullets which I can not afford in large quantities. Since I can not afford much of them, I must keep my AR sighted in with 55gr M193.

I have a very limited amount of Hornady 75gr TAP and since it is known to be a very good antipersonnel round I would like to keep a mag or two for it.

Tests show that at 25yards the TAP will shoot almost 2" higher than POA would be with 55gr. I don't think this is that big of a deal since I would mainly just have one magazine of TAP for CQB in my house.

I have no idea how different POA would be out to longer distances though. It is a shame too, since this should be very accurate ammo at longer ranges.

Anyone else have this dillema?

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"Remember that your adversary's desire to live is usually more powerful than whatever ammunition your are carrying in your firearms. Plan accordingly." -tire iron

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Lord Vader
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Friend for center mass shots 2in higher at 25yd will make no difference, but for an enemy that might be wearing level III or IV body armor you will need to take head shots but if you put your sight on the bridge of the nose it will still be OK. Another thing since you intend to use it for inside your home the difference in POI will be a lot less then 2in since most likely your enemy will not be over 25 Feet away and may even be less then 10 feet. And at extremely close range the POI of the 75gr may be even under the POA of the M193.

By the way POI is Point Of Impact. POA is Point Of Aim.

It is just my opinion but I would not switch from 55gr to 75gr for CQB like you want to do. The 55gr is just fine for close up use, it is only at longer ranges that the 75gr or 77gr are superior.

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VINCE AUT MORIRE (Conquer or Die)

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OLM-Medic
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quote:
Originally posted by Sniper_762X51:
Friend for center mass shots 2in higher at 25yd will make no difference, but for an enemy that might be wearing level III or IV body armor you will need to take head shots but if you put your sight on the bridge of the nose it will still be OK. Another thing since you intend to use it for inside your home the difference in POI will be a lot less then 2in since most likely your enemy will not be over 25 Feet away and may even be less then 10 feet. And at extremely close range the POI of the 75gr may be even under the POA of the M193.

By the way POI is Point Of Impact. POA is Point Of Aim.

It is just my opinion but I would not switch from 55gr to 75gr for CQB like you want to do. The 55gr is just fine for close up use, it is only at longer ranges that the 75gr or 77gr are superior.

Oops I don't know why I kept saying POA.

I know you are right about the heavier grains for longer distance. The 75gr stuff has shown to be a very good round when it comes to fragmentation though, so I was going to keep one magazine of this loaded in my AR.

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"Remember that your adversary's desire to live is usually more powerful than whatever ammunition your are carrying in your firearms. Plan accordingly." -tire iron

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Archangel1
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What is the zero distance for the rifle using 55gr projectiles, when the 75 gr projectile is 2" high at 25 yards? Wouldn't Zero distance affect the POI at 25 yards?

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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OLM-Medic
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quote:
Originally posted by Archangel1:
What is the zero distance for the rifle using 55gr projectiles, when the 75 gr projectile is 2" high at 25 yards? Wouldn't Zero distance affect the POI at 25 yards?

Well I zero my rifles for 50/200yards. The 75gr was just 1-2" higher than the 55gr was when I was shooting at 25yards.

--------------------
"Remember that your adversary's desire to live is usually more powerful than whatever ammunition your are carrying in your firearms. Plan accordingly." -tire iron

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Archangel1
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OLM, Thanks.
I didn't expect that much difference at 25 yards. I got to the range too late to test various weight projectiles the other weekend.

Can you direct me towards bullet drop ballistics for 55gr vs 75 gr projectiles with 1/9 and 1/7 twist barrels?

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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Lord Vader
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quote:
What is the zero distance for the rifle using 55gr projectiles, when the 75 gr projectile is 2" high at 25 yards?
I have no idea what range the rifle was zeroed at

quote:
Wouldn't Zero distance affect the POI at 25 yards?
The range or distance a rifle is Zeroed will effect the POI at 25 yd and at all other ranges.

I don't know how much you or the other members of this board know about Ballistics, so I will say this.

The hight of the sight line above the bore line and the Zero Range will effect the POI at all other ranges.

Since all sights that I know of except for LASERs mounted under the barrel, are above the Bore Line, a bullet when fired will appear to rise upon firing.

What happens is the Bore is lower then the line of sight so when lets say you sight in at 25 yd the bullet must rise (gain hight) in order to strike the POA.

The AR-15 has a very high line of sight vs bore line which can be easily seen by looking at the front sight.

The POI at 25 yd would be the Rifles Near Zero, the bullet will continue to rise until it starts back down and at some point it will again cross the POA which would then be the Rifles Far Zero.

The Bullet crosses the POA twice once at close range and once again at longer range.

Now since I am not shooting in competition I really don't care if the POI and the POA are exactly the same as long as it is close enough, so I use what is referred to as a Combat Zero.

I sight in so that it is Zeroed at 200 yd which puts the POI about 2 in high at 100 yd and is Zeroed again at closer range like 25 to 50 yd. The POI will be several inches low at 250 yd.

The exact POI at 100 yd with a 200 yd Zero depends on the hight of the line of sight and the Barrel Length.

In combat from close range out to app 250 yd you can just engage the enemy without having to know the exact range. Or course if you have the time and you know the exact range you should set the sight for the correct range but for most normal combat, if there is such a thing as (normal combat) using a combat zero will work out just fine most of the time.

One more thing if you have an AR with the A2 Rear Sight there is one adjustment most people don't know about.

As received the Range Adjustment on the Rear Sight starts at 200 yd which means if you really want a 100 yd Zero you have to set the Zero with the sight set at 200 yd which makes the settings for longer ranges useless.

There is a way to solve this problem.

There is a small hole behind the rear sight, at the bottom of this hole is a small Hex or Allen Head screw.

I don't remember the size of the Allen Wench needed but when the screw is loosened the Range Adjuster can be Bottomed out and when the screw is tightened you now have a 100 yd position on your A2 sight.

What this does is now with the Range Adjustment bottomed out you can sight in at 100 yd and when you set the Adjustment for 200 yd the rifle will now be Zeroed at 200 yd and all the other marked ranges will also work as originally intended.

This also works for the Sight on the Removable Carry Handle.

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VINCE AUT MORIRE (Conquer or Die)

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Archangel1
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Sniper, Thanks for the lesson. I understand the concepts of projectile ballistics, although I am by no means an expert. It's basic physics, so I didn't expect the 25yd POI to be much different with a 55gr vs 75gr projectile unless the zero distance was far enough so gravity would have an effect on the projectile.

I will check the sight for the allen set screw. I suspect that my range will be <50m to ~200M. I didn't know to look for it.

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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okcmilitia
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There's always factors involved besides weights of bullets. The twists, barrel lenghts and powders along with the type of bullet vs another. For example spitzer vs a Boat tail spitzer. Each rifle is differnt in how it might shoot a particular round. Scope vs open sights too. The height/ distance from the scope in relation to the bore makes a difference. So, there are a lot of factors to consider. It sould be noted when you change ammo you most likey will have to make adjustments. Especially at longer distances say past 200 yrs for sure. I learned what I did two ways. One trying, and the second way is I'm a graudate from North Amrican School of Firearms.

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Still seeking the truth

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tire iron
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OLM,

Don't know where you got your information regarding the 75 grain stuff shooting 2 inches differently at 25 yards - cause that is 1,000% WRONG.

I use a 50 yard zero for my 75 grain Black Hills ammo. At 25 yards I am 1.26" low, dead on at 50 yards, 1.57" high at 100 yards, 1.85" high at 150 and dead on at 221 yards. The drop at 300 yards is 6.5".

With M193 55 grain ammo - it puts me at 1.26" low at 25 yards - dead on at 50, 1.02" high at 100, 2.4" high at 150 yards and back to dead on at 250 yards. The drop at 300 yards is 3.19".

In other words - there is never more than 1 inch difference until you get to 250 yards. At 25 yards they will go in the same hole.

Hope this helps,

cheers

tire iron

--------------------
An amateur practices something until he gets it right - a pro practices something until he can't do it wrong.
My Schools: http://www.acpsllc.com
http://utahguntraining.com
Utah Gun Training

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OLM-Medic
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quote:
Originally posted by tire iron:
OLM,

Don't know where you got your information regarding the 75 grain stuff shooting 2 inches differently at 25 yards - cause that is 1,000% WRONG.

I use a 50 yard zero for my 75 grain Black Hills ammo. At 25 yards I am 1.26" low, dead on at 50 yards, 1.57" high at 100 yards, 1.85" high at 150 and dead on at 221 yards. The drop at 300 yards is 6.5".

With M193 55 grain ammo - it puts me at 1.26" low at 25 yards - dead on at 50, 1.02" high at 100, 2.4" high at 150 yards and back to dead on at 250 yards. The drop at 300 yards is 3.19".

In other words - there is never more than 1 inch difference until you get to 250 yards. At 25 yards they will go in the same hole.

Hope this helps,

cheers

tire iron

The information came from an actual test I did, except it was full of human error. I didn't confirm zero with 55gr before shooting 75gr, and assumed it was zeroed...next time I realized it wasn't.

After zeroing with 55gr so it is dead on at 50yards, I again shot the 75 gr TAP. It shoots a bit high at 50 yards (not 25 as I thought), but it is not as high as I thought. It was about an estimated (I haven't measured) 1.5-2" high and about 1" to the right at 50 yards. The M193 was dead on.

For me, there is a bit of difference in POI with the two ammo types. Still, it is not that much. I keep one mag of it in my AR for HD.

--------------------
"Remember that your adversary's desire to live is usually more powerful than whatever ammunition your are carrying in your firearms. Plan accordingly." -tire iron

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Archangel1
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I found that my POI is different between brands of 5.56 and .223 ammo. That's why I try to buy Federal 193 FMJ instead of buying many brands. It's just hard to consistently find 1000 rounds of Federal 193 at reasonable prices.

TI, do you buy red or blue box Black Hills ammo? Has it become your primary AR ammo?

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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tire iron
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Archangel1,

Yep - different ammo will have a different POI. I buy the blue box 75 grain stuff. I zero my rifle with that - and then train with whatever is the cheapest stuff I can find and those rounds will impact "close enough" for training.

Hope this helps,

cheers

tire iron

--------------------
An amateur practices something until he gets it right - a pro practices something until he can't do it wrong.
My Schools: http://www.acpsllc.com
http://utahguntraining.com
Utah Gun Training

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Archangel1
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Understand. I have been building 55 gr inventory with some green tip but wonder if 75 gr should be a heavier percentage.

As I build ammo inventory, what percentage do you recommend 75 black hills vs 193 or 855?

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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tire iron
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I wouldn't stock up on any M855. In my opinion it is nearly worthless. M193 penetrates steel better than M855 out to 200 meters anyway. M855 is not a reliable performer at all. Whatever you have - sell it or trade it for M193.

I have about 250 77 grain rounds that I don't shoot. I have around a thousand M193 that I don't shoot. I shoot 55 grain Wolf or whatever is cheapest.

In other words - stock up on your "rainy day" ammo then everything you buy after that is training ammo. Don't forget the .22 converter - that is CHEAP training/ammo.

cheers

tire iron

--------------------
An amateur practices something until he gets it right - a pro practices something until he can't do it wrong.
My Schools: http://www.acpsllc.com
http://utahguntraining.com
Utah Gun Training

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Archangel1
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quote:
Originally posted by tire iron:
I wouldn't stock up on any M855. In my opinion it is nearly worthless. M193 penetrates steel better than M855 out to 200 meters anyway. M855 is not a reliable performer at all. Whatever you have - sell it or trade it for M193.

I have about 250 77 grain rounds that I don't shoot. I have around a thousand M193 that I don't shoot. I shoot 55 grain Wolf or whatever is cheapest.

In other words - stock up on your "rainy day" ammo then everything you buy after that is training ammo. Don't forget the .22 converter - that is CHEAP training/ammo.

cheers

tire iron

I have limited 855 which I can't shoot locally out of the range's fear of starting a fire. I won't buy more. Federal 193 is my prefered round so my zero remains fairly consistent.

I have some Wolf but the local ranges don't like the steel cases and my gunsmith recommended against using the steel case round as well.

I did invest in a 22 conversion kit for cheap practice. My only issue with the conversion kit is the need to rezero my sights between 5.56 and .22 rounds.

Thanks for the advice!

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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OLM-Medic
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quote:
Originally posted by tire iron:
I wouldn't stock up on any M855. In my opinion it is nearly worthless. M193 penetrates steel better than M855 out to 200 meters anyway. M855 is not a reliable performer at all. Whatever you have - sell it or trade it for M193.

I have about 250 77 grain rounds that I don't shoot. I have around a thousand M193 that I don't shoot. I shoot 55 grain Wolf or whatever is cheapest.

In other words - stock up on your "rainy day" ammo then everything you buy after that is training ammo. Don't forget the .22 converter - that is CHEAP training/ammo.

cheers

tire iron

Yeah, M855 is crap. A poor decision my the military just like the M9.

quote:
I have limited 855 which I can't shoot locally out of the range's fear of starting a fire. I won't buy more. Federal 193 is my prefered round so my zero remains fairly consistent.

I have some Wolf but the local ranges don't like the steel cases and my gunsmith recommended against using the steel case round as well.

I did invest in a 22 conversion kit for cheap practice. My only issue with the conversion kit is the need to rezero my sights between 5.56 and .22 rounds.

Thanks for the advice! [/QB]

You don't need to rezero your sights. It shouldn't be dramatically different of a zero.

--------------------
"Remember that your adversary's desire to live is usually more powerful than whatever ammunition your are carrying in your firearms. Plan accordingly." -tire iron

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Archangel1
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At 100 yards, there is a difference between 22LR and .226. I am primarily practicing with a 50-200 range with a bit at 300 and 500 yards. .22LR is not happy beyond ~150 yards.

As an aside, do you guys like the PRIVI 5.56 if I can't get Federal at a reasonable price?

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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tire iron
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Arch - use reduced sized targets for anything past about 50 yrds when working with .22lr.

I don't know if the PRIVI projectile is constructed to M193 spec or not.

cheers

tire iron

--------------------
An amateur practices something until he gets it right - a pro practices something until he can't do it wrong.
My Schools: http://www.acpsllc.com
http://utahguntraining.com
Utah Gun Training

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OLM-Medic
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There is a rumor that their bullets are not the same jacket thickness. Just get a good stock of Fed Lake City M193 and store it for a rainy day.

--------------------
"Remember that your adversary's desire to live is usually more powerful than whatever ammunition your are carrying in your firearms. Plan accordingly." -tire iron

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Archangel1
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I read that PRIVI was a NATO M193 round. I've heard about jacket thickness and velocity differences vs. Federal, hence I was hoping that you guys would steer me in the right direction.

What I can't figure out if I'm saving for a rainy day or 40 days and 40 nights.

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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OLM-Medic
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By the way, I have since decided that doing this was a dumb idea. I am not likely to use more than one magazine in an engagement. I want to make that magazine have ammo that I train with, and am sighted in to be dead on accurate for.

M193 it is.

--------------------
"Remember that your adversary's desire to live is usually more powerful than whatever ammunition your are carrying in your firearms. Plan accordingly." -tire iron

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