advise on scope

[larrydickman]

Looking at replacing my old tasco 4x32 scope on my ar15. I have a buddy that will sell me his Nicon PROSTAFF 3-9X40 MATTE BDC for 100$. Is this a good scope to put on my gun that will imporve the results of my bad groupings of 8 inches at 100 yards? I may have another problem. When I bought my upper and built my gun on a PWA lower I bought it from a friend who had a [legal] machine gun in Florida many years ago. He was putting on a different twist for his gun and sold me his upper to build my gun. I have always wondered if the guns barrel was heated up too much and could this be why it seems like the gun will not shoot as accuratly as my Colt? Or is it the 29$ walmart tasco scope? The thing is I have had several of these cheap scopes on guns like my Remington 700 and they shot at 100 yards fine.

[JLA]

#1 - a 300 dollar scope for 100 bucks is a great deal, BUY IT BEFORE I DO!

#2 - 8" @ 100 yds sucks, somethings wrong...

#3 - an upper from a full auto has seen 2 things, lots of heat and lots of rounds. Heat causes the barrel to foul worse than a cool barrel, Im betting the bore may be either severely fouled or its shot out.

[GunHugger]

Originally Posted by JLA

#1 - a 300 dollar scope for 100 bucks is a great deal, BUY IT BEFORE I DO!

#2 - 8" @ 100 yds sucks, somethings wrong...

#3 - an upper from a full auto has seen 2 things, lots of heat and lots of rounds. Heat causes the barrel to foul worse than a cool barrel, Im betting the bore may be either severely fouled or its shot out.

Throat erosion, not fouling is the problem.

[JLA]

wouldnt that mean its shot out???

[GunHugger]

First of all a cheap 4X is not a good scope for tight groups at 100 yards.

Second, we don't know the shooting skill or how the shooting was done, off hand or from a solid bench setup. Not questioning the guys skill, I just don't know.

Mil barrels are rated for 15,000 rounds, that takes into account Full Auto fire.

Fifteen cases of ammo is a lot of shooting.

John (Noveske) commented "We see our chrome lined barrels go to about 25K (sometimes more) in the hands of trainers and military individuals in relatively heavy use. Some more, some less, based on the shooters accuracy requirements and the rate of fire the barrels have seen."

I would suggest having a good look at the barrel to see if there is throat erosion. Shine a good light and have a look at the bore just in front of the chamber. If it is pitted and ugly the barrel is shot out.

And give the Nikon a try, sounds like a fair deal and a far better scope than a 4X Tasco for shooting groups at 100 yards.

One more thing...what ammo and what is the barrel twist? Mismatched ammo and twist rate will not shoot tight groups no matter what scope is used. Also what is the barrel chambered for 5.56 or .223?

1x7 - technically too tight of a twist for any .224 bullet widely available, including the 80 gr. Manufactured originally to stabilize SS109 and/or tracer ammo, but further military testing has shown other twists to be superior. Some of the very heavy custom stuff (87 gr?) may work well, but why????

1x8 - great twist for 69-80 gr bullets. Sierra once informed me that the perfect twist for their 80gr was 1x8.2xxxxx (blah blah blah big long engineers explanation followed).

1x9 - good all around twist ratio. Best suited for 52-69 gr, but either end of the envelope will be questionable.

1x10 - practically the same as 1x9, but favors the lighter side a little more.

1x12 - great for the 40-52 gr bullets. Most often found on bolt action rifles as their primary use is varminting. All right for the 55 gr, but not the best.

1x14 - if you want to understabilize the .224 bullet, use this twist. Useless except for tumbling effect it causes upon bullet impact. IMHO, better to shoot straight with a good HP bullet as your chances to hit are better and damage will most likely be greater also.

[larrydickman]

I doubt the barrel is shot out. The gun had only about 800 rounds through it on full auto. The person I bought the upper from is not a liar. I don't know if the bbl is the slight different for the leade for 223 or 5.56 but from all that I have read it only makes a slight bit of accuracy difference not what I am experiencing. The main difference is in the case of the round being thicker in military ammo for higher pressures. All this will not affect accuracy to the extent I am experiencing at 100 yards. The throat looks shiny and is chrome lined like the bbl. My only concern was if it over heated and warped. If that is not the problem than I don't think its the barrel. I am buying the scope and putting it on and that should rid the problem if its the scope. I have only had the Tasco and never been able to shoot it with good close groups. I have a colt and can shoot that gun at 100 yds iron sights at the DCM comps at expert. I shoot the PWA on a rubber rest with two hand in the rear holding it like a tripod braced on a flat base. And I know how to use breathing control to fire. I will mount the Nikon and give the bore an extra good cleaning with the usual copper solvent that I clean with and we will see if thats the problem. The thing that makes me think it may go to something else is I purchased a NcStar colt knock off because I liked the way it looked on the gun and hoped for just reasonable accuracy at 100 yds. It shot the same groups at 100 yds. This gives me pause as to it being a scope problem. I know the NcStar is a POS cheap scope, but I had a Tasco 4x32 on my Ruger 77 22 mag and could pop the head off of a Lincoln penny at 100 yds. [ not joking it was that on]

[mncarpenter]

Gunhugger has good advice. I'm guessing too, that your scope mounts suck. Get a good one piece mount and lap it properly and see what happens.
An old machine gun barrel(M-16?) may well have a 1-12 twist.
How does it shoot with iron sights??
New barrels are pretty cheap.

[larrydickman]

You know I bought this over 25 years ago from a friend in Fla. that built an m16 when they were legal to build and reg. He changed barrels and it very well could be a 1 in 12 twist. I could put a new bbl on it but this one is in very good condition ext. and rifling. It has not been shot out and the lands and groves are still sharp. I will start with the scope because its the easiest to replace. The mount is a aluminum rail mount that was made by weaver. I don't think its the scope mount. I had a problem with it getting on paper at 25 yds and then shooting high at 100 but this was paralex error. I zeroed in best I could at 100 but it still was not all that great. I should be able to hit 2 inch groups at 100 even with a cheap scope. It may be the bbl is not up to spec.

[JLA]

remount the better scope and a new mount and grab a box of lightweights from the gunshop. something in the 40-50 gr range...

[larrydickman]

Lighter grain being more accurate with a 1 in 12?

[JLA]

yes, the slower twist is better suited to shorter bullets. 1:12 in a .224 bore suits it to 36 to 50 grainers, with the ideal weight somewhere in the middle...

[larrydickman]

I just checked the barrel and its a 1 in 9 twist. I checked it three times and came up with 1in9 all three times.

[GunHugger]

What ammo have you been shooting?

Brand, 5.56 or 223, bullet weight and type of bullet?

[larrydickman]

Originally Posted by GunHugger

What ammo have you been shooting?

Brand, 5.56 or 223, bullet weight and type of bullet?

I have been shooting china sports. Norinco ammo from the 90s. 55 gr. FMJ

[JLA]

thats actually some fairly decent shootn stuff despite being made in china. Try a few different brands. your barrel may not like the seating depth those rounds are set at.