What would make a new barrel shoot this bad?


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fatelk
January 30, 2011, 04:28 PM
I know that there are some very knowledgeable folks here that might have some suggestions, though this isn't the typical 'how can I make this thing shoot' question.

Two rifles with brand new (US made) barrels installed, both shoot about 10" 'patterns' at 100 yards, from the bench. They are Bulgarian ak74 rifles put together on US made receivers, in 5.45mm. The barrels came from a company called Apex, but I don't know who made them. One rifle is mine, and the other belongs to a friend. Yes, we can both shoot just fine. I can easily shoot around 2.5"/100yrds with my M1 Garand.

no sign of any 'keyholing' at the target - nice round holes, just scattered
headspace is good
crowns look good
bore and rifling looks good, no signs of any burrs or damage
twist looks right- about 1:8.5
I slugged the bores - .221" across the grooves and .215" on the lands
we tried 3 different types of ammo - consistently bad
function is perfect on both
empties look ok, no sign of any obvious chamber issues
the fired primers are a little cratered out, like some kind of pressure issue, but it doesn't look too suspicious

Could there be an issue with the throat or something that could cause this terrible accuracy? Anything I could be missing, or just garbage barrels? I called the place I got them from and they said they hadn't had any reports of problems with them.

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gunmn74
January 30, 2011, 04:51 PM
I had a similar problem when trying to sight in a Mini14 .223 with
Malasian milspec ammo. I was adjusting the scope back and forth.
I put in some good BlackHills target and the problem ended.
I would suspect the ammo over the barrel but I could be all wet.

fatelk
January 30, 2011, 05:32 PM
We tried Wolf ammo, Russian surplus, and Bulgarian surplus. I'm pretty sure that effectively rules out an ammo problem. I'm not expecting the accuracy I get with my M1, but this is ridiculous by any standards.

NCsmitty
January 30, 2011, 05:39 PM
Barrel dimensions appear to be right, have you checked the bullets for size? I'm guessing you are using surplus ammo? Any sign of keyholing?

Missed the no keyholing!


NCsmitty

NCsmitty
January 30, 2011, 05:48 PM
Were the rifles shot before converting or were they piece parted from scratch?



NCsmitty

T Bran
January 30, 2011, 05:49 PM
I have had similar problems in the past shooting surplus ammo as well as that wolf junk it is ok for plinking but not much else. Try some rem or fed and see if your problem persists. Im no expert but it solved my dilema. Keep us posted weve all had weird problems like this you might save someone else from a brain strain.

fatelk
January 30, 2011, 06:50 PM
No, they were assembled on US receivers from like-new parts kits and US barrels and triggers. We had help with the proper tools and headspacing.

Try some rem or fed and see if your problem persists.
It's NOT an ammo problem. Sorry, don't mean to be rude, just that about ten people have told me already that it must either be bad ammo or I can't shoot. For one thing, were talking groups of almost a foot, not 5 or 6 inches. I've never heard of Wolf or any other ammo being that bad in any otherwise good gun. Last I checked, Remington and Federal don't load 5.45mm (wish they did). I could try some Hornady 5.45, but if Wolf and two nationalities of surplus scatter so badly, it wouldn't matter if Hornady ammo did shoot good. I would not want to own a rifle that was that picky about ammo. No, not an ammo issue. Something else is going on, just don't know what it is.

Barrel experts? Could an out-of-spec chamber or throat cause this? Could it have the wrong kind of crown or something? These are brand new, US made barrels. I'm wondering if something could have been a little bit off during manufacture.

jester_s1
January 30, 2011, 07:13 PM
I'm no expert, but to answer you question, yes. An out of spec chamber or throat could cause bad accuracy. A bad crown (burred, damaged, or crooked) could definitely do this. An improper assembly job could also. You've ruled out ammo as a cause apparently, even though none of the stuff you've tried is quality. Other possibilities are loose sights and loose stock fit. It sounds like it's time to get these to a gunsmith who can cast your chambers and check over your assembly job.

fatelk
January 30, 2011, 08:12 PM
You've ruled out ammo as a cause apparently, even though none of the stuff you've tried is quality.
OK, I've shot a lot of wolf and surplus ammo over the years, many different types and nationalities. I've tried quite a bit of it for accuracy from a bench with sandbags. Much of it is not quality, but never once have I ever had any surplus shoot this bad in a rifle that is capable of a lot better. I've even shot lousy ammo through a very accurate rifle, and you would be surprised at the reasonable accuracy you can get with terrible ammo if the barrel is good. If the barrel and ammo are incompatible somehow then it's a different story.

If they were shooting 5 or even 6" groups, I might blame the ammo, but this is double that.

The rifles were put together carefully and properly. The stocks and sights are tight on both. There is the proper amount of play in the receiver cover and gas tube. We've checked out all the obvious problems. I don't claim to be an expert, but I'm not a novice either. I know about the importance of a good crown. I'm not going to spend money on a gunsmith. Before I do that I will just buy a new barrel, one that's mil-spec and chrome lined.

Nothing against gunsmiths. They earn their money, but it would end up costing more than a new barrel.

An out of spec chamber or throat could cause bad accuracy.
Bad accuracy is one thing, like a bench rest rifle that used to shoot .25 moa wearing out a barrel throat and shooting 1.5 moa. Can a improperly cut throat make a rifle that should be capable of 4 moa shoot as terrible as 10+moa?

BBBBill
January 30, 2011, 09:14 PM
1. Do a chamber ( & throat) cast with Cerrosafe (get it at Brownells).
2. Scope the bore.
3. Check your attachment of trunnion to receiver and barrel to trunnion.

jester_s1
January 31, 2011, 12:41 AM
It shouldn't cost that much to get a chamber cast done. Although truthfully, I'd be surprised to see it be off enough to cause accuracy that bad unless it's crooked (barrel bent?). You say the function is fine, so nothing is too tight. And reamers don't make looser chambers as they wear, so it's not likely too loose. I'd still suspect an assembly error, but if you don't want to get the gun to a gunsmith to have it checked over I'm not too sure what else to tell you.

fatelk
January 31, 2011, 01:04 AM
I'll check it over closely one more time, talk to the guy with the tools and know-how. Everything seems solid and well-done. From researching and trying to figure this one out I learned a lot.

I really do hate to blame the barrel. Eyeballing it down the bore, it sure looks perfectly straight. Bore and crown look clean, slug measures and looks good. It seems like the lead slug would come out scraped if there was a burr or bore problem that I couldn't see. I've seen barrels that looked terrible that shot better than this.

If I can't figure anything else out, I could do a chamber cast. It would be good to have some cerrosafe anyway. If I do, I'll post the measurements.

The barrel and trunion are tight. The trunion is riveted to the receiver, rivets crushed with a big bolt-cutter type of tool. It took a shop press to push the barrel into the trunion. The only thing that wasn't tight was the rear sight base. The barrel was undersized a couple thousandths there, but he used a punch to peen around the barrel so the sight base would fit tight. I guess we could press that off again and check it. Come to think of it, that is one thing both rifles had in common - the barrels were both undersized for the sight base, and we fixed them both the same way. They don't feel loose though.

fatelk
January 31, 2011, 08:53 PM
We pulled the rear sight base off last night, carefully peened all around the circumference of the barrel where it fits so it's practically knurled, pressed it back on and pinned it. I just got back from the range where I shot several groups at 50 yards. They were all around 5 to 6 inches at 50, consistently as bad as before.

So I THINK I've eliminated assembly problems:

The trunion is solidly riveted to the receiver
The barrel is solidly pressed and pinned in the trunion
The sight bases are solidly pressed and pinned to the barrel
Rear trunion and stock are solid
Fit of cover and gas tube are correct

I may still cast the chamber if I get some cerrosafe and time, but on second thought I don't know if it's even worth it. If there is a problem it would probably be more expensive to get it fixed than just get a new barrel. I can shine a bright LED light into the muzzle and see the throat area pretty good. I'm not an expert but it looks good to me. Perhaps the crown is cut wrong? What do you all think?

A friend has offered to just buy it from me for what I paid for the parts kit, tapco trigger, and US receiver. I may just sell it, then it's his headache.

Jim K
February 1, 2011, 01:09 AM
Rifling twist?

JIm

mes228
February 1, 2011, 06:59 AM
I shoot a lot of rifles because I trade quite a bit. I've encountered MANY rifles that were so inaccurate it bordered on unbelievable. I'm talking new Remington's, Ruger's, Savage etc. rifles that sell for hundreds of dollars and look beautiful. They shoot atrocious though, and the barrels cast rounds everywhere in shotgun patterns. Especially as they heat up. In fact the ONLY new rifle I've fired recently that was acceptable to me was the Thompson Center Venture. I have no idea what the problem is - but it's real. Gun magazines never find rifles that are dogs. Though some will have a caveat that "accuracy improved after 200-300 rounds" which is a joke. That's the cost of some rifles in ammo. I'd not shoot 300 rounds through anything hoping it would eventually "shoot". Rant over.

Mizar
February 1, 2011, 08:51 AM
fatelk, is it possible that the barrel throat of your AK is miss-aligned or not properly beveled? Barrel throat on AK is known for deforming soft point rounds - could that be the reason (I know that you use FMJ)? One more thing - are you absolutely sure that there is no movement between the barrel and receiver? One quick way of telling that is to put your receiver in a heavy vise and press hard on the barrel at the muzzle end in different directions.

Boris

fatelk
February 2, 2011, 07:16 PM
Rifling twist?
As close as I can tell, the rifling is 1 turn in 8.5 inches. From looking around, I think this is right for this round. I think I have a couple boxes of 70gr ammo somewhere. Next time I get out I will try some out, but even if it shoots OK, the barrel is no good if it won't shoot cheap surplus.

Mizar, I have wondered about the throat, but it sure looks OK when I hold a bright light at the muzzle and look in the breach. I probably wouldn't be able to tell if something was off, but it looks pretty clean to me. The barrel is pressed and pinned solidly, and the trunion is riveted. I can't detect any movement of any sort. It feels solid as a rock to me.

I think it needs a good Bulgarian barrel. At this point, I think I will sell it to a friend, and let him mess with it.

Jim K
February 2, 2011, 10:01 PM
He may be your friend when you sell it to him, but will he remain your friend?

Jim

fatelk
February 2, 2011, 11:30 PM
He is fully aware of the issues with it, and has been helping me try to figure it out. He offered to buy it for the cost of the parts kit and the receiver.

I would never sell anything without full disclosure.

jester_s1
February 3, 2011, 01:02 AM
One other idea, although it's a long shot. You may have an issue with the trip from the magazine to the chamber. Why not try a 5 shot group dropping the rounds in by hand? I know the extractor isn't supposed to work that way, but I can't see how 5 shots would hurt it.

frankenstein406
February 3, 2011, 01:40 AM
Also why not buy some good ammo? You can't ruled it out till you tried it...

Kenneth
February 3, 2011, 12:47 PM
A bad crown would thrown your POI off in the same direction most of the time.
You mentioned slugging the bore, do you remember if the slug went down easier or harder as it went along? If it went down harder as you pushed from the muzzle to the breach then the bore is wider at the muzzle end.

In my opinion, the most likely cause of your accuracy problems has something to do with the contact and attachment points on the barrels. Try shooting with the lower and upper hand guards off. Make sure the gas cylinder, and the suppressor front sight assembly are tight. Check for excessive slop in the piston. Make sure the lower hand guard spring is not missing.

I agree with you that your problem is not likely ammo related, however I should point out that service ammo is often not the most accurate loading for the rifle that it is used in. Once you solve the main problem you might want to try a little heavier bullet.

fatelk
February 4, 2011, 08:07 PM
Also why not buy some good ammo? You can't ruled it out till you tried it...
I should point out that service ammo is often not the most accurate loading for the rifle that it is used in. Once you solve the main problem you might want to try a little heavier bullet.
I don't think you guys understand my intentions for this rifle. It's a cheap plinker, and how it might shoot with better ammo is irrelevant. Cheap surplus ammo should be capable of at least 5moa in any decent rifle, and if it won't shoot cheap surplus with at least mediocre accuracy, it's worthless to me.

I have checked the proper assembly of everything several times, and had someone else who is more knowledgeable also check it. Everything is tight, pressed, and pinned. There is no possibility anywhere for movement, from the trunion to the barrel to the sight bases. I even tried a couple different handguards for fit. Everything is as it should be. Function is flawless.

That said, I did get a chance to compare it closely to an original mil-spec barrel. The crown is quite different. I did the bullet test, and as you can see the US barrel nearly swallows the bullet compared to the military barrel. The crowns look quite a bit different too, but I couldn't get a decent photo of them.

Kenneth
February 6, 2011, 04:37 PM
The crown is quite different. I did the bullet test, and as you can see the US barrel nearly swallows the bullet compared to the military barrel. The crowns look quite a bit different too, but I couldn't get a decent photo of them.
It's highly unlikly to be the crowns on both barrels, as I said before, a bad or damaged crown is more likly to throw the POI off consistantly in one direction than to cause the sort of accuracy problem you are describing. If it was the crown the defect or damage would be clearly visible. If everything else is as well put together as you say it is then the barrels themselves are the only thing left to consider.

Mizar
February 6, 2011, 04:55 PM
Fatelk, I might be wrong, but the barrel on the right does not look like a military AK 74 barrel. The crown is different and the outside diameter is wider on the military one.
Boris

Jim K
February 6, 2011, 05:10 PM
It sounds like the bore diameter is too large, which would certainly result in the type of inaccuracy you describe. You say the groove diameter is .221; what do the bullets mike?

Jim

fatelk
February 7, 2011, 02:16 AM
The bullets measure right at .221". I tried two different types of ammo today, Ulyanovsk 70gr FMJ, and Wolf 60 gr. The best 5rnd group at 50 yards was 3.25" and the worst was 5", pretty bad.

We pulled the barrel off this afternoon. It pressed off fairly hard, so I don't think that was the problem. There was no sign at all that it was moving in any way. I tried to take some photos of the chamber and crown of each, the good chrome-lined barrel, and the US barrel in question. It's hard to really see, and harder to take a good photo, but the throat seems to have less taper where it starts on the groove diameter, and more free-bore on the lands, if that makes any sense.

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