Gentlemen,

We get quite a number of both Sako and Brno rifles here.

All are chambered for the 223 Remington.

We also have factory ammo loaded with 55 grain bullets, and 69 grain bullets.

Here is the strange part.

2 identical rifles, same make and model.

One will shoot the 69 grain bullets accurately, and the other keyholes!

Anyone has any explanation for this?

I consider that you already checked if the rifling rate is the same in both rifles.

Strange things sometimes happen in manufacturing.

Aseed, I do not know, but, a friend called the owner of a barrel manufacturing company, my friend explained to the owner what he was building and what he wanted, the owner informed my friend he would personally pick the barrel and get it into the mail, with that kind of attention “WHAT COULD GO WRONG?”

The barrel arrived, my friend built the rifle for the next prairie dog hunt/vacation. He took the rifle to the firing range, he did not have any better luck that you experienced with one of your rifles, the twist rate was checked, he ordered a barrel with a 1 in 9 twist, the barrel he received had a 1 in 14 twist, my friend does not have a shortage of rifles to choose from when he hunts, he was disappointed.

The proud owner of that barrel manufacturer was also disappointed, he let one of his friends down, a new barrel was shipped and now installed, next year.

F. Guffey

walter was shooting the one that keyholed seriously i've had several 223's that would not shoot the 69 grainers well even though they were 8" twist barrels. then again i have had a couple with 12" twists that shot them just fine so no explanation other than walter

quote:

One will shoot the 69 grain bullets accurately, and the other keyholes!

First off when dealing with physics is there is no magic.

First verify the ammo is good if you have other rifles that work with that ammo.

If the ammo is good then isolate to the individual barrel.

The barrel must have the right twist.
Measure the twist.
The barrel must have the right bore and groove diameter.
Slug the barrel to determine the groove diameter.

Now the difficult part.
The barrel must have uniform finish on the interior and it must have uniform diameters all the way through.

If the bore has smooth spots and rough spots you can often tell when you push a brush through. The rough spots will drag.

Then take a soft lead slug like a pure lead cast bullet, buck shot or lead fishing weight and push it through the bore with a hard wood dowel. If you find loose spots the slug will slip easily until you hit a tight spot.

If you find tight spots and loose spots the bore may be no good. If you have tight spots and loose spots that vary .0005" inch or more accuracy will suffer. More than .001 or .0015 and you will likely shoot groups about the size of a car tire.

Also push a slug through from the breech to the muzzle. If it gets looser as you approach the muzzle the bore is trumpet shaped which is not good. If the trumpet shape is significant - more than say .0005" larger at the muzzle than at the breech accuracy with suffer.

Saeed
The problem you describe is often ran into by cast bullet shooters. Cast bullet shooters often are able to diagnose these issues and deal with them or at least lap the bore and use a larger bullet with a rare rifle.
With jackets bullets you often do not have a good way to deal with a poor bore and have to scrap the barrel.


Here is an anecdote that I was involved with on line.

The shooter had a new match grade barrel made by a premium company for his Contender.
It was "chambered in .257 TCU".
It hit nothing at 25 yards. He tried several different loads and asked for help. Most questions focused around the weight of the bullets and the twist rate. He shot it again and still hit NOTHING.
I asked him to drop a loose .257 bullet into the chamber with the breech open.
So now you know where this is going.

The .257 bullet went right through and fell on the floor.

The new barrel had a 6.5mm bore with 6.5 TCU chamber.

He squawked to the barrel manufacturer and they were embarrassed. They made him a new barrel but he liked the 6.5mm and decided to keep it too.

I would also check the rate of twist first. Not impossible for one or two of the wrong barrels to get the production line and be mis-labled.

If twist rate's the same, I'd chrono them and see if maybe one barrel is a little faster and it's just enough that the bullet can't quite stabilize.

1. Wrong rifling twist
2. Damaged / cut wrong crown
3. Bore is too large

Demons...

Same reason one rifle shoots .5" groups with factory loads and the very next one off the line won`t do better then 1.5" no matter what you feed it.

Along similar lines, and perhaps a partial answer: I have a Colt Hbar Elite, 24" 1 in 9 twist SS barreled 5.56 NATO chambered rifle. I had been having superior results shooting Hornady 75 A-Max bullets loaded long and single fed. Along comes a new lot of bullets, gone is the accurate rifle and now a shotgun like effect on paper.

What I believe happened was the so called ragged edge of stability was compromised by a slight change in the bullet maker die, and increased length of the projectile. Hence the twist was no longer workable.

I think Saeed that one of your rifles twists is not what you think it is.

Best regards

All granted but keyholing is a lot more radical issue than a simple change in POI or loss in accuracy. Something much bigger than "barrel preference" is at work?

key holing is caused by non stabilization.
it could be a matter of twist rate/velocity.

it could also be caused by the diameter of the barrel.
either throughout the whole length or just near the muzzle.

whomever turned the barrel on the outside diameter could have over profiled it causing the muzzle end to be larger than the breech end.

As we all know there are innumerable variables that affect our guns. That is why each gun has to be treated as an individual. It's not magic but it is sometimes mysterious. To eliminate an oversized bore you could try lighter bullets to see if they shoot well and don't keyhole. It may be a non-concentric bore/rifling combination. slugging the bore might help find it but what you can do about it is limited. If it likes lighter bullets then you have a rifle that will shoot lighter bullets.

Whatever you find - good luck with it.

TWIST!

quote:

Originally posted by JTEX:
TWIST!

+1
I bought a M700 off of Gunbroker. Turned out it was made about 1971 in 1:14 twist. Keyholed everything above 45gr. Had it rebarreled in 1:9.

Saeed, I have noted the same phenomenon a number of times: Barrels of the same measured twist (sometimes in otherwise identical rifles), one of which will stabilize a particular bullet and one of which will not.

What this tells you is that there are more factors at work than simply rate of twist. Just as some rifles show a distinct preference for one bullet over another, bullets show a "preference" for one rifle over another.

I can't say the exact cause of this conundrum, but suffice it to say there may be a dozen or more factors which tip the balance to create the phenomenon you've observed.

While I don't doubt that the poster above experienced poor accuracy with bullets of greater than 45 grains in his 1-14 twist barrel, his conclusion that the rate of twist was to blame is entirely erroneous. Most 1-14" barrels stabilize conventional cup-and-core bullets of up to 60 grains without a hiccup, and blunter bullets of somewhat heavier weight.

quote:

Originally posted by Stonecreek:
Saeed, I have noted the same phenomenon a number of times: Barrels of the same measured twist (sometimes in otherwise identical rifles), one of which will stabilize a particular bullet and one of which will not.

What this tells you is that there are more factors at work than simply rate of twist. Just as some rifles show a distinct preference for one bullet over another, bullets show a "preference" for one rifle over another.

I can't say the exact cause of this conundrum, but suffice it to say there may be a dozen or more factors which tip the balance to create the phenomenon you've observed.

While I don't doubt that the poster above experienced poor accuracy with bullets of greater than 45 grains in his 1-14 twist barrel, his conclusion that the rate of twist was to blame is entirely erroneous. Most 1-14" barrels stabilize conventional cup-and-core bullets of up to 60 grains without a hiccup, and blunter bullets of somewhat heavier weight.

Except when you live in California and are limited to monometal bullets.

I have a Rem 700 in 222 that I bought in 1969 or so. I have been shooting 55grn Sierra spitzers with stellar accuracy all these years.

One of my more humorous episodes with a 1/14" twist 6X47 40X-BR involved some long Winchester 85 grain 6mm Match bullets. Five rounds were fired at a target and no hits - not even keyholes - were made.

quote:

Originally posted by Stonecreek:
Saeed, I have noted the same phenomenon a number of times: Barrels of the same measured twist (sometimes in otherwise identical rifles), one of which will stabilize a particular bullet and one of which will not.

What this tells you is that there are more factors at work than simply rate of twist. Just as some rifles show a distinct preference for one bullet over another, bullets show a "preference" for one rifle over another.

I can't say the exact cause of this conundrum, but suffice it to say there may be a dozen or more factors which tip the balance to create the phenomenon you've observed.

While I don't doubt that the poster above experienced poor accuracy with bullets of greater than 45 grains in his 1-14 twist barrel, his conclusion that the rate of twist was to blame is entirely erroneous. Most 1-14" barrels stabilize conventional cup-and-core bullets of up to 60 grains without a hiccup, and blunter bullets of somewhat heavier weight.

I suspect Saeed is baiting you guys into something here!

Actually, I think Walter wasn't holding his mouth right when he pulled the trigger

Reminds me of my 1885 Commemorative 25-06. Now we all know that all 25-06 factory rifles are made witha 1 in 10 twist to shoot 87-120 gr bullets well .... right ?

Mine would keyhole anything over an 87 gr Sierra varmint bullet. One hole with them. Ran across a Browning commemorative collector at Cody who said "not so fast son". Browning apparently believed that all commemoratives would be wall hangers and were not to concerned about little things like twist. Back to the bench and it is 1 in 13". Happily, Barnes decided to come out with a 80 gr TTSX with not a lot of bore riding surface. The rifle loves these and will push them out @3997 fps (30" bbl") with 3 in one hole. Kill Antelope size game like a 12 bore slug between the eyes.

Put 115 TSXs in it and you might get 5 in 12" @200 yards. Why 1 in 13" of all things ?, who made the otherwise perfect barrel ?, all unsolved mysteries that are not all that rare (according to the collector) in special editions Brownings of the 1990s.

W/O Barnes it would have been relegated to a Yote rifle but now, thanks to Barnes, (if i cared to) even an Elk (broadside) would be toast.