I've been reloading for quite a while but have never seen anything like this.

-Rifle, Brno 8x57mm military 98 Mauser with good bore. Fired 10 rounds (@100 yds) each with the following ammo:

(1)Romanian steel case surplus 180g (.323) spire point. Groups (more like a shotgun pattern) were 12" to 14"!

(2)Remington 8mm 185g (.323) core-lokt PSP. Six inch group with what appeared to be slight bullet tipping from holes on the paper.

(3)Hornady 8mm 175g (.323) Interlock round nose. Three quarter inch (.750 moa) group! Fired another 10 rounds at 200 yards that grouped just under two inches!

I know some rifles prefer certain bullets but this is so dramatic there must be a measurable reason. The Remington and Hornady bullets were both seated about .005" off the lands. WW cases, WLR primers, and 45g VV150. Redfield target receiver/apature sights were used. Can someone explane why the Hornady round noses shoot so well? Thanks...

Jon

What is the twist rate on your BRNO? Your description sounds like a classic case of slow twist where the longer spitzers wobble and keyhole, while the shorter RN stabilizes and shoots like a lazer.

I suggest you try the same test with 150 grain bullets. If they shoot well, it is a strong indicator that the twist rate is not fast enough to stabalize the heavier spitzer bullets.

as is almost always the case RNs and FPs are much easier to stabilize. You may, however, be affected by many other things. Barrel harmonics has often been a major contributor. One military ,sporterized rifle of mine will shoot near MOA when I shoot it and 9" when my buddy shots it. He is a better shot than I. It's a mod. 36 MAS. He supports it far out on the hand gard and I support it almost under the action. Off hand shooting he has done better than I and better than on the bench. Our off hand holding is almost the same. roger

Just finished checking the twist. As near as I can measure with a rod and tight patch it's between one turn in 9 1/8" and 9 1/4".

Jon

Twist rate needed to stabalize a bullet is actually determined by bullet length and not weight. Your rate of twist may better stabalize a shorter round nose then a longer spitzer type.
Just one idea.

quote:

Originally posted by Jon:
Just finished checking the twist. As near as I can measure with a rod and tight patch it's between one turn in 9 1/8" and 9 1/4".

Jon

Jon,

Using the Greenhill formula and some estimating:

150 x.323 x.323 / 1.2 = 13

A 1:13 would be the slowest twist needed to just stabilize those 8mm bullets. Since you measured closer to 1:9, the twist rate in your barrel should not be the problem if grooves are in good shape!?

Thanks to all for the comments. I agree the twist should not be a problem and the barrel is in very good shape for it's age.
The only major difference (other than length) I can see between the SP and RN bullets is that the RN's have almost twice as much bearing surface in contact with the bore. Maybe I can find some SP's with sharper ogives and longer bearing surfaces to try however, there are not a lot of choices out there in 8mm.

Try puting some forward pressure under the barrel for starters. roger

I am not sure which brno 98 you have, but get yourself some turk surplus 8mm, its loaded to the max and acutally shoots pretty well out of those old brnos seeing as most where sold to turkey anyways, turk loaded surplus 8mm is loaded to more than a 30-06 can do, which brings up another point, if your gun is a brno turkish rifle, if the lugs aren't set back they aint gonna, because that turk stuff is so over pressure

quote:

Originally posted by Jon:
...(3)Hornady 8mm 175g (.323) Interlock round nose. Three quarter inch (.750 moa) group! Fired another 10 rounds at 200 yards that grouped just under two inches!

I know some rifles prefer certain bullets but this is so dramatic there must be a measurable reason. ...

Hey Jon, Take a 0.0001" capable Micrometer and measure that excellent Hornady RN:
1. Forward of the Cannelure.
2. Aft of the Cannelure.

You "might" find the Fore portion Bore Diameter and the Aft portion Groove Diameter. Hornady "used to" have a lot of 2-diameter Bullets and they were all very accurate for me.

I know the Hornady 30cal 150gr RN is still 2-Diameter. It is nearly BenchRest accurate in rifles I've used them in. And the Pressure is actually Reduced because there is a smaller Contact Patch.

Though I also like Spire Point Bullets, the good old RNs have never fallen out of favor with me. Most RNs perform on Game just the way we want them to, 1-shot Kills.

Best of luck to you.

Hotcore...You're right. The Hornady's mic:

-Forward of cannelure .32160".
-Aft of cannelure .32270".

Also, the weight of the Hornady's only vary by about two tenths of a grain. The Remington cor-loks vary by as much as two and a half grains!

BARTSCHE...
I have tried this Mauser barreled action in a sporter stock with the barrel free-floated and used shims (target paper) of different thickness to control barrel vibration. It made no difference. The barreled action is now back in the origional military stock with upper wood and barrel bands. For some reason this stock does not screw up accuracy like they usually do. Even after things start heating up point of impact does not change. Go figure!

Some old Remington 8mm bullets are some bastard small size.

OK, I dug 'em out.

quote:

Remington Keanbore 8m/m Mauser Hi-Speed Remington Dupont 170 gr soft point core-Lokt Bullets
20 centerfire smokeless cartridges 8068

I measure .3195"

It should be .323"

That is .0035" undersized.

I don't know if that would keyhole.
I have a .303 that has .318" grooves. It keyholes with military
surplus .303 ammo that measures .309", but shoots the .310" well.

That means that in my 303, .008" undersized does not key hole, but .009" does keyhole.

If the grooves of the 8mm are more than .00175" deep, and Calhoon says that .223 has .003" deep grooves, then the small Rem bullets woould not cause the key holing.

Hey Jon, That is great news for "you". Hornady makes some fine RNs when they are used at the proper Velocities, but they can be over-driven in some Mags.

I've sure sent a LOT of RNs out to 400yds and they performed just fine on Deer.

Now that you have one Bullet that works well for you, you can take all the time you want Experimenting with the others. You just never know what might get them shooting well too.

But..., you do have a fine Bullet to use until the others get sorted out.

Good Hunting and clean 1-shot RN Kills.

Interesting about the old Remington bullet diameter. I wonder if this was a compromise meant to work in both the older J bores and later S bores.

RBinNM has it right, much of the factory 8mm ammo actually uses a bullet that is undersized so it fits the old "J" .318" bore instead of the "S" .323" bores. This ammo also is loaded to a lower than normal pressure - it's all about liability if the ammo is used in an old "J" bore rifle and it "KaBooms".