P17 keyholing 150gr Hornady boat-tails at 100M

[agit-prop]

Load data as follows:

RP brass
48.5 gr of H4895
CCI large rifle primers
Hornady 150 gr boat-tail SST bullets
light crimp
Cases trimmed to 2.480"
This was the second firing for these cases & they were full length sized
OAL 3.285"
Bullet OAL 1.2"
approx length of seating contact 0.225"

The rifle was BSA commercial sporterized P17.

Is it most likely to be the bullets, or the rifle?

 

[todbartell]

has the rifle shot other loads with accuracy and no keyholing before?

was it 150 gr. bullets?


could be a bad batch of SST's...of center wobble or something..? :?

 

[bigbull]

Load data as follows:

The rifle was BSA commercial sporterized P17.

Is it most likely to be the bullets, or the rifle?

Is the rifle original, 30-06 caliber?
Have you checked your rate of twist?
If both of the above are OK, then your barrel is worn out or your bullets are not the right diameter.

Keyholeying is a sign of instability that is traced to the bullet or the barrel twist or lack of it!
bigbull

 

[Gibbs505]

Agreed!

 

[Six Star]

Even though the rifling in the barrel 'looks' good, I'd be inclined to slug the barrel. I'd try some different bullets first, though...I have heard of some issues with SST bullets.
Edited to add: The M1917 is capable of superb accuracy for a mass-produced military rifle.

 

[Hitzy]

Edited to add: The M1917 is capable of superb accuracy for a mass-produced military rifle.

I agree. My M1917 is crazy accurate for a military gun.
No such thing as a P17 although most folks will know what you are talking about, it's incorrect nomenclature.

 

[maynard]

Same thing happened to me when I tried to work up a load for buddy's 7X57.
The rifle would heyhole shots with 175 gr Sierra Game Kings. 3 out of 5 never touched the paper. Changed to 175 RN Winchester bullets with the same load and can get all three shots touching.
The 175 Winchester bullets are ugly compared to 175 SGK, but they work

 

[Hitzy]

Same thing happened to me when I tried to work up a load for buddy's 7X57.
The rifle would heyhole shots with 175 gr Sierra Game Kings. 3 out of 5 never touched the paper. Changed to 175 RN Winchester bullets with the same load and can get all three shots touching.
The 175 Winchester bullets are ugly compared to 175 SGK, but they work

The shorter round nose bullet would stabalise with that twist rate, while the longer spitzer would not, even though they are the same weight. It's the length of the bullet that affects stabalisation, not the weight. The M1917 has a 1in10 twist, so it should handle up to 220g spitzers easily......

 

[bigbull]

Same thing happened to me when I tried to work up a load for buddy's 7X57.
The rifle would heyhole shots with 175 gr Sierra Game Kings. 3 out of 5 never touched the paper. Changed to 175 RN Winchester bullets with the same load and can get all three shots touching.
The 175 Winchester bullets are ugly compared to 175 SGK, but they work

The shorter round nose bullet would stabalise with that twist rate, while the longer spitzer would not, even though they are the same weight. It's the length of the bullet that affects stabalisation, not the weight. The M1917 has a 1in10 twist, so it should handle up to 220g spitzers easily......

X2
bigbull

 

[maynard]

It's the length of the bullet that affects stabalisation, not the weight.

If what you are saying is true, would that mean a round ball is more stable then a spitzer type bullet of the same weight?
I think the reason the 1.220" long RN stablized and the 1.410" long spitzer didn't is because the RN even though shorter has a longer bearing surface.
The round nose is also a flat base bullet where the SGK is a boattail. I am thinking maybe the boattailed bullet is not an advantage at the lower velocity of the 7X57 compared to say a higher velocity 7mm Rem Mag.

Maybe the short range benchrest shooters are on to something by using Flat Base bullets?

 

[bigbull]

Sorry Maynard, it is not the way it is.

The longer bullet requires a faster twist to stabilize that's all. Your round ball comment doesn't hold any water. The round ball is very stable in flight it just doesn't have any ballistic coeficient and is thus a poor flyer in the air, that's all. Weather Bt or flat base the same rules apply, the length of the bullet governs it's ability to be stabilized in any given twist. IMO
bigbull

 

[agit-prop]

I've fired some Winchester flat tail powerpoints through it, the same weight, without the keyholing. The accuracy didn't seem to be up to par though. The "group" covered the better part of my target at 300M.

I'll try slugging the barrel and see what I get.

 

[maynard]

Your round ball comment doesn't hold any water.

I am trying to stir the pot here

The longer bullet requires a faster twist to stabilize that's all

Yes, but in this case the shorter bullet has a longer bearing surface. Would the longer bearing surface not have more effect then a longer bullet with a shorter bearing surface? Not pot stirring this time.

Flat base bullets can shoot OK out to about 600 yards before becoming unstable, the same weight bullet in a BT will still be stable at 1000 yards in most cases. In most cases the flat base bullets have a lower BC then a BT bullet of the same weight.

I have never seen where a longer bullet requires more twist, unless you are to assume that the heavier bullet is longer.

At this pont I am sticking to my longer bearing surface theory as to why the RN bullets stablize and the 175 SGK's don't. But as always, I am up for a good debate :lol:

 

[Hitzy]

Your round ball comment doesn't hold any water.

I am trying to stir the pot here

The longer bullet requires a faster twist to stabilize that's all

Yes, but in this case the shorter bullet has a longer bearing surface. Would the longer bearing surface not have more effect then a longer bullet with a shorter bearing surface? Not pot stirring this time.

Flat base bullets can shoot OK out to about 600 yards before becoming unstable, the same weight bullet in a BT will still be stable at 1000 yards in most cases. In most cases the flat base bullets have a lower BC then a BT bullet of the same weight.

I have never seen where a longer bullet requires more twist, unless you are to assume that the heavier bullet is longer.

At this pont I am sticking to my longer bearing surface theory as to why the RN bullets stablize and the 175 SGK's don't. But as always, I am up for a good debate :lol:

Bearing surface has nothing to do with it. It's not theory, it's fact BTW :wink: but you can stick to your theory if you like. Based on your theory, a 175g spitzer would stabalise better than a 140g spitzer as it has a longer bearing surface, but you know that isn't the case........ :?
There are a few factors that affect bullet stabalisation but length of the bullet and twist rate are the most critical.

I have never seen where a longer bullet requires more twist, unless you are to assume that the heavier bullet is longer.

How about the US military and the 5.56 cartridge? The original M16 had a 1/14 twist, later a 1/12, which handled the 55g bullets well. When they switched to 62g bullets, they were not stabalising with these twist rates so they went to a 1/7 twist. It wasn't the 7g that made the difference, the 62g bullet used a steel insert in the tip which made it considerably longer than the 55g.

 

[maynard]

Bearing surface has nothing to do with it. It's not theory, it's fact BTW but you can stick to your theory if you like. Based on your theory, a 175g spitzer would stabalise better than a 140g spitzer as it has a longer bearing surface, but you know that isn't the case........

No the 140gr. is lighter so is requires less twist to stablize. My theory is that a heavier bullet requires more bearing surface to stablize. The BC of the 175 RN is about 1/2 that of the 175 SGK. The lower BC means more drag.

Here is what Shilen has to say.
http://sst.benchrest.com/shilentwist.html

 

[Hitzy]

Bearing surface has nothing to do with it. It's not theory, it's fact BTW but you can stick to your theory if you like. Based on your theory, a 175g spitzer would stabalise better than a 140g spitzer as it has a longer bearing surface, but you know that isn't the case........

No the 140gr. is lighter so is requires less twist to stablize. My theory is that a heavier bullet requires more bearing surface to stablize. The BC of the 175 RN is about 1/2 that of the 175 SGK. The lower BC means more drag.

Here is what Shilen has to say.
http://sst.benchrest.com/shilentwist.html

Of course when using the same bullet materials, a heavier bullet with the same profile will be longer and that is why bullet and barrel makers have recomended twist rates. Make a 2.5 inch long solid aluminium 120g bullet and it will not stabalise in your rifle. You are forgeting that the bullet swages to the bore diameter when fired so the bearing surface of the bullets is pretty much the same. Also, a spitzer is more aerodynamic than a round nose, so if drag had anything to do with it, the spitzer should be more stable than the round nose, not less.
Anyway, your theory is wrong. This has been proven and is common knowledge for the last 100 years........

 

[maynard]

I am thinking maybe the boattailed bullet is not an advantage at the lower velocity of the 7X57 compared to say a higher velocity 7mm Rem Mag.

OK, I will recant my bearing surface theory. I will stand corrected.

Three things will effect stability. Bullet weight, twist and velocity. Velocity more so when the twist may be marginal, as is the case here.
With that being said the higher velocity of a 7 mm mag may or may not stableize a 175 spitzer with the same marginal twist. :?:

If buddy would have bought a .300 Win Mag when I told him to... :shock:
But then look at the fun we would have missed. :mrgreen:

 

[bigbull]

Three things will effect stability. Bullet weight, twist and velocity. Velocity more so when the twist may be marginal, as is the case here.
With that being said the higher velocity of a 7 mm mag may or may not stableize a 175 spitzer with the same marginal twist.

OK Maynard your asking for it! :lol:
Here you go with the weight thing again. I will give you an example why weight is not the governing factor. I know I know the heavier bullet is longer, yada yada yada!
You can have two bullets of the same weight but different shapes, one is a VLD and the other is your everyday Spitzer the VLD sprays it's shots all over the paper and keyholes while the spitzer (actually it was a boat tail) puts them into a 1/4", the only difference was their length. Just to make it even more juicy as a second example two bullets one is 105gr VLD and the other is 107gr VLD both are 6mm fired in a 8.5" twist barrel the heavier bullet shoots one holers ond the lighter bullet keyholes, the lighter bullet is "longer" and doesn't stabilize! Both personal experiences.

You are right about marginal twists being able to handle heavier bullets but it is rare, but possible. The bullet/twist combination has to be on the edge where those extra 100 fps will impart enough rpm's to stabilize an otherwise unsuitable barrel/bullet combo. If you go to Bergers Bullets web site you will find a list of bullets they make and the reccomended twists. You will be shocked to find that "normal weight bullets" require very fast twist barrels to stabilize. This is based strictly on the bullets "length", it is as good as an example as I can give.
bigbull

 

[agit-prop]

OK, I have just slugged the bore as follows:

I took a once fired cartridge, and bored out the head to 5/16. I put the drill bit into the case, shank first, until it seated against the shoulder. I put the whole arrangement into a vice, and filled tthe neck of the case with lead that I melted from a couple RNHP bullets.

Once cooled, I removed the drill bit, chambered the case, and hammered the slug through using a taped rod with a rounded tip

The measurement for the grooves appears to be somewhere between .308 to .309, while the lands measure somewhere in the .3035 to .3045 range. Measuring this is difficult with a vernier caliper, hence the margin of error.

I'm thinking I don't have a barrel problem contributing to inaccuracy. Considering that this is a sporter profile barrel with zero float,and no action bedding, I think I may be able to make some improvements by bedding/floating.

 

[savagefan]

Don't know why but 300gr rn hornadys make very tight cloverleafs in my 375hh CZ, any brand or weight of spitzer opens up to about an inch. Slight loss in accuracy but better long range capability so I hunt with the accubonds.