Thread: What causes key holing in sub loads

Originally Posted by Fireflite

Hey Marty, does bearing surface length come into play with that formula?
Cheers

Dont think so, its the Greenhill formula worked out by the royal artillery back in the 1850s. Works for solid lead and copper jacketed lead bullets only. Weight doesn't feature either Its still used today so they got it pretty much right first time.

@Bill999 If they touch the lands do they still tumble? If poss show us a photo of the projectile and give us the dimensions.

Take weight out of the back.
It like a mortar. They don’t fly backwards


Sent from my iPhone using Tapatalk

The twist calculator on the Berger website is very good from memory

Try the 170g ones from shooter nz,i use 8.5g trail boss and they shoot an inch @ 50m thru my sako A7,I find they feed better than the 151g ones as they are a longer bullet and pointed profile not flat nose.

And pays not to jam them in the lands as you will sometimes end up pulling the projectile from the case and filling the action with powder if you try and eject the unfired round,,I know from experience..

Originally Posted by Marty Henry

Two gas checks? Measure the length of one and whack it in this formula 150 x the bullets diameter in inches squared divided by the bullets length. The answer is the twist rate
eg bullets diameter is .308, length is 1.5 inch
150x.095/1.5 = 9.5 the twist needed is 1:9.5
My 185 grainers measure 1 inch, I run them at 1450 fps with no gas checks but a good lube.
Maca has raised a good point even with a gas check if you try and push them too fast they will strip, tumble and give you a big cleaning job. A lack of lubricant will also do you in.

My sub guns action is Stained with the lube that comes with the projectiles so I think there is plenty of lube
The bullets measure 0.984inches
Am I right to think a gas check is a recessed ring at the base of the projectile filled with lube? As there's two of those and one more above that's not lubed

If I replace 1.5 inches with .984 it gives me 144 which I imagine is 14.4 inch twist
One gun is 1/10 and the other is 1/11 both seem to keyhole around a third of shots
I'm not having this issue with 165gr ballistic tips at around 1050fps
The only lead bullet Iv recovered so far was too damaged to tell if it's taking the rifling or pushing past it

Originally Posted by Marty Henry

@Bill999 If they touch the lands do they still tumble? If poss show us a photo of the projectile and give us the dimensions.

If I seat them out they won't mag feed into the barrel with the flat face at all
If they won't mag feed I'm going to change projectiles regardless of accuracy as it won't work for the follow up shots which I sometimes need due to such low expansion/terminal effect
So Iv limited myself to brain shots this far with ballistic tips which works great because the load is accurate
But they are too hard to expand at subsonic speed so it more like poking with a knitting needle

Originally Posted by Bill999

Am I right to think a gas check is a recessed ring at the base of the projectile filled with lube? As there's two of those and one more above that's not lubedAttachment 97609

No a gas check goes on the bottom of the projectile to protect the lead base from the propellant gases, mainly used for supersonic

https://en.wikipedia.org/wiki/Gas_check

@Bill999 thanks for the photos the bullet looks to be a flat base and the two red rings are lube. The third groove is a crimp groove and shouldnt be lubed. A gas check is a little copper cup crimped onto the bullets base there should be a recess to allow this.
The recovered bullet shows one rifling groove that looks to extend up to the mushroom.
The bullet is what is called a bore rider where the nose of the bullet is just land diameter with the grease grooves being slightly over groove so for a 308, the nose is usually 300 to 303 with the lube grooves being 309-310.
At that length they should stableise in a 10 twist but I have found that some rifles are quite picky about what they eat with cast bullets. The expansion looks normal for a lead bullet made from hard alloy.
I suggest you have chat with shooter nz about other cast bullets. I run a 170 grain round nose ungas checked in my 3030 and 308 over 10 grains of blue dot if thats any help. Flat nosed bullets feed fine in the 3030 as thats what the design is for but you need an ogive to run the bullet up with most box mag rifles.

Originally Posted by Bill999

If I seat them out they won't mag feed into the barrel with the flat face at all
If they won't mag feed I'm going to change projectiles regardless of accuracy as it won't work for the follow up shots which I sometimes need due to such low expansion/terminal effect
So Iv limited myself to brain shots this far with ballistic tips which works great because the load is accurate
But they are too hard to expand at subsonic speed so it more like poking with a knitting needle

Hi Bill999, You got those 200 grain flat points off me, In theory they should be stabilised with a 1:13" twist at 1050fps, I have two .308s one shoots them the other won't
it's just one of the mysteries of shooting, I have a new mould for .30 cal casts a 200 grain HP PM your address and I will send you 50 to try no cost.

Thats a good bugger right there.

Originally Posted by Marty Henry

Thats a good bugger right there.

not wrong

Originally Posted by shooternz

Hi Bill999, You got those 200 grain flat points off me, In theory they should be stabilised with a 1:13" twist at 1050fps, I have two .308s one shoots them the other won't
it's just one of the mysteries of shooting, I have a new mould for .30 cal casts a 200 grain HP PM your address and I will send you 50 to try no cost.

That sounds great mate
Is HP hollow point?

I'm getting the feeling that I'm not setting these ones up right.
Are there hard and fast rules to getting lead projectiles right?
I'm pushing them with 8.5 gr trailboss to get under the sound barrier

With cast projectiles the first lesson that needs to be learnt is that " Forget what you already know and work from there " .
For subs soft lead is all you need . You don't need gaschecks and soft lead will " fill " the bore better .
Generally projectiles should be bore size to .003 thou bigger . I get good results at .002 thou .
Projectiles should be up close and personal with the lands . And carry a break down cleaning rod .