Gas check woes

[Stoats]

I am getting good results with Lee's 312-160 bullet without the gas check at 1100 ft./s in my 303. Load is 6.4 gn of fast powder, Bullseye equivalent. Accuracy is consistently 2 minutes of angle or less.

But, when I apply Hornady gas checks using the Lee 314 sizer and try to push them a little faster with 13-14 grains of Unique-equivalent, accuracy drops off to about 8 minutes of angle.

Is it the gas check which is doing this because of the way I am applying it, or am I doing something else wrong?

Could I run the bullets without the gas check at the faster velocities (I'm looking for about 16-1800 feet per sec). Would they run better with the gas check and faster, i.e. greater than 2000 feet per sec?

Thanks.

[Bret4207]

You have a fit issue. The nice slow boolit is gripping the rifling enough at that pressure to give you decent results. When you up the pressure you're going beyond the alloys ability to grip the rifling. My guess is you have an undersized boolit. What size is your Lee sizer ACTUALLY sizing them? Just because it says .314 doesn't mean it's .314. What size is your throat? What size is the case mouth of a case fired with a full powered load?

My guess is you'll need a larger boolit and the GC to get above 12-1400 fps. If your 303 is war time production it may run as large as .316+. Some times sizing an 8mm boolit down is easier than trying to drop a really, really fat 314 cal.

[Stoats]

The 314 sizer does not actually size the bullets, which drop at 313.

The rifle is post-war with a good barrel, but I don't have the facilities to measure a 5-groove slug.

My alloy is fairly hard -- heat-treated 4% antimony 2% tin, no arsenic. It's not quite as hard as Linotype.

I have had the same phenomenon with my tight-throat, tight-bore 7.62 x 39, with Lee 309 bullets sized to 309.

Thanks

[870TC]

Are you shaving lead off the base of the bullet as the check is applied? (ie gas checks to small for the base) Look for a sliver of lead just above the check, only on one side.

[Stoats]

Are you shaving lead off the base of the bullet as the check is applied? (ie gas checks to small for the base) Look for a sliver of lead just above the check, only on one side.

No. Not the case.

[StarMetal]

Bret was on track. I tend to agree with what he said. Even at .314 your bullet may be too small for the bore/groove. If you have no means to measure the bore you could do this. Take a soft lead slug and slug your bore. After you have the slug carefully run it through your .314 sizer. If it sizes it you know at least your bore is larger then .314.

Joe

[Bret4207]

The 314 sizer does not actually size the bullets, which drop at 313.

The rifle is post-war with a good barrel, but I don't have the facilities to measure a 5-groove slug.

My alloy is fairly hard -- heat-treated 4% antimony 2% tin, no arsenic. It's not quite as hard as Linotype.

I have had the same phenomenon with my tight-throat, tight-bore 7.62 x 39, with Lee 309 bullets sized to 309.

Thanks

Okay, I'm guessing you have a Lee Enfield or Enfield. .313 may well be too small. What does the case mouth of a full powered load measure? That's a rough guess way to get a boolit size to aim for.

Same for the 7.63x39. If that's a normal barrel .309 is .003-.005 smaller than most folks find works.

[wiljen]

I have the Lee 312-185 and had to lap it and beagle it to get a bullet large enough to make my 5 groove happy. On mine it is not so much a fat 30 anymore as it is a small 8mm. You might be surprised by yours too. Remember also that the throats on those guns can be way way over bore diameter so using a .318 slug with a .315 barrel to get it to fit the throat isnt all that uncommon either.

[Stoats]

Thanks for the replies. Will try going larger.

By the way, my 7.62x39 has a .308 bore since it's a custom rifle.

[1874Sharps]

Stoats,

There is much good advice above and I will not repeat what is already said. I will add, though, that if you are having problems with a tight fit of gas checks on your boolits you can try an 8mm gas check on your 303 Brit bullets and it will tighten the fit right up. I had to do this for boolits cast from one of my 30 caliber molds, as I would shoot the boolits and see the check land short in the dirt and the boolit often go wild. Using a slightly larger 8mm check fixed this problem. Hope this helps and good luck!

[Stoats]

If the bore and/or throat does turn out to be rather on the large side, would the Lyman 319247 sized down with a custom Lee sizer be the way to go?

Also, how fast is practical without gas checks?

[Bret4207]

You can also try annealing the GC, this gets rid of the spring back issue in the GC and results in a tighter fit.

On the 7.62x39- it can still be a size issue. Just because your barrel is supposed to be .308 on the nose doesn't mean it is, plus some guns want a fatter or skinnier boolit, usually fatter. You have to figure out what the gun wants as you increase the pressure. Fit comes first and is one of the easier things to change, start with a good clean barrel too.

Also- how or why are you heat treating an alloy with no arsenic present? It is my understanding that w/o arsenic in the alloy no hardening will come of any heat treatment. Have you had different results?

Lets also remember that hardness alone isn't an indicator of how well the alloy will react to pressure. The shear strength of an alloy may not increase with hardening.

[1874Sharps]

Stoats,

If your throat is much larger than the bore, it will likely be better to choose a bullet diameter that matches, or slightly exceeds the chamber diameter, even though it will be unusally larger than the bore diameter. Perhaps that may sound a little strange, but I believe it is true. I think around 1800 fps is what you can reasonably expect from a standard plain based boolit under best conditions.

[Stoats]

You can also try annealing the GC, this gets rid of the spring back issue in the GC and results in a tighter fit.

On the 7.62x39- it can still be a size issue. Just because your barrel is supposed to be .308 on the nose doesn't mean it is, plus some guns want a fatter or skinnier boolit, usually fatter. You have to figure out what the gun wants as you increase the pressure. Fit comes first and is one of the easier things to change, start with a good clean barrel too.

Also- how or why are you heat treating an alloy with no arsenic present? It is my understanding that w/o arsenic in the alloy no hardening will come of any heat treatment. Have you had different results?

Lets also remember that hardness alone isn't an indicator of how well the alloy will react to pressure. The shear strength of an alloy may not increase with hardening.


My alloy does heat treat -- I can't get it quite as hard as Linotype though. Any alloy containing at least 2% antimony will heat treat, however arsenic helps a lot.

The reason for using this alloy is that lead wheel weights have been obsolete here for quite a long time, so difficult to get hold of in any quantity. I did, however, come into 300 kg of Linotype, which I want to make last as long as possible. Hence, I mix it up with roofing lead and 1% extra tin to give the stated alloy.

It sounds like I should try bigger in both cases -- I have a Lyman 130 grain 311 mould coming for the 7.62 x 39, and I might consider also getting their 314-200 grain or that 319.

[1874Sharps]

Stoats,

Wahoo, 300 Kg in linotype!!! What a treasure!

[Stoats]

It did set me back about 450 US, and getting it home in my compact was... interesting!

[Bret4207]

Well, hardness alone won't solve your problem. For the PB I would lower 74 Sharps est to around 1400 in 30ish calibers. Work on the fit issue. Start with "as cast" boolits if they'll chamber and see what they do. This takes time to play with. Sorry, there's no "magic bullet" that I can pass on.