Has anyone studied ...........
same mould, brass, powder, charge, primer, seating depth,   range conditions, etc. .............
the only difference being the ratio of (certified) lead:tin?

Given, 25:1 produces slightly heavier bullets than from 20:1.   

Is there an effect 200 yards down range?  due to ...... weight  of bullet? ability of bullet to maintain pressure throughout the time in the barrel?

Will the difference in weight of +- 2% bullet weight affect accuracy? 

My next range tests will be addressing these issues. Can anyone save me some time?   

Thanks.

I, personally, think that very small variance is unlikely to make a difference in most rifles. How much before any rifle shows a dislike (assuming you started with a "like"), is probably each rifle's decision. I have one that is fairly tolerant, but a fellow I shoot with sometimes thinks any variation is intolerable by him, and his rifle. Do some tests and you'll know what your rifle likes. Good luck.

I had slightly better accuracy using 20:1 over 30:1 when I was testing in the early 90s in my 33-47 Stevens Pope barrel. The 30:1 was slightly better with about .2 gr less 4227 than the 20:1 shot best with, but the 30:1 at its best was still inferior to 20:1. I did not notice any change in impact at 200 yards. Pope said 15:1 should shoot better but they would be too had to breech seat, so I didn't go there. 

Have fun, it takes lots of lead and powder in good conditions to see the difference and get consistent results.

Ray I have and the improvement has more to do with controlling nose slump than it does bullet weight and it shows even more so when using a long unsupported nose spitzer and I typicaly use 1-16. I tend to get a little leading if going harder and the only reason I don't. 

JLouis

Every Pope Mold I have is significantly Tapered. He may have been able to Breach seat 15/1 is where I am going with this description. Think it over, HTH 
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You have a very good point there. Westerner cast up some Pope 33's for me to shoot in my rifle. Mine is .330 bore and .337 groove. The 6 band Pope bullet measured .328 for the frist 3 bands, then .332, .336, with the base band at .340. Note the first 3 bands where .002 under size of the bore.

I have no idea what a "standard" bore and groove would have been in a Pope barrel but, I would have thought a bore of .327 - .328 and a groove of .338, for a .005-6 groove depth. Seems a little deep for those days.

Back to my rifle, I shoot 2 ten shot groups, one with the Pope bullet and one with my bullet. I was very surprised of the out come. Remember, the Pope was .002 smaller than the bore on the first 3 bands.

My bullet shot about a 2.5 group @ 200 and the Pope, about 3.1 but, they both had 6-7 shot clusters of about 1 5/8. I WAS VERY SURPRISED!

MY BULLET WAS CYLINDERICAL @ .337 with a .340 base band, 5 bands. The Pope, of course BSed easy. I wish I had more bullets to re-read a few times.

I can post pictures of the 2 groups later.

Frank

I don't know how Bruce did it but in my case with my 38-50 and a long nosed DT mini-groove from a Paul Jones mould it was easy to see the difference on the rams at 500 meters. Unexplained fliers with 20 to 1 disappeared with 16 to 1 after reading DT's recommendation on alloy for the bullet.

joe,
2 points (approx 2 moa) less comeup required with 12:1 than 16:1, and similar with 16 and 20:1.
as described in the previous post, i am confident this is due to better retention of nose shape, which in turn translates to higher b.c.
it also translates into less time of flight, and therefore less wind deflection. this also seems to hold true in windshear situations.
the differences in moa at 500/600 yds is about 1 moa. it gets better the further out you go.
keep safe,
bruce.

I am unclear as to what exactly "nose slump" is and when and where it occurs. It seems to me the shape of the bullet does not change; rather, the centerline of the flight path develops a downward position at some point. In the barrel? Early in its path? ..... or near its time of discharge from the barrel? In the air?

I expect to see very minor differences on the target from my testing, but feel every little detail contributes to the overall performance. I value all my range time as learning experience and always shoot with reason and hope of finding another piece to the puzzle.

Thank you all for your helpful input. You are all my mentors, for better or worse and I always consider all points of view and knowledge presented while making my own decisions - again, for better or worse.

Happy New Year and Good Shooting to all.

Ray