does a rifle with a long throat that allows one to seat the bullet longer than SAAMI specifications, allow for more powder before reaching max pressure? Assuming a modern rifle is being used, no issues with magazine length, .030 from lands, starting at min loads working up, and all the other normal conditions.

Yes, you are increasing the volume of the case, thereby reducing pressure; which allows you to use more powder to make the same pressure as with the smaller case volume. Will you get more velocity as a result; sometimes. For example, I have a Ruger 257 with a really long throat; it allows bullets to be seated out so that only .1 inch of bullet is in the case. I get some velocities you wouldn't believe, at safe pressures.

It is generally accepted that there is an advantage and especially so when using the slower burning powders where case capacity can limit the full advantage being gained by using slow burners. Barrel length also comes into play here too.

The Weatherby and Danish made Shultz and Larsen rifles had 26" barrels and were generously free bored allowing the magnum cartridges to produce high velocity with cases full of slow burning powders.

"Yes, But..." applies here. Long throated chambers allow longer seating and potentially more powder, however, as one approaches the leade, pressures can spike appreciably, so caution is advised.

An example is the 223 rem long throated chambers( AMU, Wylde, NATO etc), the max load with mag length bullets ( 77/75 etc), is less than the charge for long seated 80s, and velocities of these "heavies" exceeds the mag length 77/75 by quite a bit.

Leaving a .015 to .030 "jump" between the ogive and leade allows safe performance, while "jamming" into the leade often results in popped primers ( expanded pockets/head) and unsafe pressures.

As eagle 27 states, Wby "free bores" the mags so the bullet basically does not engrave for a significant distance down the bore-allowing internal capacity to be used w/o significant resistance before the pressure building engraving process begins- a big "jump" with a soft landing in the lands if you will.

All of the above stated 223 variation chambers also use a shallower leade angle ( the 223 Rem SAAMI chamber has a 2.5 deg leade, and .025 freebore) while the rest have 1.25 to 1.5 deg leade and .050-.067 FB- offering a softer /longer distance to engraving, moderating the spike in pressure to a degree.

Keep such "long" ammo segregated and well marked- as chambering in a short throat may be difficult and firing can be risky.

Thanks guys!

Roy Weatherby's rifles all have long throats. He knew he could get every FPS he could and not get dangerous pressures.

But Weatherby didn't use the long throats for extra powder; he used them to keep pressures down. His bullets have to jump a long ways to the rifling; contrary to what the OP is trying to accomplish.

see below for 257 bob...
here's the math...

take the percentage increase in capacity - call that Y...(unitless)
divide by 4..
multiply that by the vel you normally get in fps, and this will be the fps at the same pressure

case in point, 3000fps normal round, increase by 0.10
0.10/4=0.025

3000fps*0.025=75fps gain

my 257bob is on a 1903 -- i love it ... i can reload at 62K psi, which is about 15% higher pressure than "book" or EXACTLY the same pressure as winchester published +p loads, and get amazing results, at standard length.. not AI ... but the rifle also has a long throat, which i think many bob reamers have...

i don't have to play any interest shenaniagans to get fast loads out of it, just load to winchester +p loads, that olin used to publish

further, i like your thoughts on -.03 .. my default load is -.-.0275, but 30 works great, too

Once again, thanks for the info. At this point, I am not attempting to accomplish anything, just curious if I could experiment a bit with my single shot blaser in 7x57. Also, I am thinking of having a ruger #1 that already has a short throat reamed out beyond normal length, to increase both case capacity as well as distance to lands.

The Brno mod. 21 and 22 come with long 30-06 magazines and matching throats in 7x57 and 8x57 and can be loaded beyond std. magazines and short throats...The use of H414 powder adds another dimension to this caliber in this rifle btw.

Yes, mine likes the H414. Have been experimenting with Norma URP lately, so far I like it too.

Even with long throats and all my rifle have long magazines and long throats, but I never let the bullet touch the lands (rifleings), I back of a several thousands depending on caliber. I get some awesome velocity with all bullet weights in my 7x57s, accuracy is excellent..My loads of H414 are beyond book max by quite a bit, but my pressure is in a very safe range, cases last up to 14 reloads, primers remain snug and I will trim about every 4th or 5th firing.