I'm making some 45-70 loads for my bfr, and it was suggested to me to use sr 4759. I'm wondering how these will perform in my guide gun. In one of my speer manuals it lists 4759 as a reduced load round, but could I work these loads up a little hotter? Or do I need to switch powders. I've had good success with rl-7 in my guide gun, but some have said this doesn't do too well in a 7 1/2" barrel. I'd like to come up with a middle of the road round that will work good in both, then make some special taylored rounds for accuracy later. Thoughts?


I'm going huntin for Bigfoot.

Once had a friend that used IMR 4759 as a "somewhat substitute" for Unique. For sure, work up you own load.

Rev

In a nutshell---AA5744 for smokeless!

SR-4759 is real close to 5744 on the burn rate chart just a little hotter. I use 5744 with heavy bullets because it is bulker. For hotter loads I use 4198, it seems to work real good with 300 gr. jacketed bullets.

Really? I don't have any AA5744 on hand, but the data tables in QuickLOAD give it a bulk density of 0.86 that of water. That is slightly more dense than IMR4198, which is about 0.83. SR 4759 is used in a lot of rifle reduced loads because its bulk density is low, so it fills the case well at a low charge weight. The same size can that holds 1 lb of IMR 4198 is used to sell just 8 ounces of SR 4759, though they don't fill it all the way. QuickLOAD doesn't have 4759 in its database, but since I do have a can in stock, I'll trundle down to the mad science lab (er, basement) and measure it.

Later:
OK. 30cc's in a crude but accurate plastic dosing cup weighed in at about 330 grains. That's 21.38 grams. 21.38/30 gives us just a fraction over 0.71 the density of water. So, .86/.71 gives SR 4759 1.21 times greater bulk (space consumed per grain) than AA5744, or 1.21 times lower bulk density, whichever way you want to say it.

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Nick

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Huh?

What about RL-7 in a 7 1/2" barrel?

Correcting which powder had less density and more bulk.

Not enough information to tell? Need to know what the bullet weight and length and composition are? Heavy bullets have more inertia and therefore give the propellant gases more resistance to expand against. That gives slower powders more time to generate pressure and take advantage of the extra gas they can make for a given peak chamber pressure (assuming the case has room for a big enough charge). This is part of why a same pressure load of slow powder can outperform a faster powder with heavier bullets, but will underperform the faster powder with light bullets, which don't let the slow powder burn well enough to get them up to speed. Longer barrel length also lets a slow powder have more time to burn, but if the bullet isn't heavy enough, it still won't be a top performer for the chambering and bullet combination because it won't achieve adequate peak pressure.

IMR 4759 is high bulk, low density, so it will be necessary to know how far your bullet base seats into the case to know how much room is left for powder to see if enough of it can fit in the case to let you work the load up where you want to or not?

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Nick

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"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity." Homer Powley

Currently I'm burning up an old box of lasercast 350g hardcasts. I'm using 28.5g of 4759 working up to 31.5g per suggestion by bfrshooter.

28.5g only fill the case up about 2/3

Must be I was told an old wives tale about 5744. Read somewhere that it was the best powder to use for duplication of back powder loads because of it's bulk. Maybe because of the mess it leaves in the bore? It does seem to leave a lot of unburnt powder in my 32" barrel (and in a 16" 454). I guess I will have to by a pound of 4759 and give it a try.
I guess I should buy a copy of Quickload which would cost me the equivalent of 7.5 pounds of powder. But it is sure fun burning powder. And if I burn enough maybe someday I will be able to hit what I am shooting at.

I don't know what length those are? I put a .895" long 350 grain bullet into QuickLOAD's database and it looked like AA-7 would shoot in the gun OK. It is a little fast for the .45-70 in a rifle, which is why you don't see it listed in the published loads on Accurate's site, but for a revolver that may be OK? I got a calculation that reached peak SAMMI pressure at around 29 grains for a velocity of 1450 fps with a 350 grain lead bullet. That powder is so fast that it fills the case poorly. About 44% at that load.

IMR4759 isn't in the QuickLOAD database, so I can't give you a calculated performance projection. Burning rate is only one of several factors you need for that, but it sounds like you have room to go up if you just keep watching for pressure signs.

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Nick

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"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity." Homer Powley