For those of you with chronographs and marlin guide guns (45-70), what velocities are you getting with cast bullets?

I expect the short barrel handicaps it a bit, but what real world velocities can be expected with cast bullets and near maximum loads. I'm especially interested in bullets in the 300 to 405 grain weight range.

or jacketed bullets?

I clocked my original 450 Marlin ported bbl at 2,043 with the Hornady 350 gr FP. This was with a near max load of H322 using Hodgdon data. I've since had the barrel replaced with a nonported one. I shoot mostly cast with it now. I've clock 420 gr GC bullets at 1,700 to 1,800 fps. 550 gr GC bullets will do around 1,550. These are near maximum loads from pressure tested data. Anything the 450 Marlin will do, the 45-70 GG will as well. It can be pushed slightly above these numbers due to the slight case capacity (3-5 gr) advantage. Most find that velocity loss, when going from a 22" bbl, to a 18 1/2" one, is approximately 25-40 fps per inch. Hope it helps

Before you push that Guide gun too fast,take a minute and read Randy garretts thoughts on his web page. Makes sense about the meplate issue/possible ignition of the magazine tube.
backing off a little is the prudent thing to do here, the elephant won't know the difference.

In my mental days I used to clock 2250fps from a 300gr Sierra JHP using a near max load of AR2207.
The splat factor of this load on feral goats was impressive to say the least.
Holes big enough to stick your head into, no joking.

These days, with far greater age, maturity, insight and alcoholic haze, I load a 405gr Rem soft point with a moderate load of the same powder for about 1700fps.
It's easier on the shoulder and knocks them down just as easily.

I came to realise after a while that the big ol 45/70 simply dosn't need to have every last foot per second extracted from it to kill cleanly.

Any bullet that big at moderate supersonic velocities is going to drill a big deep hole into anything it hits, no question.

Bullet construction is more important than outright velocity with this calibre in my experience.

It's an old thumper, not some modern hotshot, I wouldn't be worried about any slight loss of performance at all from that shorter barrel, it will make no difference.

Everyone just seems so caught up in this feet per second business. If you want big speed get a 264 Win mag or 257 Weatherby.

Thanks, my main reason for asking is I am in the process of trying to choose a first mold for the rifle and wondering if the velocities in the short barrel are going to be fast enough to require a gas checked bullet. I'm not that worried about wringing velocity out of it but I do want higher than factory velocities. It is apparent from the info posted that I should go with a gas check.

As I've said before, the "need" for a gascheck, and coversley the isseue of leading is related to much more than simply muzzle velocity. All the factors you need to consider are bullet alloy, bullet hardness, bullet size, barrel/throat size, rifling twist rate, and lube.

While you may only load your guide gun to say 1800 fps, and while that may be acceptable with a plain base bullet, I'd advise the use of a gas check design. It will be more tollerant of sizing, twist rate and bullet hardness. I've yet to see any advantage in accuracy with a plainbase bullet. The only advantage of plainbase is cost savings, but I have a feeling a box of 1000 gas checks will last you many years with a guide gun, and is a minor cost in the overall cost of ammo.

For handgun plinker loads, I'm plainbase all the way. But for full power and hunting loads, gas checks hurt none and often help much.

Personally I think the 350 gr cast bullet at some 2000 fps from a guide gun would be perfection for all but the biggest toughtest NA game, and then I wouldn't go much over 400 gr.

Iv never shot any 350s from my guide but I have clocked 300s at 2400fps, 405s at 2000fps and 500s at 1650fps. The 300gr and 405gr loads are from the Hodgdon #27 manual and the 500gr load was from a highly qualified individual. These load develope quite heavy recoil and I actually suffered some whiplash shooting the 500s from the bench. I dont do it anymore. Iv only killed deer with both cast and jacketed 405s and the damage is severe at this level. If you hit too much into the shoulder or backstrap you loose allot of meat. Iv thougth about backing off a little. From what I hear you dont loose as much velocity per inch of barrel loss with larger diameter bores. The cast bullets I use by the way are gaschecked.

I finally got to chrony some 45-70 loads in two differnt Marlin rifles. First off the load was 40 grains of H4198 under a 425 grain gc cast bullet. The primers were Federal LR.

Marlin 1895 22 inch barrel--chronied at 1706 fps
Marlin GS 18.5 inch barel---chronied at 1635 fps
I really doubt that anything hit with either load will be around for a second shot.

One of the most accurate loads in my 1895GS is a 405gr plain base cast bullet made my Oregon Trail. I push it to 1500 fps with SR4759.

My 1895 Cowboy doesn't like them but spits them around 150 fps faster. It leads a bit more at that velocity. I suspect it is a lube issue.

With Beartooth and TrueShot GC cast bullets I have not had leading issues at velocities up to 1800 fps which is a fast as I care to push a 425-430gr bullet.

I am in the market for a 350gr or bigger mold for my 45-70's. I would prefer a gas check design as I beileve it does improve velocity and mitigate leading.

I don't know what mould you will end up buying, but I am placing an order for an LBT 350gr. LFN mould and will be tryin it out in a few weeks as soon as all my new casting stuff gets in.

I have had many different moulds, but the LBT brand has been by far the best performer for me.

I'll let you know of the accuracy when I start shooting my new 1895.