I need some guidance as I develop loads for my new 6.5x55

[Longwalker]

I have just purchased a nice used Merkel drilling in excellent condition, 20 ga. 3" / 6.5x55. I've never owned or hand loaded the 6.5x55 cartridge before. I am a very experienced reloader, but this project has me nervous. I'm trying to create some traditional 160 gr. RN loads which I think will pair nicely with the open sighted drilling for bush hunting for medium sized game. I bought a box of Hornady 160 gr. RN Interlock bullets to start. I have two powders, RL22 and H4831SC that seem to be in the correct slow burn rate suggested by most sources.
But reload data is highly variable depending on the source. For example:

Hornady 8th edition:
H4831 42.3 gr. Max for 2300 fps 29" barrel
No RL 22 Data

Hodgdon 26th ed:
H4831 45gr. Max for 2454 fps 28" barrel
RL 22 47gr. Max for 2605 fps 28" barrel

Lyman 50th ed:
H4831 46gr. Max for 2388 fps 24" barrel
RL 22 46gr. Max for 2361 fps 24" barrel

meanwhile Norma, the Swedish company with what I presume has the most experience with the cartridge, suggests the following with the Hornady 160 gr. RN
Norma MRP ( some sources say it is the same as RL22?) 46 gr. for 2533 fps with no barrel length specified.

I think I trust the Norma data the most but can't get MRP. Various sources say RL22 and MRP are different lots of the same powder from the same factory - but I don't know how differently they burn. In your experience is RL 22 close enough to MRP to substitute?

I'd like to get near maximum performance from the little cartridge, perhaps 2500 fps with the 160 grain, in case I would have an opportunity to use the drilling for moose or bear. But I have no idea how to approach working up towards maximum loads in a break action gun. It would certainly seem different than the usual approach with a bolt action rifle. I'd want to quit increasing the powder charge long before the kind of pressures that would give a bolt action sticky bolt lift or very flat primers. I usually use velocity measured by chronograph as another guide and as an indicator of pressure, but the published velocities are all over the place.

I purchased some Norma "whitetail" ammunition with 156 gr. RN bullet to compare with. Box claims a velocity of 2559 fps, again with no barrel length specified. I will compare that factory load velocity claim with actual results from my rifle and chronograph as a starting point.

Your experienced thoughts please?

 

[375er]

So, a drilling changes the equation due to the shotgun barrels over it. Per standard reloading methods, start low and work up. When you find something that gives you the accuracy you are satisfied with start your chronographing at that load. I have tried hotter loads in drillings to find reduced accuracy.

 

[Frederik]

I doubt you will struggle to get 2500fps with the 160gr Hornady bullet just bear in mind its a non bonded soft.
In my Sweed with 23" barrels I got good results with 44.5gr N560 that was running at 2420fps which is good enough for the soft bullet.
Performed well on game no meat damage and good bullet penetration at that speed.

 

[GuttormG]

Look at loads using Norma MRP, this is the same powder as your RL22.

the RN 160grs is very well talk about among Scandinavian moose-hunters (but now everyone "knows" you need a superdesign expensive bullet to get the job done..).

In your drilling, keep away from the max loads, they have a reputation to getting "loose" if shot much with max.loads.

 

[flatwater bill]

I have loaded 40.0 grains of IMR 4350 under a 156 or 160 RN with good results. This is a mild load, and a good place to start from IMO.........FWB

 

[GuttormG]

In your experience is RL 22 close enough to MRP to substitute?

Very close, it is the same powder; but lot-variations is a thing so do not jump on max-loads.