Your first step is to see what bullet(s) your barrel likes - most barrels have preferences caused by the interactions of barrel internal dimensions, bullet diameter and shape.
As Mike says, the 1-13 inch twist and short throat was designed specifically for 155gn bullet Palma and Fullbore Rifle loads, so a good starting point is any of the better 155s - Lapua Scenar, two Sierras, Berger 155.5gn BT Fullbore are the outstanding models, maybe Hornady A-Max for shorter ranges. The original lower BC 155gn Sierra MatchKing (p/n 2155) is a very forgiving design and is often a good starting point.
Despite the slow twist barrel, you're not limited to 155s, as this twist rate will stabilise the older and lower BC 168s that often shoot really well at shorter (up to 600 yards) ranges - the Sierra MatchKing and its near copies from Hornady (the HPBT Match model and A-Max), Speer and Nosler CC, also the 167gn Lapua Scenar. It also just stabilises the 175gn Sierra MK, another extremely tolerant design that shoots well in most barrels, likewise the superb but pricier 175gn Berger LRBT, even just stabilises the 185gn Berger LR BT 'Juggernaut' in warmer weather if it's a true 1-13" twist barrel. (Not the VLD and Hybrid versions of Berger 168s, 175s and 185s - they're too long for the twist and need higher spin rates.)
The problem as Mike points out is that you'll need to seat them pretty deep because of the short throat. (That can be sorted cheaply by a gunsmith - the throat can be lengthened by use of a hand-reamer that doesn't need the barrel taken off, 'clocked-up' in a lathe and other expensive, time-consuming work.)
So far as recipes go, there are scores to choose from using many powders. The US [Palma] Rifle Teams Long Range Forum has plenty of threads on this subject, but go into it and click on the 'Precision Handloading' section and you'll find an overview of basic loads right up top as a 'pinned topic' called 'Palma Loads'.
http://www.usrifleteams.com/lrforum/
The norm for these guys uses around 45-46.5gn Varget with 155s, but lots and lots of powders work well - Viht N140 and N150, IMR and H4895, IMR and Accurate 4064, Alliant Re15, Ramshot TAC and so on and so forth. The Viht and especially Hodgdon powders are prized for their lack of temperature sensitivity.
To a certain extent, what you load for and to depends on the distances you plan to shoot over. If you're planning on 'short range' (defined as up to 600 yards in TR and F/TR, but you can in practice add 800 too), you have a lot of leeway as your loads aren't velocity-critical. What you need is something that groups really tight and holds its elevation at all distances. 900 and 1,000 yards are a completely different ball game that needs ballistically suitable bullets (NOT the 168s excluding all three Berger models which are OK, but two if which aren't suited to 13-inch twist barrels anyway) at suitable MVs. The minimum standard is a high BC 155 that remains stable at long ranges (NOT the A-Max) allied to a minimum 2,950 fps MV to keep the bullets supersonic at this distance - plus of course retaining precision and small elevation spreads. Bear in mind that the US Teams
Long-Range Forum is exactly as per its name, so its advice is normally tailored to meet these rather exacting requirements - a 155gn bullet load that shoots really well at 2,750-2,800 is fine at short to mid ranges.
If you enter any matches shot to true Target Rifle / Palma Rifle rules, you are limited to bullets 'that weigh less than 156gn', but most US matches allow any bullet, hence ballistics guru and US national Palma team member Bryan Litz using the 185gn Juggernaut for any bullet matches and 155.5gn BT Fullbore for 'Palma Rules' entries - Berger of course as he is its ballistician and bullet designer.