Have 5 week old girl and have always had a certain amount of posseting (since day 3). Squeals before any poos which are explosive sounding - can hear them across a large room. Occasional curdled milk possets and about once a week entire feeds come back, usually more than 15 minutes after the feed, entire time propped up on raised legs or held up in arms. Sometimes fresh sometimes curdled. Did have colic symptoms (knees up, unconsoleable crying).
Eliminated the usual dietary suspects (spice, citrus, gassy veg, chocolate, what little caffeine I have and tomatoes) and colic more or less disappeared but posseting/bigger regurges continued with occasional colics which appeared to be egg related (ice cream/brioche). Squealing before poos continues as does explosive sounds. Tried bringing back various lower level suspects (white chocolate, pizza with tomato sauce, small quantities of tomato) with no major issues.
Sick of lack of fruit and with incipient cold I tried 1 orange, colic returns 
.
2 days later OH on call I risk gnocchi (egg free per label) with tomato sauce from jar and next morning mega regurg of 2nd feed, all over bouncy chair I put her in more than 20 minutes post feed (which was relatively upright)
No distress even with the entire feed regurges (apart from hunger afterwards). These have some range but aren't across the room. Generally happy/relaxed. She's definitely growing - reached birth weight (EBF) by day 10 and 7.3 (from 6.11), 1 week later. Not been weighed since but is much longer than she was - well and truly out of original newborn babygrows but more due to length than width - still stuck with size 1 nappies as pretty slim legs and waist.
Does sound pretty mucussy without much coming out. Sleeps pretty well at night.
Not been measured officially we think 75th for length and was on 25th for weight.
Will obviously mention to GP at scheduled appointment next week but unless the differential between weight and length percentiles is an issue I doubt they'll be that interested.
Mega essay, sorry!
Thanks in advance,
R