If you look at the end of the t34 gun barrel in the picture here, you can see at the end of the barrel, there is a line, making it look like multiple pieces
https://i0.wp.com/militaryhistorynow.com/wp-content/uploads/2015/03/T-34_85.jpg

in this one it does not look like there is the line at the end, looking like this barrel is 1 piece
https://pekobooks.com/wp-content/uploads/2018/02/vol17_108.jpg

was there different versions?

The earlier T-34/85's were armed with the D-5T gun and the later production had the ZiS-S-53 gun.

Different 85 mm guns were developed/adapted to rearm the T-34.
"By 1942, the 76.2mm F-34 tank gun of the T-34 medium tank was found to be lacking in range and penetration compared to the German 75 mm Pak 40 anti-tank gun, new mounted on the Stug III and Panzer IV, and markedly inferior to the 88-mm gun of the Tiger I. Military planners directed the design bureaus of both Gen. Vasiliy Grabin and Gen. Fyodor Petrov to modify the 85mm anti-aircraft gun for use as an anti-tank weapon.

Petrov's bureau developed the D-5 85mm gun. Though much too large for the T-34 turret, it could be mounted in the chassis of the SU-122 self-propelled gun to create a tank destroyer. This was done, and the SU-85 tank destroyer went into production. Meanwhile, efforts were underway to redesign the T-34 turret to make it large enough to accommodate the newly developed gun.

Grabin, who had been working on a second 85mm gun, the ZiS-53, at Joseph Stalin Factory No. 92 in Gorky near Moscow, was reassigned to the Central Artillery Design Bureau (TsAKB) in Moscow. His project was turned over to 23-year-old A. Savin. A third team led by K. Siderenko was assigned to yet another 85mm gun project, and developed the S-18, to be used in the modified T-34 turret.

The resulting guns were tested at Gorokhoviesky Proving Grounds near Gorky, with Grabin's ZiS-53 winning the competition. However, the new T-34/85's turret had been designed to accommodate the already-available D-5 gun, and did not mate properly with Grabin's gun. The T-34/85 tank went into production making use of the D-5 gun (designated D-5T, for "tank").

Savin was put to work modifying Grabin's gun to fit the new turret and incorporate other improvements. His initial was added to his gun's designation in recognition of his contribution: the ZiS-S-53. From T-34/85 Model 1944 onwards, all T-34/85s used Savin's ZiS-S-53. It went into production in the spring of 1944. A new antitank gun was then developed, the 100 mm field gun M1944 (BS-3). "
Text borrowed from https://en.wikipedia.org/wiki/85_mm_air_defense_gun_M1939_(52-K)

/ Robin

The first one looks like it has a thread relief groove machined into the tube. This was a preparatory step to machining a thread for a muzzle brake. If a decision was made not to mount a brake the tube would not be threaded.

Sometimes a number of tubes had been made to this point in the process when the brake omission was made, so grooved tubes can be quite common. For example, Jagdpanzer 38 and Jagdpanzer IV L/70(V) tubes.

KL

the ICM t34/85 barrel has a small piece at the end of the barrel. it is slightly bigger than the rest of the barrel, making it look like the first barrel in the picture, with the line.

i was looking at metal barrels to replace it and some had the line and some didnt. however, i couldnt figure out which is more correct.

if the line is accurate like the icm includes, then i will just keep it.

ZiS-S-53 barrel


Side view of turrets with D-5T barrels/guns

I read somewhere that one of those guns had an assymetric mantlet or something.

Some more images of T-34/85 with D-5T gun here:
https://www.themodellingnews.com/2020/04/preview-miniarts-new-t-3485-wd-5t-plant.html

It's a thread protector.

The production guns weren't intended to have muzzle brakes so they weren't threaded. The thicker cylinder at the muzzle of later guns is an integral reinforcement, like on the US M68 105mm.

KL