MarinePMI

The RRS TFCT-34 is pretty expensive, and a bit much to swallow, price wise. That being said, I went down the "trying to keep it reasonable" route, and wish I had just got the 34L package to begin with. It would have saved time, money and frustration. The lower cost ones work, no doubt about it. But the parts wear out quickly and have no where near the stability, rigidity and smooth tracking as a 34 and an anvil 30 ball head. No where near. Still, it's understood that is a lot of coin to drop on something that doesn't go "bang!". So, what many do is, go less pricey on the tripod, and spring for the anvil 30 ball head. It's a decent compromise, and will get you in the field, or game, until you finally upgrade the tripod. Standing, shooting rabbits off a tripod at 500+ yards tends to change your mind about the state of the possible for long shots in tall grass, and drives home the value of a high quality tripod and ballhead in the field. JMTCW...

A Sawtooth ARCA rail on my AI. FYI: The anvil 30 ball head in this photo will latch to picatinny, as well as ARCA, rails.

If you need a quicker response, let me know. One of the guys I shoot with does a lot of testing for them.

Kind of a dated solution that is nowhere near as stable, or versatile, as a ARCA rail and tripod/bullhead fitted for ARCA.

You might be able to fit a Sawtooth ARCA rail to that GRS stock... Shoot them an email, he may be interested in making one for the GRS.

I'm not sure if the ship to the UK and support UK power requirements, but here in the US, LEM is pretty much the gold standard. All high quality stuff. https://www.lemproducts.com/

Don't have any data, but wanted to point out that barrel twist is going to be an issue. You'll have to step down to the lighter weight bullets to get them to stabilize at subsonic speeds, and even then you may run into issues. From personal experience with a .300 Whisper, to shoot the 240gr SMK, you'll need a 1-7 or 1-8 twist to stabilized reliably at longer ranges...