The tikka T3 synth stock i use is a pretty smooth item, & i find the bag i use is a thousand times better than a bipod in terms of consistant recoil--its just not as convenient...
I also spent couple hundred bucks on what i thought was a decent front rest & got a bucket load of horizontal happenings...used it twice & now it gathers dust...
There are various reasons for this, but i believe a big factor is how light weight these modern rifles are, & i think this makes learning to manage recoil a bit harder.
Gaz-Re the bag, you will find it may take a bit of use until the fill you use settles into the bag & gives a good consistant shape--even with regular use you may find it still settling six or more months later..i found.until this happens the recoil was sometimes still inconsistant as marksman says with grabby areas...however with my bag/stock combo i found shoulder tension a far greater variable than the grabby bits on the bag.
One way i avoid this & it works with the T3 stock is to put a microfibre cloth in the top of the bag...my stock then glides through the top channel in the bag like a puk on ice...
As for a rear bag i use a sock filled with the plastic i mentioned earlier--but i find you have to set the up nice & symetrically for good even recoil--not the "best" rear rest for testing but a reasonable one in the field that costs zippoh...!!
Also, if trying this naturally remove any strap/sling & take out the sling attachment doova's...
I also found it very helpful to give the bag a good smack down so it settles well & smack the rifle a few times in the top of the bag channel if doing testing--that way the bag wont settle "AS" you work through different charge weights & you're shooting off constant 'hardness'.
But let me be clear--im NOT at all suggesting this is "THE BEST" way to go for a rest...im merely suggesting as a cheap altrrnative & i can honestly say it has extended my range by a good 80 yds with a higher kill rate on bunnies & foxes for that quickly jump out the car over the bonnet shot...
When i used to shoot off a bipod i would get varying amounts of muzzle jump & recoil direction depending on the surface shooting off of & how evenly you load up the legs--but now whether i shoot off bonnet ground tree or fencepost with this bag OR with my rear bag (sock filled with plastic granules) the recoil is more consistant & more heads burst..
Im not knocking bipods, just better results off a bag for my kind of shooting which is mostly driving around & sitting at a warren for 20 mins then move on to the next.
Ultimately there are far better shooters & greater professional experience in this thread compared to me, so certainly take their advice over mine Gaz.
But ive no doubt you will get crackingly better results with that bag as i had some similar issues as you before i tried the bag set-up.
Hope im of some help even if it means you using/trying a different approach.sometimes hearing peoples experience gives you ideas in the opposite direction that work for you..& sometimes they just babble too much crap like me...
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The man who knows everything, doesnt really know everything...he's just stopped learning...