I couldn't imagine ripping off with a bunch of 308. That sounds more like cruel and unusual punishment from doing something wrong than "fun" to me. LOL
I had bought a PTR 91 Pistol (308) with the intent of SBR-ing it but with the sear installed I can put a stock on it, anyway, in FA, after the 3rd round you were pointing skywards so unless you were shooting at targets coming down a hill it wasn't very effective ... and yes, its not pleasant even with the HK21 clubfoot stock and heavy buffer! I ended up selling it because I didn't shoot it ... sometimes I regret letting it go, but it helped to fund my 6.5 Creedmoor which I do shoot!
(https://s20.postimg.org/8k3480n59/8e389878-d1d8-43cc-a05d-6facd43ca2a2.jpg)
My first MP5 clone is a Coharie CA89, which I'd SBR'd just before Obama took office in (received my stamps on January 19th 2008); turn around on the stamp was 62 days.
The MP5K and MP5SD are the new Omega's I've bought in the last year ... I just bought the barreled receivers to save a few $$$ and I had a few HK parts including housing and SA trigger packs ... the thing I liked about them is they came "sear ready" and their customer support ... a few of their early guns had problems but they were taken care of promptly, and there were posts from the satisfied customers.
When I bought my SD, the ad said "After you take possession of the barreled receiver you can add your favorite trigger pack and suppressor ."
I should have known better but I didn't realize it had to be a favorite SD suppressor and kind of whined about it on several forms but I also included my fix for the problem which included removing a few of the baffles from my "favorite suppressor" and using the direct thread adapter I'd bought for my Scorpion EVO ... within a few months they started offering fake SD suppressors or the SD with the K barrel (instead of an actual SD barrel) inside the SD shroud so you could actually install your favorite 3lug suppressor or if memory serves you could get a threaded K barel.
(https://s20.postimg.org/gctrzyitp/image.jpg)
Later I realized I had a approved form 1 stamp for an 11" can in 45 caliber that I hadn't built yet ... although it has a .5" hole it works for the 9mm very well and its made its home on the SD ... originally it was for another project but while I was waiting 11 months for my approval that project got scraped, fortunately I didn't cancel the stamp. This is an older picture, currently I have a folding brace that has the shockwave blade on it.
(https://s20.postimg.org/v8sb7hwsd/image_2.jpg)
OK ... I've been rambling on enough.
YES ... SBR is worth it!