After my experience yesterday sighting in my MP5, I thought I would check in with the group here to maybe save myself some trial and error.  I hit the local indoor range yesterday to sight in my Aimpoint Comp M5 on my HK MP5 and ended the session in frustration because I ran out of time and couldn’t see this through resolution.

The gun is a genuine HK94 that I had converted years ago by IGF to MP5-N configuration that until recently just sat in the safe as an investment.  Earlier this year when KAC re-released the RAS I decided to make the gun useful and added that, and recently an Aimpoint Comp M5.  I also run a Gemtech Multimount suppressor attached with their 3-lug adapter.  Yesterday I sighted it in with Winchester 124gr NATO ball ammo and was getting great groups at 50 yards.   Just before my range time expired I loaded up some Federal HST 124gr +P to see what the POI shift is and it wasn’t good.  After 2 5-round groups at 50 yards only two rounds were on paper and I can’t even call it a grouping- one about 6” high and right about 4” and one straight off to the right about 6”, both barely on the paper.  For comparison, my groups with the 124 gr FMJ at 50 yards were averaging about the size of the 2 MOA dot on the Comp M5

As I said, I ran out of time and had to leave but I’m scratching my head on this one.  Of course I will need to follow up on this and get back on the range to sort it out but I guess my main questions right now are is a shift of this magnitude considered “normal” (with two 124gr projectiles) and is the MP5 platform “finicky” when it comes to a JHP round that shoots accurately?  I know I shouldn’t draw conclusions off this brief time with the HST but I’ve got a few things bouncing around in my head- effects of +P through the can, velocities, etc.  I have read that the Winchester 124gt NATO FMJ is slightly over standard pressure so I thought it would be close enough to the +P HST to be useful for roughly sighting in the setup before slinging pricey HSTs downrange.

As I said, just reaching out to hear the experiences you guys have had and if there is something I am missing in regards to the appropriate JHP round for this setup.  Otherwise, I guess I need to just hit the range again and zero for the HST but that disappoints me because I’d like to plink with FMJ as well and would hate to have to re-zero every time I switch ammo.  Thanks for any input offered.

yes different rounds do make different groups but they shouldn't be that bad.

I also don't know what "on paper" means as you didnt give dimensions

start with easy stuff first, check the m5 and mount your using

take off the can

shoot groups

have someone else shoot groups

that will tell you if its the ammo or something else.

If it is the ammo-try another one.

I only see a significant difference if i go from 115 to 147/158 at longer ranges

This

I have all mine sighted in at 25 and use irons.

As far as HPs in them I have only used the gold dot G2 rounds in my gun as I have a lot of them. I dont notice it shoots any different than ball

My clone has very little POI shift with 147gr HST standard pressure compared to 124 NATO. I would suspect something is working loose. Another option that would be far more unfortunate and unlikely but I have seen it with 9MM AR’s is bullet setback from poor feeding causing varying case pressures and thus velocities. A bit of a stretch, yes. But possible.

I have not noticed much of any change POI with 147's hollow points.  I have run a number of brands without issue, however HST's are my go to.