Anyone had this problem...?

[mosigdude]

I just finished my first 300 Fireball build on an AR platform and started on load development. I topped the flat-top upper with rings of the appropriate height and set the scope. I tested subsonic loads with no difficulty or problems. When I switched to testing my supersonic work-ups the problems occurred...
Shots #1,2,3... no problems, decent accuracy, consistent velocity and no signs of excesive pressure. Recoil was a bit stiffer than I am used to out of .223, but I'm also pushing a slug about 3x the weight so I didn't think much about it. Either way, it was nothing that alarmed me and was not what I would consider excessive. Shot 4... I noticed that the chrono errored and I didn't see the shot on the target. Upon further inspection, I found that the chrono was shot (thus the reason for the error) and the bullet appeared to have struck the chrono at a very steep downward angle. I had been shooting off bags with plenty of clearance on the chrono, as I have done for years and years with other load work-ups with zero problems. I took the rifle apart, checked for damage and found nothing alarming. I reassembeled the rifle, moved the chrono and fired three additional shots at the same target. All three shots made a very nice group at the base of my target backer (approximately 24" lower than the original first 3 shots and point of aim).
Finally, unable to determine the cause, I removed the scope and found that the "guts" of the scope were loose and rattling around inside. This scope was not overly expensive and I had just planned to use it as a temp scope for load development so I was not, at first, concenrned. I replaced the scope with another nearly identical, continued load testing a few days later and had the same result again after 14 shots.
I know the actual recoil of the 300 Whisper is minimal and even inexpensive optics would have no difficulty with this. My question is this, does the AR platform generate a different recoil signature that is damaging to optics by the buffer striking the rear of the buffer tube or are these scopes just junk. I purposely didn't mention the brand of scope because I don't want to get into a ford/chevy brand war, but I am concerned that when I put my better scope on that this will occur again. I will say I've used this brand of optic in the past on several different rifles, from rimfire to 300 Win Mag with very good results.
Any input is appreciated.

[Colorado Osprey]

semi-auto's tear up scopes if they are not high quality....experience gained like yours.

I have had luck with Weaver classic scopes though.
Probably the best value that seems to hold up on the AR platform.

[pug]

I have had several different scopes on several different 300/221 rifles and never had one come apart from the recoil. I did have a low priced one that the reticle came loose on but it was mounted on a 5.56 AR-15 and I found the scope was just plain cheap made after cutting it open.

[amafrank]

I had a problem with a cheap scope dropping the reticle on my bolt action 300. It was a cheap ass tasco that came with a 10/22 in a package deal though they were listed for use with rifles. It was all I had that would clear the barrel for the rings I had though...oh well, a $10 scope down the tubes.
I stuck another tasco that I've used on many rifles on the bolt gun and it works fine. No drift or troubles. I'm looking for a decent scope now that will be appropriate for the rifle and not be a cheap crappy stop-gap.

I had a little trouble with subsonic loads and consistancy using H110 and 147gr tracers. I think there is too much room in the case with this powder and also the tracers have a much longer bearing area when compared to a standard 150gr bullet. The tracers all light much to my surprise but one will go right to point of aim and the next will either be high by many feet or drop in the mud 50yds out. Supersonic with the same bullets they are deadly and right on target. We didn't see this sort of inconsitancy with the heavier 220 and 240 gr slugs either sub or supersonic. We just bought some Vihta Vouri N110 and loaded a bunch of 220gr subs with it. Consistancy of velocity was much better than the H110 and the powder is bulkier. I think it might work well with the light bullets as it fills the case more. We were surprised when we went from the bolt action to the AR when the velocity dropped by about 100fps. I wonder if the gasport leaks enough gas that the drag of the remaining barrel slows down the bullet. Not any help with supersonic loadings for you but it seems there is a big difference in loadings for different types of guns as well as oddities in consistancy.

Frank

[mosigdude]

Ok, thank you very much for the responses. It sounds like the scope may be the culprit. I just wanted to make sure that this wasn't going to be a problem when the rifle gets topped with a more expensive scope. I've shot many rifles and have never before had this happen, it was really odd to have it happen twice on the same rifle. It must be the combination of semi-auto and the sharp "blow" of the buffer hitting the rear of the tube. Now to replace the chrono...

[mosigdude]

and while I'm at it...

Anyone have any tested recommendations on a nice 4-16X40 or 6-24X40 (or 42, 44) mil-dot scope?
I'd like to stay under $500 if possible

[Artful]

I have mixed bag results with cheap scopes, I have a friend that picked up a Nikon for his AR10 and I'm so far impressed with it.

If you want me to get the model number I will - it was under $150 from either Cabella's or Sportsman Warehouse as I recall - maybe my next purchase after tax time.

[mosigdude]

If you happen to talk to him, I'd appreciate knowing the model number. Right now I'm open to just about any suggestions. As soon as I know a few that people have had good luck with I'll do a bit more research.

Thanks in advance!