USMC Unertl scopes

[sf180a]

Im looking at doing a M40A1 build and need some education concerning the Unertl scopes. What mods were done to convert them 7.62 to .50 cal and how hard is to convert back to 7.62? Also, who does the conversion? What is the USO modification? Any help/advice is appreciated.
Dale

 

[Stevo86]

USO mod is taking the leaf springs out and installing a coil spring and plug.

 

[Stevo86]

@Skunk will come along and give more Insite to the rest of your questions

 

[Mister Ridge]

As far as I know, the 50 cal scopes had completely different internals and converting to 7.62 would require replacing the appropriate parts. Not something that can be done DIY and I don't know if anyone would have the parts. Side note, I believe, but am not certain, that you could use a 50 cal scope on a 7.62, at least somewhat. You can find the adjustment data for the BDC turret online and try to adapt those amounts to 7.62x51mm.

 

[Skunk]

On the .50cal scope, the elevation/BDC knob is different (obviously), the center screw is dual-lead, and the differential screw is threaded appropriately to accept the dual-lead center screw. In layman’s terms, the whole elevation knob assembly is unique to the .50cal scope.

To convert a .50cal scope to 7.62, you’d need to have all these parts.

As mentioned above, the “USO Mod” was a cost-cutting measure employed during the refurbishment process in which the leaf erector springs were replaced with a conical coil spring and cup. Using the springs/cups from the other scopes in the USO line-up was cheaper and easier than having the leaf springs in the original Unertl design reproduced.

Internet legend says the change was made to accommodate the 30MOA base used on the M40A3 rifle. A standard leaf spring scope works just fine on a M40A3.

 

[Stevo86]

Never had any issues zeroing my original usmc unertls on my A3… so idk where that myth started.

 

[lonegunman762x51]

Odcmp.com, make an account and start bidding when you see one you want, they generally go between $2500-3500 dollars. Some have rings even. The only rifle they look good on is an M40A1.

Zeroing them is harder than usual but mine hammers at the factory setting to 1000yds. It just took a bit of effort to set it to zero at 100. Well worth it.

 

[sf180a]

Thanks. I’ve been checking CMP auctions and other sites. There is one on GB but he’s asking 5K.

 

[ODCMP]

On the .50cal scope, the elevation/BDC knob is different (obviously), the center screw is dual-lead, and the differential screw is threaded appropriately to accept the dual-lead center screw. In layman’s terms, the whole elevation knob assembly is unique to the .50cal scope.

To convert a .50cal scope to 7.62, you’d need to have all these parts.

As mentioned above, the “USO Mod” was a cost-cutting measure employed during the refurbishment process in which the leaf erector springs were replaced with a conical coil spring and cup. Using the springs/cups from the other scopes in the USO line-up was cheaper and easier than having the leaf springs in the original Unertl design reproduced.

Internet legend says the change was made to accommodate the 30MOA base used on the M40A3 rifle. A standard leaf spring scope works just fine on a M40A3.

Tokiwartooth posted some pictures a few years ago of Unertl scope 1045 that he converted back from .50 Cal to .30 cal. The key was that he had the .30 Cal parts, so was able to "re-convert" it back to .30 Cal.

I think anyone else would be better off to just buy a .30 Cal scope if that is what they want.

As far as I know, the 50 cal scopes had completely different internals and converting to 7.62 would require replacing the appropriate parts. Not something that can be done DIY and I don't know if anyone would have the parts. Side note, I believe, but am not certain, that you could use a 50 cal scope on a 7.62, at least somewhat. You can find the adjustment data for the BDC turret online and try to adapt those amounts to 7.62x51mm.

Adding to that thought, you can always use any scope on any rifle in any caliber, it's just that the calibration on the dials won't corelate. I would not hesitate to put a .50 Cal Unertl on a .30 Cal rifle, but would need to find the proper settings at every distance. I wouldn't have any interest in actually changing it back.

 

[sf180a]

I think for my purposes either scope would work. I am just a casual/recreational shooter, not a competitive shooter. 200-300 yds max. Would probably zero at 100 and just hold a bit over. I am in no rush so keeping an eye out for what’s available on the various sites. As I understand it the CMP still have some that might come up for auction in the future. Thanks for everyone’s input.