I have a couple pointed questions about the 762 -

Will the A4 adjustable gas block work on an A1 barrel ?

Will an A1 barrel work with an A4 upper receiver ?

Will the A1 upper receiver work on an A4 lower ?

Apologies if this has been asked, I was not able to find the answers.

Thanks

Will the A4 adjustable gas block work on an A1 barrel ? - Yes, the thread below speaks ad nauseam about it.

https://www.hkpro.com/threads/hk416a5-mr556a4-agb-on-mr223a3.583858/

Will an A1 barrel work with an A4 upper receiver ? - Yes

Will the A1 upper receiver work on an A4 lower - Yes

 

Will the A4 adjustable gas block work on an A1 barrel ? - Yes, the thread below speaks ad nauseam about it.

https://www.hkpro.com/threads/hk416a5-mr556a4-agb-on-mr223a3.583858/

Will an A1 barrel work with an A4 upper receiver ? - Yes

Will the A1 upper receiver work on an A4 lower - Yes

Is the adjustable gas regulator compatible with non-A4 models? Will it be available as a spare part at some point?

The MR556A4 adjustable gas block is pressed onto the barrel. We will be offering the adjustable gas block separately for sale on the HK USA Webshop, but it will not be directly compatible with the A1 barrel due to changes to the roll-pin location.

In regards to the A1 barrel working with the A4, I was under the impression there is a different tab or some sort of interface that is different.

 

No, confirmed by HK due to roll pin locations.
No, if info about 556A1 and 416A5 information I gathered transfers over the same.
Yes

 

I understand the differences between the 556/416 A1/A4/A5 I am asking about the 762 specifically.

 

I believe unless specified as 556, the "A4" designation applies to the entire series of that family of rifles.

 

Does anyone wit the 762 A4 have any pics with the handguard taken off? Are there still 2 roll pins?

 

The A4 barrel and adjustable gas block use only one roll pin.

 

Did the question ever get a clear answer? Will the MR762 A4 AGB fit the A1 barrel? I know the 223/556 A4 version needs its indexing tab shaved to fit the MR223 and it also only uses one roll pin, so I’m curious if it’s the same modification for the MR762.

 

The indexing tab on the MR762A1 gas block and barrel is 3mm.
The indexing tab on the MR762A4 gas block and barrel is 5mm.

From what I've measured, the diameters of the barrel at the gas block are the same at 19mm, although I do not know if the vent holes or roll pins are in the same location. I will remove and measure tomorrow.

My LT A1 barrel assembly installed into my A4 upper.

The A4 handguard did not seem to fit over the lower lug of the A1 gas block. Or at least, I wasn't going to force it.

 

You're a Saint. Thanks for figuring this out. I have an early A1 looking to slap that AGB on if it’s as easy as shaving the indexing tab. I’m looking forward to the follow-up.

 

I'm not going to get around to removing the actual roll pins and blocks just yet but...

I measured 30mm from shoulder to port on my stripped A1 barrel. Both lower bores (4mm) in the gas blocks sit 30mm from the shoulder. I'm guessing the ports to the pistons are located exactly opposite those in the blocks so the port in A1 barrel should line up with the port in the A4 GB.

I measured 5mm from shoulder to rear roll pin on my stripped A1 barrel. Both rear roll pins in the A1 and A4 GBs seem to sit at 5mm from the shoulder (although its hard to grab exact references with the caliper because of the roll pin asymmetry). The A4 barrel does not appear to have a slot for a front roll pin and the seat for the gas block is shorter.

The barrel diameter at the gas block measured 18.984mm on my stripped A1 barrel.
The barrel diameter at the gas block measured 18.968mm from what I could grab in front of the A4 GB. The A4 GB might be a tight fit on the A1 barrel by about 0.0005"-0.001" depending on tolerances.

Without taking everything apart and getting gage pins from work to take all of the measurements this is the best I can do for now.

 

Thank you! That’s enough info to make me think it’s worth a shot. Now to find an A4 gas block.