If anybody is going to buy something from Adams Arms, make damn sure they have it in stock before you order it.  On March 1st I ordered the parts to convert a recip handled upper to piston op. Received the box a week or so later and, although the shipper says the XLP gasblock was shipped, it's not in the box.  Got with Adams and they say it's backordered.  "Should be a couple of weeks" they say, Fine, I'm good with it.
3 weeks go by and I check again, 'couple more weeks' they say.  Next week when I check it's '4 more weeks'.  
I checked 2 weeks ago and the story was, "We're shipping now.
Emailed them Monday last and the story is, "We had a supplier problem and it will be 2 to 3 more weeks".
So here I am with a finished .300 blkout build waiting on a gasblock.  All dressed up and no place to go waiting 11 WEEKS for Adams to ship the last part.  I send an email Tuesday telling them I'm out of patience and I will send all the UNUSED parts they DID send and they can keep their gasblock, just send me my money back and I'll go someplace else.  
The reply I get back tells me,"Sorry for the delay, you can send the parts back any time you want but we will charge you a 15% restocking fee" WTF!!!!?????
Maybe they make good stuff, maybe not but with that kind of customer service and the admitted quality problems, I'm not going to put their shit in my gun.

Assuming you paid by credit card, I'd get on the phone to the card provider's fraud dept., explain that you got an incomplete order, that the merchant strung you along saying the missing part would ship, that without that part, what you have is a useless collection of parts, and see if it's not too late to issue a chargeback.  Then let Adams contact you about arranging return shipping for their parts.

It's not worth fighting with them over something like this, if you have an easier way to be made whole.  

I'm still conflicted/worried about Adams.  They make neat stuff, but they seem to have a number of serious operational issues (quality control, parts availability, shipping with known improper/defective/half-ass improvised parts when the right parts are "backordered").  It's almost like they're trying to run themselves out of business.

As an update it would seem mentioning the regional BBB and Local Chamber of Commerce as well as informing them on the finer points of the FEDERAL Consumer Protection Act seems to get people's attention. Although Adam seems to be a bit of a hot head, his Customer Service Representative seems to have his head on straight.
I was apologized to, repeatedly, for the tone, It was offered that he would go "in the back and grab one of the 10 or so he thought was back there", (which raises a question or two) and he would personally ship it out today.
I told him that I wasn't really happy with them and I would prefer that we swap what belongs to the other and go about our business.
So that's what we're going to do. I will wait on an envelope with a check and a return sticker.  When the check clears, the parts are in the mail.
I was also offered a 25% discount on anything in the store for my troubles. Not that it's ever gonna get used........

A shame to be out that much time and not get anything accomplished.
If you care to not do business with AA, I can't blame you.

There are more than a few well rated piston conversion companies.

Such as? Thanks in advance.

Superlative Arms would get my vote if I were looking for a piston kit.
However, please do yourself a favor and research them and other kits that are available.

I'd return the whole purchase.

Long time lurker. :)

I'm running two ARs with AA pistons...and love them. That's all about the product and the engineering, not the customer service.

I'm certainly not trying to argue that you got screwed: you did. However, my experience has not been the same as yours. From my experience, and reading here, AA seems to have a very good customer service reputation.

My issue is a little different than the "normal" build and I think this contributed to the problem.  
I am building a recip. bolt handled piston AR in .300 blk.  I can't buy the "conversion kit" as i don't want, and have no need for, the kit supplied BCG.  That leaves me to use a modified gas key with MY BCG (that is drilled and tapped for the bolt handle).  
Adams offered that replacement key whereas Superlative does not.  I didn't want to mix and match parts and suppliers until I was a little more familiar with the system.  So Adams was the choice by default.  
I like the adjustability of the Superlative gas block just on GP but was wondering how much it would really be needed.  They would have been my first choice if not for the parts problem with the gas key.  My mind tells me it shouldn't be that big of a problem but my gut tells me I don't know enough about it to be sure. And I want to be pretty close to convinced before I put my face next to something moving that quick.

If you haven't received your XLP block yet I have one in great shape sitting around.  I'll sell it to you for cheap or trade for something you want to get rid of.